CHAPTER FIVE
ADVANCED
WORLDBUILDING
Mark struggled up the Mark peeked back over the ridgeline; he saw the
hillside, hoping to reach renegade tramping across the valley floor. It wouldn’t
the shelter of the rocks take more than an hour for him to reach Mark’s ridge.
he had seen from the
valley’s floor. Sweat The light grew brighter still.
poured down his Mark glanced up, just in time to see the star flare.
face, straining his A brilliant white light appeared on the star’s upper
suit’s ability to defog limb, spreading madly, throwing every element of the
his faceplate. He landscape into sharp relief.
could smell himself, Mark thought quickly, then turned to lumber down
rank with fear and the slope, toward the overhang he had picked out a
old perspiration. moment ago. It ought to be enough to shadow him.
The flare would be pouring radiation across the plan-
Any moment, he et’s surface in a few minutes. Enough to seriously
expected to feel the harm anyone caught in the open.
searing agony of a The renegade was in the open, long minutes away
laser burn in his back. from any shelter. Mark permitted himself a wolfish
He couldn’t imagine how smile.
the renegade had managed
to miss him so far.
“Arcadia Base, this is
Mark Keenan. Emergency
call. Emergency call.” Mark
panted, climbing over a saw-toothed
ridge of stone. Dust scattered in the trace atmosphere
as his boots hit the surface on the other side. “Arcadia
Base. Any overflight unit. Eagle’s Wing control.
Anybody.”
No use. His radio was dead.
The light was rising as Mark reached the crest of
the ridge. He reflexively looked over his shoulder, and
looked full in the face of the planet’s red dwarf sun as
it loomed huge on the horizon. Second sunrise, as the
planet receded from its periastron. Prominences and
starspots were scattered across the star’s face, an
unusual number of them. Mark flinched away from
the sight, and then remembered the infrared filters in
his faceplate. It was safe enough to look.
Down in the valley, a long shadow pointed back to
another human figure. It wore a suit like Mark’s. It
lifted a laser rifle.
Mark ducked, just as a stone a few feet away
popped and flew into shards. Then he was hunkered
down behind the ridgeline, scattering eons-old dust
and looking frantically for some kind of shelter.
There, an overhang, the space beneath still in
shadow.
ADVANCED WORLDBUILDING 99
GENERATING STAR SYSTEMS
The rest of the world-building sys- containing a world, including other In either case, the following steps
tem picks up where Chapter 4 left off. worlds that may exist orbiting the will help the GM create a single com-
At this point, the GM may have worlds same star. Or he may simply wish to plete solar system. This portion of the
placed on his campaign map, ready generate a whole solar system from world-building sequence uses more
for adventure. He may now wish to scratch, to see what worlds appear at mathematical computation, and more
generate the rest of any star system random. detail will be generated.
Stellar Classification STEP 15:
NUMBER
Stars fall into a few very well defined groups according to their phys- OF STARS
ical properties. Astronomers classify stars using their spectral class,
essentially a way to sort stars by color and size. This step determines how many
stars exist in the target star system.
The first component of the spectral class is the star’s spectral type or Many stars travel in pairs or larger
“color,” denoted by a single letter. The most important spectral types are groups, bound together gravitationally
O, B, A, F, G, K, and M – remembered by astronomers using the jingle so that each orbits the center of mass
“Oh, Be A Fine Girl, Kiss Me!” of the entire system. In such star sys-
tems, the component stars are named
The sequence of spectral types also defines the relative surface tem- using letters of the alphabet, with the
perature and luminosity of stars. O and B stars are hot and bright, while most massive tagged A, the next most
K and M stars are cool and dim. Spectral types are sometimes referred massive B, and so on. The A-compo-
to as “early” (toward the bright, hot end of the range) or “late” (toward nent is also called the primary star of
the dim, cool end). This nomenclature comes from the early days of stel- the system, and the other components
lar astronomy, when it was widely believed that all stars began their are companions.
lives as O or B type and slowly moved down to K or M type before dying.
This theory of stellar evolution has long since been discarded, but the About half of all star systems are
“early-late” jargon persists. composed of single stars, with most of
the rest being binary pairs. Trinary
The spectral type can be further specified by a decimal classification, (three-star) systems are uncommon
using the digits 0 through 9. A subtype of 0 indicates a “standard” star but possible. Multiple star systems
of that spectral type, while subtypes 1 through 9 indicate progressively with more than three members are
cooler, dimmer stars. Sol, for example, is of spectral type G2, and can fairly rare, and shouldn’t be placed at
be considered two-tenths of the way between a standard G-type and a random. Select a number of stars, or
standard K-type star. roll 3d on the Multiple Stars Table and
note the result.
The second component of a spectral class is the star’s luminosity
class or “size,” which is denoted by a Roman numeral. Luminosity and Modifiers: +3 if the system is locat-
size are related; two stars with the same spectral type (i.e. the same sur- ed within an open cluster (p. 70).
face temperature) will be of different brightness if one is larger and has
more surface area to radiate energy with. The luminosity classes are I Multiple Stars Table
(for “supergiant” stars), II and III (for giant stars), IV (for a class of “sub-
giant” stars), V (for average-sized “main sequence” stars), and VI (for a Roll (3d) Number of
rare class of “subdwarf” stars). Sol, for example, is a G2 V star.
Stars
One set of stars doesn’t fall into this classification scheme: the white
dwarf stars. In a sense, these are not stars at all. A white dwarf is the 3-10 1
remnant of a star that has finished its stable lifespan, has passed
through a period as a giant star, and is now unable to continue fusion 11-15 2
burning. Stars that die in this fashion lose much of their mass, in
processes that can be quite violent. The most common remnant of such 16 or more 3
a star-death is a white dwarf, a small but extremely dense body that
shines dimly due to the retained heat of its final collapse. Astronomers Example: Returning to his pre-
use an elaborate classification scheme for white dwarf stars, but this designed world of Haven (see Chapter
book simplifies by assigning them all the luminosity class D without 4), the GM decides to generate the rest
spectral type. of the star system. Based on his earli-
er concept for the world, he decides
In the region of space around Sol, most stars are of luminosity class that Haven is located within an open
V. These are stars in the main part of their stable lifetime, burning star cluster. He rolls 3d+3 for a result
hydrogen fuel and evolving very slowly, most of them across billions of of 14, and notes that the Haven star
years. About 90% of nearby stars are main-sequence stars (p. 104), and system is composed of two stars.
most of the rest are white dwarfs.
100 ADVANCED WORLDBUILDING
STEP 16: likely to appear in a space campaign, assume a first roll of 6; on a 3-4,
STAR MASSES have mass of 3.0 solar masses or less. assume a first roll of 7; on a 5-6,
Stars larger than about 2.0 solar mass- assume a first roll of 8.
This step determines the mass of es don’t appear likely to have planets
each star in the system. A star’s evolu- at all, so this world-design system It’s always reasonable to vary the
tion depends very strongly on its mass won’t examine such stars in great final result slightly, so long as the star’s
and age, and somewhat less strongly detail. Stars with life-bearing planets mass is closer to the rolled result than
on its initial composition. are most likely to mass between 0.6 to the results on either side of it. If a
and 1.5 solar masses. star has mass between two entries on
A star’s mass is measured in solar the Stellar Mass Table, the results on
masses, so that a star with mass 1.0 is Primary Star Mass several of the tables that follow will
exactly as massive as our own sun. have to be interpolated.
Objects smaller than about 0.08 solar Select a mass for the primary star
masses can’t maintain nuclear fusion of the target star system. To generate Companion Stars
in their cores, and so can’t be consid- the primary star’s mass at random, roll
ered stars (but see Brown Dwarfs, p. 3d twice on the Stellar Mass Table, If there are any companion stars in
128). Some gargantuan stars seem to making a note of the mass given for the target star system, each must have
have about 100 solar masses, although the first and second rolls. a mass equal to or lower than that of
such “hyperstars” are extremely rare. the primary star. Select a mass for
For every massive star that burns Exception: If a Garden world has each companion.
briefly and brightly, there are many already been generated for the star
small stars that burn dimly and hoard system, then replace the first roll with To generate each companion star’s
their nuclear fuel. The vast majority of the following procedure. Roll 1d: on a mass at random, roll 1d-1. If the result
stars, including almost every star 1, assume a first roll of 5; on a 2, is 0, then the companion star has
almost exactly the same mass as the
Stellar Mass Table primary (i.e. its mass is given by the
same entry in the Stellar Mass Table). If
First Roll (3d) Second Roll (3d) Mass (solar masses) the result is 1 or greater, then roll that
2.00 many d6, and count down as many
3 3-10 1.90 entries as the dice indicate from the
1.80 primary star’s entry on the table. If the
11-18 1.70 bottom of the table is reached, then
1.60 stop. (No star may have a mass lower
4 3-8 1.50 than about 0.08 solar masses.) The
1.45 resulting entry indicates the mass for
9-11 1.40 that companion star.
1.35
12-18 1.30 Example: The GM begins by gener-
1.25 ating the mass for the Haven system’s
5 3-7 1.20 primary star. Since Haven is a Garden
1.15 world, he rolls 1d instead of 3d for the
8-10 1.10 first roll; he gets a result of 3, which
1.05 translates into a first 3d roll of 7. His
11-12 1.00 second 3d roll is an 11. Haven’s pri-
0.95 mary star has a mass of 0.90 solar
13-18 0.90 masses.
0.85
6 3-7 0.80 To generate the companion star’s
0.75 mass, the GM begins with a roll of 1d-
8-9 0.70 1, with a result of 3. He rolls 3d for a
0.65 result of 14, and counts down on the
10 0.60 Stellar Mass Table that many entries
0.55 from the mass of the primary star. The
11-12 0.50 companion’s mass is 0.20 solar masses.
0.45
13-18 0.40 STEP 17: STAR
0.35 SYSTEM AGE
7 3-7 0.30
0.25 This step determines the age of the
8-9 0.20 star system. All of the stars in the sys-
0.15 tem (and their planets, if any) will nor-
10 0.10 mally be the same age, as measured
from the moment that the primary
11-12 star ignited nuclear fusion in its core.
13-18
8 3-7
8-9
10
11-12
13-18
9 3-8
9-11
12-18
10 3-8
9-11
12-18
11 Any
12 Any
13 Any
14-18 Any
ADVANCED WORLDBUILDING 101
At this writing, the universe itself is Example: The GM determines the STEP 18:
estimated to be about 14 billion years age of the Haven system by rolling STELLAR
old, and our own galaxy is not much on the Stellar Age Table. Since Haven CHARACTERISTICS
younger than that. Stars older than 12 is a Garden world, he rolls 2d+2 for a
billion years of age are rare in the total of 8. Haven is an intermediate Now that the mass of each star
galactic disk, and are usually ancient Population I star. The following two and the age of the star system as a
stars of the galactic halo that are sim- 1d-1 rolls yield results of 2 and 0. The whole are known, the current prop-
ply passing through the disk at the star system’s age is 2 + (0.6 ¥ 2) + (0.1 erties of each star in the system can
moment. A typical range of ages ¥ 0) = 3.2 billion years. be determined.
would be about 4-8 billion years.
Referring to the discussion of A star begins its life in the main
Select an age for the star system. open clusters on p. 70, the GM sequence, a class of stars with very pre-
To determine an age at random, begin notices that the Haven star system is dictable properties, characteristic of
by rolling 3d on the Stellar Age Table to probably too old to be a member of stable hydrogen fusion in their cores.
determine what population the stars of the open cluster in which it is cur- A massive star will burn very brightly,
the target system belong to. If a rently located. The GM decides that spending relatively little time in the
Garden world has already been gener- the cluster is recently formed, still main sequence. Stars about as mas-
ated for the star system, roll 2d+2 rich with bright young stars. Haven’s sive as our own sun will spend a few
instead. Population II stars are the presence inside the cluster is coinci- billion years in the main sequence,
oldest, leftovers from the formation of dence – the binary star is simply while the least massive stars will
the galaxy. Population I stars were passing through on its independent remain there for many billions (even
formed in the galactic disk, and can be orbit around the galactic core. trillions) of years.
much younger. Haven’s night sky is probably very
impressive, full of brilliant nearby As a star of moderate or high mass
Once the star system’s population stars! Meanwhile, the coincidence approaches the end of its stable lifes-
is determined, roll 1d-1, multiply the probably helps hide Haven from the pan, the hydrogen in its core becomes
result by the Step-A value, then roll imperial authorities, who don’t depleted. Stars can continue to survive
another 1d-1, and multiply that result expect to find a habitable planet in by fusing heavier elements – helium,
by the Step-B value. Add both results this region of space. then carbon, and so on – but each new
to the Base Age to get the age of the fusion process requires higher mass,
star system in billions of years. and will be much hotter than ordinary
hydrogen fusion. The pressure of the
Stellar Age Table greater heat causes the star to swell
and redden, causing a transition to the
Roll (3d) Population Base Age Step-A Step-B “red giant” stage of evolution.
0 0 0
3 Extreme Population I 0.1 0.3 0.05 Eventually, these later forms of
2 0.6 0.1 nuclear fusion run out of fuel in their
4-6 Young Population I 5.6 0.6 0.1 turn. The star then dies, losing part of
8 0.6 0.1 its mass and leaving behind a stellar
7-10 Intermediate Population I 10 0.6 0.1 remnant. In the case of a star about
the mass of our sun, this process is rel-
11-14 Old Population I atively peaceful – the outer layers of
the star blow away to form a short-
15-17 Intermediate Population II lived “planetary” nebula, leaving
behind a white dwarf remnant. A
18 Extreme Population II more massive star will die in a super-
nova explosion, leaving behind a more
exotic remnant such as a neutron star
or black hole.
Aside from a star’s mass and age,
its most important characteristics are
its effective temperature, its luminosity,
and its radius.
The effective temperature of a star
is the temperature of its visible sur-
face, measured in kelvins. It is the pri-
mary factor determining the “color” of
the star’s light (more precisely, the dis-
tribution of the star’s radiant energy
across the electromagnetic spectrum).
Spectral type mainly depends on
102 ADVANCED WORLDBUILDING
effective temperature, although the much energy as the Sun. Note that not surface. Most stars are quite compact,
star’s material composition is also a all of a star’s radiant energy will be in but some very massive or luminous
factor. the form of visible light. In fact, at the stars are so large that they are likely to
extremes of the range of spectral have absorbed their innermost plan-
The luminosity of a star is a meas- types, most of a star’s output may be ets.
ure of its total energy output. outside the visible range.
Luminosity is usually measured in To determine the characteristics of
solar luminosities, so that a star with The radius of a star is simply the each star in the target star system, use
luminosity 1.0 radiates exactly as distance from its center to its visible the Stellar Evolution Table.
Stellar Evolution Table
Mass Type Temp L-Min L-Max M-Span S-Span G-Span
0.0012 – – – –
0.10 M7 3,100 0.0036 – – – –
0.0079 – – – –
0.15 M6 3,200 0.015 – – – –
0.024 – – – –
0.20 M5 3,200 0.037 – – – –
0.054 – – – –
0.25 M4 3,300 0.07 0.08 70 – –
0.09 0.11 59 – –
0.30 M4 3,300 0.11 0.15 50 – –
0.13 0.20 42 – –
0.35 M3 3,400 0.15 0.25 37 – –
0.19 0.35 30 – –
0.40 M2 3,500 0.23 0.48 24 – –
0.28 0.65 20 – –
0.45 M1 3,600 0.36 0.84 17 – –
0.45 1.0 14 – –
0.50 M0 3,800 0.56 1.3 12 1.8 1.1
0.68 1.6 10 1.6 1.0
0.55 K8 4,000 0.87 1.9 8.8 1.4 0.8
1.1 2.2 7.7 1.2 0.7
0.60 K6 4,200 1.4 2.6 6.7 1.0 0.6
1.7 3.0 5.9 0.9 0.6
0.65 K5 4,400 2.1 3.5 5.2 0.8 0.5
2.5 3.9 4.6 0.7 0.4
0.70 K4 4,600 3.1 4.5 4.1 0.6 0.4
3.7 5.1 3.7 0.6 0.4
0.75 K2 4,900 4.3 5.7 3.3 0.5 0.3
5.1 6.5 3.0 0.5 0.3
0.80 K0 5,200 6.7 8.2 2.5 0.4 0.2
8.6 10 2.1 0.3 0.2
0.85 G8 5,400 11 13 1.8 0.3 0.2
13 16 1.5 0.2 0.1
0.90 G6 5,500 16 20 1.3 0.2 0.1
0.95 G4 5,700
1.00 G2 5,800
1.05 G1 5,900
1.10 G0 6,000
1.15 F9 6,100
1.20 F8 6,300
1.25 F7 6,400
1.30 F6 6,500
1.35 F5 6,600
1.40 F4 6,700
1.45 F3 6,900
1.50 F2 7,000
1.60 F0 7,300
1.70 A9 7,500
1.80 A7 7,800
1.90 A6 8,000
2.00 A5 8,200
Here, Mass is the star’s mass in If a star’s age is no greater than the star. Once a star has exhausted its sta-
solar masses, Type is its most likely main sequence span given for its ble span, subgiant span, and giant
spectral type while it is on the main mass, then it is a main sequence span, then it has ended its lifespan as
sequence, Temp is its most likely (luminosity class V) star. If its age is a star. The dying star leaves behind a
effective temperature (in kelvins) greater than the main sequence span, stellar remnant – which, for the stellar
while it is on the main sequence, L- but no greater than the main sequence masses given on this table, is always a
Min is its initial luminosity on the span plus the subgiant span for its white dwarf (luminosity class D).
main sequence, L-Max is its maxi- mass, then it is a subgiant (luminosity
mum luminosity on the main class IV) star. If its age is greater than Using the table, classify each star
sequence, M-Span is its main the main sequence span plus the sub- in the star system as a main sequence
sequence span in billions of years, S- giant span, but no greater than the star, subgiant star, giant star, or white
Span is its subgiant span in billions main sequence span plus the subgiant dwarf. Refer to the appropriate sec-
of years, and G-Span is its giant span span plus the giant span for its mass, tion of the following text to determine
in billions of years. then it is a giant (luminosity class III) each star’s spectral type, effective tem-
perature, and luminosity.
ADVANCED WORLDBUILDING 103
Main Sequence Stars The luminosity of the star is equal A white dwarf’s mass will normally
to the L-Max value from the Stellar be between 0.9 and 1.4 solar masses,
While a star is a member of the Evolution Table. This value can be var- and can actually be significantly
main sequence, its effective tempera- ied by up to 10% in either direction if smaller than the mass of the original
ture will change very little, but it will desired. star. If a star has become a white
tend to grow larger and more lumi- dwarf, ignore the mass originally
nous as its core temperature slowly To determine the star’s current rolled on the Stellar Mass Table. Select
increases. effective temperature, use the follow- a mass between 0.9 and 1.4 solar
ing formula: masses. To generate a mass at ran-
The Stellar Evolution Table gives dom, roll 2d-2, multiply by 0.05 solar
the spectral type (under Type) and T = M – [(A/S) ¥ (M - 4800)] masses, and add the result to 0.9 solar
effective temperature (under Temp) masses.
for a main sequence star of a given Here, T is the current effective tem-
mass. It would be reasonable to vary perature in kelvins, M is the star’s A white dwarf will have negligible
the spectral type by one subtype in effective temperature during its main luminosity, rarely higher than 0.001
either direction, or to vary the effec- sequence period (the Temp value from solar luminosities. Its radius will be
tive temperature by up to 100 K in the table), A is the star’s age as a sub- quite small – a white dwarf star is
either direction. giant (i.e. its total age minus its main only a few thousand miles across,
sequence span), and S is the star’s sub- about the same size as the Earth! The
To determine the current luminosi- giant span (the S-Span value from the effective temperature of a white
ty of a main sequence star, use the table). It would be reasonable to vary dwarf can be quite high, but in this
following formula: the final result by up to 100 K in either case it is rarely of any significance in
direction. world-building.
L = MIN + [(A/S) ¥ (MAX - MIN)]
The star’s current spectral type will Determining
Here, L is the current luminosity in be that of a main sequence star with Star Radius
solar luminosities, MIN is the L-Min about the same effective temperature.
value from the Stellar Evolution Table Refer to the table to find the most like- For every luminosity class except D
for the star’s mass, MAX is the L-Max ly spectral type. (white dwarfs), a star’s radius is exact-
value from the table, A is the star’s age ly determined by its effective tempera-
in billions of years, and S is the main Giant Stars ture and its luminosity. Use the follow-
sequence span (M-Span) from the ing formula:
table. It would be reasonable to vary After its period as a subgiant, a star
the final result by up to 10% in either will rapidly swell to red giant status, R = (155,000 ¥ square root of L)/T2
direction. going through several transitions as its
core settles to relatively stable helium Here, R is the star’s radius in AUs,
Note that for stars of 0.4 solar fusion. Its effective temperature falls L is its luminosity in solar luminosi-
masses or less, no L-Max or M-Span further, but its radius and luminosity ties, and T is its effective temperature
values are given. Such low-mass stars grow tremendously. A star of 2.0 solar in kelvins. Main sequence stars will
change in luminosity very slowly; in masses or less won’t be able to make almost always be a tiny fraction of an
the lifespan of the universe, they have the transition to carbon-burning or AU in radius, but giant stars may well
not had time to grow significantly more exotic forms of fusion, so this be much larger.
brighter. For such stars, the L-Min phase of its evolution will be the last.
value can be taken as the actual lumi- Once the red giant phase is over, the Example: Referring to the Stellar
nosity, and may be varied by up to star will die. Evolution Table, the GM notes that
10% in either direction. Haven’s primary star is still well with-
If a star is in the giant phase, its in its main-sequence lifespan. He
Meanwhile, for stars with mass effective temperature will be between notes that the star is most likely to be
greater than 0.4 solar masses, but no 3,000 and 5,000 kelvins. Select a tem- of spectral type G6 V (G6 from the
greater than 0.9 solar masses, L-Max perature, or roll 2d-2, multiply by 200 entry on the table, V because of the
and M-Span values (but no other span K, and add the result to 3,000 K. The star’s status on the main sequence).
values) are given. Such stars are auto- star’s spectral type will be the same as He also notes that the star’s effective
matically on the main sequence, but that of a main sequence star with temperature is 5,500 kelvins.
they may have had time to grow sig- about the same effective temperature.
nificantly brighter since their forma- Its luminosity will be about 25 times The GM then applies the luminosi-
tion. The procedure above can be used its luminosity as a subgiant star, and ty formula, using entries from the
to estimate their current luminosity. can be varied by up to 10% in either table and the known age of the star
direction if desired. system: 0.45 + [(3.2/14) ¥ (1.0 - 0.45)]
Subgiant Stars = 0.58 solar luminosities. He records
White Dwarf Stars this as the star’s current luminosity.
Once a star leaves the main Finally, the GM applies the formula
sequence, it enters the subgiant branch After it completes the giant stage of for star radius: (155,000 ¥ square root
of stellar evolution. During this peri- its evolution, a star with 2.0 solar of 0.58)/(5,500)2 = 0.0039 AU, or about
od, its luminosity changes relatively masses or less will die and leave 360,000 miles.
little, but its effective temperature falls behind a white dwarf remnant.
as it swells toward red giant status.
104 ADVANCED WORLDBUILDING
Going through the same proce- Orbital Separation Table
dures for the companion star, the GM
determines that this star has spectral Roll (3d) Separation Radius Multiplier
type M5 V, effective temperature of 0.05 AU
3,200 kelvins, luminosity of 0.008 6 or less Very Close 0.5 AU
(rounded up), and radius of 0.0014 AU 2 AU
or about 130,000 miles. 7-9 Close 10 AU
50 AU
STEP 19: 10-11 Moderate
COMPANION
STAR ORBITS 12-14 Wide
Stars in a multiple star system 15 or more Distant
will follow orbital paths that circle
the center of mass of the system. The The initial result from this table known, select an eccentricity for each
simplest way to approach their gives a general idea of how widely sep- companion’s orbit. To select eccentric-
orbital mechanics is to assume that arated the primary is from its com- ity at random, roll 3d on the Stellar
companions will follow circular or panion. Roll 2d and multiply by the Orbital Eccentricity Table.
elliptical orbits centered on their pri- given radius multiplier to get a value
mary stars. The important element for the average radius of the orbit for Modifiers: -6 if the two stars are
to determine here is how distant the that companion. It would be reason- Very Close, -4 if they are Close, and -2
stars in the system are from each able to vary the final result by up to if they have Moderate separation.
other at any given time. This step half of the radius multiplier in either
determines that information. direction. Stellar Orbital
The relevant parameters of any A distant companion may have a Eccentricity Table
orbital path are its average radius companion of its own, on a roll of 11
(measured in AU) and its eccentricity. or higher on 3d. This is the only way to Roll (3d) Eccentricity
This last is a measure of the amount get more than three stars in a multiple
by which the orbit deviates from a per- system when using the random-gener- 3 or less 0
fect circle, and takes values between 0 ation method. If so, the companion is
and 1. An eccentricity of 0 indicates a treated in all respects as the primary 4 0.1
perfectly circular orbit, while values star for its own companion. Generate
approaching 1 indicate elliptical orbits stellar characteristics for the “sub- 5 0.2
that are more and more elongated. companion” as in Step 15. Generate
Stars normally have orbital paths of an average radius for the subcompan- 6 0.3
moderate eccentricity, with values ion’s orbit around its primary star,
between 0.4 and 0.7 being most likely. applying a -6 modifier to the roll on 7-8 0.4
the Orbital Separation Table.
Members of a multiple star system 9-11 0.5
can fall at a variety of distances from Note that the orbital radius of the
each other. At one extreme are “con- second companion in a trinary system 12-13 0.6
tact binaries,” stars whose outer must be larger than that of the first
atmospheres actually mingle as they companion, and will normally be 14-15 0.7
whirl about each other in hours or much larger. Similarly, the orbital
days. At the opposite extreme are very radius of a subcompanion must be 16 0.8
wide pairs, which may take many smaller than that of its primary
thousands of years to complete a sin- around the central star of the system. 17 0.9
gle orbit. Adjust the orbits if necessary to ensure
these relationships. 18 or more 0.95
Select orbital distances and eccen-
tricities to suit, or use the following Once the average orbital radius for For each primary-companion pair,
procedure. each primary-companion pair is compute and record the minimum
separation and the maximum separa-
Begin by rolling 3d on the Orbital tion between the two stars:
Separation Table for each companion.
MIN = (1 - E) ¥ R
Modifiers: +4 for each companion MAX = (1 + E) ¥ R
if a Garden world has already been
generated for the star system; +6 Here, MIN is the minimum separa-
for the second companion in a tri- tion in AU, MAX is the maximum sep-
nary system. These modifiers are aration in AU, E is the eccentricity of
cumulative. the companion’s orbit, and R is the
average orbital radius in AU.
ADVANCED WORLDBUILDING 105
Example: The GM rolls 3d+4 (the STEP 20: LOCATE form in a stable orbit within a certain
+4 since Haven is a Garden world) on ORBITAL ZONES distance. Once a star moves into the
the Orbital Separation Table, and gets a subgiant or giant phases of its evolu-
result of 15. The red dwarf companion This step prepares for the place- tion, existing planets that find them-
in the Haven system is at distant sepa- ment of worlds in the star system. The selves too close may be vaporized by
ration. The GM rolls 2d for a 7, multi- GM must determine where planets the swollen star’s intense heat.
plies by 50 AU, and notes that the two can be placed, and must also deter-
stars have an average separation of mine where gas giant planets (which For each star in the target star sys-
350 AU. dominate the planetary-formation tem, compute the inner limit radius
process) will appear. Compute and using both of the following formulae.
Since the companion star is at dis- make a note of the inner limit radius, The inner limit radius that applies will
tant separation, it may have its own the outer limit radius, the snow line be the larger of the two values. For
companion. The GM rolls 3d for a 10, radius, and any forbidden zones almost all stars on the main sequence,
and makes a note that there is no sec- around each star in the system. the first of the two formulae will be
ond companion star in the system. the one to apply – the second formula
Inner Limit Radius becomes dominant for extremely
The GM rolls 3d on the Stellar luminous stars.
Orbital Eccentricity Table, and gets a Planets will not form too close to a
result of 12. The eccentricity of the star. Even while a star is on the main I = 0.1 ¥ M
companion star’s orbit is 0.6. The min- sequence, a planet is very unlikely to I = 0.01 ¥ square root of L
imum separation of the two stars is
140 AU, and the maximum separation Here, I is the inner limit radius in
is 560 AU. AUs, M is the star’s mass in solar units,
and L is the star’s luminosity in solar
units.
Outer Limit Radius
Planets will also not form too far
away from a star. At a large distance,
orbital movements are leisurely.
Protoplanets will have much less
opportunity to sweep up matter before
the star ignites and the process of
planetary formation is halted.
For each star in the target star sys-
tem, compute the outer limit radius
using the following formula.
O = 40 ¥ M
Here, O is the outer limit radius
in AUs and M is the star’s mass in
solar units. Planets will be able to
form anywhere between the inner
and outer limit radii, so long as
no other stars interfere with their
gravitational influence.
Snow Line
Next, compute the snow line radius
for each star. This is the distance from
the star at which water ice could exist
during planetary formation, marking
the most likely region for the forma-
tion of the star’s largest gas giant plan-
et. The snow line radius can be found
using the following formula:
R = 4.85 ¥ square root of L
Here, R is the snow line radius in
AUs and L is the star’s initial luminos-
ity on the main sequence (the L-Min
value from the Stellar Evolution Table).
106 ADVANCED WORLDBUILDING
Forbidden Zones information for the red dwarf including some of pleasant tempera-
companion. If the companion seems tures in the “life zone.”
If a star system includes more than likely to become important to some
one star, then each component of the future adventure, information about Conventional Gas Giant: The star
system may have a forbidden zone in its planets can be generated then. has one or more gas giant planets, all
which planets can’t form even if they beyond the snow line, following near-
are otherwise at a proper distance STEP 21: ly circular orbits. Rocky planets are
from the star. A forbidden zone is a PLACING FIRST very likely, including some in the life
region in which no stable planetary PLANETS zone. This is the situation that holds in
orbit is possible. our own solar system.
Once all the orbital zones have
The inner edge of the band of for- been located, the first planets can be Eccentric Gas Giant: In this situa-
bidden orbits is at one-third of the placed in orbit around each star in the tion, one or more gas giants formed
minimum separation between a star system. beyond the snow line and have
and its closest companion (as com- migrated some distance inward. Their
puted in Step 18). For the third com- Arrangement orbits have become “scrambled” due
ponent in a trinary star system, the of Gas Giants to random close encounters among
closest companion is the primary themselves. These orbits are now
star of the system. If a distant com- Traditional models of planetary eccentric (non-circular) or fail to fall
panion has its own subcompanion, formation call for the tidy arrange- in the same plane. Any rocky planets
then those two stars will automati- ment of worlds we see in our own in the inner system have probably
cally be closest companions for each solar system: small rocky planets been ejected from the system after a
other. inside the snow line, large gas-giant close encounter with one of the gas
planets outside. Unfortunately, in giants.
The inner edge of the forbidden recent years astronomers have detect-
zone may be closer than the inner ed over 100 planets in other star sys- Epistellar Gas Giant: At least one
limit radius for that star, in which tems – almost none of which follow gas giant planet has migrated down
case there will be no planets between this model! to a very tight circular orbit around
the star and its companion. the primary star. This gas giant may
Alternatively, the inner edge of the This finding doesn’t doom the tra- have absorbed some of the material
forbidden zone may be beyond the ditional model entirely, since these available for building rocky planets,
outer limit distance for the star, in strange “hot Jupiters” are the only but such planets may have been able
which case the companion will have ones we are likely to detect given cur- to form anyway after the gas giant
no significant effect on the planetary rent methods. Astronomers using finished its migration. Other gas
system. those methods and looking at our own giants may exist in the outer star
solar system from a distance wouldn’t system, as in the conventional
The outer edge of a star’s forbidden be able to detect the presence of arrangement.
zone is at three times the maximum Jupiter or Saturn (at least not yet).
separation between the star and its Hence many star systems may follow Choose an arrangement of gas
closest companion (again, as comput- the traditional model without our giants for each star in the star system.
ed in Step 18). If this outer edge is being able to verify the fact. If a star’s snow line radius falls within
closer than the outer limit distance, a forbidden zone due to the presence
planets may form circling the pair as a Still, it seems clear that large gas- of a companion star, then it will have
whole. In this case, assign these plan- giant worlds can be found almost any- No Gas Giant. Otherwise, choose an
ets to the primary and don’t generate where in a star system, including the arrangement or roll 3d on the follow-
such planets for both stars. This can infernal regions within a few million ing table.
happen even when the stars are sepa- miles of the primary star. The current
rated fairly widely, although in such leading theory is that gas giants still Gas Giant
cases the outer edge of the forbidden form in the cold outer regions of a star Arrangement Table
zone is likely to be beyond the outer system, but that mechanical processes
limit distance. cause some growing gas giants to Roll (3d) Arrangement
migrate inward. 10 or less No Gas Giant
Example: The GM determines the 11-12 Conventional Gas Giant
orbital zones for Haven’s primary star. To reflect this possibility, deter- 13-14 Eccentric Gas Giant
The star’s inner limit radius is at 0.09 mine the general arrangement of gas 15-18 Epistellar Gas Giant
AU, its outer limit radius is at 36 AU, giants in orbit around each star in the
and its snow line is at 3.3 AU. There is target star system. Several possible Place First Gas Giant
a forbidden zone due to the presence arrangements exist.
of the companion star, but its inner Once the arrangement of gas giant
edge is at 47 AU, outside the outer No Gas Giant: If the protoplanetary planets around each star in the star
limit radius. The companion has no nebula had little mass, gas giants may system has been determined, the first
significant effect on the arrangement not have formed at all. The star may gas giant can be placed for each star.
of planets in the primary’s system. have a few rocky planets instead,
No Gas Giant: No gas giant will be
At this point, the GM decides not placed around this star.
to bother generating any more
ADVANCED WORLDBUILDING 107
Conventional Gas Giant: In this Here, R is the orbital radius in AU, and Haven’s orbit is quite large
case, the star’s first gas giant planet B is the world’s blackbody tempera- (3.5/0.68 = 5.15), there’s no conflict
will normally form outside, but not ture, and L is the star’s luminosity and both planets can be left where
too far from, the snow line radius. in solar units. Compute this orbital they are.
Select an orbital radius for it, or roll radius for each of the stars, and
2d-2, multiply by 0.05, add 1, and choose one of them to be the pre- STEP 22: PLACE
multiply the snow-line radius by the designed world’s primary. PLANETARY
result. ORBITS
Note that the proper distance may
Eccentric Gas Giant: In this case, fall inside the inner limit radius, out- Once any pre-designed world and
the star’s first gas giant planet will be side the outer limit radius, or within a the first gas giant for each star (if any)
found somewhere between the star’s forbidden zone for a given star. In this have been placed, all of the planetary
inner limit radius and the snow line case, the world cannot be placed in orbits for each star can be determined.
radius. Select an orbital radius for it, orbit around that star.
or roll 1d, multiply by 0.125, and mul- Early astronomers spent consider-
tiply the snow-line radius by the It’s also possible for the pre- able time trying to discover why the
result. designed world to end up being too planets’ orbits are arranged as they
close to the star’s first gas giant, if any. are. One early effort was “Bode’s law,”
Epistellar Gas Giant: In this case, Determine the ratio between the two an observed mathematical relation-
the star’s first gas giant planet will be worlds’ orbital radii, by dividing the ship among the orbital radii of the
found very close to the star, possibly larger radius by the smaller. If the known planets. Although Bode’s law is
even inside the inner limit radius. This ratio is less than 1.4, then the two simple, and doesn’t clash too badly
is an exception to the usual rule pro- worlds are too close together – the gas with the existing orbital radii, it does-
hibiting planets from being placed giant’s gravitational influence will n’t actually account for the forces that
inside the inner limit; the planet did tend to make the pre-designed world’s control the distribution of planets.
not form so close to its primary star, orbit unstable. The pre-designed
but migrated into that position. Select world cannot be placed in orbit Planetary orbits tend to be spaced
an orbital radius for it or roll 3d, mul- around that star. logarithmically – that is, the ratio of
tiply by 0.1, and multiply the inner one orbital radius to the next is fairly
limit radius by the result. Given these two restrictions, it’s consistent. This is because certain
possible for a pre-designed world to ratios lead to unstable situations, as
Regardless of the arrangement of have no place to go. If this happens, neighboring planets exert gravitation-
gas giants, record the orbital radius consider returning to Step 15 to gener- al attraction on each other.
of the first gas giant (if any) for each ate a new star or set of stars to fit, or
star in the target system. Its other choosing a different arrangement of Orbits are usually arranged so that
properties (mass, density, diameter, gas giants for one or more of the stars. the ratio of adjacent orbital radii is
number of moons, and so on) will be between 1.4 and 2.0. Some ratios in
generated later. One more thing to consider: the this range encourage orbital instabili-
pre-designed world may be a moon ty because of a “resonance” between
Note that it’s possible for a gas rather than an independent planet. In the two planets’ orbital periods, but
giant to fall within a forbidden zone particular, a Tiny or Small world of these ratios appear to be less likely
using the above procedures. The GM any type, or a Standard (Hadean) rather than entirely forbidden. In this
should move the gas giant out of the world, is very likely to be the moon of step, planetary orbits will be placed so
forbidden zone if possible, although a gas giant. If the pre-designed world that this relationship between adja-
he may accept the situation as an is difficult to place because it appears cent radii holds.
unstable or transient feature of the to fall too close to a star’s first gas
star system’s evolution. giant, then consider moving the gas For each star in the target star sys-
giant – altering its orbital radius tem, always begin with the first gas
Placing a slightly so that the pre-designed world giant’s orbital radius. If no gas giant
Pre-Designed World can be one of its moons! has been placed for a star, locate the
greatest orbital distance at which that
If a world has already been Example: The GM rolls 3d for a 12 star can have planets – usually the
designed for the star system using the on the Gas Giant Arrangement Table. outer limit distance, or the inner edge
basic world-building sequence in Haven’s primary star has a of a forbidden zone. The first plane-
Chapter 4, then that world should also Conventional Gas Giant arrangement. tary orbit to be placed will be inside,
be placed at a specific distance from Without bothering to roll the dice, the but not too far from, this outermost
one of the stars in the system. GM places the system’s first gas giant legal distance. Select an orbital radius
planet just outside the snow line at 3.5 for it, or roll 1d, multiply by 0.05, add
The exact orbital radius for the pre- AU. 1, and divide the outermost legal dis-
designed world depends on the lumi- tance by the result.
nosity of its primary star (as generated At this point, the GM is ready to
in Step 18) and the world’s blackbody place Haven itself within the star sys- From the first planetary orbit to be
temperature (as generated in Step 5). tem. Applying the formula for its placed, work your way both inward
Use the following formula: orbital radius, he gets (77,300/2952) ¥ (toward the inner limit radius or the
square root of (0.58) = 0.68 AU. Since
R = (77,300/B2) ¥ square root of L the ratio between the gas giant’s orbit
108 ADVANCED WORLDBUILDING
edge of a forbidden zone) and out-
ward (toward the outer limit radius or
the edge of a forbidden zone). Always
place the next planetary orbit so that
the ratio between adjacent orbits is
between 1.4 and 2.0. Select an appro-
priate ratio each time, or roll 3d on the
following table.
Orbital Spacing Table
Roll (3d) Ratio
3-4 1.4
5-6 1.5
7-8 1.6
9-12 1.7
13-14 1.8
15-16 1.9
17-18 2.0
When working outward, multiply work inward toward Haven’s primary Haven’s primary star. From the inner-
each orbital radius by the ratio in star and place planetary orbits. His most to the outermost, the radii are
order to get the next radius. When first roll on the Orbital Spacing Table is 0.22 AU, 0.38 AU, 0.68 AU (Haven),
working inward, divide each radius by a 16, yielding a ratio of 1.9; the next 1.1 AU, 1.8 AU, 3.5 AU (first gas
the ratio in order to get the next orbit inward from the gas giant is at giant), 6.0 AU, 10 AU, 17 AU, and 27
radius. When using the dice, it would 3.5/1.9 = 1.8 AU. The next roll is an 11, AU. Haven’s primary star appears to
be reasonable to adjust the ratio by up yielding a ratio of 1.7; the next orbit have a full system of worlds, with up
to 0.05 in either direction at each step. inward is at 1.8/1.7 = 1.1 AU. The GM to 10 planets in it.
observes that the ratio between 1.1
In the innermost region of a star’s and 0.68 (the radius of Haven’s orbit) STEP 23:
orbital space, the orbits will be very is about 1.6 to 1, so he simply assumes PLACE WORLDS
close together in absolute terms. that Haven’s orbit is the next one
Always space orbits out so that they inward. The next die rolls are 13 (ratio In this step, objects will be allocat-
are at least 0.15 AU apart, even if this of 1.8, orbital radius of 0.68/1.8 = 0.38) ed to orbits.
means that the ratio between two and 11 (ratio of 1.7, orbital radius of
orbital radii is unusually large. If this 0.38/1.7 = 0.22). The next orbit inward An empty orbit may occur if there
can’t be done without placing an orbit would have to be at 0.07 AU or less in wasn’t enough material in that region
inside the inner limit radius, then order to avoid placing two orbits with- of the star system to form an object of
stop. in 0.15 AU of each other, but 0.07 AU significant size, or if a large object (a
is inside the inner limit radius, so the companion star or a migrating gas
Remember that no planetary GM stops. giant planet) swept the orbit clean of
orbital radius can be larger than the material.
outer limit distance. Aside from the Now the GM works outward from
case of an epistellar gas giant, no plan- the first gas giant’s orbit. His rolls on An asteroid belt is an orbital region
etary orbital radius can be smaller the Orbital Spacing Table are 10 (ratio occupied by many small, stony
than the inner limit distance. If an of 1.7, orbital radius of 3.5 ¥ 1.7 = 6.0 objects. Asteroid belts normally form
orbit falls inside a forbidden zone, AU), 9 (ratio of 1.7, orbital radius of when a gas giant or companion star
stop placing planetary orbits in that 6.0 ¥ 1.7 = 10 AU), 11 (ratio of 1.7, disturbs the early mass of asteroids,
direction. orbital radius of 10 ¥ 1.7 = 17 AU), and pulling them out of the stable orbits
8 (ratio of 1.6, orbital radius of 17 ¥ that would have permitted them to
If there is a pre-designed world in 1.6 = 27 AU). The next orbital radius form a planet. The few asteroids that
orbit around one star, the above proce- would be at least 27 ¥ 1.4 = 38 AU, and survive this winnowing process make
dure won’t necessarily place an orbit this is outside the star’s outer limit up a stable system. A world of the
in exactly the right place for that radius, so the GM stops. Asteroid Belt type is, of course, an
world. Feel free to adjust one or more asteroid belt.
orbits so that one of them falls exactly To summarize: the GM has gener-
as required for the pre-designed ated a complete set of orbits for
world, and then continue with the pro-
cedure as before.
Record the sequence of planetary
orbital radii for each star in the target
star system.
Example: Beginning with the first
gas giant’s orbit, the GM begins to
ADVANCED WORLDBUILDING 109
A terrestrial planet is a small, stony will always have at least one. In all of needed; if a terrestrial planet is placed,
body with relatively little atmosphere. these arrangements, orbits outside the choose its size class (Tiny, Small,
Terrestrial planets are most likely to snow line are almost always occupied Standard, or Large) at this point.
be found in the inner system, inside by gas giants.
the snow line radius. They are unlike- To generate a random placement,
ly to have many moons, or large ones. Place gas giants in orbits as need- roll 3d for each orbit not already con-
Terrestrial planets are classified as ed. To generate a random placement, taining a gas giant or other object, and
Tiny, Small, Standard, or Large in size. roll 3d for each orbit not already con- refer to the Orbit Contents Table.
All of the world types described in taining a gas giant or other object. In
Chapter 4 (except for Asteroid Belt) each case, compare the roll to the Modifiers: -6 if the orbit is adjacent
can be terrestrial planets. appropriate target number from the to a forbidden zone caused by the
Gas Giant Placement Table. If the roll presence of a companion star; -6 if the
A gas giant is a massive planet, succeeds, a gas giant will occupy the next orbit outward from the primary
composed mostly of hydrogen and orbit. star is occupied by a gas giant; -3 if the
helium. Because of a gas giant’s pow- next orbit inward from the primary
erful gravity, it is likely to have many Once all gas giants have been star is occupied by a gas giant; -3 if the
moons and will affect the formation of placed, determine the size of each orbit is adjacent to either the inner
other planets in nearby orbits. Gas (Small, Medium, or Large). To deter- limit radius or the outer limit radius.
giants are most likely to form outside mine sizes randomly, roll 3d on the All of these modifiers are cumulative.
a star’s snow line radius, but they may Gas Giant Size Table.
migrate inward and can be found at Orbit Contents Table
any distance from the star. Gas giant Modifiers: +4 if the gas giant is
planets are classified as Small, inside the snow line radius, or if it is in Roll (3d) Object
Medium, and Large. the first orbit beyond the snow line
radius. 3 or less Empty Orbit
As a result of previous steps, one or
more orbits may already be filled. A 4-6 Asteroid Belt
few gas giants may already be in place
since Step 21. A pre-designed world 7-8 Terrestrial Planet
may also already be in place, filling
one orbit with an asteroid belt, a ter- Gas Giant Size Table (Tiny)
restrial world, or even a second gas
giant (with the pre-designed world as Roll (3d) Size 9-11 Terrestrial Planet
one of its moons). This step fills the
rest of each star’s orbits. 3-10 Small (Small)
Every star system has a great deal 11-16 Medium 12-15 Terrestrial Planet
of debris in it: scattered asteroids out-
side the main belts, comets and tiny 17 and higher Large (Standard)
rogue planets in the dark outer
fringes. These objects will not be 16 or more Terrestrial Planet
placed in detail (but see Asteroids and
Comets, p. 130). (Large)
Place Gas Giants Fill Remaining Orbits Example: Haven’s primary star has
the Conventional Gas Giant arrange-
For each star, begin by placing gas Once gas giants have been placed, ment, so there will be no gas giants
giants in their orbits. fill the rest of the orbits. inside the snow line. The GM rolls for
the four orbits outside the first gas
Some stars may have the No Gas Empty orbits and asteroid belts are giant’s orbit, rolling 15 or less for all
Giant arrangement (p. 107), either most likely to occur very close to the four. The outermost five orbits in the
because of the presence of a compan- primary star, in an orbit adjacent to system are all occupied by gas giant
ion star or because that arrangement that of a gas giant, or in the outermost planets. Referring to the Gas Giant
was selected earlier. In this case, skip orbit before a forbidden zone caused Size Table, the GM rolls 3d+4 for the
to the placement of asteroid belts. by the presence of a companion star. first gas giant and 3d for the other
Otherwise, at least one gas giant has All of these locations are places where four, getting results of 15 (Medium),
already been placed – but there may the gravitational influence of a large 10 (Small), 13 (Medium), 14
be more in orbits that are not yet object may interfere with the forma- (Medium), and 6 (Small).
filled. tion of a terrestrial planet. If a terres-
trial planet does form in such a loca- Now the GM prepares to place
If a star has the Conventional Gas tion, it is likely to be small. Massive objects in the orbits inside the snow
Giant arrangement, orbits inside the terrestrial planets will usually form line, rolling on the Orbit Contents
snow line radius will never have gas only in regions that are not subject to Table for each. The innermost orbit is
giants. A star with the Eccentric or the gravitational interference of gas adjacent to the inner limit radius; it
Epistellar Gas Giant arrangement will giants or companion stars. gets a 3d-3 roll of 2, indicating an
usually have one gas giant for every
4-6 orbits inside the snow line, and Place empty orbits, asteroid belts,
and terrestrial planets in orbits as
Gas Giant Placement Table
Arrangement Inside Snow Line Outside Snow Line
Do not roll
No Gas Giant Do not roll 15 or less
14 or less
Conventional Gas Giant Do not roll 14 or less
Eccentric Gas Giant 8 or less
Epistellar Gas Giant 6 or less
110 ADVANCED WORLDBUILDING
That’s no moon. It’s a space station. Almost all gas giants in the outer
– Obi-Wan Kenobi, Star Wars reaches of a star system will have
rings, and some of those that have
empty orbit. The next orbit gets a 3d moons are worlds in their own right, migrated inside the snow line radius
roll of 12, indicating a terrestrial plan- and will be given a size class (Tiny, will as well. Gas giant rings are com-
et of Standard size. The next orbit is Small, Standard, or Large) just like a posed of billions of small particles,
already occupied by Haven. The next terrestrial planet. orbiting in a flat disc close to the plan-
gets a 3d roll of 11 (terrestrial planet of et. The rings are largely composed of
Small size). The last orbit inside the Terrestrial planets and gas giants particles thrown off the gas giant’s
snow line has a gas giant in the next can each have satellites, but they are inner moonlets during meteoroid col-
orbit outward; it gets a 3d-6 roll of 4, very different in the kind of satellites lisions. A large number of inner
indicating an asteroid belt. they are likely to have. moons means that more particles will
feed the ring. It also increases the
To summarize, Haven’s primary Terrestrial worlds, especially those chance that some of the moons will be
star has the following objects in its orbiting inside the snow line, are in a position to act as shepherds, main-
system, from the innermost to the out- unlikely to have extensive satellite sys- taining the ring particles in their
ermost: 0.38 AU (Standard world), tems. A terrestrial world may capture orbits through a complex gravitation-
0.68 AU (Haven), 1.1 AU (Small a few asteroid moonlets, but it is al interaction. Normally a gas giant’s
world), 1.8 AU (asteroid belt), 3.5 AU unlikely to have any major moons. rings are fairly thin and wispy, but
(Medium gas giant), 6.0 AU (Small gas there are exceptions – such as the
giant), 10 AU (Medium gas giant), 17 A terrestrial world that suffers a spectacular ring system of Saturn in
AU (Medium gas giant), and 27 AU specific kind of massive impact late in our own solar system.
(Small gas giant). The innermost orbit its formation era may develop a major
allocated earlier turned out to be moon; planetary material is scattered Science fiction has sometimes used
empty, and one orbit is occupied by an into orbit and then coalesces into an the notion of an Earthlike world with
asteroid belt, so the solar system has independent body. Such a major a ring system. This situation may be
eight planets in it, only three of them moon will then undergo tidal interac- unlikely, but it’s not impossible. A
terrestrial. tions with its parent world, driving it moonlet might spiral too close to its
into an unusually wide orbit. As a parent world and shatter, or a major
At this point, the GM decides to result, terrestrial worlds are very impact on a moon might scatter
concentrate on Haven and the world unlikely to have more than one major enough debris to form a ring. Most
at 1.1 AU, leaving further development moon. With their orbits changing so such systems will be unstable, with
of the rest of the star system for later. rapidly, it would be very difficult for the particles falling to the planet or
multiple major moons to fall into a escaping into space within a few mil-
STEP 24: stable configuration. Instead, they lion years at most. The rules that fol-
PLACE MOONS would tend to collide with each other low won’t permit the random genera-
or with their parent world. tion of a terrestrial world with rings,
Gas giant planets almost always but the GM may wish to place such a
have moons, and some terrestrial Gas giant worlds often have exten- world as a rare case.
planets will have them as well. This sive systems of satellites. A gas giant’s
step determines how many moons powerful gravity allows it to compete Gas Giants
each planet in the target star system effectively with its primary star. Early
will have, and their rough sizes. in the planet’s history, it attracts plenty The satellite systems of gas giants
of material for the formation of major are always very complex. A gas giant
This book classifies satellites as moons. Later, it captures a number of will normally have up to three distinct
moonlets or major moons. Moonlets small asteroids to serve as moonlets. families of satellites.
are asteroid-sized satellites, no more The only gas giants that are unlikely to
than about 500 miles in diameter, and have large satellite systems are those The first family is a cluster of
can be described using the rules in that have migrated deep into their pri- moonlets orbiting close to the planet.
Asteroids and Comets (p. 130). Major mary star’s gravitational influence. These moons orbit very close together,
sometimes even sharing orbits in a
One feature that is probably “resonant” pattern that prevents their
unique to gas giants is the ring system. collision. To determine the number of
moonlets in this family, roll 2d.
Modifiers: -10 if the planet is within
0.1 AU of the primary star, -8 if the
planet is between 0.1 AU and 0.5 AU of
the primary star, -6 if the planet is
between 0.5 AU and 0.75 AU of the pri-
mary star, -3 if the planet is between
0.75 AU and 1.5 AU of the primary
star.
ADVANCED WORLDBUILDING 111
The size of this first family of satel- the planet is between 1.5 AU and 3 For example, if a Standard world has
lites will determine the level of ring AU of the primary star. a major moon whose size class is “two
system the planet has. If a gas giant size classes smaller,” then the moon’s
planet has at least 6 satellites in this Make note of the number of satel- size class will be Tiny. The minimum
family, its ring system will be visible lites in each of the three families. size class for a major moon is Tiny.
from anywhere in the star system, at For the purposes of this table, a gas
least in moderately powerful tele- Terrestrial Planets giant planet is considered a Large
scopes. If there are 10 or more satel- world.
lites in this family, the ring system will Roll 1d-4 (minimum 0) to deter-
be comparable to Saturn’s, easily visi- mine the number of major moons Moon Size Table
ble even in small telescopes from a dis- orbiting a terrestrial planet. If the
tance and spectacular from close up. planet has no major moons, it will Roll (3d) Size Class
have 1d-2 (minimum 0) moonlets.
The second family of satellites is a 11 or less Three size classes
group of major moons. Roll 1d to Modifiers (for both rolls): Do not
determine the number of moons in roll if the planet is within 0.5 AU of the smaller
this family. primary star, -3 if the planet is
between 0.5 AU and 0.75 AU of the pri- 12-14 Two size classes smaller
Modifiers: Do not roll if the planet is mary star, -1 if the planet is between
within 0.1 AU of the primary star, -5 if 0.75 AU and 1.5 AU of the primary 15 or more One size class smaller
the planet is between 0.1 AU and 0.5 star, -2 if the planet is Tiny, -1 if it is
AU of the primary star, -4 if the planet Small, +1 if it is Large. Make a note of the size class of
is between 0.5 AU and 0.75 AU of the each major moon in the star system.
primary star, -1 if the planet is between Make note of the number of
0.75 AU and 1.5 AU of the primary star. moonlets and major moons for each Example: The GM checks to see if
terrestrial planet. the two worlds he intends to develop
The last family is another group of in detail have moons. For Haven the
moonlets, captured asteroids that Moon Size Classes roll for major moons is 1d-7 (1d-4, and
are often in eccentric, highly inclined, -3 because Haven is close to its pri-
or even retrograde orbits. Roll 1d Major moons are worlds in their mary star), so it can’t have any major
to determine the number of these own right, and will have a size class. moons. The roll for minor moons is
moonlets. Most major moons are Tiny or Small 1d-5; the GM rolls and gets a result of
worlds, although there will be rare 0. Haven has no moons.
Modifiers: Do not roll if the plan- exceptions. Assign a size class to each
et is within 0.5 AU of the primary major moon, or roll 3d on the Moon For the Small world at 1.1 AU, the
star, -5 if the planet is between 0.5 Size Table to determine each moon’s two rolls are 1d-6 and 1d-4. This world
AU and 0.75 AU of the primary star, size class. can’t have any major moons either, but
-4 if the planet is between 0.75 AU when the GM rolls 1d-4 he gets a
and 1.5 AU of the primary star, -1 if A major moon’s size class depends result of 1. This world apparently has
on the size class of its parent planet. a single moonlet, probably an object
captured from the nearby asteroid
belt.
112 ADVANCED WORLDBUILDING
GENERATING WORLD DETAILS
If the sky hadn’t been such a perfect empty. Terrestrial worlds and major In several cases, more than one
shade of Terran blue, if the warm sun- moons are all in place, and the first world type is possible for a given size
shine hadn’t been so exactly as it is on a portion of each one’s world type (the class and blackbody temperature. Use
May morning in Virginia, maybe we size class) is known. In this step, the the following guidelines to decide
wouldn’t have been so all-fired home- rest of the world type for each terres- which type to assign.
sick. But they were, and we were. trial planet and major moon will be
designated. Tiny (Ice) or Tiny (Sulfur) Worlds:
The sun wasn’t Sol. We were seventy Tiny (Sulfur) worlds appear as major
light-years from the Lincoln Memorial Blackbody Temperature moons of gas giant planets. Any
and the Statue of Liberty. Still, I caught given gas giant world is likely to have
myself wondering if the Orioles would First, the blackbody temperature no more than one Tiny (Sulfur)
finally make it in the American League (p. 84) must be computed for each moon, with the rest being of other
this year. world. Use the following formula: types. To make the assignment at
random, roll 1d for each gas giant
– Stephen Tall, B = 278 ¥ (fourth root of L)/(square with at least one moon that could be
“A Star Called Cyrene” root of R) of Tiny (Sulfur) type. On a 1-3 there
is one moon of that type, almost
The broad outlines of the target Here, B is the blackbody tempera- always the innermost of the major
star system are now known. The fol- ture in kelvins, L is the primary star’s moons.
lowing steps can be used to generate luminosity in solar units, and R is
detail for individual worlds. the average orbital radius of the Standard (Ammonia) or Standard
Although these rules could be used to world (or of the planet of which the (Ice): Worlds in this temperature
generate details for every planet and world is a moon). Note that the range may or may not have abun-
moon in a star system, that isn’t their blackbody temperature will be the dant ammonia in the atmosphere.
intended use. Instead, the GM same for a planet and for all of its Ammonia is sensitive to ultraviolet
should apply them only to those moons. Record the blackbody tem- light, and will break down chemical-
worlds that are likely to be of interest perature for each world, rounded to ly if subjected to it over long periods.
in his campaign. the nearest kelvin. A Standard (Ammonia) world will
therefore appear only in orbit
STEP 25: Designate World Types around a cool star that emits rela-
WORLD TYPES tively little ultraviolet. If this choice
It’s now possible to assign a world is available and the primary star’s
At this point, every orbit around type to each terrestrial planet and mass is no greater than 0.65
each star in the target system has major moon in the star system. Refer solar masses, then the world will be
been filled with some object, or has to the following table. of Standard (Ammonia) type.
been specifically designated as Otherwise it will be of Standard (Ice)
type.
World Type Assignment Table
Size Class Blackbody Temperature Complete World Type
Tiny (Ice) or Tiny (Sulfur)
Tiny 140 K or lower Tiny (Rock)
Small (Hadean)
Tiny 141 K or higher Small (Ice)
Small (Rock)
Small 80 K or lower Standard (Hadean)
Standard (Ice)
Small 81-140 K Standard (Ammonia) or Standard (Ice)
Standard (Ice)
Small 141 K or higher Standard (Garden) or Standard (Ocean)
Standard (Greenhouse)
Standard 80 K or lower Standard (Chthonian)
Large (Ice)
Standard 81-150 K Large (Ammonia) or Large (Ice)
Large (Ice)
Standard 151-230 K Large (Garden) or Large (Ocean)
Large (Greenhouse)
Standard 231-240 K Large (Chthonian)
Standard 241-320 K
Standard 321-500 K
Standard 501 K or higher
Large 150 K or lower
Large 151-230 K
Large 231-240 K
Large 241-320 K
Large 321-500 K
Large 501 K or higher
ADVANCED WORLDBUILDING 113
Standard (Garden) or Standard ruins, looking for items that might STEP 28:
(Ocean): Worlds in this temperature give them an edge in any battle CLIMATE
range may or may not have abundant against the Galactic Empire. The GM
free oxygen in the atmosphere. Free names this planet Carson’s World, At this point, the procedure in Step
oxygen must be maintained in the after the rebel scientist who first 5 should be reversed for every world of
atmosphere by photosynthetic life, explored it. interest. Instead of computing each
which takes time to evolve even on a world’s blackbody temperature based
world that is hospitable for it. A STEP 26: on a known average surface tempera-
Standard (Garden) world is very ATMOSPHERE ture, the GM computes an average
unlikely to be less than a billion years surface temperature based on the
old, and will normally be at least 3.5 The atmosphere of each terrestrial blackbody temperature computed in
billion years old. To make the assign- planet and major moon can be deter- Step 25.
ment at random, roll 3d and add 1 for mined from its world type, as in Step
every full 500 million years of the star 3. Refer to the procedures beginning For each world, compute the black-
system’s age (to a maximum of +10). on p. 78 and apply them for each body correction using the procedure
On an 18 or more the world is a world of interest in the target star under Step 5 (p. 83). To determine the
Standard (Garden) world. Otherwise system. average surface temperature of a
it is a Standard (Ocean) world. world, multiply its blackbody temper-
Example: Haven’s atmosphere is ature by the blackbody correction.
Large (Ammonia) or Large (Ice): As already known. Carson’s World is of Make a note of the average surface
with a Standard world for which this the Small (Rock) type. It will have a temperature for each world of inter-
choice is possible, the presence of negligible atmosphere, so the GM est, along with the climate type from
ammonia in the atmosphere depends doesn’t bother to generate its atmos- the World Climate Table (p. 83).
on the amount of ultraviolet light pheric mass or set its composition.
emitted by the primary star. If the pri- Example: Haven’s climate data are
mary star’s mass is no greater than STEP 27: already known. Carson’s World has a
0.65 solar masses, then the world will HYDROGRAPHICS blackbody temperature of 231 kelvins,
be of Large (Ammonia) type. determined in Step 25. As a Small
Otherwise it will be of Large (Ice) type. The hydrographic coverage for (Rock) world, it has an absorption fac-
each world can be determined from its tor of 0.96, and this is equal to its
Large (Garden) or Large (Ocean): As world type, as in Step 4. Refer to the blackbody correction. The average
with a Standard world for which this procedures beginning on p. 81 and surface temperature on the planet is
choice is possible, the presence of free apply them for each world of interest 231 ¥ 0.96 = 222 kelvins (about -60º
oxygen in the atmosphere depends on in the target star system. Fahrenheit). Its climate type is
the evolution of photosynthetic life. Frozen.
Such evolution is significantly less Example: Haven’s hydrographic
likely on a Large world. To make the coverage is already known. Since STEP 29:
assignment at random, roll 3d and Carson’s World is of the Small (Rock) WORLD SIZES
add 1 for every full 500 million years type, it automatically has 0% hydro-
of the star system’s age (to a maximum graphic coverage. The GM assumes As in Step 6, the density, diameter,
of +5). On an 18 or more the world is that it has significant deposits of sub- mass, and surface gravity of each
a Large (Garden) world. Otherwise it surface ice, which once supported the world can now be determined. These
is a Large (Ocean) world. alien colony and are now used by the quantities can also be determined for
rebels. each gas giant planet.
Example: Haven itself is already
known to be a Standard (Garden)
world. The world in the next orbit out-
ward is already known to be of the
Small size class. It has a blackbody
temperature of 278 ¥ (fourth root of
0.58)/(square root of 1.1) = 231 kelvins.
This means that the world must be of
the Small (Rock) type.
The GM thinks about this second
world. Clearly it’s a Mars-like planet:
small, dry, nearly airless, and proba-
bly very cold. The GM decides to
make it more interesting by assuming
that some long-lost civilization once
settled there, leaving behind ruins,
odd works of art, and mysterious
technological artifacts. The rebels of
Haven are slowly investigating these
114 ADVANCED WORLDBUILDING
Terrestrial Planets density slightly (say, by up to 10%) planet, and several other features of
and Major Moons from that given in the table. each world’s movement through
space.
Determining the size parameters Make a note of the mass and densi-
for terrestrial planets and major ty of each gas giant. To determine the Stellar Orbital Period
moons follows the same procedure as diameter of the gas giant, use the fol-
in Chapter 4. First determine the den- lowing formula: If the star system includes more
sity of each world, then its diameter than one star, the orbital period of any
and surface gravity (in either order, as D = cube root of (M/K) given pair of stars can be computed as
convenient), and then its mass and follows:
exact atmospheric pressure. Here, D is the diameter of the
world in Earth diameters (multiply by P = square root of (R3/M)
Gas Giants 7,930 to get the diameter in miles). M
is the mass of the planet in Earth Here, P is the orbital period in
Gas giant worlds vary in composi- masses, and K is the planet’s density in years, R is the average orbital radius
tion much less than smaller worlds do, units of Earth’s density. of the companion around its primary,
and so a gas giant’s mass and density and M is the sum of the masses of the
are closely related. Small gas giants A gas giant has no solid surface. To two stars (in solar masses). Multiply P
are composed primarily of ices. determine its gravity at the planet’s by 365.26 to get the period in days.
Larger gas giants are dominated by cloud tops, use the formula for surface
hydrogen and helium, which com- gravity on p. 86. In trinary or larger star systems,
presses under gravity. In the cores of orbital periods can sometimes be
very large gas giants, the hydrogen is Example: Haven’s size data are computed by treating several stars as
compressed into an exotic “degener- already known. For Carson’s World, one. For example, suppose a trinary
ate” state, far more dense and com- the GM rolls 3d on the World Density star system involves an A-component
pact than any normal matter. A very Table, using the Small Iron Core col- and B-component orbiting one anoth-
large gas giant can actually be denser umn, and gets an 11 (density of 0.8). er at moderate separation, with a
than a terrestrial world, its average The minimum and maximum diame- smaller C-component orbiting at a
density higher than that of solid iron. ters for Carson’s World are 0.41 and much greater distance. Then the
0.51 Earth diameters. The GM arbi- orbital period of A and B can be com-
A Small gas giant is between 10 trarily chooses a diameter of 0.50 puted using the above formula and
and 80 Earth-masses, a Medium gas Earth diameters (about 3,970 miles). ignoring C, after which the orbital
giant between 100 and 500 Earth- Local surface gravity is 0.8 ¥ 0.5 = 0.4 period of C around the A-B system can
masses, and a Large gas giant between Gs, and the planet’s mass is 0.8 ¥ be computed by treating the masses of
600 and 4,000 Earth-masses. A larger (0.5)3 = 0.1 Earth masses. Carson’s A and B as that of a single star.
world actually ignites nuclear fusion World automatically has a Trace
in its core for at least a brief period, atmosphere, since it’s a Small (Rock) Planetary Orbital Period
and becomes a brown dwarf (p. 128). world.
The orbit of any planet around its
Select a mass for each gas giant in STEP 30: primary star can be computed using
the target star system, or roll 3d on the DYNAMIC the same formula as for stellar orbits:
following table. When using the dice, PARAMETERS
it would be reasonable to vary the P = square root of (R3/M)
mass of the gas giant in either direc- In this step, several parameters of
tion, up to halfway to the next entry. the target star system can be generat- Here, P is the orbital period in
To determine the density of the gas ed: the orbital period of any compan- years, R is the orbital radius of the
giant, read the entry from the table – if ion stars, the orbital period of each planet, and M is the mass of the plan-
the gas giant’s mass is between two planet, the orbital period of each et’s primary star in solar units.
entries, interpolate the density as well. moon, the rotation period of each Multiply P by 365.26 to get the period
It would be reasonable to vary the in days.
Gas Giant Size Table
Small Gas Giant Medium Gas Giant Large Gas Giant
Roll (3d) Mass Density Mass Density Mass Density
100 0.18
8 or less 10 0.42 150 0.19 600 0.31
200 0.20
9-10 15 0.26 250 0.22 800 0.35
300 0.24
11 20 0.22 350 0.25 1,000 0.4
400 0.26
12 30 0.19 450 0.27 1,500 0.6
500 0.29
13 40 0.17 2,000 0.8
14 50 0.17 2,500 1.0
15 60 0.17 3,000 1.2
16 70 0.17 3,500 1.4
17 or more 80 0.17 4,000 1.6
ADVANCED WORLDBUILDING 115
Note that this formula assumes Satellite Orbital Radius generate a radius at random: roll
that the mass of the planet itself is 3d+3, and if the result is 15 or more
negligible – usually a good assump- Before the orbital period of a satel- add another roll of 2d. Divide the final
tion, unless the star is very light (an lite can be computed, the radius of its total by 2 (retaining any fraction) and
M5 V or lower) and the planet is very orbit around its planet must be deter- multiply the result by the planet’s
massive (a Large gas giant of 2,000 mined. This radius depends on the diameter. If any two of the major
Earth-masses or more). If greater satellite’s origins and its planet’s type. moons orbit within one planetary
accuracy is desired, add the mass of diameter of each other, re-roll or
the planet into M; a planet’s mass in Gas Giants: Recall that a gas giant assign new orbits to both.
solar units is equal to 0.000003 times has three families of satellites. The
its mass in Earth-masses. first family is a set of moonlets orbit- The third family of moonlets
ing close in, the second is a set of begins at 20 planetary diameters and
Planetary Orbital major moons orbiting at medium sep- can extend out to several hundred
Eccentricity aration, and the third is a set of moon- diameters. If the orbital radius for one
lets orbiting at large distances. of these moonlets is needed in play,
A planet’s orbit around its primary simply select a radius as needed.
star can be eccentric, just as a com- The first family of moonlets orbits
panion star’s orbit can be. For each at distances between 1 and 2.5 times Terrestrial Planets: A terrestrial
planet, choose an eccentricity for its the planet’s own diameter. In most planet will occasionally have a major
orbit, or roll 3d on the Planetary cases, specific orbital information for moon (and, in very rare cases, more
Orbital Eccentricity Table. these moonlets won’t be required. If than one). If there are no major
the orbital radius for one of these moons, it may have one or more
Modifiers: +4 if the star has the moonlets is needed in play, select a moonlets.
Eccentric Gas Giant arrangement and radius, or roll 1d+4, divide by 4
the world is a gas giant inside the (retaining any fraction), and multiply Major moons will usually be found
snow line radius; -6 if the star has the the result by the planet’s diameter. between 5 and 40 planetary diameters.
Epistellar Gas Giant arrangement and The larger the moon is in relation to
the planet is a gas giant in the epistel- The second family of major moons its planet, the wider its orbit will be
lar position; -6 if the star has the orbits at distances between 3 and 15 due to tidal effects. Select an orbital
Conventional Gas Giant arrangement. times the planet’s own diameter. Select radius as needed. To generate an orbit
When using the dice, feel free to mod- a radius for each moon as needed. To at random, roll 2d.
ify the result by up to half of the dis-
tance to an adjacent entry on the table.
Planetary Orbital
Eccentricity Table
Roll (3d) Eccentricity
3 or less 0
4-6 0.05
7-9 0.1
10-11 0.15
12 0.2
13 0.3
14 0.4
15 0.5
16 0.6
17 0.7
18 or higher 0.8
For each planet, compute and
record the minimum separation and
the maximum separation between the
planet and its primary:
MIN = (1 - E) ¥ R
MAX = (1 + E) ¥ R
Here, MIN is the minimum separa-
tion in AU, MAX is the maximum sep-
aration in AU, E is the eccentricity of
the planet’s orbit, and R is the planet’s
orbital radius in AU.
116 ADVANCED WORLDBUILDING
Modifiers: +2 if the moon is two most major moons are tide-locked to Rotation Period
size classes smaller than its planet, +4 their planets – they rotate exactly once
if the moon is one size class smaller per orbital period, so that they always In general, more massive worlds
than its planet. Multiply the result by present the same face to the planet. rotate more quickly, but this is mod-
2.5, and then multiply by the planet’s Some planets orbiting close to their ified by many factors and can
diameter. If two major moons orbit primary stars are tide-locked to the depend on sheer accident during the
within 5 planetary diameters of each star, causing them to have a day face formation of the star system. Tidal
other, re-roll or assign new orbits to in permanent light and a night face in braking also has a powerful effect on
both. permanent darkness. the rotation of planets and moons.
Moonlets will orbit close in, at dis- To estimate the level of tidal force If the total tidal effect (computed
tances between 1 and 5 times the plan- being exerted on a planet by each of its above) on a world is 50 or higher,
et’s own diameter. If the orbital radius moons, use the following: then the world is tide-locked; its
for one of these moonlets is needed in rotation period is equal to its orbital
play, select a radius as needed. To gen- T = (17.8 million ¥ M ¥ D)/R3 period. If it is a planet, it is tide-
erate a radius at random: roll 1d+4, locked to its innermost major moon
divide by 4 (retaining any fraction), Here, T is a measure of the tidal if it has one, or to its primary star
and multiply the result by the planet’s force on the planet, in terms of the otherwise (in the latter case, see Tide-
diameter. tidal force exerted by Earth’s Moon Locked Worlds, p. 125). If it is a satel-
upon the Earth. T = 1 indicates an lite, then it is tide-locked to its pri-
Satellite Orbital Period ocean tide averaging about 2 feet at mary planet.
high tide in deep ocean, although the
The orbit of any satellite around its exact amplitude of tides will very If the world is not tide-locked,
planet can be computed using almost widely depending on the local geogra- then its rotation period can vary
the same formula as for stellar orbits: phy. M is the mass of the satellite in widely. Select a rotation period, or
Earth masses. D is the diameter of the roll 3d, add the total tidal effect on
P = 0.0588 ¥ square root of (R3/M) planet in Earth diameters, and R is the the world, and add the appropriate
radius of the satellite’s orbit in Earth modifier from the Rotation Period
Here, P is the orbital period in diameters. Table.
days, R is the orbital radius of the
satellite around its planet in Earth The same formula can be used to Rotation Period Table
diameters, and M is the sum of the estimate the level of tidal force exerted
masses of planet and satellite in Earth on a moon by its planet. In this case, World Size Class Modifier
masses. If the satellite is very small use M for the mass of the planet in
compared to its planet, its mass can be Earth masses, and D for the diameter Large Gas Giant +0
ignored. of the moon in Earth diameters.
Medium Gas Giant +0
Tidal Braking To estimate the tidal force exerted
by the primary star on a planet, use a Small Gas Giant +6
A planet orbiting its primary star very similar formula:
will not experience that star’s gravity Large Terrestrial World +6
uniformly. The star will exert more T = (0.46 ¥ M ¥ D)/R3
gravitational force on the near side of Standard Terrestrial World +10
the planet than on the far side. Since a Here, T is the same measure of the
planet is not a perfectly rigid body, it tidal force on the planet. M is the mass Small Terrestrial World +14
will respond by deforming slightly, of the star in solar units. D is the
forming a pair of “tidal bulges” point- diameter of the planet in Earth diam- Tiny Terrestrial World +18
ing toward and away from the star. eters, and R is the radius of the plan-
However, if the planet rotates with et’s orbit in AUs. The result is an initial value for the
respect to its primary star, the star- world’s rotation period in standard
ward bulge will be offset slightly from An important factor is the total hours (divide by 24 to get the period in
a line pointing directly toward it. The tidal effect on a world: standard days).
star’s gravity tends to pull on this
bulge, exerting torque on the planet’s E = (T ¥ A)/M If the result is greater than 36
body and slowing its rotation. hours or the initial 3d roll was a natu-
Here, E is the total tidal effect. If ral 16 or greater, the planet or satellite
This tidal braking also works when the world is a planet, then T is the sum will have unusually slow rotation. In
a planet has a major moon; the moon’s of all the tidal forces exerted by its this case, roll 2d on the Special
gravity creates tidal bulges and slows major moons and its primary star. If Rotation Table, and use that result
the planet’s rotation by pulling back the world is a satellite, then T is the instead.
on the nearest bulge. Likewise, a plan- tidal force exerted only by its primary
et exerts tidal forces on its moons, planet. A is the age of the star system Special Rotation Table
slowing their own rotation. As a result, in billions of years, and M is the mass
of the world in Earth masses. Round Roll (2d) Rotation Period
the total tidal effect to the nearest 6 or less Use initial value for
whole number, and make a note of it
for later computations. period
7 1d ¥ 2 standard days
8 1d ¥ 5 standard days
9 1d ¥ 10 standard days
10 1d ¥ 20 standard days
11 1d ¥ 50 standard days
12 1d ¥ 100 standard days
ADVANCED WORLDBUILDING 117
If the rotation period yielded then the day length will be very close The two stars orbit one another in
above is longer than the period a to the rotation period. If day length is square root of [3503/(0.9 + 0.2)] =
world would have if tide-locked, then negative, as often happens if the plan- 6,200 years. The GM decides that the
it will be tide-locked. Any rotation et is in retrograde rotation, the pri- two stars are currently close to their
period derived from the tables can be mary star will appear to rise in the minimum separation, making it con-
treated as approximate, and varied by west and set in the east. venient in case his players decide to
part of an hour, several hours, or sev- explore the red dwarf’s planets.
eral days as appropriate. Rotation On a satellite, the day length is
periods can also be recorded with computed by setting S equal to the par- Haven orbits its primary star in
precision down to the minute or sec- ent planet’s orbital period. Otherwise square root of (0.683/0.90) = 0.591
ond, although this is useful mostly the computation is the same. years, or about 215.9 days. Carson’s
for local color. World orbits the primary in square
The apparent length of a moon’s root of (1.13/0.90) = 1.22 years, or
The rotation period generated here orbital cycle, as seen from the surface about 444.2 days. The GM rolls 3d-6
is the sidereal period, the time it takes of the parent world, is found by setting on the Planetary Orbital Eccentricity
the world to complete one rotation S to the moon’s orbital period and R to Table for both Haven and Carson’s
with respect to a distant fixed point. the planet’s rotation period. If the World, and gets negligible eccentricity
The apparent length of the local day length of the cycle is negative, as often for both worlds’ orbits.
may be different. happens for very close-in moons, the
moon will rise in the west and set in Haven has no moon. To see where
In most cases, a planet or satellite the east. A close-in moon may orbit Carson’s World single moonlet orbits,
will rotate in the same direction as its close to the planet’s geosynchronous the GM rolls 1d+4 for a 5. Dividing by
orbital motion. Some worlds have the distance, in which case the moon will 4 and multiplying by the planet’s
opposite tendency, rotating in the spend long periods in the sky as seen diameter, he finds that the moonlet
direction opposing their orbital from any given location, keeping pace orbits at a radius of 0.63 Earth diame-
motion. Such retrograde rotation is with the planet’s surface. ters (about 4,960 miles) from the cen-
more common than one might expect ter of the planet. The moonlet’s orbital
– in our own solar system, two out of Axial Tilt period is 0.0588 ¥ square root of
the eight major planets exhibit retro- (0.633/0.1) = 0.093 days. The moonlet
grade rotation. Assign retrograde rota- The angle between a planet’s rota- orbits very quickly, completing a cir-
tion as needed, or roll 3d for each tion axis and a vector perpendicular to cuit in a little over 2 hours!
world. A planet will have retrograde a star’s ecliptic plane is called the axial
rotation on a 13 or more, and a satel- tilt of the planet. The major planets of The GM then begins to estimate
lite will have it on a 17 or more. our own solar system have a wide vari- the tidal effects on the two worlds.
ety of axial tilt values, and there seems Neither world has a major moon, so
Local Calendar to be no correlation to their other all of the tidal effect on each will come
properties. An arbitrary selection from the primary star. On Haven, the
At this point, the GM can deter- would be appropriate. star exerts a tidal force of (0.46 ¥ 0.90
mine the length of various celestial ¥ 1.05)/(0.68)3 = 1.38. The total tidal
cycles from the point of view of To generate a random axial tilt, roll effect on Haven is (1.38 ¥ 3.2)/1.27 =
an observer on a world’s surface. One 3d on the Axial Tilt Table. If necessary, 3.48, rounded to 3. On Carson’s World,
formula can be used for all of these roll 1d on the extended table. In any the star exerts a tidal force of (0.46 ¥
computations: case, roll 2d as indicated and record 0.90 ¥ 0.50)/(1.1)3 = 0.16. The total
the end result. tidal effect on Carson’s World is (0.16
A = (S ¥ R)/(S - R) ¥ 3.2)/0.1 = 5.12, rounded to 5.
Axial Tilt Table
A is the apparent length of the Since neither world has a very high
cycle in question, S is the sidereal Roll (3d) Axial Tilt tidal effect, the GM rolls on the
period of the cycle, and R is the rota- Rotation Period Table for each. For
tion period of the world. All of these 3-6 0 + (2d-2) degrees Haven, the roll is 3d+13 (+3 for total
must be in the same units, usually tidal effect, +10 for being a Standard-
hours or standard days. If the world 7-9 10 + (2d-2) degrees size world), and the GM gets a result
rotates retrograde, R is negative. If S of 23. Haven rotates in about 23
and R are equal, then the formula 10-12 20 + (2d-2) degrees hours. For Carson’s World, the roll is
gives an undefined result – in this 3d+19, and the result is 29 hours. The
case, assume that the apparent length 13-14 30 + (2d-2) degrees GM may vary these periods slightly
of the cycle is infinite, or that there is later, but for now he simply records
no apparent motion. 15-16 40 + (2d-2) degrees both results for use during adventures.
On a planet, the day length (the 17-18 Roll on extended table Since the orbital period is much
time between sunrises) is computed longer than the rotation period for
by setting S equal to the planet’s Roll (1d) Axial Tilt both worlds, the GM doesn’t bother to
orbital period and R to the planet’s 1-2 50 + (2d-2) degrees compute the exact day length for
rotation period. If the orbital period is 3-4 60 + (2d-2) degrees either. The rotation periods are close
much longer than the rotation period, 5 70 + (2d-2) degrees enough. The apparent length of the
6 80 + (2d-2) degrees orbital cycle for the moonlet of
Example: At this step, the GM
determines the dynamic parameters
for several parts of the Haven star
system.
118 ADVANCED WORLDBUILDING
Carson’s World is about (2.2 ¥ 29)/(2.2 Modifiers: Divide the world’s sur- be brought to the surface by volcanic
- 29) = -2.4 hours. The moonlet face gravity (in Gs) by its age (in bil- activity will be virtually absent. New
appears rise in the west and set in the lions of years). Multiply the result by volcanoes never appear, but there may
east, passing through the sky against 40, round to the nearest whole num- be extinct volcanoes remaining from
the movement of the sun and stars, ber, and add the final result to the dice the world’s early history. Examples in
and makes a complete cycle in about roll. +5 if the world is a terrestrial our own solar system include
2.4 hours. planet with one major moon, +10 if it Mercury, Mars, and the Moon.
is a terrestrial planet with more than
The last item is the axial tilt for one major moon; +60 if the world is of Light: The world is quiet, but the
each of the two worlds. The GM rolls Tiny (Sulfur) type; +5 if the world is a core is still hot and there are a few
on the Axial Tilt Table for each, getting gas giant’s major moon of some other areas of active volcanism. New volca-
a roll of 9 for Haven and a roll of 13 for type. noes appear on a time-scale of
Carson’s World. For Haven, the roll of many thousands or even millions of
2d-2 yields a 1, so Haven’s axial tilt is Volcanic Activity Table years. Trace elements that would
only 11º. Haven probably has a very normally be brought to the surface
gentle seasonal cycle (especially since Roll (3d) Activity Level by volcanic activity will be present,
its vast oceans will work to smooth but uncommon.
out regional temperature variations). 16 or less None
For Carson’s World, the roll of 2d-2 Moderate: There are many regions
yields an 8, so the axial tilt of Carson’s 17-20 Light of active volcanism, but volcanoes
World is 38º. Carson’s World probably tend to be separate, and most volca-
has a strong seasonal cycle, causing 21-26 Moderate noes are only occasionally active. New
vast annual sandstorms and large fluc- volcanoes appear on a time-scale of
tuations in the size of its polar ice 27-70 Heavy decades or centuries. There is plenty
caps. of volcanic “recycling” of trace ele-
71 or higher Extreme ments in the environment. Examples
STEP 31: in our own solar system include
GEOLOGIC None: The world is geologically Earth.
ACTIVITY dead. The core may be a solid mass,
with no semi-liquid or liquid layer.
A world’s level of geologic activity Trace elements that would normally
can affect its resource richness, as well
as its habitability. This step deter-
mines how volcanically active the
world is, as well as whether it has an
active system of plate tectonics.
Volcanic Activity
Volcanism has a profound effect on
a world’s surface environment. A
world with too much volcanism can
be a very dangerous place. On the
other hand, a world with too little vol-
canism can be inhospitable as well.
Volcanoes concentrate certain trace
elements in the upper crust: sub-
stances like potassium that are critical
for biological processes, along with
useful minerals like thorium or urani-
um. Without active volcanism, these
substances will never arrive on the
world’s surface – or they will tend to be
lost to erosion over time, winding up
on the ocean bottoms. A world with-
out volcanoes is a world with critical
resource deficiencies!
Select a level of volcanic activity
from the options below. To generate a
level of volcanic activity at random,
roll 3d on the Volcanic Activity Table.
ADVANCED WORLDBUILDING 119
Heavy: Volcanism is very common 14 or less (for Extreme volcanism), the Modifiers: Do not roll for a Tiny or
across the world’s surface. There may atmosphere is Marginal regardless of Small world; the world has no tecton-
be regions where individual volcanoes any results obtained earlier. ic activity. -8 if the world has no vol-
cluster and merge, permitting magma canic activity, -4 if it has Light volcanic
to well up through great wounds in Tectonic Activity activity, +4 if it has Heavy volcanic
the crust. New volcanoes appear every activity, +8 if it has Extreme volcanic
few years. There is plenty of volcanic Any world with a solid surface is activity; -4 if the world has no liquid-
“recycling” of trace elements in the likely to experience some level of tec- water oceans, -2 if its hydrographic
environment. tonic activity, the movement and coverage is less than 50%; +2 if the
deformation of crustal plates over mil- world is a terrestrial planet with one
Extreme: The world’s surface is lions of years. High tectonic activity major moon, +4 if it is a terrestrial
dominated by volcanism. The planet’s causes earthquakes, but it also makes planet with more than one major
surface is generally unstable, and new a planet more likely to be habitable. moon.
volcanic eruptions can take place Tectonic activity causes mountain-
almost anywhere and at any time. The building, which helps ensure that ero- Tectonic Activity Table
atmosphere is very unlikely to be sion doesn’t wear all of a planet’s land-
breathable, even if it would otherwise forms down to nothing. As crustal Roll (3d) Activity Level
have the proper composition. There is plates move, some plates slide under
plenty of volcanic “recycling” of trace others into the mantle, recycling 6 or less None
elements in the environment. crustal materials. The movement of
Examples in our own solar system crustal plates also helps prevent the 7-10 Light
include Jupiter’s moon Io. formation of massive “shield” volca-
noes, which can have a serious effect 11-14 Moderate
If a Standard (Garden) or Large on planetary climate.
(Garden) world has Heavy or Extreme 15-18 Heavy
volcanism, this may render its atmos- A Tiny or Small world never has
phere Marginal (p. 80). In this case, significant tectonic activity. For other 19 or higher Extreme
the most likely contaminants for the worlds, select a level of tectonic activi-
atmosphere are sulfur compounds or ty from the options below. To generate None: The world is tectonically
pollutants. Set the atmosphere to a level of tectonic activity at random, dead. The world’s crust is very thick
Marginal as needed. To test this possi- roll 3d on the Tectonic Activity Table. and immobile, not divided into any
bility at random, roll 3d; if the roll is distinct plates. Crustal quakes are
an 8 or less (for Heavy volcanism) or a weak and extremely rare. If there is (or
has been) any volcanic activity on the
world, it has formed massive shield
volcanoes, like Earth’s Mauna Loa or
120 ADVANCED WORLDBUILDING
Mars’ Olympus Mons. There is no Earth. The roll on the Tectonic Activity secondary colonies established from
mountain-building on the world. Any Table is 3d with no modifiers, for a the first one. The procedure for deter-
mountains are accidental geologic fea- result of 11, indicating Moderate tec- mining the population of these sec-
tures, and will quickly be worn down tonic activity as well. ondary settlements depends on
by erosion if there is a significant whether a pre-designed world is in the
atmosphere. Carson’s World has surface gravity star system or not.
of 0.40 and an age of 3.2 billion years.
Light: The world’s crust may be The modifier for the roll on the Selecting the
divided by fault lines into a few plates, Volcanic Activity Table is (0.40/3.2) ¥ 40 Main World
which move past each other with = 5 exactly. The roll of 3d+5 yields a
some limitations. Crustal quakes are total of 14, indicating no volcanic If there is no pre-designed world,
powerful but not common, and are activity. Meanwhile, since Carson’s begin by selecting the main world of
generally restricted to plate bound- World is Small, it automatically has the star system. In almost all cases, the
aries. If there is any volcanic activity, no tectonic activity. world with the highest affinity score
shield volcanoes are common, but will be the main world of the system.
there are a few “chains” of smaller vol- STEP 32: If there is a tie for the highest affinity
canoes along plate boundaries. RESOURCES AND score, choose one of the tied worlds as
Mountain-building is infrequent, but HABITABILITY needed, or select one at random. If no
there is likely to be at least a few old world in the star system has an affini-
mountain chains, which are well- The Resource Value Modifier, hab- ty score greater than 0, then any world
weathered if there is significant itability score, and affinity score for can be selected as the main world.
atmosphere. each world can be determined from its
world type, as in Step 7 (p. 87). Refer If the star system includes a pre-
Moderate: The world’s crust is to the procedures in Chapter 4 and designed world, that world can usual-
divided into a number of plates, which apply them for each world of interest ly be assumed to be the main world of
move freely around and past each in the target star system. the system. The most common excep-
other. Crustal quakes can be very pow- tion is when the pre-designed world
erful, are quite common near plate A world’s level of geologic activity turns out not to have the highest affin-
boundaries, and can even occur in affects both its Resource Value ity in the star system. In this case, the
mid-plate regions. Shield volcanoes Modifier and its habitability score. GM has a choice. He can alter the star
are uncommon, and most volcanoes When rolling for the RVM of a terres- system’s design so that the highest-
are small ones of the “chain” or “arc” trial planet, modify the 3d roll for affinity world is the main world and
type. Mountain-building occurs in RVM by -2 for no volcanism, -1 for has the highest population; this may
cycles, and there are likely to be a Light volcanism, +1 for Heavy volcan- mean removing or reducing any popu-
number of young, high mountain ism, and +2 for Extreme volcanism. lation on the pre-designed world if it
ranges. Tectonic activity does not affect a turns out to break the rules for sec-
world’s RVM. A world’s habitability ondary settlements. Alternatively, the
Heavy: The world’s crust is divided should be modified by -1 for Heavy GM can come up with a reason why
into many plates. Crustal quakes can volcanism or Heavy tectonic activity, the world that appears most attractive
be very powerful and can be experi- and by -2 for Extreme volcanism or was not the one most heavily settled.
enced almost anywhere on the world. Extreme tectonic activity, to a mini-
Almost all volcanoes are small ones of mum of -2. Apply both modifiers if If the main world was not pre-
the “chain” or “arc” type. Mountain- both forms of activity are present. designed, its settlement type can be set
building is almost constant, and most using the guidelines in Step 8. Refer to
of the world’s mountain ranges are Example: Haven’s RVM, habitabili- the procedures beginning on p. 89 and
likely to be young and high. ty, and affinity scores are all known. apply them to the main world. The
For Carson’s World, the GM rolls 3d-2 main world’s other social parameters
Extreme: The world’s crust is frag- (-2 for its lack of volcanic activity) on will also need to be generated before
mented and unstable. Crustal quakes the Resource Value Table, getting a 13. the population of any secondary
are powerful, and can be experienced Carson’s World has Average resources worlds can be determined – proceed
anywhere on the world at any time. and an RVM of 0. Its habitability is 0, with Steps 34 through 39 for the main
Landforms are likely to be highly and its total affinity score is 0. world before returning to this step for
chaotic, including a large number of the secondary worlds.
very young, high mountains. STEP 33:
SETTLEMENT Settlement Types for
Example: At this point, the GM TYPE Secondary Worlds
determines the levels of geological
activity for both Haven and Carson’s This book assumes that one world A secondary world will only be set-
World. – the main world – in each star system tled if the main world has the space
will be settled first, and that any later infrastructure to support colonization
Haven has surface gravity of 1.15 settlements in the star system will be and the secondary world is somehow
and an age of 3.2 billion years. The attractive to settlement.
modifier for the roll on the Volcanic
Activity Table is (1.15/3.2) ¥ 40 = 14.4,
rounded to 14. The roll of 3d+14 yields
a total of 24, indicating Moderate vol-
canic activity comparable to that of
ADVANCED WORLDBUILDING 121
Space infrastructure is a function
of a world’s available technology, its Colonial Requirements Table
population, and its economic invest-
ment in space industries. If the main Main World TL Distance of Secondary Colonies
world is settled only by an outpost (p.
90), or the main world’s population is TL6 or less None
less than 1 million, then no other
world in the star system will be settled. TL7 Any world within 0.1 AU
If the main world is a home world or
TL8 Any world within 1 AU
TL9 Any world within 10 AU
TL10 or higher Any world within same star system
colony with at least 1 million people, in some cases. For example, it would rolls 3d+3 on the Tech Level Table (+3
other worlds may be settled if the local be unusual for a spacefaring civiliza- since the settlement is an outpost)
technology can support the effort. tion to place outposts on distant plan- and gets a 9. The result is Standard
Refer to the following table. ets, but none on the moons of its (Delayed). Since Haven is at TL10,
Here, the distances refer to the dis- home world. the GM places Carson’s World
tance between the two worlds at the Example: Haven’s settlement type is at TL10 also, but notes that local
point of closest approach in their already known; its affinity score of 7 is industries are (like those of the main
orbits. For example, two planets will almost certainly the highest in the star world) not quite up to galactic stan-
come within 1 AU of each other at system, so it can safely be treated as dards.
some point, if their respective orbital the main world. Rather than roll dice,
radii are no more different than that. the GM decides that there is an out- STEP 35:
At the same time, any satellites of post on Carson’s World, populated by POPULATION
either world will also come within 1 scientists and prospectors studying
AU of each other. If the star system the planet’s prior inhabitants. The population of the main world
includes more than one star, and the can be determined as in Step 10. Refer
minimum separation between the two STEP 34: to the procedures beginning on p. 91
stars is 10 AU or less, then worlds TECHNOLOGY and apply them to the main world of
orbiting one star will come within 10 LEVEL the star system.
AU of worlds orbiting the other at
some point. If a secondary world is The TL of the main world can be For each inhabited secondary
within the proper distance of the main determined as in Step 9. Refer to the world, begin by computing the world’s
world, then a settlement may have procedures beginning on p. 90 and carrying capacity and then use the fol-
been established there. apply them to the main world of the lowing procedures to set the world’s
star system. population. As for the main world, a
If the affinity score of a secondary secondary colony or outpost’s popula-
world is greater than 0, a secondary Secondary settlements are unlikely tion will not generally exceed its carry-
colony will automatically be ing capacity.
established.
If the affinity score of a secondary to have a TL higher than that of the
world is 0 or less, then a secondary main world, and may be one or two Secondary Colonies
outpost may be established. Refer to TL behind the main world if they are
the following table, and roll 3d for not yet self-sufficient. Assign TL to To set the population of a second-
each such world that is within the secondary settlements as needed. To ary colony at random, refer to the
proper distance of the main world. generate these TLs randomly, roll on Colony Population Table on p. 92.
the Tech Level Table (p. 91) for each Find the total dice roll that corre-
Modifiers: Add the Habitability secondary settlement, applying all the sponds most closely to the popula-
score for the world. If the 3d roll is appropriate modifiers. For a second- tion of the main world. Subtract the
greater than or equal to the target ary settlement, define the “Standard” modifier for the main world’s affinity
number for the main world’s TL, then TL as that of the main world, not of score, and then add the modifier for
an outpost will be placed there. the setting as a whole. the secondary world’s affinity score.
Then subtract another 3d roll. The
You may wish to override the ran- Example: Haven’s TL is already final result gives a new entry on the
dom placement of secondary outposts known. For Carson’s World, the GM Colony Population Table, which will
give the population for the secondary
Secondary Outpost Placement Table colony.
Main World TL Target Number Secondary Outposts
TL6 or lower Do not roll
TL7 5 or lower The population of a secondary out-
TL8 6 or lower post can be determined using the
TL9 7 or lower same procedures as in Chapter 4,
TL10 or higher 9 or lower probably by a roll on the Outpost
Population Table (p. 93).
122 ADVANCED WORLDBUILDING
Example: Haven’s population is Example: The CR of Haven is Example: The annual per-capita
already known. Carson’s World has a already known. Since Carson’s World income on Carson’s World is only
total carrying capacity of 20 million has the Colony special condition with about $34,000 (50% of the standard
¥ 1 ¥ 0.52 = 5 million. To generate the Haven as its governing society, its CR income for TL10). The most typical
population for Carson’s World, the is one less than that of Haven: CR 1. Wealth level on Carson’s World is
GM rolls 3d on the Outpost The GM notes that Carson’s World is a Struggling. The total economic volume
Population Table and gets a 12, indi- rather rough-and-tumble frontier set- of the settlement is 34,000 ¥ 6,000 =
cating a population of about 6,000 tlement, with very little in the way of $200 million per year. The GM doesn’t
(PR 3). strict law enforcement. bother to estimate trade volume for
Carson’s World, simply assuming that
STEP 36: STEP 38: most of the planet’s economy is driven
SOCIETY TYPE ECONOMICS by imports from Haven.
The society type of the main world The economic parameters for each STEP 39:
can be determined as in Step 11. Refer world can be determined as in Step BASES AND
to the procedures beginning on p. 93 13. Refer to the procedures beginning INSTALLATIONS
and apply them to the main world of on p. 95 and apply them to each world
the star system. in the star system. Military and space facilities can be
assigned to each world using the pro-
Secondary settlements are very When computing the trade vol- cedures in Step 14. Refer to the proce-
likely to be colonies of the main world. ume between worlds in the same star dures beginning on p. 96 and apply
In most cases, a secondary colony or system, be certain not to use a dis- them to each world in the star system.
outpost will have a World Government tance of 0 in the trade volume formu-
with the Colony special condition, and la! If interplanetary distances are Example: The GM decides that
will have the same society type as the already being taken into account in Carson’s World is too small a settle-
main world. the formula, this will not be a prob- ment to have a variety of local bases
lem. If trade volumes are usually and installations. Without rolling the
Assign a society type to each sec- computed over interstellar distances, dice, he places a Class II spaceport on
ondary world as needed. To generate use a distance equal to half the aver- the planet, and also places a govern-
a secondary world’s society type at age distance between neighboring ment research station (PR 2) dedicat-
random, roll 3d and add the PR of the worlds on the interstellar map (as ed to archaeology. The design of
secondary colony. On a 20 or higher, determined under Playing With Carson’s World is complete.
the secondary world is socially and Shapes, p. 72).
politically independent. In this case,
roll on the World Unity Table, the
Society Types Table, and the Special
Conditions Table (p. 94), all as if the
secondary world was the main world
of its own star system. If the second-
ary world is not independent, tie its
society type to that of the main world
as described above.
Example: Without bothering to roll
dice, the GM decides that the Carson’s
World outpost is still socially depend-
ent on Haven. He places a World
Government with the Colony special
condition and the Representative
Democracy society type, matching
Haven.
STEP 37:
CONTROL RATING
The Control Rating for each world
can be determined as in Step 12. Refer
to the procedures beginning on p. 94
and apply them to each world in the
star system. Note that most secondary
settlements will have the Colony spe-
cial condition – their Control Ratings
will be tied to that of the main world.
ADVANCED WORLDBUILDING 123
The Solar System
As an example of star system design, here is a sum- Orbit 5 (Asteroid Belt): Orbital radius 2.7 AU, world
mary of the major objects in our own solar system as type Asteroid Belt.
they are described by the world-building rules in this
book. Orbit 6 (Jupiter): Orbital radius 5.2 AU, diameter
89,000 miles, density 0.24, mass 320, blackbody temper-
Primary Star (Sol): Spectral type G2 V, mass 1.0 solar ature 122 kelvins, world type Medium Gas Giant. Four
masses, age 4.7 billion years, effective temperature major moons: Io – Tiny (Sulfur), Europa – Tiny (Ice),
5,800 kelvins, luminosity 1.0 solar luminosities, radius Ganymede – Tiny (Ice), and Callisto – Tiny (Ice).
0.0046 AU.
Orbit 7 (Saturn): Orbital radius 9.5 AU, diameter
Orbit 1 (Mercury): Orbital radius 0.39 AU, diameter 75,000 miles, density 0.13, mass 95, blackbody temper-
3,900 miles, density 0.98, mass 0.055, blackbody tem- ature 90 kelvins, world type Small Gas Giant. One major
perature 445 kelvins, world type Tiny (Rock). No major moon: Titan – Small (Ice).
moons.
Orbit 8 (Uranus): Orbital radius 19 AU, diameter
Orbit 2 (Venus): Orbital radius 0.72 AU, diameter 32,000 miles, density 0.24, mass 14, blackbody temper-
7,500 miles, density 0.95, mass 0.82, blackbody temper- ature 64 kelvins, world type Small Gas Giant. No major
ature 328 kelvins, world type Standard (Greenhouse). moons.
No major moons.
Orbit 9 (Neptune): Orbital radius 30 AU, diameter
Orbit 3 (Earth): Orbital radius 1.0 AU, diameter 7,900 31,000 miles, density 0.32, mass 17, blackbody temper-
miles, density 1.00, mass 1.00, blackbody temperature ature 51 kelvins, world type Small Gas Giant. One major
278 kelvins, world type Standard (Garden). One major moon: Triton – Tiny (Ice).
moon: Luna – Tiny (Rock).
Notice that Pluto isn’t listed as a planet here. Indeed,
Orbit 4 (Mars): Orbital radius 1.5 AU, diameter 4,200 present-day scientists aren’t in agreement on whether
miles, density 0.71, mass 0.11, blackbody temperature Pluto has any claim (other than tradition) to planetary
225 kelvins, world type Small (Rock). No major moons status. Instead, it can be considered an unusually large,
(but two moonlets). but otherwise typical, object of Sol’s Kuiper Belt (p. 131).
SPECIAL CASES
Several special cases can arise dur- tion-hostile places in our solar system. moon’s surface composition. A Tiny
ing world design. These require spe- If a gas giant’s moon has a signifi- (Ice) moon that suffers a great deal of
cial treatment – but they can also pro- tidal flexing will actually lose most of
vide interesting local situations for cant atmosphere, this will help protect its light volatiles through volcanism,
play. visitors from the radiation belts. Even leaving sulfur and sulfur compounds
a moon with a substantial atmosphere behind on the surface. The result is a
GAS GIANT will still have significant background Tiny (Sulfur) world, like Jupiter’s
MOONS radiation on the surface, but the blan- moon Io.
ket of air may make the difference
A gas giant’s major moons are like- between “inhospitable” and “instantly A lesser degree of tidal flexing caus-
ly to be interesting worlds in their own fatal!” es differentiation of the moon’s materi-
right, but they are subject to forces als, causing stony and metallic materi-
that most worlds are not. Tidal Effects al to sink toward the center while ices
rise to the surface. Greater differentia-
Radiation A gas giant’s major moons will be tion leads to subsurface oceans, as
subject to powerful tidal forces from water ice gathers close to the surface
A gas giant will normally have a the gas giant itself. If there are multi- and melts due to tidal heating.
very powerful magnetic field, which ple major moons, they will also exert Differentiation also means that the
tends to collect charged particles given tidal forces on each other, and those surface is “cleaner,” more likely to be
off by the primary star. A gas giant’s forces will actually change in direction composed of fresh ice without a dust-
major moons will often be placed so and strength as the moons orbit their ing of stony material (this will lower
that they orbit in this charged-particle parent planet. All of these forces will the absorption factor used in comput-
zone, subjecting their surfaces to tend to flex and strain the body of ing world surface temperatures).
intense radiation. For example, the each moon, heating them internally
surfaces of Jupiter’s large Galilean and encouraging volcanic activity. When designing a gas giant’s sys-
satellites are among the most radia- tem of moons, assign each Tiny (Ice)
In the case of icy moons of the Tiny moon its own degree of differentia-
(Ice) or Tiny (Sulfur) types, this tidal tion. In general, the innermost moon
flexing has a profound effect on the
124 ADVANCED WORLDBUILDING
may become a Tiny (Sulfur) world, Resonant Worlds coverage, or average surface tempera-
while other moons will experience ture. The planet gets heated evenly
decreasing differentiation as they are If a planet has orbital eccentricity over long periods, although the days
farther from the gas giant. A moon of at least 0.1, it’s possible for it to fall and nights are very long and so tem-
with greater differentiation is more into a stable resonant pattern rather perature variations may be very wide.
likely to have extensive subsurface than becoming completely tide-
oceans. locked. In this pattern, the planet One unusual feature of a resonant
rotates exactly three times in every world is the apparent motion of its pri-
TIDE-LOCKED two orbits, alternately presenting mary star. The length of the day is
WORLDS opposite faces to the primary star at actually twice that of the planet’s year.
every close approach. Since the planet’s orbital velocity
A world that is tide-locked to its changes depending on its position in
primary star experiences uneven Assign a resonant-world situation its orbit, the rate at which the sun
heating – its “day face” is constantly whenever it seems appropriate, or roll appears to move through the sky
being heated by stellar radiation, 3d for any planet with high enough changes at different times of day. In
while the “night face” is in constant orbital eccentricity that would other- particular, when the planet approach-
shadow. Heat can be transferred to wise be tide-locked to its primary star. es its periastron, the point of closest
the night face by conduction through On a 12 or higher, the world will be approach to the star, the sun appears
the planet’s body, or by circulation of resonant. to slow down in the sky, actually
the atmosphere or oceans (if any). If reverse its direction for a while, and
these transfers aren’t sufficient, then A resonant world will not be then return to its usual pattern of
the world’s supply of volatiles will tide-locked for the purpose of deter- motion!
tend to freeze out on the night face, mining its atmosphere, hydrographic
leaving the day face dry and nearly
airless.
Whenever a tide-locked world is
generated, refer to the following table
to adjust its physical parameters. The
required adjustments depend on the
original pressure category of the
world’s atmosphere.
Multiply the computed average
surface temperature (in kelvins) by
the day face entry to get the average
surface temperature on the day face.
Likewise, multiply the computed
average surface temperature by the
night face entry to get the average
surface temperature on the night
face. Adjust the pressure category for
the planet’s atmosphere to be equal
to the final atmosphere entry (and
alter the exact surface pressure to
fit). Finally, add in the hydrographics
penalty to the original hydrographic
coverage of the world (to a minimum
hydrographic coverage of 0%).
Tide-Locked Worlds Average Temperature Table
Original Atmosphere Day Face Night Face Final Atmosphere Hydrographics Penalty
None or Trace 1.2 0.1 None -100%
Very Thin 1.2 0.1 Trace -100%
Thin 1.16 0.67 Very Thin -50%
Standard 1.12 0.80 Standard -25%
Dense 1.09 0.88 Dense -10%
Very Dense 1.05 0.95 Very Dense -0%
Superdense 1.0 1.0 Superdense -0%
ADVANCED WORLDBUILDING 125
MASSIVE STARS As a massive star evolves off the field. As infalling matter moves
main sequence, its luminosity actually through this field, it gives off high-
The world-building system in this increases relatively little – perhaps by energy radiation, which is emitted as
book only covers stars of up to 2.0 a factor of 3-4. However, its effective intense beams of electromagnetic
solar masses in significant detail. temperature will fall well into the red radiation from the star’s magnetic
More massive stars are somewhat giant range and even below (2,500- poles. Most neutron stars rotate very
rare, and are unlikely to have planets 4,000 K). Given the formula for a star’s quickly (on the order of one rotation
of their own. However, if used sparing- radius (p. 104), it’s easy to see that a every second), so these beams of radi-
ly they may be interesting locations “red supergiant” star will be huge, pos- ation are sometimes swept through
for adventure in their own right. sibly several AU across! space. Anyone happening to lie on the
path of one of the beams will see the
When placing a massive star in the Such a swollen star might be a very star “blink” or pulse – hence the term
campaign, simply select its mass. exotic place to visit. A durable and pulsars.
Masses between 2.0 and 5.0 solar heat-resistant spaceship could even
masses are uncommon but not impos- dive inside the star, since its outer Pulsars can serve as very accurate
sible in any part of the galaxy. Masses atmosphere would be very tenuous (a clocks, since the “blinking” is very reg-
above 5.0 solar masses are extremely “red-hot fog”). ular. They can also serve as natural
rare, and no campaign is likely to need navigational beacons, since every pul-
more than one or two. Neutron Stars sar has a slightly different rotation
rate. If a ship that has managed to get
Luminous Stars Stars of two to eight solar masses lost in the galaxy can locate at least
end their lives much like less massive three known pulsars, it will be able to
Massive stars burn very brightly, stars – at the end of the red giant triangulate its position very clearly.
but not for very long. They appear very phase, much of the star’s mass is lost,
unlikely to have planets – in fact, the and the core collapses to form a white A neutron star always has a mass
most massive stars don’t exist for long dwarf. More massive stars die much between 1.5 and three solar masses.
enough to permit planets to form. A more violently, in a supernova explo- Select a mass, or roll 3d+12 and mul-
system with one of these massive, sion that blows off many solar masses tiply by 0.1 solar masses. The neutron
bright stars in it most likely has noth- of material in a single violent cata- star’s optical luminosity will usually be
ing but a scattering of asteroidal clysm. A single supernova will briefly negligible, although a few pulsars
debris (plus the usual cloud of comets shine more brightly than an entire flash visible light as well as radio
at a considerable distance). galaxy! waves.
A massive star’s neighborhood For stars of about eight to 25 solar Black Holes
can be a very dangerous place to masses, the supernova explosion gives
visit. Even the smallest stars in this rise to an exotic stellar remnant. The A star whose initial mass is greater
class give off a great deal of ultravio- stellar core’s gravity compresses it than 25 solar units faces the ultimate
let radiation, and a strong charged- beyond the degenerate level found in a end. Not even the pressures generated
particle stellar wind. Some of the white dwarf’s core. Free electrons are by neutronium can hold up the stellar
most massive stars are the so-called driven down into the atomic nuclei, core as it is compressed by gravity.
Wolf-Rayet variables, which give off forming an incredibly dense material The whole mass of the star’s core col-
an extremely strong stellar wind, called neutronium. The stellar rem- lapses into a gravitational singularity,
occasionally ejecting their topmost nant becomes a neutron star, a body the kernel of a black hole.
layers into space to form nested only a few miles across, more massive
shells of hot, ionized gas. than our own sun. A black hole, like a neutron star, is
an object only a few miles across. Its
The following table gives approxi- A neutron star’s surface gravity is gravitational influence is so strong
mate statistics for main-sequence extremely high, billions of times that not even light can escape. The
stars of 3.0 solar masses and above. greater than that of our Earth. It also gravitational singularity is surrounded
has an extremely powerful magnetic by an event horizon, marking the
Massive Stars Table
Mass Luminosity Temperature (K) Stable Span (years)
9,800 330 million
3.0 90 14,000 70 million
18,000 20 million
5.0 700 20,000 9.0 million
26,000 2.6 million
7.5 3,600 32,000 1.1 million
36,000 570,000
10 11,000 40,000 330,000
42,000 40,000
15 58,000 50,000 9,000
20 180,000
25 440,000
30 920,000
60 15 million
100 110 million
126 ADVANCED WORLDBUILDING
distance at which everything, includ- RED DWARF Flare stars produce flares on an
ing light, is trapped forever. Anything STARS irregular schedule, usually with an
that falls through the event horizon is hour to a few days between flares.
effectively cut off from the universe Red dwarfs (M-type main sequence More than one flare can be occurring
for the rest of time. stars) are one of the galaxy’s most at the same time. A flare takes only a
common stellar types. The range of few minutes to reach peak brightness,
The powerful gravity of a black habitable orbits around a red dwarf then declines slowly over the course of
hole has a number of odd effects. It’s star is quite narrow, and any planet up to an hour.
possible for light to go into orbit falling in that range is very likely to be
around a black hole, and light that is tide-locked to the star (see p. 125 for On a nearby planet, a flare will cre-
directed away from its vicinity will guidelines on the generation of tide- ate a “heat pulse,” raising surface tem-
lose a great deal of its energy. locked planets). As a result, a red peratures by up to 20% (measured in
Spaceships that venture too close will dwarf is unlikely to have any habitable kelvins) immediately after peak
be torn apart by tidal effects even if Garden worlds. Still, red dwarfs are so brightness. The heat pulse will be
they don’t fall past the point of no common that they may account for a weaker, but will last longer, on a world
return. significant portion of the galaxy’s hab- with a significant atmosphere. The
itable planets. flare will emit ultraviolet and X-ray
On the other hand, at a large dis- radiation as well. Those exposed
tance a black hole doesn’t have gravity Many red dwarf stars are flare stars. directly to the flare in vacuum will
any more powerful than that of a nor- A flare star throws off stellar flares, receive about 1 rad per hour of radia-
mal star of the same mass. Contrary to sometimes similar in size to the flares tion exposure. Those on a planet’s sur-
a great deal of TV science fiction, it that occur frequently on the surface of face will be somewhat protected by
won’t reach out and “suck in” matter our own sun. However, since a red any atmosphere.
that is safely in orbit or is passing by dwarf flare star is normally much dim-
quickly. It’s just that a black hole is mer than Sol, a Sol-sized flare on such Worlds near a flare star will be
much more compact than a normal a star can vastly increase its brightness unusual places. A lifeless world will
star, so the gravity in its immediate – doubling it or even more while the still have strange chemical com-
neighborhood is extremely intense. flare takes place! Meanwhile, red pounds on the surface, as flare radia-
dwarf flares are different from those of tion interacts with common ices and
A black hole always has mass of at a brighter star in one respect: they emit minerals over long periods of time. If
least three solar units; a good estimate many times as much ultraviolet and a world has life, that life will have
for its final mass is about one-eighth X-ray radiation. This radiation can be exotic adaptations to a high-radiation
that of the original star. Its luminosity, quite dangerous for any life on a world environment . . . and it may use the
of course, is zero (although matter orbiting close to the star. high-energy pulse of a flare in order to
falling into the hole will give off X-rays fuel bursts of unusual activity.
and other powerful radiation).
ADVANCED WORLDBUILDING 127
Assign flare stars as needed wher- dwarf stars in his setting, the follow- of the star can be determined. Refer to
ever red dwarf stars appear. To place ing optional rules can be applied. the Brown Dwarf Evolution Table
them randomly, roll 3d for any red (opposite); the luminosity and diame-
dwarf star; on a 12 or higher, the star Placing Brown Dwarfs ter given are those of a brown dwarf of
is a flare star. A flare star can be desig- the given mass at one billion years of
nated in its spectral type by an “e” Brown dwarfs should be assigned age.
added to the luminosity class. For as needed. If every star in a region of
example, an M5-type flare star has the space is to be placed on a map, then Now refer to the following table.
complete spectral type M5 Ve. brown dwarfs should make up at least Multiply the star’s base luminosity by
50% of the total. the Luminosity Multiplier for its age,
BROWN DWARF and multiply the star’s diameter by the
STARS For a more moderate placement, in Diameter Multiplier for its age. If the
which the occasional brown dwarf is brown dwarf is less than one billion
Occasionally she called up an of interest but most of them will be years old, treat it as if it were one bil-
inscape view of the outside. Erythrion ignored, use the following procedure. lion years old. The results are the cur-
itself was visible now, a gigantic red Whenever an M-type red dwarf star (p. rent luminosity and diameter of the
eye in the night. The halo world was a 127) is to be placed, roll 3d. On a 7 or brown dwarf.
brown dwarf, sixty Jupiters in mass, less, the star is a brown dwarf instead.
too small to be a sun and too big to be This applies both to solo red dwarf Brown Dwarf Satellites
a planet. Like countless billions of oth- stars and to red dwarfs placed as part
ers it moved through the galaxy alone of multiple star systems. Treat the brown dwarf in all
in the spaces between the lit stars. So respects as another star in the star sys-
small and invisible were the halo Brown Dwarf Properties tem. In Step 20, compute the inner
worlds that they hadn’t even been limit and outer limit radii normally.
known to exist until the end of the The most important properties for When computing the snow line
twentieth century. But to Rue, a brown dwarf are its mass, luminosi- radius, use the star’s base luminosity
Erythrion was huge and magnificent ty, and diameter. A brown dwarf’s (that is, the luminosity it had at one
and all the civilization she hoped to mass is by definition between about billion years of age). In Step 21, apply
ever see. 0.015 and 0.07 solar masses. Select a a modifier of -4 to the roll on the Gas
mass as needed, or roll 3d on the Giant Arrangement Table (p. 107).
– Karl Schroeder, Permanence Brown Dwarf Mass Table.
From that point on, the normal
Between the most massive planets Brown Dwarf Mass sequence of steps can be applied. The
and the lightest M-type stars comes a Standard (Ammonia) and Large
class of barely luminous objects, the Table (Ammonia) world types may appear as
brown dwarf stars. brown dwarf satellites. The Standard
Roll (3d) Mass (Garden) and Large (Garden) will
Unlike a gas giant planet, a brown never appear naturally, as a brown
dwarf is massive enough to ignite 8 or less 0.015 dwarf emits far too little visible light to
nuclear fusion in its core, burning support photosynthetic life.
the deuterium isotope of hydrogen. 9-10 0.02
Once the deuterium runs out, nuclear ROGUE WORLDS
fusion shuts down and the brown 11-12 0.03
dwarf begins to cool slowly. The The world had condensed, sunless,
fusion stage lasts only a few hundred 13-14 0.04 from a minor knot in some primordial
million years at most, but the cooling nebula. Dust, gravel, stones, meteoroids
process can last billions of years, as 15 0.05 rained together during multiple
heat leaks from the star’s core and is megayears; and in the end, a solitary
renewed by the process of gravita- 16 0.06 planet moved off among the stars. Infall
tional contraction. had released energy; now radioactivity
17 or more 0.07 did, and the gravitational compression
Brown dwarfs are difficult to
detect from any distance, but modern Brown dwarf stars evolve very
astronomy is beginning to locate them quickly for their first billion years or
in large numbers – both as compan- so of existence. After that, their further
ions to visible stars, and as independ- evolution follows a predictable pat-
ent stars in deep space. It’s possible tern. Once the age of a brown dwarf is
that brown dwarfs actually outnum- established (using the procedures in
ber the “lit stars” that are easily visible Step 17), the luminosity and diameter
across distances of many parsecs.
Some recent science fiction has begun Brown Dwarf Base Parameters Table
to use them as a background for sto-
ries. If the GM wishes to use brown Mass Luminosity Diameter (Earth diameters)
0.015 0.00073 17.5
0.020 0.0016 16.8
0.030 0.0045 15.9
0.040 0.0097 15.3
0.050 0.017 14.8
0.060 0.028 14.5
0.070 0.042 14.2
128 ADVANCED WORLDBUILDING
of matter into denser allotropes. Brown Dwarf Evolution Table
Earthquakes shook the newborn
sphere; volcanoes spouted forth Age Luminosity Diameter
gas, water vapor, carbon dioxide,
methane, ammonia, cyanide, hydrogen (billions of years) Multiplier Multiplier
sulfide . . . the same which had finally 1.0
evolved into Earth’s air and oceans. 1 1.0 0.96
0.94
But here was no sun to warm, irra- 2 0.41 0.93
diate, start the chemical cookery that 0.91
might at last yield life. Here were dark- 3 0.24 0.90
ness and the deep, and a cold near 0.90
absolute zero. 4 0.16 0.89
0.88
– Poul Anderson, Satan’s World 5 0.12 0.88
0.87
As a new star system is born, many 6 0.097 0.87
objects of about Earth’s mass or larger 0.87
may form, only to be ejected from the 7 0.080 0.86
system by a close encounter with one
of the coalescing gas giant planets. 8 0.067
These rogue planets are likely to wan-
der through interstellar space forever, 9 0.057
except in the unlikely event that they
are captured by another star. 10 0.050
Rogue planets are dark, cold 11 0.044
places. A sufficiently massive rogue
will generate some heat in its core, 12 0.040
due to radioactive decay and the
release of gravitational potential ener- 13 0.036
gy. Some of this heat may be trapped
for very long periods, melting ice 14 0.032
under (or even on) the surface. It’s not
impossible for primitive life to appear suit itself. Many worlds are suitable comets can be moved to impact on the
on such interstellar wanderers. for terraforming, the process of engi- world’s surface, bringing needed
neering a planet to be more hospitable volatiles. A Standard or Large world
Rogue planets would be very hard to settlement. can retain a breathable atmosphere
for any civilization to detect. They indefinitely, once it has one. Smaller
might provide valuable stepping- The GM may wish to assume that worlds will lose a breathable atmos-
stones between stars, especially for a terraforming has been common in his phere over time, but the process may
civilization that has no access to an universe. Perhaps most settled worlds take millions of years for a Small
FTL stardrive. Interstellar nomads have been “improved” in some man- world, or thousands for a Tiny one –
might even settle a small rogue, min- ner to make them more hospitable. Or time enough for a civilization to take
ing it for useful minerals and volatiles. perhaps a previous civilization left root.
behind terraformed worlds that are
Place rogue planets on the cam- still habitable. In these cases, the most A world that has too much atmos-
paign map as needed. To generate likely point to consider terraforming is phere is a considerable terraforming
their details, treat them as normal after Step 32, when the world’s physi- challenge. Atmosphere can be
planets with a blackbody temperature cal parameters have been established stripped away by forcing planetoids to
of about 30 K. Rogue planets are but before settlement patterns are graze the world. A larger body can be
unlikely to have satellites, and natu- established. forced into a collision, splashing large
rally they have no “day” or “year” portions of the atmosphere away.
based on their movement around a Atmosphere Neither of these techniques is very
luminous star. useful if the terraformers want to
If a world has a substantial atmos- leave the surface of the world more or
TERRAFORMED phere, but the atmosphere isn’t less intact . . .
WORLDS breathable, then its composition can
be changed. Most Marginal atmos- Hydrographics
The world design sequence in this pheres can be made completely
book generates worlds that are natu- breathable by tampering with the A world that has no liquid-water
rally stable over very long periods of local ecology, introducing large-scale oceans can be provided with them, or
time. Humans and aliens will find chemical plants or engineered life existing oceans can be expanded. Ice
these worlds as they are – but sapient forms that will change the composi- deposits can be melted with the appli-
life tends to alter its environment to tion of the atmosphere. A Standard cation of heat. If ice is not available on
(Ocean) or Large (Ocean) world can the surface, cometary material can be
be changed to Garden type with the introduced to provide it.
introduction of photosynthetic life.
Other transformations are more of a Reducing a world’s hydrographics
challenge. can be more difficult. If the world can
be cooled, ice caps will grow and lock
A world that has little or no atmos- up some of the world’s water.
phere can be given one. If a world is Removing water entirely presents
icy, the “makings” of an atmosphere many of the same problems as remov-
are already present on the ground and ing atmosphere.
need only to be heated up. Otherwise,
ADVANCED WORLDBUILDING 129
Climate insolation of the world. Meanwhile, a world, while the ecological “take-up”
world that is too hot can be cooled by of such gases can cool it.
A world’s climate is among the eas- placing a large shade in orbit between
iest items to adjust. Terraformers have the world and the primary star. Stellar To reflect these forms of terraform-
a number of options to heat or cool a radiation can be cut down to any ing, the GM can change the parame-
world, and many of them can be desired level if the shade is large and ters that control average surface tem-
implemented on a timescale of years opaque enough. perature. Subtle terraforming will
rather than centuries. adjust the absorption factor or green-
If such brute-force methods don’t house factor of a world. Brute-force
A world that is too cold can be appeal, a world’s reflectivity and terraforming with orbital mirrors or
heated with stellar mirrors or lenses greenhouse effect can be adjusted lenses actually adjusts the blackbody
placed in orbit to focus more light on slightly, changing average surface temperature of a world, and can even
the surface. Small mirror or lens temperature by several degrees. Dust, alter its effective world type. The
assemblies (called solettas) can heat pollen, or ice crystals can be seeded in blackbody temperature can be raised
regions to adjust local climate clouds or on surface ice, to make them by up to 20% (measured in kelvins), or
patterns. Large ones can be placed in more or less reflective. The release of reduced by as much as 50%.
a wider orbit to increase the total greenhouse gases can warm the
OTHER OBJECTS
“Start with the cometary halo,” Asteroid Belts contain chondrules, small beads com-
Carlos told me. “It’s very thin: about posed of iron, nickel, and other useful
one comet per spherical volume of the The world-building system some- metals. C-type asteroids are very old
Earth’s orbit. Mass is denser going times places asteroid belts in specific objects, remnants of the formation era
inward: a few planets, some inner orbits around a star. of a star system. They are quite com-
comets, some chunks of ice and rock, mon, representing about 75% of all
all in skewed orbits and still spread Asteroid belts vary widely in con- asteroids.
pretty thin. Inside Neptune there are tent. In a typical belt, the largest aster-
lots of planets and asteroids and more oids will usually be about 300-600 S-type (stony-iron) asteroids are
flattening of orbits to conform with miles in diameter. Perhaps a few hun- primarily composed of stony miner-
Sol’s rotation. Outside Neptune space dred asteroids will be at least 30-60 als, with a significant amount of metal
is vast and empty. There could be miles in diameter, and there may be also present. They make up 15-20% of
uncharted planets. Singularities to millions of asteroids at least a mile in all asteroids.
swallow ships.” diameter. Despite their sheer num-
bers, the asteroids in even a thick M-type (metallic) asteroids are
Ausfaller was indignant. “But for asteroid belt will not sum up to the almost entirely composed of nickel
three to move into main trade lanes mass of a small planet. They’re useful and iron. They make up 5-10% of all
simultaneously?” primarily because all of that mass is asteroids. Given their rarity and high
immediately accessible, not tied up in metal content, they are popular
“It’s not impossible, Sigmund.” a planet’s core . . . among asteroid miners.
“The probability – ”
“Infinitesimal, right. Bey, it’s . . . Asteroids are not all found at the Almost any asteroid may contain
near impossible. Any sane man would same orbital radius. For example, the water or other ices, although these are
assume pirates.” so-called Main Belt in our solar sys- most common among C-type aster-
tem has a mean orbital radius of 2.7 oids. In fact, these asteroids somewhat
– Larry Niven, AU, but most of the asteroids have resemble comets, and some of them
“The Borderland of Sol” individual orbits with radii between may be comets that have wandered
about 2.1 and 3.3 AU. Asteroidal orbits into the inner star system . . .
Aside from stars and planets, star are often mildly eccentric, or inclined
systems contain any number of other to the ecliptic plane. All of this means Stray Asteroids
objects, many of which can be inter- that an asteroid belt will take up a lot
esting elements in a campaign or plot. of space. A large asteroid’s nearest Asteroids can be found outside the
neighbors are usually millions of miles main asteroid belts of a star system. In
ASTEROIDS away, making collisions very rare. A general, any gravitationally stable
AND COMETS spaceship’s journey through a belt is orbit or region of a star system is like-
likely to be quite safe, asteroid-dodg- ly to contain asteroids or asteroidal
Asteroids (also called planetoids) ing scenes in science-fiction movies to debris.
are small stony bodies, usually found the contrary.
in the inner regions of a star system. One common place to find aster-
Comets and other icy objects are Asteroids are classified according oids is near the Lagrange or “Trojan”
found in the outer star system. The to their composition. points of a gas giant planet’s orbit.
world-building system doesn’t design These are points of gravitational equi-
these objects in detail, but they can be C-type (carbonaceous) asteroids are librium, always 60 degrees ahead and
assumed to exist in almost every star very dark, and are composed of light 60 degrees behind the planet’s position
system. compounds and minerals, including a on its orbit. An object in one of these
significant amount of carbon and pos- points will tend to stay there, and an
sibly some bound water. They also
130 ADVANCED WORLDBUILDING
object can take up an “orbit” that wan- wandering in its outer reaches, their the most famous of these are the
ders around one of the points but total mass adding up to that of a small “planet” Pluto and its satellite Charon.
never strays too far from it. A massive planet. Comets are remnants of the Dozens more have been discovered,
gas giant will tend to collect asteroids primordial star system, existing most notably the planetoid Sedna.
near its Trojan points. For example, almost unchanged across billions of
several hundred are known to exist in years, unless they happen to fall into Comets and larger objects in the
Jupiter’s Trojan points in our own the inner star system. Kuiper Belt may be useful objects for
solar system; there are likely to be space travelers. They are rich in ices,
thousands not yet known. Many comets exist in a flattened and can be used to supply water or
disk called the Kuiper Belt. The inner other useful volatiles. They are dark
Other asteroids are “planet- edge of this belt is at about the same and thinly scattered, and might pro-
crossers,” objects whose orbits cross orbital radius as the most distant plan- vide good places for a hideout or a
the orbit of one of a star’s major plan- ets, but the belt normally extends out- quiet rendezvous. They could even be
ets. If the orbits cross too closely, the ward for hundreds of AU. The comets settled by a sufficiently advanced civi-
asteroid is likely to collide with the and other objects of the Kuiper Belt lization.
planet, or to be ejected into a different are essentially “failed” protoplanets,
orbit after a close encounter. Any objects that never coalesced to form The Oort Cloud
given planet in a star system is likely another planet.
to have dozens of associated planet- On the very edge of a star system is
crossing asteroids, all of them subject Comets are sometimes shunted the Oort cloud, a “reservoir” of comets
to orbital change over time. into the inner star system, usually stretching from about 1,000 AU out to
through gravitational interaction with a distance of one to two light-years.
Some planet-crossing asteroids are some other object. When this hap- Unlike the Kuiper Belt, the Oort cloud
“quasi-satellites” of the major planets. pens, the comet takes up a more or forms an even sphere around the
A quasi-satellite is an object that orbits less eccentric orbit, often approaching inner system, and its comets can
the planet’s primary star, its orbital the primary star so closely that its icy approach the primary star from any
period equal to that of the planet, but materials boil off to form a long direction. The Oort cloud likely con-
with higher eccentricity. From the gaseous “tail.” After a number of pass- tains large protoplanetary objects, just
planet’s viewpoint, the quasi-satellite es through the inner system, a comet as the Kuiper Belt does, but so far
appears to follow a loop around the can meet a number of fates. After none such have been detected.
planet, never approaching too close or
wandering too far away. Quasi-satel- Comets are often described as “dirty snowballs”
lite orbits are not very stable, and usu- – they are dominated by water and other ices, but
ally change over time until the quasi- they also contain grains of silicate dust, metals,
satellite status is lost. and organic compounds. Any given star system
may have trillions of comets wandering in its
Planet-crossing asteroids are inter- outer reaches, their total mass adding up to
esting because they are often easy to that of a small planet.
reach from the associated planet. An
early spacefaring civilization may losing too much of its icy body, it can The Oort cloud provides some of
send expeditions to such asteroids fragment and add to the system’s pool the same plot hooks as the Kuiper
during its first ventures in off-planet of asteroidal debris. A close encounter Belt, although in this case the question
industrial development. A quasi-satel- with a planet can change its orbit, of finding any Oort cloud object
lite may also be a convenient place to causing it to take up an asteroid-like becomes very difficult. In the dark
put an observation post watching the path that stays in the inner system. Or fringes of a star system, any object is
associated planet, especially if the a comet can collide with a planet . . . hard to see by reflected light – and in
planet has no true satellites or if a the Oort cloud, comets are likely to
closer approach would be dangerous. The Kuiper Belt also contains larg- spend most of their time billions of
er objects, with compositions similar miles apart. There may be Pluto-sized
The Kuiper Belt to the comets but of size comparable objects in the Oort cloud as well;
to large asteroids. The largest of these Earth-bound astronomers have found
Comets and other icy bodies orbit objects will usually be 300-600 miles none in our own solar system, but this
in the cold outer reaches of a star sys- in diameter, and there are likely to be may only be because such objects are
tem, most of them never approaching hundreds or thousands in the 30-60 almost impossible to detect.
the habitable worlds of the inner sys- mile range. In our own solar system,
tem.
A comet is usually between one
and 30 miles in diameter. Comets are
often described as “dirty snowballs” –
they are dominated by water and
other ices, but they also contain
grains of silicate dust, metals, and
organic compounds. Any given star
system may have trillions of comets
ADVANCED WORLDBUILDING 131
ARTIFICIAL Who Needs
STRUCTURES Planets, Anyway?
Any star system can contain artifi- Human beings evolved on the surface of a planet, and are dependent
cial structures – objects that were built on several aspects of the planetary environment for their survival. They
or placed in the system by sapient need air to breathe, water to drink, and a pleasant temperature to live
beings. in. Even the planet’s gravity is important.
Asteroid Habitats Still, none of these requirements have to be met by living on the sur-
face of a ball of rock and metal massing sextillions of tons. Living on a
People living in deep space can planet has its disadvantages – most of its mass is buried and inaccessi-
build a home for themselves, turning ble, and in the meantime it’s very difficult and expensive to get off!
an asteroid or comet into a habitat.
Most of the techniques for building Many science fiction writers have speculated about civilizations that
asteroid habitats appear at TL9, when make almost no use of planets at all. Instead, they can use found mate-
extensive deep-space travel and indus- rials – the results of asteroid or cometary mining – to build artificial
try are possible. There are several vari- habitats. They can even settle the asteroids and comets themselves, tun-
eties of asteroid habitat. neling into the stone or ice and carving out habitable spaces.
Beehive habitats are three-dimen- Asteroids and comets can provide all of the raw materials for breath-
sional mazes of tunnels and cham- able air, drinkable water, and edible food. If there is no space for arable
bers, burrowed into the body of an land, agriculture can use hydroponics or outright food synthesis
asteroid or comet. Beehive habitats instead. Fusion power can be fueled by hydrogen liberated from volatile
usually have some surface installa- ices. Metals can be used to drive industrial production, including the
tions, such as landing pads, airlocks, industries needed to build spaceships or more habitats.
vents, tool sheds, and antenna farms.
They are almost indefinitely extensi- The major difficulty with deep-space settlement is gravity, or rather
ble, as the inhabitants continue to the lack of it. Humans who live in microgravity for a long time suffer
carve out new tunnels and chambers. progressive loss of health. The immune system declines, muscles
Their major disadvantage is that they and bones atrophy, and the cardiovascular and renal systems suffer
are hard to provide with gravity. problems.
Asteroids are rarely symmetrical, so
tunnels are driven in any convenient To overcome this obstacle, a habitat can be spun, providing an arti-
direction and “spin gravity” will rarely ficial substitute for gravity through centrifugal “force.” Alternatively, it’s
be perpendicular to the floor. If super- possible for genetic engineering to produce a human body that doesn’t
science gravity generation is available, suffer degradation in microgravity. Of course, superscience “artificial
this may not be a problem. Of course, gravity” can provide a healthy environment for human life too. Any
inhabitants that are genetically adapt- of these advances can give rise to a society that regards planets as
ed to microgravity will be able to live inconveniences rather than homes.
comfortably.
artificial gravity is provided by spin. rim. The spokes serve as elevators,
Cole habitats are built out of metal- A thick shell of slag, left over from the leading to a microgravity environment
lic (M-type) asteroids, melted with manufacturing process, provides at the hub where special manufactur-
stellar heat and reshaped to create a radiation shielding. ing processes can be run. A Stanford
hollow metal-hulled shell. A Cole habi- torus can house about 50,000 people.
tat is usually cylindrical, and is rotated O’Neill Cylinders: These are the
on its long axis to provide spin gravity. largest and most expensive space Bernal Sphere: A sphere, up to a
Nuclear power or stellar mirrors can habitats. A giant cylinder, as much as mile in diameter, with several smaller
be used to light the interior. The inte- several miles in length and a mile or cylinders attached. The sphere rotates,
rior surface can be terraformed with more in diameter, rotates on its axis to providing spin gravity in a strip
soil, water, and plants, permitting provide spin gravity. Inside is a com- around its equator, but the cylinders
“natural” agriculture and a pleasant plete terraformed environment, com- are left unrotating to house micro-
lifestyle. plete with park and urban zones. If gravity manufacturing. The sphere is
more living space is desired, cylinders easy to build, but the lack of spin grav-
Artificial Habitats can be paired, rotating in opposite ity across most of its inner surface can
directions – this also makes docking be inconvenient. A Bernal sphere can
With or without a convenient aster- easier. An O’Neill cylinder can house house several thousand people.
oid to use for building material, artifi- up to several million people.
cial habitats can be built in space. Smaller Stations: These range from
Aluminum, steel, and titanium can Stanford Torus: Smaller than the the classic wheel-shaped space station
be mined and launched into space O’Neill cylinder, the Stanford torus is that spins for gravity and has plenty of
with mass drivers. Power is provided shaped like a bicycle wheel, with spin radiation shielding, down to the much
by solar panels or nuclear plants, gravity and landscaping on the outer more basic “work shack” that lacks
132 ADVANCED WORLDBUILDING
much of either. Work shacks are usu- A rosette is useful primarily as a unless the hole is patched quickly.
ally cylinders or spheres, 30 to 300 feet convenience – the components are Finally, a ringworld is dynamically
in diameter and (if cylinders) up to guaranteed to remain close to each unstable; if it has a star at its axis,
five times as long. Some of these crude other at a fixed distance. A civiliza- there are no forces tending to keep
stations are made from old fuel tanks tion that builds many space habitats the star centered, and eventually it
or cast-off cargo containers. The only may use rosettes to keep them in may collide with the ringworld.
radiation shielding may be a cramped order. A much more advanced society
“storm cellar” that the crew uses to might place whole planets in a rosette Even with these disadvantages, a
ride out solar storms. configuration, possibly with a star at ringworld may be one way for an
the center of mass. advanced civilization to get lots of liv-
MEGASTRUCTURES ing room. If the engineering chal-
Macropower Stations lenges of an Earth-orbit-sized ring-
The light source was small and bril- world can be met, it will provide mil-
liant white, very like a view of Sol as Many objects in space can be lions of times as much habitable space
seen from the general neighborhood of tapped for power. Luminous stars, as a typical Earthlike world. Even a
Jupiter. The ring was huge in diameter, brown dwarfs, and even massive gas much smaller ringworld can house
wide enough to stretch half-across the giants all have powerful magnetic billions of people without crowding,
darkened surface of the dome; but it fields, which can be used to generate and can be designed to avoid some of
was narrow, not much thicker than the electric power. Electrically conduc- the concept’s drawbacks.
light source at its axis. The near side tive material is stretched through the
was black and, where it cut across the magnetic field, carrying massive cur- Ringworlds were invented by SF
light, sharp-edged. Its further side was a rents whenever the star or planet’s author Larry Niven, who used the con-
pale blue ribbon across space. field fluctuates. cept in a series of novels attached to
his “Known Space” universe. The
If Louis was growing used Macropower stations can be used author Iain Banks uses smaller ring-
to miracles, he was not yet so blasé as for a variety of purposes. Lasers can worlds, called “Orbitals,” in his
to make idiotic-sounding guesses. transmit power across great dis- “Culture” novels. The videogame Halo
Instead he said, “It looks like a star with tances, powering ships or industrial is also set on a small, ringworld-like
a ring around it. What is it?” installations. Particle accelerators structure.
can produce antimatter in bulk, to be
Chiron’s reply came as no used in power plants across a star Dyson Spheres
surprise. system.
Solar power is abundant and
“It is a star with a ring around it,” Ringworlds effectively inexhaustible. Its main
said the puppeteer. “A ring of solid mat- disadvantage is that only a miniscule
ter. An artifact.” A ringworld takes the notion of a amount of it is available on an
“torus habitat” to the largest possible Earthlike planet. If all of the energy
– Larry Niven, Ringworld scale. A ringworld is a large, ribbon- output of a sunlike star could be
shaped ring, the flat surface turned intercepted and used, it would be
A truly advanced civilization will inward, rotated at high speed to pro- enough to support a civilization mil-
be able to perform engineering on a vide spin gravity. The inside surface is lions of times as powerful as our
grand scale, literally rebuilding star sculptured and terraformed to provide own.
systems to suit their own purposes. an Earthlike environment. The edges
Some of the possibilities are as of the inside surface have high rim Of course, to intercept all of a star’s
follows. walls, holding in the atmosphere. output, a hollow shell has to be built
Light can be provided by a nuclear around it. This can be done with mil-
Rosettes power plant at the axis of the ring, or lions of individual artificial habitats,
by a nearby star. If the ring is very big, orbiting the star in belts and shells of
Objects in space are never motion- it can be placed around a star. varying size, blanketing it in all direc-
less, so a civilization that can move tions. Alternatively, a solid sphere can
large masses around has the problem Ringworlds are mathematically be built at a fixed radius, with habit-
of making sure they stay where simple, but actually building one safe- able surface on the inside. Either of
they’re put. One solution is the ly can be a terrible challenge. A ring- these structures is called a Dyson
rosette. A rosette is composed of world the size of Earth’s orbit would sphere, after the astronomer who first
equal masses (large habitats, aster- need to rotate at hundreds of miles proposed them.
oids, moons, planets) that are placed per second to provide Earthlike grav-
at the points of an equilateral figure ity; the ring’s foundation structure Dyson spheres are among the most
and given equal velocities around the would need to have more tensile detectable megastructures. As one is
system’s center of mass. The resulting strength than is theoretically possible built, it cuts off the visible light from a
system is dynamically stable. The for normal matter. Ringworlds are star, replacing it with the infrared
components will continue to orbit also vulnerable to meteor impacts. radiation of the sphere’s waste heat. A
their common center of mass, main- Any penetration of the ringworld Dyson sphere could probably be
taining their separation as long as floor will spill all the air into space detected by alert astronomers from
they’re not disturbed by any outside many parsecs away.
gravitational influence.
ADVANCED WORLDBUILDING 133
CHAPTER SIX
ALIEN LIFE AND
ALIEN MINDS
I emptied the magazine of my gauss rifle into the charging “You’re alive! How? I saw those myrmidons drag the three
myrmidon. Most of the shots glanced off its thick exoskeleton, of you into their tunnels.”
but a few found vital spots between plates and it went down
twitching. I reloaded, then scanned the area with my hand “It’s all right,” said Captain Panatic. “Toshiro here shot the
analyzer, checking for the unique electrical signature of the queen with a grenade launcher. Blew her all to bits. The hive’s
myrmidons’ nervous system. Nothing. destroyed.”
Then I heard a noise from the edge of the jungle and The feeling of relief at seeing them alive was cut by a cold
swung my gun up. Had they somehow learned to mask pang of fear. “Captain, do you know what happens in a
themselves from detection? The myrmidons were incredibly swarm-mink when the queen dies? It doesn’t kill the hive – it
adaptable, but how could they know what we were using to just stops the pheromones she produces to keep the soldiers
find them? My finger tensed on the trigger. from being fertile. If these creatures work the same way, you’ve
just replaced one queen with thousands!”
“Don’t shoot! It’s us!” I recognized Captain Panatic’s voice.
A moment later, he and Toshiro stepped into the cleared space “Oh.” He looked crestfallen. “I guess we’ll have to evacuate
around the perimeter fence, waving cheerfully. They had some the colonists and go nuclear.”
ugly-looking cuts and one of Panatic’s arms was in a crude
sling, but they were both alive and in good spirits. “As I recommended from the start.” Military men. They just
don’t understand that sometimes overkill is the efficient
option.
134 ALIEN LIFE AND ALIEN MINDS
ALIENS IN THE CAMPAIGN
Alien life in a space campaign can their animal models. If people aliens on attributes of inanimate or non-
fill a vast number of roles. The social tap into ancient travelers’ tales about living things. Plasma-beings that look
and political categories for alien exotic lands, beasts come from fairy like living flames are things, as are
species noted in Chapter 1 are pretty tales and fables about talking animals. cyborg races that have turned them-
much independent of biology – it Larry Niven’s Kzinti are beast aliens selves into machines.
doesn’t usually matter if the dominant based on Terran cats. Genetically
species are carbon-based or silicon- modified animals provide a rigorously MONSTERS
based, aquatic or aerial. “hard SF” way to use beast archetypes
even in a game universe without any Aliens as monsters are probably
From a dramatic standpoint, how- aliens at all. the oldest role of all – consider
ever, alien beings can fit into four cat- Grendel in Beowulf or the gorgons of
egories, and their biology and appear- Beasts are very effective because Greek myth. They are menaces, pure
ance do affect which one they belong they come with a ready-made and fair- and simple. Recent films like the
to. In science-fiction stories and films, ly consistent set of assumptions. Aliens series show the trope is alive
alien beings seem to naturally clump Eagles are fierce and solitary, so eagle- and well.
into types: people, beasts, things, and like aliens make good “proud warrior”
monsters. cultures. Some of those assumptions Monsters may or may not be intel-
about the relationship between eco- ligent. If they are, their cleverness only
PEOPLE logical role and personality inform the adds to the threat they present. The
alien-design rules in this chapter. whole point of a monster is that it’s
Aliens as people are probably the dangerous. If the monster can be
most common in modern science fic- Game Masters can also make use negotiated with or placated, it ceases
tion. They don’t have to look like of the mythical and legendary associa- to be a monster and turns into some
humans – Poul Anderson created tions of Earth animals when creating other kind of alien. The process of
many fascinating alien “people” with beast aliens. Snakes aren’t evil, but “reclassifying” monsters is an old and
very unusual shapes – but a humanoid because they have long been used as highly useful science-fiction plot.
appearance does make it easier to icons of evil in many Terran mytholo-
view them as “folks like us.” People- gies, a civilization of serpent-men Purely animal monsters may be
aliens have understandable motives aliens make natural campaign villains. “only” dangerous predators, or may
and rational goals. If they are in con- Lions aren’t particularly noble, but have some other reason for hunting or
flict with humans, the fight is likely to their association with royalty make attacking the heroes. Again, discover-
be about something like resources or lion-aliens good candidates for honor- ing the reason behind an animal mon-
living space. able aristocrats. ster makes a good adventure.
Sometimes, though, a monster is just
They don’t have to act exactly like THINGS a monster.
Earth humans, though. Often people-
aliens have one or more human traits “Happy b-b-birthday, you thing from In appearance monsters may be
cranked up to an inhuman degree. another world, you.” terrifying “things,” or beasts drawing
Some of these caricature traits are so on monstrous archetypes like Terran
common in fiction as to be standard – Porky Pig, Duck Dodgers wolves, or deceptively human-seem-
types: the warrior Race, the mystics, in the 24 1/2th Century ing “people” with a deadly secret
the ultra-rationalists. Their societies nature. In cinematic settings, mon-
can also parody an aspect of modern The most alien aliens are perceived sters may even look like demons or
human life. as “things” – icky and creepy, possibly undead.
not even really alive. They draw on our
Some readers have criticized peo- nearly reflexive reactions to things WORKING
ple-aliens as being just “humans in that sting and bite or spread decay. BACKWARD
funny suits” but others like the idea For a long time SF used alien things
that a mind is a mind no matter what simply as monsters, as when H.G. The bulk of this chapter is con-
body it wears. The issue will no doubt Wells used octopuses as the model for cerned with how to create realistic
remain in dispute until humans actu- his bloodsucking Martian invaders of alien species from scratch. There are
ally meet aliens and find out. Earth. But things don’t have to be even tables for randomly generating
automatically hostile; they may simply things like ecological niches and mat-
BEASTS be mysterious and incomprehensible ing styles. Given that humans won’t be
to humans. Things are intrinsically able to choose or predict what kind of
Beast aliens make use of arche- alien. If humans ever learn how they creatures we meet out there, random
types drawn from human perceptions think, things can turn into funny-look- creation or just doing what sounds
of Earthly animals. They can fit many ing people. cool is a reasonable and even realistic
of the same roles as people-type aliens, way to create aliens.
but their behavior and culture reflect While things often use “creepy-
crawly” animals like spiders and
squids for a model, they can also take
ALIEN LIFE AND ALIEN MINDS 135
But GMs may have a particular Some Common Aliens
role in mind when creating an alien
species, and sometimes the random Aliens in SF often fit into a standard type, and when used wisely
results won’t match. It’s a pain when those types can add a lot of resonance to a space campaign. Some
the planned “aggressive conquering common alien stereotypes include:
menace” turns out to be a species of
peaceful, sessile filter-feeders. Comic Aliens
When you know what kind of alien Foreigners are funny. Alien foreigners must therefore be even more
you want, the solution is to work back- funny. Certainly SF writers have gotten a lot of comic mileage out of
ward. Consult the alien personality aliens with bizarre and silly customs or their laughable incomprehen-
trait tables (see the box Alien Creation sion of our entirely normal and reasonable habits. Often comic aliens are
X) to select a proper mindset. Consult physically cute or funny-looking, typically unthreatening beast arche-
the modifiers for those tables and types like teddy bears, ducks, penguins, or otters. Comic Things are also
assign ecological niches, mating common.
habits, and other details that encour-
age those mental traits. From there, go Primitives
through the process and either select
or randomly generate other features Aliens that are much less technologically advanced than humans (at
of the species. least at the time of contact) are often “noble savages,” living lives
untainted by the corruptions of civilization. Or they can be just plain
savages who want to eat visiting space travelers. Either way they fit
into many of our stereotypes about “primitive” humans. They are often
people-aliens or beast-aliens. In appearance they tend to either fragile
beauty or menacing ugliness.
Example: Sean wants his alien Superminds
Andromedans to be a civilization of
“evil masterminds” for his campaign. Superhuman intellects can be mystical philosophers or ultra-
He consults Alien Creation X and advanced technologists, and sometimes are both. They are usually
decides he wants them to be benevolent (if a bit patronizing), but may be dangerous opponents if
Chauvinistic, Single-Minded (to let they think they’re being threatened. In appearance superminds are
them devise grandiose master plans), often physically frail with huge brains; disembodied brains supported
Curious (to encourage ethically- by machinery may be things. Superminds may also be completely
challenged weird science research), immaterial beings of “pure thought.”
Selfish, Callous, Imaginative, and
Paranoid. Consulting the modifiers, Warriors
he sees that they should have a small
-group social structure in which Warrior aliens are very aggressive, either from natural combative-
males keep harems, be pouncing car- ness or a militarized society. Sympathetic warriors may be bound by
nivores, have strong K-strategy, and honor and duty, while enemy warriors are often faceless hordes to be
be fairly small in size. At this point, mowed down. Beast-aliens based on carnivores are often warrior races.
Sean could choose to make them
beast-aliens modeled on Terran cats, and distinctive. He decides to give over egg-laying. To make them more
but he wants something more exotic them lots of body segments and an formidable he assigns them superior
exoskeleton like Terran insects, with senses, including Night Vision and
long legs for fast sprinting and a Acute Taste/Smell. There are still
poison-tipped tail. Since they’re some details to be filled out, but the
K-strategists, he chooses live birth Andromedans are definitely taking
shape.
LIFE
Being living things, we naturally LIFE AS WE most real-world searches for life on
think we know what life is. We’re alive, KNOW IT other planets. If it’s made of the same
rocks aren’t. But what about alien life? chemicals as Terrestrial life and does
How will astronauts landing on anoth- The simplest way to define life is to the same things, it’s alive.
er world be able to tell what’s alive and
what isn’t? say that it’s “like life on Earth.” This Life on Earth is based on nucleic
acids – enormously long molecules
has been the operating theory behind like RNA and DNA. They in turn are
136 ALIEN LIFE AND ALIEN MINDS
evolve. Ultimately the nucleic acids
Clashing Definitions evolved to the point where they
encased themselves inside billions of
Defining life has been a troublesome part of the search for living cells organized into huge mobile com-
things beyond Earth. Some scientists take a narrow definition: life must plexes controlled by powerful brains
be based on DNA in a water matrix, using proteins and getting energy capable of writing and playing RPGs.
from photosynthesis or the breakdown of organic molecules. Earth life,
in other words. This may sound restrictive, but it has its advantages. We Carbon and Water
know a lot about Earth life, and we can design experiments to detect it, Earth life is based on complex car-
even across interstellar distances. When you’re building a multi-billion- bon compounds for several reasons,
dollar space probe, that’s an important consideration. and those reasons make it likely that
living things elsewhere in the universe
Other scientists, especially those who have studied “extremophile” may do the same. First, carbon is one
organisms on Earth, are willing to allow for some weirdness in alien of the four most common elements in
life. They postulate life that gets its energy from sulfur or iron com- the universe, so just about any world
pounds, like some bacteria found in ocean volcanic vents. But they still is likely to have a substantial supply.
assume those organisms will be based on DNA and liquid water. Second, the electron structure of the
carbon atom makes it capable of
Researchers fond of wild speculation have adopted much looser forming large and complex molecules.
standards. They postulate that life is any system that can locally No other element known can do that
increase the level of organization, or that life is any system capable of as well as carbon.
undergoing evolution. These definitions allow for just about any kind of
life – including plenty of types nobody has imagined yet. Liquid water is also considered
crucial for life. On Earth, life formed
For the purposes of this book, we’re going to split the difference. in water, and just about all Earth life
We’re defining life broadly, including everything from energy-based uses water as a solvent and circulatory
organisms living in interstellar nebulae to nearly human creatures on fluid. Water has some properties that
nearly Earthlike planets. But we’re also assuming that Earthlike life is make it especially suited for use by liv-
the most common form, or at least the type most characters are going
to spend their time interacting with.
ing things. It is liquid over a fairly
broad temperature range (180 degrees
made up of smaller units called Which brings up the third useful Fahrenheit), so a planet can have large
nucleotides. Three interesting features ability of nucleic acids. Because DNA amounts of liquid water without an
make nucleic acids the fundamental is a long chain of units, parts of the unreasonably uniform climate.
molecules of life. The first is that they strand can change without destroying Second, water has a large heat capaci-
can replicate themselves. A DNA helix the rest of the molecule. So DNA can ty. This is important on several levels.
can pull apart into two strands, which mutate. Environmental factors and It means a planet with large water
can then each assemble new matching replication errors can create different oceans will have a fairly stable cli-
strands out of free-floating nucleotide daughter chains, which encode differ- mate, and it means that active organ-
molecules. When the first nucleic ent proteins. This lets DNA molecules isms won’t easily boil themselves with
acids started doing that in the primor- metabolic heat.
dial seas of Earth, one can say that life
began. In a very real sense, everything
done by living things on Earth since Alternate DNA
then simply reflects more and more
complex and sophisticated ways for The DNA and RNA molecules used by Earth life aren’t the only ones
nucleic acids to replicate themselves. possible. Scientists have discovered several nucleotide molecules (the
building-blocks of a DNA helix) that don’t occur normally, but which
The second useful ability of nucleic can plug right into DNA and function just fine. So even life very similar
acids is their ability to encode infor- to Earth life, based on DNA, might use a different “alphabet” at the
mation, in the form of nucleotide molecular level. Extending that metaphor, it’s also possible to use the
chains. This is important because dif- same nucleotides but encode proteins using entirely different sequences
ferent chains of nucleotides can – the same “letters” but a different “language.”
encode the formulas (known in the
trade as “sequences”) for building pro- The double-helix form is also not the only way to organize a DNA
tein molecules. That ability to molecule. Scientists have created complicated branching nucleotide
“remember” information and build chain structures, and alien life might use something like that instead.
“tools” let the nucleic acids alter their
environment – membranes to sur- Proteins are extremely complex and versatile molecules themselves.
round themselves for protection, It’s entirely possible that some type of carbon-based life uses giant self-
organelles to process organic mole- replicating protein molecules instead of nucleic acids as the carrier of
cules for energy, and so on. genetic information.
ALIEN LIFE AND ALIEN MINDS 137
Finally, water has an unusual prop- Organisms that breathe a gas other organics would have to be manufac-
erty: when it freezes it expands, so ice than oxygen use the same rule as tured by photosynthesis.)
floats. Most liquids get denser when water-breathers as described under
they freeze. This means a water ocean Gills (p. B49): it’s a 0-point feature that Hydrogen life from a low-energy
develops an insulating cover of ice balances their need for life support environment (like a supercold Pluto-
when it gets cold, whereas a freezing with the ability to breathe something type world) would probably be slug-
sea of ammonia would chill from the toxic to humans. If humans normally gish compared to humans, with
bottom up. Living things can survive can breathe the organism’s native Decreased Time Rate and a reduced
in a water ocean even when the air atmosphere but it contains some trace Basic Speed. However, astronomers
temperature is below freezing. This element missing from Earth-standard have identified gas giants orbiting
advantage of water also has its draw- air, that would qualify as a quite close to some stars where energy
backs – when an Earth organism Dependency, typically at the -25 or -50 is plentiful, so the possibility of very
freezes, the expanding water crystals point level. active hydrogen-based organisms
rupture its cells, killing it. (Some fish from a high-pressure environment
and frogs have evolved natural OTHER exists.
“antifreeze” chemicals to avoid this.) CHEMISTRIES
Organisms using a different solvent Ammonia Chemistry
might survive freezing with no ill While carbon molecules in water
effects. are the most plausible basis for life, Ammonia could replace water as a
they are by no means the only possi- medium for life. Ammonia has a nar-
Metabolism bility. And in a sufficiently big uni- rower liquid temperature range than
verse, even unlikely forms of life may water, so it would require a planet
Originally, Earth life did not find congenial conditions. Just about with a very stable climate between -
breathe oxygen, because billions of all aliens with variant chemistries 108° Fahrenheit (-78° C) and -27° F (-
years ago there was no oxygen to should take the Unusual Biochemistry 33° C). In that cold environment, it’s
breathe. Early life on Earth was anaer- disadvantage in human-centered possible for something like Terrestrial
obic, getting energy by fermentation campaigns. nucleic-acid chains to function, or for
and related processes. Even today complex chains of nitrogen or carbon
there are whole kingdoms of anaero- There are several ways in which life and nitrogen to serve the same pur-
bic bacteria to which free oxygen is could have a different chemical basis pose. Since complex nitrogen mole-
pure poison. from Earth life. It could use different cules become highly unstable at liq-
solvents, like ammonia or hydrocar- uid-water temperatures, ammonia-
Humans breathe oxygen because bons in place of water. It could use dif- based organisms could be made of liv-
plants and cyanobacteria produce it as ferent molecules to store genetic infor- ing high explosive! (This does not
a waste product of photosynthesis. In mation, like silicate chains or complex require the Explosive disadvantage,
effect, we’re breathing pollution. If nitrogen compounds. It could use an however, because the temperatures
green plants and algae did not con- entirely different family of com- involved would kill the being
stantly renew the supply, Earth’s pounds for metabolism, genetics, and long before its molecules became
atmosphere would lose its oxygen, tissues. unstable.)
becoming a mix of nitrogen and car-
bon dioxide. (Any other world that has Hydrogen Chemistry Ammonia-based life could conduct
highly reactive atmospheric gases is a photosynthesis if it evolved on a cold
good candidate for life, since some- Hydrogen is the most abundant Earth-type planet, or might tap the
thing has to be making them.) Oxygen element, and giant planets like Jupiter heat differential between layers of a
is very reactive, and oxygen-breathers are essentially big balls of hydrogen. If gas giant world’s atmosphere. Such
can support a very active lifestyle. hydrogen-based life is possible, the creatures probably would not be oxy-
Aliens from a world with a different Universe holds a lot of potential places gen-breathers, since the chief source
atmosphere might not be able to sus- for it to arise. In extremely dense of oxygen molecules for Earth-type
tain the level of activity found on hydrogen (near the core of a gas giant, life (carbon dioxide) is a solid at
Earth. for instance) crystals of solid hydro- ammonia-life temperatures. Instead,
gen could store “genetic” information ammonia-based organisms might
Chlorine is quite reactive, and in a lattice structure. breathe free hydrogen, either in a gas
would serve as a good oxygen replace- giant atmosphere or liberated from
ment, on a world where the local At more normal pressures and very methane molecules on a cold
plants use photosynthesis to break up low temperatures (-250° F or below) Terrestrial world.
salts and store energy in sodium com- lipid molecules (akin to fats found
pounds. The result would be a chlo- in Terran life) could be the basis Living creatures based on ammo-
rine-laced atmosphere and oceans of of life in a medium of liquid hydro- nia should define their Temperature
bleach. Because chlorine is a much gen. Hydrogen-chemistry organisms Tolerance range as centered some-
less abundant chemical than oxygen, would use “reduction” reactions to where between -100° F and -25° F;
such worlds are probably vanishingly release energy by combining organic they are not automatically Cold-
rare, but chlorine-breathers have a molecules with hydrogen. (The Blooded in the sense defined by the
long history in science fiction. disadvantage of that name, however.
Hydrogen-breathers may take the
138 ALIEN LIFE AND ALIEN MINDS
disadvantage Fragile (Combustible) if
they spend lots of time in oxygen envi-
ronments, as their “air” can catch fire.
Since chemical reactions are slower at
ammonia temperatures, either a low
Basic Speed or Decreased Time Rate
might be appropriate.
Hydrocarbon Life equally ignorant of the flimsy water- underground “ocean” of liquid sul-
based life hugging the cold outer sur- fur. In the absence of free oxygen,
The Huygens probe found signs of face of the planet.) sulfur-based life could use carbon-
ancient methane lakes on Titan, and sulfur compounds, fluorocarbons, or
one might imagine larger worlds with Silicon-based life would naturally silicates as the basis of life. They
seas of heavier molecules like octane – set its comfortable temperature much could breathe hydrogen sulfide (the
gasoline oceans, in other words. Life higher than humans: somewhere gas that makes the “rotten egg”
on a “petrochemical planet” could around 300° F for sulfuric acid/silicon smell) or free hydrogen.
make use of the fantastic versatility of creatures, 500° F for silicon/liquid sul-
carbon in ways Terran life has only fur organisms, and 2500° F or higher Another possible solvent for sulfur-
begun to explore. Organisms made of for silicon/liquid rock beings. Silicon- based life is sulfuric acid. On Venus,
complex polymers (“plastic”) or lipids based fluorine-breathers adventuring the clouds contain fairly large
(“fats”) could swim in those oily seas. in an oxygen environment should take amounts of sulfuric acid, and it’s not
Instead of oxygen respiration, organ- the Combustible disadvantage, and impossible to imagine a slightly cooler
isms on a hydrocarbon world would possibly Increased Life Support to Venusian world with lakes or small
probably make use of the “reduction” reflect the extraordinary difficulty of seas of acid on the surface. Since a
reaction, breathing hydrogen. handling fluorine gas. strong acid like sulfuric acid can dis-
solve rocks, sulfuric acid would also
Hydrocarbon-based organisms are Since high temperatures speed up be a good medium for silicon-based
likely to be Fragile (Combustible), if chemical reactions, silicon beings life using sulfur chemistry for metabo-
not Fragile (Flammable) or even might live faster than us cold and slug- lism. Civilization on such a world
Fragile (Explosive), but only when gish humans. This can mean either an might never develop metal-based tech-
adventuring off-planet in oxygen envi- increased Basic Speed, or the advan- nology, as only “noble metals” like
ronments. As with ammonia-based tages Altered Time Rate or Enhanced gold would be able to resist the fantas-
life, hydrocarbon organisms from a Time Sense. tic corrosion of an acid-laced atmos-
cold environment might have low phere for very long. Instead one can
Basic Speed or Decreased Time Rate. Sulfur-Based Life imagine silicon-based organisms
developing a combination of “biologi-
Silicon and Silicones Sulfur-based life could use liquid cal” ceramics and silicones as their
sulfur as a solvent much as we use primary materials for tools and
On hot planets, silicon-based life water. On Jupiter’s moon Io, vol- machinery.
becomes a possibility. Silicon is chem- canos pour out large amounts of sul-
ically similar to carbon, though it has fur, indicating the possibility of an
no gaseous forms. Large silicon
objects on Earth are known as rocks,
but interesting chemistries become
possible when the silicon atoms alter-
nate with oxygen to form silicate
chains, or combine with carbon to
make the class of molecules known as
silicones.
Oxygen respiration is barely pos-
sible for silicate or silicone life, but
in the hot environment of a world
like Venus or Mercury, silicon-based
organisms could also get energy
from sulfur metabolism or reactions
involving fluorine. Silicon life using
iron chemistry for metabolism and
liquid rock as a solvent might thrive
in places like the Earth’s mantle,
hundreds of miles below the crust.
(For all we know the Earth’s mantle
is home to a busy ecosystem that is
ALIEN LIFE AND ALIEN MINDS 139
Sulfur-based life probably should
take the Increased Life Support disad- “I haven’t seen anything like that except, uh,
vantage among oxygen-breathers, to molecular acid.”
reflect the difficulty of handling large
amounts of sulfuric acid or molten “It must be using it for blood.”
sulfur. It’s possible that a sulfurous
organism would have a Bad Smell – Dallas and Brett, Alien
among oxygen-breathers, since pro-
tective suits might not be able to elim-
inate the rotten-egg odor. Sulfur-based energetic nebula) can store energy would be tens of kilometers long. Of
life from a high-temperature environ- and information in the form of elec- course, living on a star would certain-
ment might have Altered Time Rate. tric charges and magnetic fields. A ly provide enough room.
NON-CHEMICAL self-replicating pattern of electromag- Plasma life would be “immaterial”
LIFE netism could function as the “DNA” compared to solid creatures like
for plasma-based life. The plasma humans. This would best be modeled
organisms could get energy by tap- by the Body of Fire meta-trait. It
All of the “weird life” we’ve dis- ping the hotter layers lower down in would require Increased Life Support
cussed involves various chemicals the star’s interior. outside its native environment (as it
used to store energy and information. would need something like a fusion
But there are other ways to do those A “cell” of plasma-based life would reactor containment torus to live in
things. be larger than its chemical analogue, comfortably).
because all the processes of life would
be happening at nearly the speed of
Plasma Life light. The fundamental units of plas- Magnetic Life
ma-based life would probably be on
Organisms made of hot ionized the order of a centimeter in size, On a neutron star, matter is incred-
which means that highly complex ibly compressed by the gravity and the
plasma (within the photosphere organisms big enough for intelligence intense magnetic fields. Atoms take on
new shapes, their electron orbitals
of a star, or in a dense and highly
squeezed into rod shapes by magnetic
Alien Creation I field lines. In those conditions, normal
chemical laws break down, and it
Throughout this chapter there are boxes detailing how to create becomes possible for chains of single
alien life in GURPS terms. They are set up so the user can either make atoms to behave like DNA. The intense
decisions based on the game setting and the needs of the campaign, magnetic fields also provide an energy
or roll randomly. This system can also be used to create non-sentient source, leading to the possibility of an
creatures. entire ecosystem.
Life made of “degenerate matter”
Chemical Basis like this would be extremely different
from Earth life. It would be much
Select the alien’s biochemistry based on the climate of its home- smaller – a creature containing as
many atoms as a human would be
world, or roll randomly on 3d. GMs should feel free to disallow certain compressed down to microscopic size.
types of life or adjust the probabilities to suit a given game universe.
Roll (3d) Type of Life The smaller size and tremendous sup-
ply of energy allows a much faster
3-5: Hydrogen-Based Life pace. The physicist Robert Forward
wrote a fascinating novel, Dragon’s
(Frozen worlds below -250° F or Gas Giants) Egg, about life on a neutron star; in
the course of the story a civilization
6-7: Ammonia-Based Life arises on the star, develops science and
technology, and finally goes exploring
(Frozen worlds between -100° F and -30° F) the stars, all during the course of a few
days while bemused human scientists
8: Hydrocarbon-Based Life (Cold to Cool worlds) look on!
9-11: Water-Based Life (Cold to Hot worlds) Magnetic-based life on a neutron
star would be certain to have
12: Chlorine-Based Life (Cold to Tropical worlds) Enhanced Time Sense and several lev-
els of Altered Time Rate; they would
13: Silicon/Sulfuric Acid Life also require four levels of Increased
Life Support to duplicate neutron-star
(Warm to Infernal worlds between 50° F and 600° F) conditions.
14: Silicon/Liquid Sulfur Life
(Infernal worlds between 250° F and 750° F)
15: Silicon/Liquid Rock Life
(Infernal worlds above 2500° F, or mantle)
16: Plasma Life (Infernal worlds or stars above 4000° F)
17-18: Exotica
(Nebula-dwelling life, Machine life, Magnetic life)
140 ALIEN LIFE AND ALIEN MINDS
Artificial Life
An extremely plausible kind of non-biological life is self-replicating machine, erasing its original purpose
machine life. Humans are close to being able to build and leaving it no goal other than that of creating as
machines capable of creating copies of themselves, and many offspring as possible. Mutations (or conscious
some scientists have proposed launching self-replicat- design changes) in the offspring machines could even-
ing space probes toward other stars. Each probe would tually create an entire mechanical “ecosystem” of
create copies of itself and send them further off into predators, parasites, and prey. If the machines aren’t
space. In time the whole galaxy would be infested with intelligent to begin with, evolution might eventually
probes, all for the cost of a single launch. Others have produce sentience.
proposed similar techniques to create asteroid mining
robots or terraform other planets. Author Fred Alternately, artificial intelligence machines might
Saberhagen imagined “Berserkers” – self-replicating deliberately set out to create their own civilization
robot spaceships dedicated to annihilating all life they apart from organic life. In an advanced civilization
encounter. with “uploading” technology (like that presented in
Transhuman Space), the distinction between bio-life
Machine life need not have any physical existence at and machine life might seem as unimportant as the dif-
all: there could be entire civilizations of artificial-intelli- ference between acoustic and electric guitar music.
gence organisms living entirely within the memory of
complex datanets. Such “virtual life” could be descend- Whatever its origin, machine life can thrive in a
ed from organic life if it becomes possible to “upload” much broader range of environments than biological
an organic intelligence into data form. life. Machine life may or may not have the Machine
meta-trait, as highly evolved machines based on nan-
Mechanical intelligence could develop from sub- otechnology could appear to be living things even at the
intelligent machinery. One can easily imagine cosmic microscopic level.
rays inducing “mutations” in the programming of a
ECOLOGIES AND NICHES
An ecology is the sum of all living In environments with a strong heat In a science-fiction setting with
things in a given area. By definition, gradient, organisms might live by ther- superscience power sources like “cold
all living things are part of an ecology. mal energy. Humans are very familiar fusion” or “zero point energy,” some
A creature’s place in its native ecology with this; it is the basis of just about all organisms may have evolved to make
determines a great deal about it. our technology. Living things might use of them. This could allow for crea-
tap heat differential in a kind of tures that can make use of incredible
ENERGY FLOW “engine” like a boiler, or could use the amounts of energy, without needing to
electric current flow in heated metal eat anything at all.
Life can’t exist without energy. dipoles. Whatever the method, heat-
Every ecosystem is based on a flow of based life must have one end in the Nutrient Sources
energy from some non-living source. heat source and one end at a heat sink
Certain organisms (called autotrophs – there must be a flow to make things In addition to energy, living things
or primary producers) tap that energy work properly. Plasma-based beings need a reliable supply of chemical
and change it into forms that life can living on the surface of a star could do building blocks. For plants and other
use. the same. autotrophs, the important nutrients
are the basic chemical elements in
Energy Sources Radioactive minerals give off ener- forms they can use. Plants on Earth,
gy. To most Earth life radiation is haz- for instance, use nitrogen but they
On Earth, the chief source of ener- ardous, but some organisms might don’t get it from the air; they require
gy is sunlight, and plants are the pri- evolve to make use of low-level radia- nitrogen compounds in the soil or dis-
mary producers. On other worlds there tion. Gamma rays may be too ener- solved in groundwater, and those com-
might be different energy sources. getic, but beta particles could be a use- pounds have to be produced by bacte-
ful source of energy. The trick would ria. Less abundant elements like phos-
Chemosynthesis is the process of be finding enough radioactive material phorus, potassium, and others can
extracting energy from available non- to keep alive. On Earth it is thought limit biological activity even when
living chemicals. On Earth chemosyn- that a combination of volcanic activity energy is abundant. In the oceans, the
thetic organisms are mostly found and water-concentrated radioactive water at great depth is often nutrient-
near active volcanic sources, as those minerals at sites in Africa, creating nat- rich, but the environment is low in
provide a steady flow of energetic ural nuclear reactors that endured for energy, while surface water is nutri-
chemicals. Iron and sulfur are the centuries. On an alien world this might ent-poor. Upwellings where currents
most common bases for chemosynthe- be more common, especially with radi- bring up nutrients are apt to be places
sis on Earth. ation-eating organisms helping the of spectacular abundance.
process along.
ALIEN LIFE AND ALIEN MINDS 141
Consumers and the grazers that feed on them. Open Ocean is kind of like a desert
Because plains are so open, the things full of water: there’s plenty of energy
One good way to get energy is to that live there are often highly mobile. but no nutrients, so life is sparse.
steal it. As soon as a population of Isolated reefs serve as “oases” where
organisms exists that extract energy Swampland environments are living things cluster.
from the environment, other organ- another interface, where land and
isms are going to start extracting ener- water (or whatever the local fluid is) Reefs are similar to jungles in the
gy from them. And then in turn other meet, but there is protection from the ocean. They are places of abundant
creatures will start to eat the eaters, mechanical force of waves on the life, often dominated by large plants
and so on. Eating other living things shore. They support abundant life, or colony creatures (coral). Living
has the advantage that the food is very especially amphibious life. things are abundant and the local food
concentrated, so consumers – carni- web is complex.
vores and herbivores – can be large Woodlands, like jungles, are mature
and active. “climax” environments of large, slow- River/Stream environments are
growing primary producers. Unlike another interface, like beach or
Environment Types jungles, woodlands are subject to swamp, but have some unique fea-
greater climate variation, usually tied tures of their own. A river flows
The GURPS rules distinguish to the seasons. Food is abundant at through different environments, creat-
among 16 different types of environ- certain times of the year, but scarce at ing lots of micro-ecologies along its
ments: eight each for land and sea (p. other times, and everything in the course. The water level in a river
B224). These environments are obvi- environment must be able to cope depends on rainfall, so it usually goes
ously based on an Earthlike setting, with the cycle. On planets with through an annual cycle of high water
but they have analogies on every kind extreme climate variation, there may and drought. The creatures that live in
of world. be no jungles, only woodlands. By a river environment must be able to
contrast, on a planet with little climate cope.
Arctic environments are any place change, woodlands would be rare
where the temperature hovers around (replaced by something akin to a tem- Salt-Water Seas are isolated bodies
the low end possible for that type of perate or cool jungle-like, high-alti- of water where the salt level is concen-
life. For Earth life, it’s places where it’s tude tropical forests). trated by evaporation. Ordinary
often below freezing. For silicon- aquatic life has trouble handling the
based life it’s a chilly 200° F! In the ocean, Banks are coastal high-salt conditions, so they are the
waters where nutrients are abundant. aquatic equivalent of desert regions.
Desert environments are any place They can support a great deal of life;
where the necessary solvents or nutri- on Earth they are the great fisheries. Tropical Lagoon environments are
ents for life are scarce. There’s often One can call banks the marine equiva- the counterpart of beach or swamp-
plenty of energy, just no stuff to use. lent of plains, since they have lots of land: a coastal zone under the water.
Deserts also tend to extremes of tem- food but most of the animal life is Lagoons in particular are sheltered
perature. Life tends to be scarce, clus- quite mobile. and shallow, and can host a great vari-
tered around oases. ety of organisms. As in the other
Deep Ocean Vents are isolated coastal zones, many lagoon species
Island/Beach environments are an places where nutrients and chemical are amphibious.
interface between land and sea, and as energy are abundant, but the organ-
such are especially suited for amphibi- isms that live there must be highly Alien Environments
ous beings. The “sea” can be any kind specialized. Because they are isolat-
of fluid, obviously. Islands in particu- ed, each vent site is an entirely sepa- Many possible alien environments
lar can support isolated micro-ecolo- rate ecosystem with unique species. are not found on Earth. Most of them
gies where species evolve in unusual On ice-covered worlds like Europa, can be modeled by analogy with one
ways. vents may be the most thriving of the types described above. In a gas
ecosystems. giant’s atmosphere, upwellings of
Jungle settings are lush, dominated material from deep layers might cor-
by huge autotrophs (trees, on Earth). Fresh-Water Lakes are full of energy respond to reefs or banks in an ocean.
They support lots of life, but often that and nutrients, but they are isolated A seafloor away from vents or reefs
life has evolved an array of defenses. from each other and from the ocean. would be like open ocean.
Jungles offer many specialized niches They are also short-lived, geologically Subterranean environments might
for life to exploit. speaking, which means life doesn’t map well to oceans, with banks or
have a whole lot of time to evolve to lagoons where magma currents pro-
Mountain environments are often exploit a particular lake. Instead, most vide lots of nutrients. A system of
poor in resources for life, simply lake organisms enter via rivers and caves with native life would resemble
because fluids drain away downhill adapt to local conditions. On alien freshwater lakes or deep ocean vents
and erosion scours away the soil. At worlds, lakes are any isolated but in terms of ecology.
very high altitudes, even air is scarce! thriving aquatic environment that
Mountains often support lots of exists for only a few thousand years. More exotic settings can work by
“micro-ecologies” specialized for a There are some similarities between analogy, based on how abundant
particular altitude. island environments and lakes, as energy and nutrients are, and how
both are typically colonized by life easy the environment is to move
Plains are wide-open regions with from other regions. around in. Plasma-beings on the
fairly abundant life, dominated by
small area producers (grass, on Earth)
142 ALIEN LIFE AND ALIEN MINDS
Alien Creation II
Habitat Ordinary Animals: Roll 3d.
First decide where in space the organism lives. Roll (3d) Trophic Level
Space-dwelling life requires no planet. Planet-bound life 3 Combined Method: roll twice.
comes in two types: those native to gas giant atmos- 4 Autotroph (1-3: Photosynthetic, 4-5:
pheres, and those living on more or less terrestrial plan-
ets. Since we’re assuming the GM has already created Chemosynthetic, 6: Other)
the home planet of the aliens, those details should be 5 Decomposer
obvious. 6 Scavenger
7 Omnivore
For terrestrial planet life, determine if it lives prima- 8-9 Gathering Herbivore
rily on land or in water. Decide, or roll 1d: on a 1-3 it is 10-11 Grazing/Browsing Herbivore
land-dwelling, 4-6 it is water-dwelling. 12 Pouncing Carnivore
13 Chasing Carnivore
Modifiers: -1 if the planet’s surface is 50% ocean or 14 Trapping Carnivore
less; -2 if it is 10% or less; +1 if it is 80% ocean or more; 15 Hijacking Carnivore
+2 if it is 90% ocean or more. On planets that are entire- 16 Filter-Feeder (becomes Trapping Carnivore
ly water, the only land environment available is
Island/Beach. Worlds with 0% ocean coverage can only in Arctic or Desert)
have Salt-Water Sea, Fresh-Water Lake, or River-Stream 17-18 Parasite/Symbiont
aquatic environments. Gas giant life uses the water table.
Sapient Organisms: Roll 3d, no modifiers.
Then determine the specific habitat type. Roll 3d:
Roll (3d) Trophic Level
Roll (3d) Land Habitat Water Habitat 3 Combined Methods (roll twice)
Banks 4 Parasite/Symbiont
3-7 Plains 5 Filter-Feeder (becomes Trapping
Open Ocean
8 Desert Fresh-Water Lakes Carnivore in Arctic or Desert)
6 Pouncing Carnivore
9 Island/Beach River/Stream 7 Scavenger
Tropical Lagoon 8-9 Gathering Herbivore
10 Woodlands Deep-Ocean Vents 10 Omnivore
Salt-Water Sea 11-12 Chasing Carnivore
11 Swampland 13 Grazing Herbivore
Reef 14 Hijacking Carnivore
12 Mountain 15-16 Trapping Carnivore
17 Decomposer
13 Arctic 18 Autotroph (1-3: Photosynthesis, 4-5:
14-18 Jungle Chemosynthesis, 6: Other)
Trophic Level and Strategy
Now determine or decide how the organism gets its
energy. There are two tables, one for a random animal
in the environment, the other for potentially intelligent
life. Note that Deep-Ocean Vent autotrophs cannot be
photosynthetic. Some beings may use two methods.
surface of a star might be like sea conduct photosynthesis. One can photosynthesis would also help,
creatures, with “banks” in nutrient- imagine other autotrophs that use allowing either less collecting time or
rich regions. The fact that the nutri- solar power via the photoelectric smaller collecting area, although a
ents are upwellings of helium from effect, or which heat up a kind of practical maximum would be around
the stellar interior or concentrated “solar boiler” for power. 50%. Photosynthesizers might have
magnetic field loops doesn’t change to remain nearly immobile during
the logic of the ecosystem. Photosynthesis has an efficiency the day, giving them the Nocturnal
of roughly 1%, so on Earth could disadvantage.
AUTOTROPHS AND produce about one calorie per hour
DECOMPOSERS per square foot of collecting area. Some microorganisms live by
Since humans need some 2,000 calo- chemosynthesis, and if suitable
Autotrophs are organisms that tap ries per day, a plant-person would sources of energetic chemicals were
directly into primary energy sources need to have huge “solar panels” available they might evolve into larger
like sunlight or reactive chemicals. By with an area of at least 200 square multicellular forms. The source of
far the most common autotrophs on feet. On a planet with more intense those energetic chemicals would be
Earth are plants, which use sunlight to sunlight, the required area naturally hard to explain, however. Volcanic
goes down, so mobile autotrophs get vents are one good possibility.
more likely. A more efficient form of
ALIEN LIFE AND ALIEN MINDS 143
Decomposers equivalent of herbivores, since the what they eat), and can get quite large.
prey they hunt (krill) are about a thou- Browsers and grazers can have a
Decomposers get their energy from sand times smaller than they are. tremendous effect on the environ-
breaking down organic materials. On From a whale’s point of view, krill ment, preserving or even expanding
Earth, fungi and many microorgan- might as well be plants. Aliens that the area covered by grassland. In this
isms are decomposers. They aren’t pri- consume nonliving food (like active chapter, browsers and grazers are
mary producers like autotrophs – they chemosynthetic organisms or lumped together.
don’t bring energy into the system – machine life that mine what they eat)
but they do tend to resemble them in are functionally herbivores. One can Gathering
“lifestyle.” further subdivide herbivores by how
abundant their food is and how much Gatherers consume high-energy
Both autotrophs and decomposers work they must do in order to get it. food. Often this means they must go to
are usually static beings, since it’s hard a lot of trouble to find it. Some gather-
for a plant or a fungus to accumulate Filter Feeding ers specialize in a single food, and
enough energy to be active. Some develop highly specialized organs to
slime molds can move about, and Filter-feeders live in a fluid envi- locate and harvest it. Others prefer to
some plants (like Venus flytraps or ronment that is so rich in food they generalize. Gatherers tend to be small-
orchids) have structures that can react can just drink it in. They don’t even er than grazers and have excellent
to stimuli, but you don’t see them have to move – many Terran filter- senses. Their digestive systems can
striding across the landscape. All feeders live rooted to a single spot for generally cope with a variety of toxic
autotrophs and decomposers would most of their lives. They simply sit and chemicals. They are often fairly intelli-
probably qualify for either the Sleepy suck in material, sifting out the good gent, especially if they live in social
or Slow Eater disadvantages, and parts. In an abundant environment, groups. Some gatherers supplement
might have No Legs (Sessile) as well. like shallow tropical seas, filter-feeders their plant diet with smaller animals,
can get quite big; some sponges and scavenged remains, or eggs.
For autotrophs or decomposers to giant clams weigh hundreds of (Gathering is analogous to machine or
be as active as animals, they would pounds. In environments like deep physical life that must seek particular
need a very concentrated source of ocean vents, the distinction between a resources that are sometimes hard to
energy, and a need to be mobile. On a chemosynthetic autotroph and a filter- find, but which are fairly rich or
world with vastly more intense sun- feeder may be too subtle to notice. rewarding.) Specialized gatherers may
light than Earth, plants could move – Because filter-feeders typically have to have the Restricted Diet disadvantage,
but why? Plants would need to be process a lot of mass, they take the while gatherers that consume lots of
mobile only if they depended on some Slow Eater disadvantage. toxic plants can have the advantage of
resource that moved about (like inter- Resistant to poison, Reduced
mittent water sources in a desert, per- Grazing Consumption (Cast Iron Stomach), or
haps). Chemosynthetic autotrophs both.
might have to move around to find Grazing organisms eat low-energy
new sources of energetic chemicals. food that is very abundant. The chief CARNIVORES
Decomposers obviously need to be problem is just eating it fast enough.
able to seek out new sources of rotting Often their food has defensive chem- Carnivores are meat eaters. That is,
material, but the energy released by icals, which the herbivore’s digestive they consume other animals, or at
breaking it down is limited. system must be able to handle. least something that can try to run
Grazers can get quite large, especial- away or fight back. Herbivores in an
One possibility is autotrophs or ly if there is never any food shortage. environment with mobile plants
decomposers that are active only dur- Standing around and eating all day would effectively be carnivores,
ing a certain life phase. Imagine a doesn’t require much in the way of because of the need to subdue dinner.
plant whose “fruit” are like small ani- brains, but many grazing animals live Animal food is high in energy, so car-
mals, using stored energy to roam in in large groups, and can develop nivores don’t have to eat as often, but
search of the ideal place to put down complex social and communication this is offset by their frequent failures
roots and take up life as a new plant. abilities. (These concepts also apply to get a meal. They come in several
Another possibility is an autotroph or to any organism or machine that lives types, based on how much effort they
decomposer that can “moonlight” as a by processing large amounts of mate- put into getting their food.
consumer, especially if the environ- rial.) Grazers typically take the Slow
ment has large seasonal changes in Eater or Increased Consumption Scavengers
availability of energy. Maybe when the disadvantages.
winter days get short, the trees can get Scavengers prey on the creatures
hungry. A related type of herbivore are that are easiest to catch – dead ones.
Browsers. Like grazers they eat lots of They devour the remains of other
HERBIVORES low-energy food, but where Terran predators’ kills or animals dead of dis-
grazers eat grass and similar plants, ease and accident. Usually they have
In this discussion, “herbivores” browsers eat leaves from trees and impressive resistance to disease and
refers to any creatures that eat essen- shrubs. They may be tall (to reach decay toxins because much of their
tially unresisting food. On Earth, her-
bivores are plant-eaters, but one might
define the baleen whales as being the
144 ALIEN LIFE AND ALIEN MINDS
toward a waiting ambush; this can
involve a high degree of social com-
munication and planning. Others are
solitary.
Pouncing hunters are usually very
fast, with excellent senses and formi-
dable natural weaponry. Pouncers that
specialize in a particular kind of prey
can have elaborately specialized hunt-
ing mechanisms: woodpeckers hunt
beetles under tree bark, and their
whole skull and beak form a highly
developed chisel mechanism. Other
pouncers may use venom to subdue
their prey quickly (a Toxic Attack).
Typical pouncer advantages include
increased Move (possibly with the
Costs Fatigue limitation) or Super
Jump, improved Perception or specif-
ic senses, weapons like Teeth or Claws,
and possibly an Innate Attack. They
may have racial skill levels in
Brawling, Jumping, or Stealth.
food is half-rotted. Their senses must traps – spiders spin webs, and ant Chasers
be good to find carcasses. Many scav- lions dig pits. They must be patient,
engers also hunt small game if they since they have no control over how Chasing hunters go after larger
can get it, and some double as gather- often something will stumble close prey and invest a lot of energy in mak-
ing herbivores. They generally operate enough to catch, and the investment ing sure they get a successful kill.
alone or in small groups, although involved in building a trap is often Often they work in groups and coordi-
often quite a crowd can gather when considerable. Though the traps can be nate the hunt by well-developed com-
one finds a carcass. Scavengers usual- quite sophisticated, they are usually munication methods. Chasers must
ly have the advantage Resistant to built by instinct, and waiting for prey have good stamina and senses, to keep
Intestinal Disease and Spoiled Food, doesn’t require much intelligence or up with a big prey animal until it falls
or Reduced Consumption (Cast-Iron keen senses. Trappers are usually soli- from exhaustion. Solitary chasers are
Stomach). Among non-carrion-eaters, tary, since too many traps close especially impressive in this regard: a
their diet can also qualify as an Odious together can’t support their makers. Komodo dragon can hunt a deer for
Personal Habit. They often have an advantage con- days. Appropriate advantages include
nected to their trap mechanism, like Fit or Very Fit, high racial HT,
Omnivores Binding or Tunneling, and frequently increased Move or Enhanced Move,
have a fast-acting Innate Attack or and at least one improved sense.
Omnivores eat both plant and ani- Affliction to subdue victims (on Earth Racial skill at Tracking is likely.
mal food. As plant-eaters they tend to this is usually poison, but aliens might
function like gatherers, concentrat- use electric shocks, acid, or psionics). Hijackers
ing on high-energy food, while as They may have racial skill in
meat-eaters they are usually pounc- Camouflage, or some form of If you’re really big and fierce, you
ing predators, seldom investing a lot Chameleon ability. may not have to do your own hunting.
of energy in hunting. They are often Just find someone else who’s made a
fairly clever, as they have to be able to Pouncers kill and chase them away. That’s what
recognize a wide variety of potential hijackers do. They are frequently pow-
food items. While some Terran omni- Pouncing hunters catch prey with erful pouncing hunters picking on
vores work in groups, they are more swift attacks, often from ambush. smaller pouncers or chasers, although
likely to be solitary. They may have to make several a big omnivore could do just as well.
attempts for each success, but the Hijackers have to be large enough to
Trappers investment in a given attack is fairly be scary, and may have racial skill lev-
small. Pouncers nearly always go after els in Intimidation and Brawling.
Trapping carnivores are almost like smaller prey, so that the kill is easy. They probably have natural attacks to
filter-feeders: they sit in one place and Sometimes pouncers combine their back up their threats. Since most
let their prey come to them. Many efforts, with one or more driving prey hijackers also hunt their own food,
help the process along by building they can have all of the abilities of a
pouncer or chaser.
ALIEN LIFE AND ALIEN MINDS 145
Parasites and Symbionts
A great many organisms have found that the best disposing of waste products, or even helping the host
place to live is inside another living thing. They let the digest certain foods. (All large organisms on Earth use
host organism do all the work of getting food or energy symbiotic bacteria or fungi to help digest food.)
and keeping away predators. Parasites have several
ways to live off their hosts. Some drink blood, others Parasites may have the advantage of Possession
simply live in the host’s digestive system and eat its (Parasitic) if they can control the host’s actions (this
food, and some eat the host’s own tissues. isn’t entirely cinematic; on Earth there are many para-
sites that at least influence the behavior of the host crea-
Parasites need to be able to resist the host’s natural ture). They may also have an Innate Attack or Affliction
defenses, and often must go to great lengths to repro- making it possible for them to get into or attach to the
duce, since it’s hard to mate with a partner that is inside host. Parasites are likely to have a whole suite of physi-
another large animal. Many parasites have an active cal disadvantages, including Blindness, No
and mobile form when young, becoming nearly immo- Manipulators, No Legs, Invertebrate, and Restricted
bile once they’ve got a cushy spot in a host. Other crea- Diet.
tures are parasitic only as larvae, becoming free adults
once they emerge. (In science fiction the most spectac- Symbionts may be Resistant to whatever defenses
ular parasitic larva is of course the monster in the film the host creature puts up, and possibly have a
Alien.) Restricted Diet if they depend on a specific substance
produced by the host. Based on relative point values,
Symbionts differ from parasites in that they provide symbionts and their hosts may count as Dependents,
a benefit for the host; in effect they “pay rent” in Allies, or Patrons for one another. In extreme cases, the
exchange for food or protection. Potential benefits symbiont and host pair may be simpler to model as a
include fighting off parasites or other hostile organisms, single organism.
ALIEN ANATOMY
It’s highly unlikely that creatures up their weight, it’s noteworthy that trot, because would put too much
from an alien environment will look some large dinosaurs like stress on their bones. That doesn’t
much like Earth life. There are a few Tyrannosaurus rex managed to carry matter because they can walk pretty
basic features that result from simple many tons of weight on only two legs. fast anyway because of their long legs.
physical laws: anything that moves is A creature’s walking speed depends on Creatures optimized for running can
likely to have something like a head at the length of its legs and the local add the Enhanced Move (Ground)
the front end, with sensory organs gravity. Specifically, speed is propor- advantage.
grouped near the brain. Anything tional to the square root of leg length
above a certain size on land must have times gravity. This means that one can Many creatures have specialized
some kind of structural support. All generally run faster in high gravity, feet with Hooves or Blunt Claws for
organisms must have a way to get because the higher gravity makes you traction or protection against wear.
food or nutrients, and all must have a take faster steps. To convert this to Others get by with just tough soles. On
way to reproduce. GURPS terms, Move for aliens equals present-day Earth, hooves are found
5 times the square root of (L ¥ G), among herbivores, but this is purely a
MOBILITY where L is the aliens’ height or length historical accident. Alien worlds
divided by human height of 6 feet, and might well have hoofed meat-eaters.
Most animals have some way to G is the local gravity in gees. So for a
move around. Even sessile creatures creature from a planet with a gravity Slithering and Sliding
like oysters generally have a mobile of 0.5 G, standing 10 feet tall, basic
stage before settling down. Move should be about 4.5 yards per If you don’t have legs, you can’t
round, rounded down to 4; the same walk. But you can still get around by
Walking creature on a planet with 1.2 G would slithering – undulating your body or
have a basic Move of 7! (This is only as the surface of a special foot to move
For land animals, walking is the a guideline for creatures that evolved yourself along. Slithering is slower
method of choice for getting around. in a particular gravity; visiting a high- than running, and for large creatures
On Earth there are walking animals G world doesn’t automatically make it gets quite inefficient because it does
with any number of legs, from two to one move faster.) not store the energy of motion as
dozens. Though many SF writers have walking does. Slithering creatures get
assumed that animals on high-gravity Note that really big animals like the No Legs (Slithering) disadvantage.
worlds would need extra legs to hold elephants or the larger dinosaurs When figuring movement rates, be
never move faster than a walk or a sure to take extra encumbrance into
146 ALIEN LIFE AND ALIEN MINDS
account, which can slow down large, breaching the material by doing dam- for locomotion doesn’t have to come
heavy creatures considerably. age. Diggers use the standard Digging from the organism itself, but requires
rules based on their Basic Lift (p. fairly specialized wind-catching struc-
On low-friction surfaces like water, B350). Space opera aliens that can tures, and the winds may not always
ice, or loose sand, creatures can slide move through the ground as easily as be blowing where the creature needs
along. This is especially useful if one a fish through water can take the to go. On Earth, the Portugese man-
can get help from gravity and thereby Tunneling advantage. Burrowing crea- o’war is a sailing organism. Sailing
achieve high speeds without expend- tures are likely to have poor vision and qualifies an organism for the No Legs
ing any energy. This would be Terrain smell, but can have extremely good (Aquatic) disadvantage at the -10-
Adaptation (by terrain), or a 1-point hearing and the Sensitive Touch point level. Creatures with IQ 1 simply
perk (built-in skates), which would advantage. Vibration Sense is also go with the breeze, but more intelli-
then require a racial skill level in very useful. gent beings could have racial skill lev-
Skating or Skiing. Sliding can be com- els at Boating (Sailboat) to allow them
bined with sailing (below), and proba- Swimming to tack. Navigation would be another
bly requires walking or some other useful innate skill. While oceans or
form of locomotion as a backup. Swimming works in any fluid large lakes are the best places for sail-
medium of about the same density as ing, one could also imagine land-
Climbing the organism. Naturally, just about all dwellers in deserts, grasslands, or ice-
aquatic organisms swim. Even bot- caps that use sailing in conjunction
In forests or other environments tom-dwelling walkers like lobsters can with natural skis or wheels.
that offer a lot of handholds, creatures swim when they want to move fast.
can specialize in climbing and leaping Because of the properties of a fluid Finally, some aquatic creatures just
from branch to branch. This saves a environment, swimming gets more literally go with the flow. Floating is
lot of time getting down to the ground efficient as the swimmer gets bigger. about the easiest way to get around
and climbing up again, and it keeps Tiny organisms struggle through there is, if you don’t care where you’re
the animal out of reach of non-climb- water while whales can comfortably going or how long it takes to get there.
ing predators. Some Earth creatures, cruise at speeds of up to 20 knots and Aquatic filter-feeders or trapping car-
like gibbons, are specialized for effi- sprint up to 30. Since water also helps nivores can do quite well just bobbing
cient, long-distance locomotion by support large creatures, this means along, waiting for food to arrive, and
swinging from branches; this is called that swimmers can get massive of course autotrophs can just soak up
brachiation and it takes advantage of indeed. sunlight. Many floaters have some
the same pendulum effect used in swimming ability to avoid predators,
walking. The drawbacks to brachiat- A very different type of aquatic but may just rely on size (large to deter
ing are that eventually one runs out of movement is sailing, using the power attackers, small to avoid notice) or
trees, and that a failure means a of wind for motion. This has the poison for protection.
painful landing. Climbers should get tremendous advantage that the energy
Super Climbing advantage, and possi-
bly others like Brachiator, Catfall,
Clinging, and Perfect Balance. Racial
skill levels in Acrobatics and Climbing
are also appropriate.
Digging
In any environment with sand,
snow, or loose dirt, digging provides a
way to get at prey hiding under-
ground, or to lurk in hiding and attack
things on the surface. It’s also a good
way to hide, and provides insulation
against dangerous temperatures in the
desert or winter. Magma-dwelling sili-
con creatures might dig or swim in liq-
uid rock. Because diggers have to
move through a dense medium, size
becomes a problem. On Earth nothing
larger than an aardvark lives under-
ground full-time. For most digging
animals, Digging Claws would be a
1-point perk, equivalent to having a
built-in shovel. When tackling harder
materials they simply “attack” it,
ALIEN LIFE AND ALIEN MINDS 147
Flying possible to migrate with the seasons, reliable source of new reaction mass,
or find food in desert or arctic envi- rockets are too costly. Solar sailing is
Flying requires an atmosphere. ronments. Winged flight is Flight more likely, as space life is likely to be
There are several methods of staying with the limitation Winged, or possi- large in any case, and could use itself
aloft. bly Controlled Gliding. as a solar sail to change orbit. Plasma-
based life could spin a “plasma sail” or
Buoyant flight uses hot air or Wingspan for flying creatures use magnetic fields to catch the solar
a lifting gas less dense than the sur- depends on their weight and the atmos- wind. Game Masters who have super-
rounding atmosphere to create a pheric density. For a rough rule of science reactionless drives or psionic
living balloon. Balloons have to be thumb, divide weight (in local gravity) powers may wish to give space life one
very big to produce enough lift to get by 30 lbs. and take the square root, of those as a method of moving about.
off the ground, and all their tissues then multiply by 10 feet. This can vary Most space dwellers get Flight with
must be as light as possible. Buoyant by as much as 25% depending on what the Newtonian Space Flight limita-
flight also becomes feasible for kind of flyer the creature is – long- tion, though superscience beings may
extremely tiny organisms, which can range ocean flyers have long, narrow be able to have Space Flight alone.
“swim” in the air. A swarm-type being wings, while fast and maneuverable fly-
might use this kind of particulate ers have shorter ones. Wingspan goes SIZE
buoyancy. down in denser air and up in thinner.
Very long wingspans are difficult to Compared to most living things,
Hot air requires a heat source, make with biological materials; among humans are extremely large – the vast
which in turn requires a very abun- birds the record is 17 feet for the Pacific majority of life on Earth is single-
dant source of energy. Lifting gas albatross, and for fossil pterosaurs the celled organisms. On the other hand,
requires some metabolic process to widest known span is 35 feet for the existence of whales and huge fossil
make the gas. Many such gases are Quetzalcoatlus. That’s probably about dinosaurs show that creatures can get
also flammable, depending on the the maximum possible for Earthly very large indeed. Gravity and the
type of gas and the atmosphere. bone and flesh. Note that flyers that strength of materials place some
Buoyant flyers get the Flight advan- never land could have better-designed absolute limits on size, and ecology
tage with the Lighter Than Air limita- wings and a span of perhaps 50 feet. restricts size by limiting the food a
tion and a greatly reduced Move. large organism can get.
Immobile Creatures
Small creatures like spiders or The Square-Cube Law
plant seeds can get carried by the Some organisms just don’t move. It
wind. Movement rates will be at what- saves a lot of energy, and if they don’t A very important rule in biology
ever the local wind speed is, and there have to roam around in search of food governing animal size is the square-
is no control over direction. it’s a fine strategy. On Earth, cube law. It is a simple consequence of
Windborne organisms have Flight autotrophs like plants and aquatic fil- geometry. If you increase something
(Gliding; -50%; Lighter Than Air, - ter-feeders are all immobile. However, in one dimension, it increases in all
10%) [16]. Some windborne organ- reproduction poses a problem. For dimensions unless you change its
isms take flight only once during their sexual creatures, getting together is shape. Mass is a function of volume,
lives (typically as young); in that case difficult when you’re rooted in place, which increases as the cube of the
it’s a 0-point feature. and even asexual organisms don’t organism’s linear size. Since the
want all their offspring crowding strength of bones and muscles (or
Jet propulsion uses Newton’s Third around competing for resources. their alien equivalents) depends on
Law: by expelling gas in one direction, Sessile organisms often have elabo- cross-sectional area, those elements
the flyer propels itself in the other. rate mechanisms for dispersing increase as the square of the size.
Pushing the gas requires a lot of ener- gametes or larval young. Since they Consequently, doubling a creature’s
gy, making it fairly inefficient unless can’t run away from predators, immo- height means its muscular and struc-
the creature can tap something like bile creatures need good protection, tural strength increases by a factor of
combustion for power. Some organ- often in the form of thick shells, four (two squared). So far, so good.
isms use jet propulsion as an “emer- spines, or poison. But its mass increases by a factor of
gency getaway” method, when effi- eight (two cubed), so it is proportion-
ciency becomes less important than Immobile organisms have an ally only half as strong. This is why
speed. Jet flying is Flight with the lim- appropriate form of the No Legs dis- ants can heft leaves many times their
itations Cannot Hover and either advantage, depending on whether size, but humans have to strain to lift
Costs Fatigue or Limited Use. they are truly rooted in place or can objects even half their weight. In
drag or roll themselves along. GURPS terms, this is why a creature’s
Winged flight uses large flat sur- Basic Lift is based on the square of ST,
faces to push air down, driving the Space Travel which in turn scales with length.
flyer upward. This can be used in
conjunction with gliding, which uses Space-dwelling creatures must be The square-cube law has other
the flyer’s forward motion to generate able to move around. The obvious interesting effects. Warm-blooded
lift. Especially skilled gliders can use method is some kind of rocket propul- creatures must cool themselves to
winds and thermals to gain altitude sion, but that brings up the problem of regulate temperature; cooling occurs
without a lot of flapping, and some fuel. Unless the space life has a very
(like albatrosses) can stay aloft for
days at a time. Winged flyers can
cover very large distances, making it
148 ALIEN LIFE AND ALIEN MINDS