Головна Saturn (Space!)

Saturn (Space!)

Рік: 2009
Видання: 1
Мова: english
Сторінок: 64 / 65
ISBN 10: 0761442499
ISBN 13: 9780761445593
File: PDF, 6.12 MB

Prius (Cars)

Рік: 2009
Мова: english
File: PDF, 7.24 MB
Asteroids, Meteors, and Comets
The Dwarf Planet Pluto
Earth and the Moon
The Stars
The Sun



Titles in This Series


Saturn’s distinctive rings make it one of the most easily recognizable
planets in our Solar System. But this gas giant is more than just a
ringed planet. It is the second-largest planet in the Solar System
and has more than sixty moons. Saturn explores these planetary
features and is full of many other fascinating facts. Learn about new
discoveries, innovative technologies, and incredible explorations that
have given us many answers to our questions about outer space. So
come along on this incredible journey through Space!

Terry allan Hicks


Terry allan Hicks

Marshall Cavendish Benchmark
99 White Plains Road
Tarrytown, New York 10591
Text copyright © 2010 by Marshall Cavendish Corporation
or by any means electronic or mechanical including photocopying, recording, or by
any information storage and retrieval system, without permission from the copyright
All websites were accurate and available when this book went to press.
Library of Congress Cataloging-in-Publication Data
Hicks, Terry Allan.
Saturn / by Terry Allan Hicks.
p. cm. -- (Space!)
Summary: “Describes Saturn, including its history, its composition, and its role in the
solar system”--Provided by publisher.
Includes bibliographical references and index.
ISBN 978-0-7614-4559-3
1. Saturn (Planet)--Juvenile literature. I. Title.
QB671.H53 2010
Editor: Karen Ang
Publisher: Michelle Bisson
Art Director: Anahid Hamparian
Series Design by Daniel Roode
Production by nSight, Inc.
Front cover: A computer illustration of Saturn
Title page: The surface of Rhea, one of Saturn’s moons
Photo research by Candlepants Incorporated
Front cover: Brand X / Super Stock
The photographs in this book are used by permission and through the courtesy of:
Super Stock: Pixtal, 1, 12; Digital Vision Ltd., 9, 39, 58. Corbis: 4, 5, 30, 32, 33; NASA/Roger
Ressmeyer, 14; STScI/NASA, 35. Art Resource, NY: Réunion des Musées Nationaux, 7; Erich
Lessing, 21. Getty Images: Kevin Kelley, 10. Photo Researchers Inc.: Mark Garlick, 15, 34;
The Bridgeman Art Library, 20; Mary Evans, 23; 25. A P Images: NASA, 18, 19; European
Space Agency/ESOC, 50. The Image Works: World History / Topham, 27; Oxford Science
Archive / Heritage-Images, 24. NASA: Ames Research Center, 29; J PL/Space Science
Institute, 36, 40, 41, 42, 43, 44, 45, 46, 47, 48, 55; J PL/J HUA PL, 51; Craig Attebery, 53; ESA/
J PL/University of Arizona, 54. Illustration on page 17 by Mapping Specialists © Marshall
Cavendish Corporation.
Printed in Malaysia

Chapter 1

The Ringed Planet


Chapter 2

Saturn through the Ages


Chapter 3

A Closer Look


Chapter 4

Saturn and Beyond


Quick Facts about Saturn




Find Out More






On July 1, 2004, a spacecraft approached the planet Saturn, a
mysterious celestial object that has fascinated people on Earth
for centuries. The unmanned vehicle, named Cassini-Huygens,
had been launched from the space center at Cape Canaveral,
Florida, almost seven years earlier. As the spacecraft neared
the planet, it slowed itself down and allowed Saturn’s gravity
to capture it. For at least the next four years, Cassini-Huygens
would circle—or orbit—Saturn, while the spacecraft’s highly
sensitive instruments sent back valuable new information.
Saturn is the sixth planet from the Sun and is the secondlargest planet in the Solar System. Saturn has a diameter of
74,900 miles (121,000 kilometers) and is so big that about 760
planets the size of Earth could ﬁt inside it. This yellowish-brown
planet is marked by shifting horizontal bands of color and is
surrounded by dozens of moons.

Because of its many visible rings, Saturn is one of the most recognizable
planets in our Solar System.

But what truly sets Saturn apart from the other planets in
the Solar System is not its size or its moons, but the amazing
system of rings that surround it. Thousands of multicolored
bands circle the planet at its equator, shimmering with reﬂected
light from the Sun. Other planets have rings, but none are as
dazzling as Saturn’s. Ever since they were ﬁrst discovered,
almost exactly four centuries ago, astronomers have been
struggling to understand Saturn’s rings—what they are and
how they were created.

People on Earth have been aware of Saturn’s existence since
ancient times. Anyone carefully watching the night sky could
see it for most of the year, just as we can today. To the naked
eye, it would have appeared as a yellowish spot, a little larger
and a little brighter than most of the thousands of stars that
could be seen on any cloudless night. At times, it would actually
have been the brightest spot in the night sky. But to early
astronomers, there was little about this heavenly body to make
it seem different from all the rest—except for the unusual way
it acted.
Ancient astronomers, scientists, and religious leaders in
places as far apart as Babylon and China, Egypt and India, knew
that the Sun, Moon, and stars all seemed to move across the sky.



An artifact from around 400 BCE to 350 BCE shows
astronomical observations made by Eudoxus of Cnidus,
an ancient Greek astronomer.

Most of these early sky watchers mistakenly believed that all of
the bodies in the heavens circled Earth. Scientists did not begin
to realize that this Earth-centered view of the heavens was
wrong until about ﬁve hundred years ago. The early observers
watched the celestial objects closely, trying to follow and predict
their movements. The sky watchers noticed that a very few of


these objects—including the one we know today as Saturn—did
not move the same way as the rest. These “stars” appeared to
be in different constellations, or groups of stars, at different
times. They also seemed to grow brighter or dimmer at
different times. It was clear that they were somehow different
from the other stars. But many centuries passed before people
came to understand that these unusual objects were not stars
at all, but planets orbiting the Sun, the same way Earth does.
Saturn is now perhaps the best-loved planet of all, a favorite
for astronomers to watch and for schoolchildren to draw. But it
was not always a favorite because it was not easy to see. Until
strong telescopes were invented, no one even knew about its
now-famous rings.

To anyone staring up at the sky, the size of the universe seems
absolutely overwhelming. In fact, the universe is even larger than
most of us realize—perhaps even larger than we can imagine.
The known, or visible, universe—the part we can “see” with
telescopes and other types of instruments—is about 28 billion
light-years from one side to the other. No one can even guess at
the size of the parts of the universe that we cannot see. Many
astronomers, physicists, and other scientists who study space
believe that as huge as the universe is, it may still be expanding.



The distances in the universe are so great that a special unit,
the light-year, was created to measure them. Most scientists
believe that nothing will ever be able to travel faster than the
speed of light, which moves through empty space at a rate of
about 186,282 miles (299,792 km) per second. A light-year is
the distance—about 5.9 trillion miles (9.5 trillion km)—that light
travels in a year.

It is possible that the universe is
actually inﬁnite, with no beginning and no end.
The most important bodies in
the universe are the stars, huge
balls of ﬂaming gas spinning in
space. There are so many stars
that so far, no one has even come
close to being able to count them.
About eight thousand stars are
visible from Earth without a
telescope, though only about
half of them can be seen from
any one point at any one time.

There are billions of stars in the
universe, though only some are
visible to us from Earth.


Some astronomers estimate that there may be 70 sextillion—
that is the number seven, followed by twenty-two zeros—stars
in the known universe alone.
Most stars are part of galaxies, which are enormous, slowly
revolving clusters of stars, gases, dust particles, and other
matter that are scattered throughout the universe. There are
hundreds of millions of galaxies in the known universe, and a
single galaxy may have trillions of stars. The galaxy we live in,
which is known as the Milky Way, is hardly the largest galaxy in
the universe, but it, too, contains hundreds of billions of stars.
One of those stars is our Sun—the center of the Solar System.

An image from
the Hubble Space
Telescope shows
details of the M100
galaxy. Like the
Milky Way, M100
is called a spiral
galaxy because of
its shape.



The Solar System is made up of the Sun and all the many objects
that are held in place by its massive gravitational force. (The
Solar System is named for the Sun. Sol is another name for
the Sun, and solar means “of the Sun.”) There are billions of
objects orbiting the Sun, some of them huge, many of them not
much larger than specks of dust. They include the eight inner, or
terrestrial, planets (Mercury, Venus, Earth, and Mars) and the
four outer or gas planets (Jupiter, Saturn, Uranus, and Neptune).
But many other objects circle the Sun, including at least ﬁve
dwarf planets—one of them, Pluto, was considered a regular
planet until recently—and at least 170 moons, as well as comets,
asteroids, and many other smaller bodies.

The Sun
The Sun is not the biggest star in the sky, or the brightest. The
largest star that astronomers have identiﬁed so far, which is
called V Y Canis Majoris, is more than two thousand times the
size of the Sun. The brightest star, the Pistol Star, may give off
almost 2 million times as much light, producing more energy in
a single minute than the Sun does in an entire year. Despite their
size and brightness, neither of these stars can be seen from Earth
without special instruments because they are extremely far away
and our view of them is blocked by dust clouds in space.



Scientists predict
that the Sun will
run out of hydrogen
and burn out in
about 4.5 billion
years. Until then,
this intense star will
continue to be the
central point in our
Solar System.

Even if the Sun is not the biggest or brightest, it is the most
important star for the people and other living things here
on Earth. This is because it is the one closest to us. The Sun is
roughly 93 million miles (150 million km) away from our planet.
The Sun’s light takes about eight minutes to travel to Earth. The
light from the next-closest star, Alpha Centauri, takes a little
more than four years to reach us. Some stars that have recently
been discovered in distant galaxies are more than a billion lightyears away from Earth.
The Sun is also the biggest and most powerful object in Earth’s
neighborhood. It is six hundred times larger than everything
else in the Solar System combined. It is also the most important
energy source in the Solar System, producing incredible amounts
of light and heat. The Sun also has more than 99 percent of all


the mass in the Solar System. This incredible amount of mass
creates the gravitational force that keeps everything else in the
Solar System orbiting around the Sun.
The Solar System began to come into existence about 4.5
billion years ago. Scientists believe that this happened when a
cloud of hydrogen and other gases and dust at the edge of the
Milky Way began to come together. Nobody knows exactly why
this happened, but it may have been the result of the explosion
of a nearby star. Whatever the cause, the powerful gravity at the
center of the cloud began to pull the gases and dust particles
together. They became more tightly packed, and hotter, until
an enormous explosion occurred, creating a star—the star we
know today as our Sun.

The Birth of the Planets
The force of the explosion was felt far beyond the Sun. It sent gas
and dust particles ﬂying into space. The Sun’s gravity caused
these particles to form into a ring that revolved around it, and
their own gravity caused them to collide with one another.
Slowly, over a period of at least 100,000 years, groups of particles
began to combine into small bodies called planetesimals. These
eventually became all the objects—including the planets—that
now orbit around the Sun.
The Sun’s heat, or rather the lack of it, is the main reason the
planets farthest away from the center of the Solar System—such


as Saturn—are also the biggest. The planets closest to the Sun—
Earth, Mars, Mercury, and Venus—were exposed to intense
heat, which made it difﬁcult or impossible for ice to form. The
result was that these planets were made up mostly of
dust particles that, as they
grew and developed more
and more gravity, were
forced together, forming
into metallic rock.
Farther away from the
Sun’s heat, planets formed
differently. In these colder
regions, a planet’s rocky
core could attract not only
dust particles, but also ice
and gases. The four planets that were created there
attracted more matter, so
they became larger and
acquired more mass. More
Planetesimals pick up matter as
mass meant that the planthey move through space and
collide with other planetesimals
ets’ gravity increased and
and celestial bodies.
they acquired even more
matter and mass. These


The asteroid Belt
A huge expanse of space lies between the inner and outer
planets, between the paths of Mars’s and Jupiter’s orbits.
A planet could not be created in this area, 150 to 370 million miles (241 to 595 million km) from the Sun, because it
would have been torn apart by the huge gravitational force
of Jupiter. But billions of irregularly shaped pieces of rock
called asteroids—some large, but most less than 150 miles
(241 km) in diameter—orbit the Sun in this zone. Most of the
asteroids in the Solar System are found in this area, which is
known as the asteroid belt, but the very largest asteroids are
found farther away from the Sun, on the edge of the Solar


outer planets continued growing for millions of years longer
than the inner planets. The outer planets—Jupiter, Saturn, Uranus, and Neptune—became the gas giants we know today.
The gas giants are hostile, unwelcoming places, and Saturn is
no exception. It is extremely unlikely that any human being will
ever set foot on the surface of the ringed planet. For one thing,
there really is no surface, or at least no solid matter, for anyone
to stand on. Saturn’s “surface” is mostly gas, with some liquid,
and some strange areas that are like gas in some ways and like
liquid in others. The planet’s atmosphere is made up mostly of
hydrogen and helium, which humans cannot breathe. Saturn
is also bitterly cold, with average temperatures far lower than
even the coldest places on Earth. Saturn’s surface is also swept
by powerful winds and violent storms.
Even so, human beings are still fascinated by Saturn. This
is why astronomers have been watching it since even before
they knew it was a planet. It is why we have spent many years
and many billions of dollars building advanced spacecraft to
explore Saturn. It sometimes seems that the more we learn
about Saturn, the more questions we have. And we cannot help
but wonder what other secrets this ring-circled, storm-racked,
gas-shrouded giant may still be hiding.







Of the eight main planets in our solar system, the four closest to the Sun—Mercury, Venus, Earth, and Mars—
are the terrestrial, or land, planets. Jupiter, Saturn, Uranus, and Neptune are considered gas giants. Pluto,
which was once considered a main planet alongside the others, is now known as a dwarf planet.






It is impossible to say who ﬁrst noticed Saturn in the night sky,
but it was certainly a very long time ago. People have likely been
aware of Saturn’s existence since prehistoric times. The earliest
known writing about the planet comes from the Assyrians, a
people who lived in ancient Mesopotamia (modern-day Iraq).
They were skilled astronomers who created a calendar based on
the movements of the stars and other celestial objects, possibly
as early as 3000 BCE An Assyrian tablet dating from about 700
BCE describes a “sparkle” in the heavens. The Assyrians named
it the Star of Ninib, after one of their most important gods.

An image of Saturn taken by Voyager 2 in 1981 shows the planet’s true colors
and three of its many moons.


This ancient
Babylonian tablet
displays early
observations of
the movement
of the stars and

Many other ancient peoples were aware that some of the
“stars” in the sky did not act the way other stars did. Five of
these celestial objects, in particular, changed their position and
brightness over time, seeming to follow the paths of the Sun
and the moon closely. Three centuries after the Assyrians ﬁrst
mentioned the Star of Ninib, the Greeks called these curious
bodies planetes, or “wanderers,” which is the source of the
English word planet.
The Greeks, like the Assyrians and many other people, named
the celestial objects they saw after their gods and other ﬁgures
from mythology. They named the most distant of the planetes
for Kronos, the father of Zeus, the most important of the Greek


gods. The Romans, whose mythology was similar to the Greeks’,
knew Kronos by a different name. They called him, and the
planet, Saturnus, which is where we get the modern-day name
Many ancient peoples believed that celestial objects played an
important role in affairs on Earth. There is some truth to this,
because gravitational and
other forces affect many
aspects of life on our
planet, from the ocean
tides to the seasons to
the weather. For reasons we do not entirely
understand, many of
these peoples traditionally associated the planet
we know as Saturn with
farming. Saturnus was
the Roman god of agriculture, among other things.
The scientiﬁc symbol
for Saturn represents a
sickle, the harvesting tool
the god was often shown
The Roman god Saturn is
depicted on this fourth-

century stone carving.


By the sixteenth century, a few astronomers and other scientists
were beginning to understand that the traditional view of the
heavens—that all the objects in the sky moved around the
earth—was wrong. Nicolaus Copernicus, a Polish astronomer,
developed a heliocentric, or Sun-centered view of the Solar
System. In writings published in 1543, he claimed that all
the planets, including Earth, actually orbited the Sun. A few
years later, a young German scientist named Johannes Kepler
discovered that the planets’ orbits were not perfectly circular.
This meant that their distance from Earth changed, which
helped to explain why they sometimes seemed brighter than
at other times. Their distance from the Sun also changed, and
Kepler found that the closer an object was to the Sun, the faster
it moved through space. Kepler’s ideas were very important to
the growing understanding of Saturn and its rings.
The ﬁrst person to observe Saturn through a telescope was
a great Italian astronomer, Galileo Galilei, who had been greatly
inﬂuenced by these new ideas. His telescope was a very early
model that magniﬁed objects to only twenty times their actual
size, so he could not see the planet very clearly. But what he
did see, beginning in 1610, amazed him. That year, he wrote, “I


have discovered a most
extraordinary marvel
. . . the planet Saturn
is not one alone, but
is composed of three,
which almost touch
one another.” He did
not know it, but what
he thought were two
extra planets were
actually Saturn’s rings.
As he kept watching,
he saw that Saturn
seemed to change. Two
years after his ﬁrst
observations, he found
he could no longer see
the two extra planets
at all. But four years
later, in 1616, something
else that he described
as looking like “handles” had mysteriously

Using his handmade telescope,
Galileo was able to observe
Saturn, its rings, and one of its
moons, though he did not realize
he was seeing a moon and rings.



These drawings were created in 1656 by Johannes Hevelius, a
German astronomer who observed the different appearances of
Saturn. At the time, he did not realize that the strange shapes
he was seeing next to Saturn were its rings.



It was not until forty-ﬁve years after Galileo’s discovery
that it became clear what Saturn’s strange, seemingly everchanging shape really meant. A Dutch mathematician, physicist,
and astronomer named Christiaan Huygens, had a telescope
much stronger than Galileo’s. With that telescope,
he discovered a moon orbiting Saturn—the huge one
that later came to be called
Titan. The following year, he
realized that what Galileo
had seen must have been “a
thin, ﬂat ring” surrounding,
but not touching, the planet.
The reason it had looked so
different to Galileo at different times was that he
had observed the planet at
different angles and differChristiaan Huygens was the
ﬁrst to realize that Saturn
ent points in its orbit. When
was a ringed planet, but his
Saturn was tipped toward
assumption that there was
Earth, what Galileo saw
only one ring was incorrect.
looked like extra planets or


the handles of a cup, depending on the angle. When the planet
was positioned so that the rings were horizontal in relation to
Earth, they seemed to have disappeared.
Huygens was right about Saturn being a ringed planet, but
he was wrong about some other things. He believed there was
just one ring, several thousand miles thick, made of solid rock.
One important Saturn-watcher who disagreed with him was an
Italian-French astronomer named Giovanni Domenico (or Jean
Dominique) Cassini. Cassini made many important discoveries about Saturn, including the ﬁrst sightings of four of the
planet’s moons—Dione, Iapetus, Rhea, and Tethys. Looking
through the powerful telescope at the new Paris Observatory in
1675, Cassini saw that there was a space in Saturn’s ring, which
suggested that it was actually two rings. That space is known to
this day as the Cassini Division. Cassini believed the rings were
made up of many different particles, rather than solid matter.
It took more than two hundred years before this was ﬁnally
In the decades that followed, many more discoveries were
made about Saturn, but none of them were quite as dramatic
as Huygens’s and Cassini’s breakthroughs. More rings were
discovered (and another space between rings, known as the
Encke Division) and more moons. Then, in the late nineteenth
century, the question of whether Saturn’s rings were solid was
answered once and for all.



Cassini used the strong telescopes at the Paris
Observatory in France to identify four more moons of
Saturn and to closely observe the planet’s multiple rings.
Astronomers had discovered a third, semitransparent ring,
closer to the planet’s surface than the ﬁrst two. A Scottish
mathematician and physicist, James Clerk Maxwell, suggested
that Saturn’s rings would have to be made up of different
particles, because if they were not, the planet’s powerful gravity
would pull them toward it and destroy them. He also suggested,
drawing on Johannes Kepler’s now-centuries-old ideas, that the
three known rings would have to revolve at different speeds,



Naming the Rings
Saturn and its moons, like many other celestial objects, have colorful
names taken from the mythologies of the Greeks, the Romans,
and other ancient peoples, but its rings do not. The seven major
rings that are clearly separate have simply been given letters—A,
B, C, D, E, F, and G—that reﬂect the order in which they were
discovered. The A and B rings were ﬁrst observed by Galileo in
1610, though he did not know what he was looking at. It was not
until 370 years later, in 1980, that the G ring was identiﬁed.

the one closest to the planet moving the fastest. In 1895, an
American astronomer, James Keeler, proved Maxwell—and
Huygens—right. He used an instrument called a spectroscope to
measure the speed at which the rings revolved, and discovered
that the “inside” ring did indeed move faster than the others.
Scientists continued to try to understand how these strange
rings could have been created. A nineteenth-century French
astronomer, Edouard Roche, developed a theory that the rings
might have resulted when a moon or other large celestial
object approached Saturn and was shattered by the planet’s
gravitational force. This would have left rock and other particles
ﬂoating in space, held there forever by Saturn’s gravity. Another
theory is that the rings are simply made up of particles left over
from the creation of the planet itself.



The next great step forward in mankind’s understanding of
Saturn did not come until the second half of the twentieth
century, when powerful rockets began to make space travel possible. The ﬁrst spacecraft to come close to Saturn, in 1979, was
Pioneer 11, an unmanned probe that the National Aeronautics
and Space Administration (NASA) had sent to study Jupiter.
Pioneer 11 came to within 13,000 miles (21,000 km) of Saturn
and sent back the best photographs that had ever been taken

This image taken by Pioneer 11 gave astronomers a nice
view of Saturn, its rings, and Titan (upper left).



shows the
path that
Voyager 2
took as it
passed by

of the ringed planet. (The spacecraft discovered the previously
unknown F ring and identiﬁed another moon, Epimetheus.) Pioneer 11’s instruments showed that Saturn has a magnetic ﬁeld,
which proved that the planet’s core is made of metallic rock.
The following year, two more unmanned NASA probes,
Voyager 1 and Voyager 2, began a long-planned visit to the outer
planets. They had been designed to visit all four of the gas giants,
and NASA had sent two of them, just in case one did not complete its mission. Voyager 1 reached Saturn late in 1980, coming
much closer to the planet than Pioneer 11 had. The probe sent
back the ﬁrst high-resolution images of Saturn, discovered three
more moons and the G ring, and found helium in the planet’s


atmosphere. Voyager 1 also passed close enough to Titan that
scientists learned that the moon has an atmosphere—the only
moon in the Solar System known to have one. Unfortunately, the
clouds of gas in the atmosphere made it impossible to take pictures of the moon’s surface. The companion probe, Voyager 2,
took even more dazzling pictures of the planet.
In the years that followed, other excellent photographic images
of Saturn were received, from the Hubble Space Telescope, which
orbits Earth. Then, in 1997, Cassini-Huygens—named for the
great seventeenth-century astronomers who had made so many
important discoveries about Saturn—was launched. CassiniHuygens was very different from Pioneer and Voyager. Those
spacecraft had been used to investigate many other celestial
objects, but Cassini-Huygens was intended to focus entirely on
Saturn and its neighborhood. The mission was actually designed
in two parts. Cassini, an orbiter, would circle around Saturn for
four years or more. Huygens, a separate probe, would separate
from Cassini and land on the surface of Titan.
The two spacecraft are carrying an incredible collection of
sensitive instruments. They also carry advanced cameras that
have sent back breathtaking high-resolution images of Saturn and
the surrounding bodies, especially Titan. These pictures, and the
measurements taken by Cassini-Huygens’s other instruments,
have added to our understanding of the ringed planet.


People’s fascination with Saturn has always focused on the
rings and, to a lesser extent, on the planet’s moons. But as
the scientists who study the planet learn more about Saturn,
they are coming to realize that what is inside the planet is every
bit as interesting as what is outside.

The central core of this gas giant is a sphere of solid rock. It is
small compared to the planet as a whole, though it may actually

Multiple images taken by Voyager 1 were used to create this picture of Saturn
and some of its moons.

be as large as all of Earth. The next layer is an inner mantle of
liquid hydrogen. Then there is an outer mantle, also made of
hydrogen, which is liquid deeper down and becomes gas closer
to the surface. The transition from liquid to gas makes it very
difﬁcult to tell where Saturn’s surface begins and ends. There
is actually a part of the surface, called the supercritical area,
where the hydrogen that makes up both surface and atmosphere
has some characteristics of a liquid and some of a gas.

Scientists think that Saturn is made of layers of rock and
liquid and gaseous hydrogen. Earth has been included in this
image (bottom right) to show how small it is compared to
Saturn. Our planet is almost the size of Saturn’s core.


Saturn’s Magnetism
The Voyager missions discovered that Saturn’s core sends out
radio waves. Scientists have used these radio waves to determine that the planet’s different layers rotate at different speeds.
This rotation gives Saturn its magnetic ﬁeld, which is 1,000
times more powerful than Earth’s. The magnetic ﬁeld wraps the
planet, its rings, and its moons in a “charged” area called the
Saturn’s atmosphere—which is made up of 93 percent hydrogen and 6 percent helium, with very small amounts of some
other elements—has three separate layers of clouds. The bluish
clouds closest to the planet’s surface are made up of water, in the
form of vapor and ice. Above that
is a layer of dark orange clouds
of ammonium hydrosulﬁde crystals. Then comes a layer of white
ammonia-crystal clouds, with a
pale haze above it. These shifting
cloud layers, driven by high winds,
are what make the planet’s surface
An aurora is seen in the
look as if it were covered by movatmosphere over Saturn’s south
ing bands of yellow and brown.
pole. Solar particles from the Sun

interact with Saturn’s magnetic
ﬁeld to create this colorful display.


The winds on Saturn are breathtaking by Earth standards. They
reach speeds of at least 1,118 miles (1,800 km) per hour, with
the strongest winds in the areas around the planet’s equator.
By comparison, the strongest
wind ever recorded on Earth
was just 231 miles (372 km) per
hour. The planet’s surface and
atmosphere are also affected
by sudden, violent storms. One
huge storm, known as the Great
White Spot, occurs once every
time Saturn orbits the Sun and
lasts for about a month.
Saturn is extremely cold, with
average surface temperatures
around -300 degrees Fahrenheit (-185 degrees Celsius). This
The bright orange swirls are
is not surprising because of the
part of the Dragon Storm, which
is one of many storms in the
planet’s great distance from the
planet’s southern hemisphere.
Sun’s heat and energy. What is
Because of the ﬁerce weather
surprising is that Saturn actuactivity, this part of the planet
is often called Storm Alley.
ally gives off more heat than it
takes in from the Sun. There are


many theories that try to explain this. One is that gravity draws
matter toward the core of the planet, causing friction and creating heat. Another is that the planet is slowly releasing gas that
has been trapped inside it since it was created.

Every planet in the Solar System rotates, or spins, on its axis.
However, Saturn’s rotation is unusual. The planet spins very
fast—faster than any planet except Jupiter. Earth takes twentyfour hours, or one Earth day, to spin on its axis. Even though
Saturn is much larger, its rotation takes only 10 hours and 32
minutes (measured in Earth time) at the equator, and about 30
minutes longer at the poles. This difference in rotation speeds
is responsible for another of Saturn’s distinctive features: its
“ﬂattened” shape. The planet is not a perfect sphere, but is visibly
“pushed out” along the equator. All rotating bodies, including
Earth, are like this, but the distortion of Saturn’s shape is more
distinct than with any other planet in the Solar System.
There are other things about Saturn that are highly unusual.
Despite its huge size, it has surprisingly little mass and density.
It is actually the least dense of all the planets, which makes it
extremely light—lighter than water, in fact. The entire planet
could actually ﬂoat in a bucket of water, if someone could ﬁnd
a bucket big enough.


Comparing Saturn and Earth


839 million miles
(1.3 billion km)

93 million miles
(150 million km)

74,900 miles
(121,000 km)

7,926 miles
(12,756 km)


-300 degrees
(-185 degrees C)

60 degrees
(15 degrees C)


29.5 Earth years

365 days


10 hours and 32

24 hours

61 or more



Mostly hydrogen
(gas and liquid),
with a rocky core

Mostly metals and


Mostly hydrogen

Mostly nitrogen and





For centuries, Saturn was believed to be the only ringed planet.
But in 1979, Voyager 1 discovered rings around Jupiter. Since
then, ring systems have also been found around Uranus and
Neptune. Some scientists believe
Mars may also have rings. But
one thing is certain—no other
planet has rings as spectacular
as Saturn’s.
Saturn’s complex ring system
begins only about 42,000 miles
(67,000 km) above the planet’s
surface. That is a very small distance, considering Saturn’s size.
Many of the questions scientists
have been asking about Saturn’s
Saturn’s rings are not solid
rings for centuries have now been
strips of material. They are
answered. We know, for example,
made of billions of particles
of varying size, held together
that the rings are mostly made
by gravity.
up of trillions of particles of ice,
with some pieces of rock and
other matter mixed in. Most of
the particles in the rings are small—many as small as bits of
dust—while some are as big as a truck or a house.


These particles make up a huge ring system that is 225,000
miles (362,000 km) wide, from the inside to the outside. But it
is not very thick. Scientists have widely varying opinions about
this question, but it is clear that in most places the rings are no
more than 300 feet (100 meters) from top to bottom. The rings’
thinness is what sometimes makes them difﬁcult to see.
The rings are not quite the consistent bands they seem to be
at ﬁrst glance. Each of the seven main rings is made up of thousands, even tens of thousands, of smaller rings. These ringlets
do not always follow the ring’s shape perfectly. Some are elliptical, rather than circular, and some
do not form complete rings around
the planet. There are differences
among the rings, as well. Because
they are made up of trillions of
differently shaped particles, they
reﬂect the Sun’s light differently,
which means there are subtle differences in color and brightness.
Some of Saturn’s rings, especially the B ring, have a strange
feature that scientists have not
yet been able to explain. These
Because the ring particles
are what look like “spokes” in the
are different sizes, shapes,
rings. These dark bands change
and material, they all reﬂect

the sunlight differently,
40creating a colorful glow.

rapidly in location and appearance. The F ring has what looks
like braids in it. Scientists believe
both of these phenomena might be
caused by particles being charged
by Saturn’s powerful magnetic
ﬁeld, but no one knows for cerThe smudge-like darker areas
tain what causes them.
on the lighter-colored rings
There is still much that we do
are the spokes that scientists
have observed in some of
not understand about Saturn’s
Saturn’s rings.
rings, but we do know why they
circle the planet’s equator. That is
where Saturn’s mass is greatest,
so that is where its gravity is strongest. (Some scientists have
suggested that the planet’s powerful magnetic ﬁeld may also
play a role.) But there is another important, and somewhat surprising, factor helping to keep the rings in place—the planet’s
many moons.

Saturn’s most spectacular feature, after its rings, is certainly
its moons. Only Jupiter seems to have more moons, and only
Jupiter has a moon that is larger than Saturn’s largest. (Another
name for a moon, or any other body that orbits around a larger
one, is a satellite.) We do not even know for certain exactly


how many moons Saturn has. When the
Cassini-Huygens mission began in 1997,
only eighteen moons had been identiﬁed. Today, we know of at least sixty-one
moons, and ﬁfty-two of those have been
given names.
Most of the moons of Saturn are remarkably regular in their movements. Seven of
them are aligned with the planet’s equator, just as the rings are. Unlike most
moons in the Solar System, they travel in
The close-up image of
almost perfectly circular orbits and in
Phoebe, from Cassinithe same direction. There is one notable
Huygens, shows how
exception that fascinates scientists—the
the moon resembles an
asteroid or comet.
little moon called Phoebe. Phoebe is the
moon farthest from Saturn, nearly 8 million miles (13 million km) away from the
planet. It moves in the opposite direction
of the other moons. It also rotates clockwise, while all the other
moons, and the planet itself, rotate counterclockwise.
It is not yet clear exactly how Saturn’s moons were created,
but most of them probably formed at about the same time
and in about the same way. The exception is Phoebe, which
probably began as a comet or asteroid that was caught by
the planet’s gravity.


Despite their similarities, there are also great differences
among Saturn’s moons. Some are huge and some are—by the
standards of the Solar System—tiny. The largest, Titan, is 3,200
miles (5,150 km) in diameter, which makes it even larger than the
planet Mercury and almost 50 percent larger than Earth’s Moon.
Yet the smallest of Saturn’s moons, which were discovered only
recently, are barely 2 miles (3.2 km) wide.
Titan is made up largely of rock, but the other large moons
circling Saturn are mostly formed from ice. The moons are
different from one another in
many other ways, as well. They
orbit the planet at very different
distances, from as close as 83,015
miles (133,600 km)—well inside
the ring system—to as far away
as 8 million miles (13 million km).
They look very different, too.
Some are covered with craters,
others have sharp ridges. One,
Enceladus, is coated entirely
with ice that reﬂects the Sun’s
Saturn’s A and F rings are shown
light. This also makes Enceladus
here, with Titan (orange) in the
the brightest body in the
background and Epimetheus
(white) above.
entire Solar System, apart from
the Sun.



Scientists are really fascinated with Titan, and not just because
it is the largest of Saturn’s moons. It is also the only moon in the
Solar System known to have an atmosphere which, like Earth’s,
is rich in nitrogen, one of the “building blocks” of life. Many scientists think Titan may be quite similar to the young planet
Earth billions of years ago. One of the reasons why the CassiniHuygens mission sent a probe to Titan’s surface was to try to learn
more about what Earth may have been like in its earliest days.

A colorized image
of Minas shows its
cratered surface.


Some of Saturn’s moons seem to
show traces of the violent forces at
work in the universe. Minas, for example, has an enormous crater, 80 miles
(129 km) across, that covers nearly onethird of the moon’s surface. Minas’s
crater seems to be the result of a
destructive collision with some other
body. Hyperion appears to be a piece of
a larger moon that broke apart at some
point in the past. Two small moons,
Janus and Epimetheus, may be the two
halves of one moon that broke apart
when it was struck by a meteorite.

A few of Saturn’s moons seem
to play a very special role by helping to keep the planet’s rings
in place. These small moons—
which include Atlas, Daphnis,
Pan, Pandora, and Prometheus—
orbit very close to Saturn’s ring
system. Two of them orbit inside
the rings themselves. Their gravity balances with Saturn’s to help
hold the particles in the rings in
a steady path around the planet.
Besides being the brightest
moon, the icy Enceladus has
This entire complex system, like
ice geysers that shoot out
Earth and everything else in the
ice, water vapors, and other
particles from just below the
Solar System, revolves around the
moon’s surface.
Sun. Saturn orbits the Sun, taking
its rings and its moons with it.
But it takes much longer to make
a complete orbit than Earth does. It is much farther away from
the Sun, so its orbit is much larger, about 5.4 billion miles (8.7
billion km) and moves much more slowly. Earth, moving at about
18.5 miles (30 km) per second, completes an orbit in one year—
about 365 days. Saturn revolves around the Sun at only about
one-ﬁfth of that speed—6 miles (9.6 km) per second. So a Saturn
year takes about 29.5 Earth years.


W hen Cassini-Huygens slipped into Saturn’s orbit—passing
through the gap between the F and G rings—it almost immediately
began adding information to what we already knew about the
planet. The spacecraft’s sensitive, highly advanced instruments
and cameras began sending back the most stunning images of
the ringed planet that had ever been seen.

The Cassini-Huygens mission is different from any other mission
ever launched from Earth, and the spacecraft it uses is different
from any other. Cassini-Huygens was actually created as two

The specialized equipment on Cassini-Huygens, has made it possible for us
to see the different colors that Saturn displays.

separate space vehicles, launched into space by a rocket, and
carried to Saturn together.
Cassini, which is 22 feet (6.7 m) long and 13.1 feet (4 m) wide
and weighed 4,685 pounds (2,215 kilograms) before its fuel was
loaded, is an orbiter. It was designed to complete at least seventy
orbits of Saturn and many ﬂybys of the planet’s rings and
moons over a period of four years or more. During these orbits,
it would investigate Saturn’s atmosphere, interior structure,
and magnetosphere, analyze the material in and around the
rings, and study the moons, especially Titan, Dione, Iapetus,
and Rhea.
Cassini carries twelve highly sophisticated instruments,
including two very sensitive cameras, several different types of
spectrometers and spectrographs for measuring
different types of light
and other energy, and a
cosmic dust analyzer. The
dust analyzer will actually collect particles from
the E ring, in the hope of
determining whether the
rings are made up of the
same material as Saturn’s moons. This would
Cassini was designed to orbit Saturn


and collect data on the planet’s rings,
moons, and other features.


The Cassini-Huygens mission is an international project. It is a
$3.26 billion project that involves NASA, the European Space
Agency (ESA), and the Italian Space Agency (ISA). NASA built
and controls the Cassini orbiter. However, the orbiter’s special
communications antenna, which is crucial to the mission’s success, came from Italy. The ESA built the Huygens probe. The
information the mission sends back is being analyzed by more
than 250 scientists all around the world.

help to prove that the rings were formed by the destruction of
earlier moons.
The Huygens probe is very different from Cassini. It is much
smaller—a sphere just 8.9 feet (2.7 m) in diameter and weighing
only 705 pounds (320 kg). It was designed to separate from Cassini
and descend to the surface of Titan, Saturn’s huge, mysterious
moon. Unlike Cassini, which would send information back to
Earth for years, Huygens’ work would be done in less than three
hours. During that short time, Huygens was to sample Titan’s
atmosphere, study the energy sources affecting the moon, and
take the ﬁrst up-close look at the surface.
To achieve these goals, Huygens was built with a very different set of instruments from Cassini’s. The six instruments it
carried included special cameras, tools for measuring the density and chemical composition of the atmosphere, an aerosol


collector for atmospheric
particles, and a surface science package designed to
help scientists understand
the moon’s surface. Huygens
would collect all this material and evidence in a matter
of hours and then transmit
everything it had learned
back to Cassini.
In order to achieve this
incredibly ambitious goal,
Huygens would ﬁrst have
to survive the descent to
This illustration shows the Huygens probe
detaching from Cassini and heading
Titan’s surface, which scitoward Titan (bottom left).
entist had never seen and
knew almost nothing about.
As scientists on Earth anxiously prepared for the moment when Huygens began its part
of the mission, they were also busy analyzing the incredible
amount of new information they were already receiving from
Even before entering Saturn’s orbit, Cassini-Huygens had been
adding to what scientists knew about the planet and its moons.
A close ﬂyby of the odd little moon called Phoebe showed that


it was very different from what had previously been thought.
What had seemed a very dark body was actually very bright in
places, and it is now believed that Phoebe has a considerable
amount of ice.
Not long after its arrival at Saturn, Cassini-Huygens discovered three new moons, which were later named Methone, Pallene,
and Polydeuces. Cassini-Huygens also saw what appeared to be
a number of small moons within the planet’s rings. Only one of
these, now called Daphnis, has been ofﬁcially recognized. It is
the only moon, except for Pan, that is deﬁnitely found inside the

Scientists hope that Cassini, or some other future Saturn
mission, will collect more data to prove that Rhea is the only
ringed moon in the Solar System.

rings. Cassini-Huygens was not the only observer ﬁnding new
moons. Astronomers on Earth, often working with new information they had received from the mission, identiﬁed at least
nineteen small outer moons that were previously unknown. And
Cassini-Huygens recently found evidence that one of Saturn’s
major moons, Rhea, may even have a ring system. If this turns
out to be true, Rhea will be the only moon in the Solar System
known to have its own rings.

As the end of 2004 approached, scientists, engineers, and
technicians managing the Cassini-Huygens project were
preparing for the most difﬁcult and delicate part of the entire
mission. This was the moment when the Huygens probe would
separate from the Cassini orbiter and begin the descent to the
surface of Titan.
There was no guarantee that the probe would even survive the
trip. Because of the dense clouds of methane, ethane, and other
gases shrouding the moon, scientists could only guess what the
surface was like. Even before it reached the surface, Huygens
would be subjected to the intense heat that comes when any
object enters an atmosphere at great speed. On December 25,
2004, Cassini ﬁnally released its probe.



The Huygens
probe used
a series of
parachutes to
safely descend
to Titan’s

Twenty-one days later, after a long, slow, gliding approach,
Huygens began its descent to Titan’s surface. During the descent,
it constantly sent scientiﬁc information to Cassini. Huygens’s
de scent was slowed by a system of three parachutes that helped
to keep it from being destroyed by the heat of atmospheric
The scientists on Earth had to wait a long time to ﬁnd out
whether Huygens survived its landing on Titan’s surface. The
great distance between Titan and Earth meant that transmissions
took as long as eighty-ﬁve minutes to reach us. But ﬁnally, the
Deep Space Network, a collection of highly sensitive antennas
scattered all over the world, began receiving transmissions
relayed by Cassini. It was clear that Huygens was safe and was


now farther from Earth than
any other object that had
ever landed in space. The
ﬁrst images from Huygens’s
cameras showed a harsh
rocks or chunks of ice. The
images and information that
Huygens sent back in the next
few hours changed our view
of Titan forever.
We now believe that Titan
may actually resemble a
young Earth even more closely
than was previously believed.
Huygens images like this
Titan may have many of the
one may help prove that
parts of Titan resemble a
same features as our planet,
young Earth.
including rain, snow, and
clouds—most likely made of
methane, rather than water—
and mountains and valleys. It was once thought likely that
methane seas covered much of the planet, but these liquid areas
now seem to be concentrated at the moon’s poles. Scientists
will spend many years analyzing the incredible amounts of
information that Huygens sent back in such a short time.


Huygens fell silent long ago, its batteries and its instruments
dead. However, Cassini continues to orbit Saturn. In fact, its
mission has proved so successful that it has been extended to
include sixty more orbits of the planet. The spacecraft’s controllers on Earth plan to keep Cassini traveling around Saturn
until sometime in 2010. Sometime after that, they will position
it in a “safe” orbit around Saturn—where it is unlikely to collide with any of the planet’s other satellites—and turn off its

Multiple images taken by Cassini-Huygens in 2004 were
put together to create this detailed, natural color view of
Saturn and its rings.


The Cassini-Huygens project—and the Pioneer and Voyager
missions before it—took years of planning, billions of dollars,
and some of the most advanced technology ever developed. But
it is possible to learn more about Saturn without these kinds of
resources. In fact, an amateur astronomer can begin learning
about Saturn from his or her own backyard or apartment
As the ancient astronomers knew, a telescope is not necessary
to see Saturn, but it is helpful. Even a relatively weak telescope—
one that magniﬁes objects only thirty times their size—can be
used to identify some characteristics of Saturn. This kind of
telescope—which is only slightly more powerful than Galileo’s
early instrument—can allow you to see Titan and Saturn’s
ﬂattened shape. When a slightly more powerful telescope is
used, the A, B, and C rings and the Cassini Division can be seen,
as well as several of the other moons.
Whether a telescope is used or not, the most difﬁcult part is
ﬁnding Saturn as it travels across the sky. The planet appears in
the night sky for about nine months of the year. (The rest of the
time, it appears above the horizon only in the daytime, when
the Sun’s bright light makes it difﬁcult or impossible to see.)
Unfortunately, for children who want to see Saturn, it is usually
most visible in the very early hours of the morning, when they


are supposed to be asleep. Saturn is brightest and highest in
the sky when it is at opposition, which is when the Earth is
directly between the Sun and the ringed planet.
During its long, slow orbit around the Sun, Saturn appears
in many different areas of the sky. The planet’s path changes
constantly, so special tools are needed to tell where it can be
found at any given time. One of the simplest, most useful, and
most inexpensive of these tools is called a planisphere. This is
a modern version of a device that has been used since ancient
times. It consists of two revolving discs, one on top of the other.
The bottom disc is a map of the heavens, and the top disc shows
the date and time. When the two discs are aligned properly for
a particular date and time, the star chart shows where to look
to ﬁnd a celestial object, such as Saturn.
Internet sites and computer software are available that make
ﬁnding celestial objects as simple as clicking a mouse. Some
telescopes even come with their own “star-ﬁnding” software
built in. And many cities and towns have planetariums or
observatories with powerful telescopes that allow people to see
breathtaking views of Saturn and the other heavenly bodies.
Their programs are among the best ways to learn more about
Saturn as our understanding of this fascinating planet changes
and grows.


s at u r n

Quick facts
about Saturn
ORIGIN OF NAME: Roman god of agriculture and harvest; Saturn was the
father of many other gods.
DISCOVERY: First written mention on Assyrian tablet around 700 BCE; ﬁrst
seen with telescope in 1610 CE
DIAMETER AT EQUATOR: 74,900 miles (121,000 km)
DISTANCE FROM SUN: About 839 to 938 million miles (1.3 to 1.5 billion km)
DISTANCE FROM EARTH: 743 million miles (1.19 billion km) to 1 billion miles
(1.6 billion km)
LENGTH OF DAY: 10 hours, 32 minutes
LENGTH OF YEAR: Approximately 29.5 Earth years
AVERAGE TEMPERATURE: -300 degrees Fahrenheit (-185 degrees C)
NUMBER OF MOONS: 52 are formally identiﬁed and named, but there may
be 61 or more
NUMBER OF RINGS: 7 are formally identiﬁed and named, but there are

asteroid belt—A region in space,
between the inner and outer
planets, where most asteroids
are found.
asteroid—A small body, made
mostly of rock, that orbits the
astronomer—Someone who studies
space and the objects in it.
axis—An invisible line around
which a celestial object rotates.
celestial—Related to space or the
comet—A small body, made of rock,
dust, and ice, that orbits around
the sun in a highly elliptical
constellation—A number of stars
that appear from Earth to be
grouped together in the sky
dwarf planet—A very small planet
with less mass and gravity than
other planets.
equator—An invisible line around
the middle of a planet, dividing
its northern and southern
galaxy—A huge, revolving cluster
of stars, gases, and other matter.

gravity—The force between objects
that makes them attract each
other. The force of gravity
increases as objects come closer
together and decreases the
farther apart they are.
heliocentric—To be Sun-centered.
Our Solar System is heliocentric,
because the Sun is its center.
light-year—The distance—about 5.9
trillion miles (9.5 trillion km)—
that light travels in one year
magnetosphere—The area
inﬂuenced by a planet’s
magnetic force.
mantle—An interior section of a
planet that is located between
the core and the outer crust.
mass—The amount of matter an
object contains.
moon—A natural satellite that
orbits around a planet
observatory—A place where
telescopes and other
instruments are used to study
opposition—The point where the
Earth is directly between the
sun and another celestial object.


orbit—To revolve around a celestial
physicist—A scientist who studies
matter and energy.
planisphere—A device for
predicting the movements of
celestial objects.
satellite—A celestial object (natural
or human-made) that orbits
around another body in space.


terrestrial—Relating to land
rather than to the sea or
atmosphere. Terrestrial planets
include Mercury, Venus, Earth,
and Mars.
universe—All the matter and
energy in existence everywhere

Find Out More
Barnes-Svarney, Patricia. A Traveler’s Guide to the Solar System. New York, NY:
Sterling Publishing, 2008.
Elkins-Tanton, Linda T. Jupiter and Saturn. New York: Chelsea House, 2006.
Goss, Tim. Saturn. Chicago: Heinemann Library, 2008.
Graham, Ian. The Far Planets. Mankato, MN: Smart Apple Media, 2007.
Howard, Fran. Saturn. Edina, MN: A BDO Publishing, 2008.

Cassini Equinox Mission
CoolCosmos: Saturn
Find Saturn in the Night Sky
NASA Kids’ Club

NASA Solar System Exploration for Kids

NASA Space Place: Saturn
Saturn—Explore the Cosmos
Welcome to the Planets: Saturn


The author found these resources especially helpful while researching this book.
Aguilar, David. Planets, Stars, and Galaxies: A Visual Encyclopedia of Our
Universe. Washington, D.C.: National Geographic Society, 2008.
Benton, Julius. Saturn and How to Observe It (Astronomers’ Observing Guides).
London: Springer Science Media, 2008.
Chronicle Online. “Cassini Spacecraft Provides Compelling Evidence for
Patterns Resembling Spokes on a Pinwheel in Saturn’s Outer Rings.”
Frances, Peter. Universe: The Deﬁnitive Visual Guide. London: Dorling Kindersley,
Kerrod, Robin. The Star Guide. London: Quarto, 2005.
Lovett, Laura, Joan Horvath, and Jeff Cuzzi. Saturn: A New View. New York:
Abrams, 2006.
NASA: Saturn. http://nssdc.gsfc.nasa.gov/planetary/planets/saturnpage.html
Planet Quest: Exoplanet Exploration. http://planetquest.jpl.nasa.gov/index.cfm
Saturn. http://sse.jpl.nasa.gov/planets/proﬁle.cfm?Object=Saturn
Saturn. http://www.bartleby.com/65/sa/Saturn1.html
University of Tennesse-Knoxville. “The Planet Saturn.” http://csep10.phys.utk.edu/


Page numbers in boldface indicate photos
or illustrations.

asteroid, 11, 15
belt, 15, 15
Atlas, 45
axis, 37
Cassini, Giovanni Domenico, 26
Cassini-Huygens, 5, 31, 42, 47-55, 48,
50, 53
comets, 11
constellations, 8
Daphnis, 45, 51
density, 37
Dione, 26
Dragon Storm, 36, 36
Earth, 7, 11, 12, 14, 17, 37, 45, 57
compared to Saturn, 5, 34, 34, 38
Enceladus, 43, 45, 45
Epimetheus, 43, 43
galaxy, 10, 10
Galilei, Galileo, 22-23, 23
gas giants, 15-16, 30, 58
gravity, 5, 13-14, 21, 28, 37, 45
Great White Spot, 36
Hubble Space Telescope, 31
Huygens, Christiaan, 25, 25
Iapetus, 26

Jupiter, 15-16, 17, 37, 41
Keeler, James, 28
Kepler, Johannes, 22
light-year, 6, 7
Mars, 11, 14, 17
Maxwell, James Clerk, 27-28
Mercury, 11, 14, 17
Methone, 51
Minas, 44, 44
moons, 5, 26, 41-45, 42, 43, 44, 45, 58
mythology, 20-21, 21
Pallene, 51
Pan, 45, 51
Pandora, 45
Phoebe, 42, 42, 50-51
Pioneer 11, 29-30, 29
planets, 17
dwarf, 11
See also Pluto
formation of, 13-16
terrestrial, 11
See also Earth, Mars, Mercury,
Pluto, 17
Polydeuces, 51
Prometheus, 45
Rhea, 26, 51-52, 51
rings, 6, 22-23, 24, 25-28, 30-31, 39-41, 40,
41, 43, 51, 52, 56, 58
Roche, Edouard, 28


atmosphere, 16, 31, 35, 35, 38
core, 33-34, 34
day (length of), 37, 38, 58
discovery of, 6-8, 19, 22-23, 58
distance from Earth, 58
distance from the Sun, 38, 58
formation of, 13-14, 15-16
god, 20-21, 21
magnetism, 35, 35
moons of, 5, 26, 41-45, 42, 43, 44, 45, 58
orbit, 5, 45
rings, 5, 6, 22-23, 24, 25-28, 30-31, 39-41,
40, 41, 43, 51, 52, 56, 58
names of, 28
rotation, 37
shape, 37
size, 5, 34, 38, 58
surface, 16, 34
temperature, 36-37, 38, 58
weather, 36-37, 36
year (length of), 38, 45, 58

Solar System, 5, 11-17, 17
formation of, 13
spacecraft, 29, 47-55
See also Cassini-Huygens, Pioneer 11,
stars, 8, 9, 10, 11, 12
Storm Alley, 36, 36
Sun, 5, 11, 12, 12, 13-17, 22, 40, 45, 57
telescope, 7, 22-23, 23, 56-57
Tethys, 26
Titan, 31, 44, 49, 52-54, 53, 54, 56
universe, 6
Uranus, 15-16, 17
Venus, 11, 14, 17
viewing Saturn, 19-20, 22-23, 56-57
1, 30-31, 30
2, 30-31

about the author
Terry Allan Hicks has written more than twenty children’s books about everything
from why people catch colds to how mountains form. He lives in Connecticut with
his wife, Nancy, and their three sons, James, Jack, and Andrew.