Saturn the ring world (Pathfinder edition)

EPaSArTctHiheFInNDcEeR EDITION

ON YOUR OWN

Saturn

The Ring World

By Lesley J. MacDonald

PATHFINDSEcRieEnacrteh
EDITION

It’s Time to
Explore on Your Own!

Good readers use multiple strategies as they
read on their own. Use the four key reading
comprehension strategies below:

1 Preview and
predict
• Look over the text.
• Form ideas about how the text is organized and what it says.
• C onfirm ideas about how the text is organized and what it says.

2 monitor and
fix up
• T hink about whether the text is making sense and how it relates to
what you know.
• I dentify comprehension problems and clear up the problems.

3 make
inferences
• Use what you know to figure out what is not said or shown directly.

4 sum
up
• Pull together the text’s big ideas.

Remember that you can choose different strategies at different
times to help you understand what you are reading.

Saturn

The Ring World

Pathfinder Edition

By Lesley J. MacDonald

Contents
2 Ring World
8 W hat’s in a Name?
10 Changing How We See Space
12 Concept Check

Ring Wo

2

orld By Lesley J. MacDonald
Saturn is one of the best-
known planets. Yet it is also
one of the most mysterious.
Now a spacecraft looks at
this amazing ring world.
3

ave you ever wondered what it would Lord of the Rings
be like to soar through Saturn’s rings?
A robot spacecraft got the chance to do Saturn is best known for its beautiful rings. It is
not the only planet that has rings. Three other
H that. It is named Cassini. planets—Jupiter, Uranus, and Neptune— also
In 2004, Cassini arrived near Saturn. The have rings. However, those rings are much
spacecraft had spent more than seven years thinner and harder to spot.
speeding through space. It had traveled more
than 3.5 million kilometers (2.2 million miles). From far away, Saturn’s rings look almost
Now it faced the most dangerous part of its like a single, perfect bracelet. But up close,
mission. things are much different. The planet actually
has about a thousand different rings. Some of
Cassini arrived below Saturn’s rings. It had them are even braided together.
to fly through them. The rings are made of
millions of chunks of ice and ice-covered rock. Tiny moonlets orbit alongside some of the
Some pieces are the size of a grain of sand. But rings. Their gravity may help keep the rings
others are as big as a house. Could Cassini together. Without the moonlets, particles that
avoid a collision? make up the rings might float away.

Luckily, Cassini made it through the rings Boldly Going. The Cassini
without a scratch. The spacecraft then started spacecraft rockets toward Saturn.
to orbit, or go around, Saturn.

Cassini isn’t the first spacecraft to go to
Saturn. Voyager 2 visited the ring world in
1981. But it didn’t hang around for long. After
snapping hundreds of photos, it zoomed away.

Cassini, on the other hand, isn’t going
anywhere else. It completed its mission to orbit
Saturn for four years. Now it is on an extended
mision. There’s a lot scientists want to learn
about Saturn and its rings!

A Gas Giant

Saturn is the second largest planet in our solar
system. A planet is a large object that orbits a
star. Only Jupiter is bigger. Saturn is so large
that 750 Earth-size planets could be placed
inside it.

Like its larger neighbor, Saturn is made of
gases. All we see on Saturn are clouds of gas.
However, a small solid core may be buried
deep below those cloud tops.

The gases in Saturn’s atmosphere may look
calm. They aren’t. They swirl around the sky.
Clouds, tornadoes, and hurricanes whip
around Saturn. At the equator, winds can
reach around 1,600 kilometers (1,000 miles)
an hour.

4

ring around the Planet.
saturn’s famous ring is really
about a thousand different
bands. these colors show
some of them.

5

Many Moons. Voyager 2 flew by titan
saturn in 1981. Its images appear
enceladus in this nAsA collage. now Cassini
rhea is taking new, clearer photos.

Saturn

dione Mimas
tethys

Meet the Moons Moon of Mystery

Saturn has more than 50 moons. Cassini The most amazing moon is Titan. It is the
discovered two of them. And the number of second largest moon in our solar system. And it
moons may continue to grow. may be the most fantastic. A thick atmosphere
covers Titan. The air is mostly nitrogen gas.
Scientists still have much to learn about
Saturn’s moons. Most of them are pretty small. Some scientists think that life may exist on
Not many are more than 966 kilometers (600 Titan’s surface. To find out, Cassini is giving
miles) across. Earth’s moon, in comparison, is the moon extra attention. The spacecraft
4,023 kilometers (2,500 miles) across. looked closely at Titan. Cassini gave us our first
glimpse of the moon’s surface.
Cassini is giving us clearer pictures of
Saturn’s moons. What are the moons like? Cassini saw dark streaks over part of the
giant moon. What caused them? The answer
Enceladus is one of the shiniest objects in may be blowing in the wind. Perhaps strong
our solar system. Its icy surface reflects lots of winds moved material across the surface.
light from the sun.
Cassini also saw large dark blotches on Titan.
Mimas has a huge crater. It’s 129 kilometers They might be lakes. If so, they’re not full of
(80 miles) wide and 9.6 kilometers (6 miles) water. Titan is too cold for liquid water. Instead
deep. The crater covers nearly a third of the the lakes may be filled with liquid methane. On
moon’s surface. Earth, methane is normally a gas.

Tethys has long, deep trenches. It also has
tiny moonlets. Imagine, a moon with moons!

6

Safe Landing. this picture
shows the Huygens spacecraft
landing on titan.

The Mission Continues Wordwise

Scientists still want to learn more about Titan. atmosphere: layer of air around a
The pictures that Cassini snapped do not show planet or moon
many details. One lake looks like a large cat
head. Other features look either light or dark. moon: large object that goes around
Scientists wanted a closer look at the surface. a planet

That’s why Cassini brought a tiny spacecraft moonlet: tiny moon
to Saturn. It is named Huygens. The ship was
made to land on Titan. orbit: to go around

After a bumpy ride, Huygens reached planet: large object that
the surface of Titan. Then it began gathering goes around a star
information—lots of it. The spacecraft studied
both the surface and the atmosphere. It found spacecraft: ship that flies
many rivers on the moon’s surface. through space

Cassini has just begun its great adventure.
We don’t know what other amazing discoveries
it will make. Perhaps one day, people will
follow the spacecraft to Saturn. We can only
imagine the sights they will see.

7

What’s in a
The Cassini and Huygens spacecraft
give us amazing views into space. Finding Rings
They show everything from Saturn’s
storms to moonlets dodging around the Huygens and Cassini lived in the 1600s. At the
planet. But what’s the story behind these time, people did not know much about space.
spacecraft? Why do they have such odd Scientists didn’t have spacecraft or cameras.
names? Simple telescopes were the tools of the trade.

The spacecraft are named after scientists These were just tubes with pieces of curved
who changed the way people think about glass inside. Yet in the right hands, they could
Saturn. Christiaan Huygens and Gian show amazing details of space.
Domenico Cassini lived a long time ago.
Yet their discoveries about this ringed planet Huygens used such a telescope. With it, he
were truly out of this world. saw things that no one had seen before. In
1655, he discovered Titan, Saturn’s largest
ring research. Huygens moon. The very next year, Huygens figured
below discovered saturn’s out that rings surrounded Saturn.
rings. this drawing by Huygens
shows saturn orbiting around At first, people thought he was crazy. Who
the sun right. had ever heard of rings around a planet? Yet
before long, his idea caught on. Saturn soon
became famous for its rings.

Seeing into Space.
Cassini and Huygens used
simple telescopes like this one.

8

Name?

Cassini’s Studies. Cassini
above also studied saturn. this
drawing shows a gap he found
in the rings left.

Filling the Gap Days of Discovery

Gian Domenico Cassini lived at about the Cassini and Huygens used the best telescopes
same time as Huygens. During the mid-1600s, available. But they also used their brains. First
both men worked in Paris, France. They both these scientists studied the sky. Then they put
studied the stars with a huge telescope there. their math skills to work. They did calculations
to figure out how the planets moved.
Cassini first made a name for himself with
discoveries about Jupiter and Mars. Yet Cassini By today’s standards, Cassini and Huygens
may be best remembered for his studies of used simple tools. Yet they were able to figure
Saturn. He figured out that Saturn’s rings were out how planets looked—and how they
made of rocky material. He discovered four of moved. Together, these men changed the way
Saturn’s moons. He was also the first to see a people understood space.
gap in Saturn’s ring system.
Scientists like Cassini and Huygens made
Today, this big space between the rings is amazing discoveries. But there is still much
called the Cassini Division. Cassini’s amazing to learn. Scientists find out more each day.
discoveries made him one of the most Yet every discovery leads to new questions.
respected scientists of his day. Someday you might help to find the answers.

9

Changing How

a Mountaintop View.
this building protects
a powerful telescope
on a mountaintop
in Hawaii.

Much has changed since the time Views From Earth
when Cassini and Huygens studied
space. Today we have tools that let The telescopes we use on Earth come in all
us study planets and stars in ways these sizes. Small telescopes let people study planets
scientists could never have imagined. and stars from their own backyards. But serious
scientists need telescopes with more power.
Not only do we have powerful telescopes on
Earth. We also have telescopes scooting around Some of these supersize telescopes are on
in space. We even have spacecraft with cameras mountaintops. There the sky is darker and
that send us pictures of worlds beyond Earth. clearer than in cities. Yet the sky can make
distant things look fuzzy—and some things
Tools like these let us see space like never are just too far away to be seen clearly. So
before. Each gives us new information about scientists have found ways to get a better view.
our universe. They send telescopes into space.

10

We See Space

Seeing in Space.
the Hubble space
telescope orbits earth.
It gives clear views
deep into space.

Pictures From Space Future Views

In space, telescopes aren’t clouded by lights The telescopes we use today change the way
or pollution. Their view is crystal clear. Today, we understand space. In fact, a new spacecraft
our best views of space come from spacecraft may help us learn more about a distant dwarf
loaded with telescopes and cameras. They planet called Pluto.
show details that cannot be seen with even
the largest telescopes on Earth. In 2006, the New Horizons spacecraft was
sent to Pluto. It will travel for eight or nine
Some of these telescopes orbit Earth. years before reaching the dwarf planet. Along
Others travel away from Earth and deep into the way, it will give scientists new views into
space. They send pictures back from places space. New Horizons will be the first spacecraft
where people cannot go. These spacecraft let us ever to visit Pluto. Scientists think its discoveries
explore planets, moons, and stars in new ways. will be worth the wait.

11

Concept check Saturn

Take a spin at these questions
to find out what you’ve learned.

1   How many moons do people
now think Saturn has?

2   How does Titan compare to
Saturn’s other moons?

3   What is the surface of Saturn
like? How do we know?

4   What are Saturn’s rings
made of?

5   How do scientists study
Saturn and other objects
in space?

Index Acknowledgments
Grateful acknowledgment is given to the authors, artists, photographers,
atmosphere  4, 6–7 museums, publishers, and agents for permission to reprint copyrighted material.
Cassini, Gian Domenico  8–10 Every effort has been made to secure the appropriate permission. If any omissions
Cassini (spacecraft)  4–8 have been made or if corrections are required, please contact the Publisher.
gravity  4
Huygens, Christiaan  8–10 Photographic Credits
Huygens (spacecraft)  7–8 Cover NASA-JPL; 2-3 Jason Reed, Getty Images; 4-5 Science Photo Library;
moon  4, 6–9, 11–12 5 NASA/JPL; 5 NASA/JPL/University of Colorado; 6 NASA/JPL; 7 NASA/JPL/
moonlet  4, 6–8 CalTech; NASA/JPL; 7 Science Photo Library; 7 Photo Researchers; 8 ESA;
planet  3–5, 7–11 8 Science Museum, London/Topham-HIP/The Image Works; 9 Victor Boswell, Jr.;
spacecraft  3–4, 6–8, 10–11 9 Mary Evans Picture Library/The Image Works; 10 Robert Madden, ESA;
telescope  8–11 11 Robert Madden, ESA; 12 NOAA.
Titan  4, 6–8, 12
Illustrator Credits
6-7 NASA-JPL

Neither the Publisher nor the authors shall be liable for any damage that may
be caused or sustained or result from conducting any of the activities in this
publication without specifically following instructions, undertaking the activities
without proper supervision, or failing to comply with the cautions contained
herein.

Program Authors
Kathy Cabe Trundle, Ph.D., Associate Professor of Early Childhood Science
Education, The Ohio State University, Columbus, Ohio; Randy Bell, Ph.D.,
Associate Professor of Science Education, University of Virginia, Charlottesville,
Virginia; Malcolm B. Butler, Ph.D., Associate Professor of Science Education,
University of South Florida, St. Petersburg, Florida; Judith Sweeney Lederman,
Ph.D., Director of Teacher Education and Associate Professor of Science
Education, Department of Mathematics and Science Education, Illinois Institute of
Technology, Chicago, Illinois; David W. Moore, Ph.D., Professor of Education,
College of Teacher Education and Leadership, Arizona State University, Tempe,
Arizona

The National Geographic Society
John M. Fahey, Jr., President & Chief Executive Officer
Gilbert M. Grosvenor, Chairman of the Board

Copyright © 2011 The Hampton-Brown Company, Inc., a wholly owned
subsidiary of the National Geographic Society, publishing under the imprints
National Geographic School Publishing and Hampton-Brown.

All rights reserved. No part of this book may be reproduced or transmitted in
any form or by any means, electronic or mechanical, including photocopying,
recording, or by an information storage and retrieval system, without permission
in writing from the Publisher.

National Geographic and the Yellow Border are registered trademarks of the
National Geographic Society.

National Geographic School Publishing
Hampton-Brown
www.NGSP.com

Printed in the USA.
RR Donnelley, Johnson City, TN

ISBN-13: 978-0-7362-7807-2

11 12 13 14 15 16 17 18 19
10 9 8 7 6 5 4 3 2

Product #4E90219
PATHFINDER