Saturn (2010) PDF
Saturn (2010) PDF
Saturn (2010) PDF
Saturn
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!
saturn
Asteroids, Meteors, and Comets
The Dwarf Planet Pluto
Earth and the Moon
Jupiter
Mars
Mercury
Neptune
Saturn
The Stars
The Sun
Uranus
Venus
1
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Glossary 59
bibliography 62
Index 63
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THE RINGED PLaNET
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 second-
largest 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.
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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.
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THE RINGED PLaNET
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THE RINGED PLaNET
Light-Years
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.
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.
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THE RINGED PLaNET
EARTH’S NEIGHBORHOOD
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.
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saturn
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.
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THE RINGED PLaNET
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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 mil-
lion 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
System.
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saturn
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Pluto
Neptune
Sun
Saturn
Jupiter Uranus
Mars
Venus
Earth
Mercury
Of the eight main planets in our solar system, the four closest to the Sun—Mercury, Venus, Earth, and Mars—
THE RINGED PLaNET
are the terrestrial, or land, planets. Jupiter, Saturn, Uranus, and Neptune are considered gas giants. Pluto,
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which was once considered a main planet alongside the others, is now known as a dwarf planet.
2
SaTURN THROUGH
THE aGES
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.
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saturn
This ancient
Babylonian tablet
displays early
astronomers’
observations of
the movement
of the stars and
planets.
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SaTURN THROUGH THE aGES
BEGINNING TO SEE
SATURN CLEARLY
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
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SaTURN THROUGH THE aGES
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SaTURN THROUGH THE aGES
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saturn
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SaTURN THROUGH THE aGES
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saturn
28
SaTURN THROUGH THE aGES
An
illustration
shows the
path that
Voyager 2
took as it
passed by
Saturn.
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SaTURN THROUGH THE aGES
31
3
a CLOSER LOOK
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.
A PLANET FROM
THE INSIDE OUT
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.
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a CLOSER LOOK
Saturn’s Magnetism
The Voyager missions discovered that Saturn’s core sends out
radio waves. Scientists have used these radio waves to deter-
mine 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
magnetosphere.
Weather
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 Fahren-
heit (-185 degrees Celsius). This
The bright orange swirls are
part of the Dragon Storm, which is not surprising because of the
is one of many storms in the planet’s great distance from the
planet’s southern hemisphere.
Because of the fierce weather Sun’s heat and energy. What is
activity, this part of the planet surprising is that Saturn actu-
is often called Storm Alley. ally gives off more heat than it
takes in from the Sun. There are
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a CLOSER LOOK
many theories that try to explain this. One is that gravity draws
matter toward the core of the planet, causing friction and cre-
ating heat. Another is that the planet is slowly releasing gas that
has been trapped inside it since it was created.
Rotation
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 twenty-
four 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.
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Comparing Saturn and Earth
Saturn EaRTH
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a CLOSER LOOK
39
saturn
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
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saturn
42
a CLOSER LOOK
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saturn
Titan
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 sci-
entists think Titan may be quite similar to the young planet
Earth billions of years ago. One of the reasons why the Cassini-
Huygens 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.
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a CLOSER LOOK
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4
SaTURN aND
bEYOND
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.
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SaTURN aND bEYOND
ARRIVING AT THE
SURFACE OF TITAN
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.
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SaTURN aND bEYOND
The Huygens
probe used
a series of
parachutes to
safely descend
to Titan’s
surface.
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SaTURN aND bEYOND
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 con-
trollers 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 col-
lide with any of the planet’s other satellites—and turn off its
instruments.
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saturn
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SaTURN aND bEYOND
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saturn
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
TYPE OF PLANET: Gas giant
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
thousands
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Glossary
asteroid belt—A region in space, gravity—The force between objects
between the inner and outer that makes them attract each
planets, where most asteroids other. The force of gravity
are found. increases as objects come closer
together and decreases the
asteroid—A small body, made farther apart they are.
mostly of rock, that orbits the
Sun. heliocentric—To be Sun-centered.
Our Solar System is heliocentric,
astronomer—Someone who studies because the Sun is its center.
space and the objects in it.
light-year—The distance—about 5.9
axis—An invisible line around trillion miles (9.5 trillion km)—
which a celestial object rotates. that light travels in one year
celestial—Related to space or the magnetosphere—The area
sky. influenced by a planet’s
comet—A small body, made of rock, magnetic force.
dust, and ice, that orbits around mantle—An interior section of a
the sun in a highly elliptical planet that is located between
orbit. the core and the outer crust.
constellation—A number of stars mass—The amount of matter an
that appear from Earth to be object contains.
grouped together in the sky
moon—A natural satellite that
dwarf planet—A very small planet orbits around a planet
with less mass and gravity than
other planets. observatory—A place where
telescopes and other
equator—An invisible line around instruments are used to study
the middle of a planet, dividing space.
its northern and southern
hemispheres. opposition—The point where the
Earth is directly between the
galaxy—A huge, revolving cluster sun and another celestial object.
of stars, gases, and other matter.
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saturn
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Find Out More
BOOKS
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.
WEBSITES
Cassini Equinox Mission
http://saturn.jpl.nasa.gov
CoolCosmos: Saturn
http://coolcosmos.ipac.caltech.edu/cosmic_kids/AskKids/saturn.shtml
Find Saturn in the Night Sky
http://saturn.jpl.nasa.gov/kids/activities-nightsky.cfm
NASA Kids’ Club
http://www.nasa.gov/audience/forkids/kidsclub/flash/index.html
NASA Solar System Exploration for Kids
http://solarsystem.nasa.gov/kids/index.cfm
NASA Space Place: Saturn
http://spaceplace.nasa.gov/en/kids/cassini_make3.shtml
Saturn
http://www.nineplanets.org/saturn.html
Saturn—Explore the Cosmos
http://www.planetary.org/explore/topics/saturn/
Welcome to the Planets: Saturn
http://pds.jpl.nasa.gov/planets/choices/saturn1.htm
61
bibliography
The author found these resources especially helpful while researching this book.
Frances, Peter. Universe: The Definitive Visual Guide. London: Dorling Kindersley,
2006.
Lovett, Laura, Joan Horvath, and Jeff Cuzzi. Saturn: A New View. New York:
Abrams, 2006.
Saturn. http://sse.jpl.nasa.gov/planets/profile.cfm?Object=Saturn
Saturn. http://www.bartleby.com/65/sa/Saturn1.html
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Index
Page numbers in boldface indicate photos Jupiter, 15-16, 17, 37, 41
or illustrations.
Keeler, James, 28
asteroid, 11, 15 Kepler, Johannes, 22
belt, 15, 15
Atlas, 45 light-year, 6, 7
axis, 37
Mars, 11, 14, 17
Cassini, Giovanni Domenico, 26 Maxwell, James Clerk, 27-28
Cassini-Huygens, 5, 31, 42, 47-55, 48, Mercury, 11, 14, 17
50, 53 Methone, 51
comets, 11 Minas, 44, 44
constellations, 8 moons, 5, 26, 41-45, 42, 43, 44, 45, 58
mythology, 20-21, 21
Daphnis, 45, 51
density, 37 Pallene, 51
Dione, 26 Pan, 45, 51
Dragon Storm, 36, 36 Pandora, 45
Phoebe, 42, 42, 50-51
Earth, 7, 11, 12, 14, 17, 37, 45, 57 Pioneer 11, 29-30, 29
compared to Saturn, 5, 34, 34, 38 planets, 17
Enceladus, 43, 45, 45 dwarf, 11
Epimetheus, 43, 43 See also Pluto
formation of, 13-16
galaxy, 10, 10 terrestrial, 11
Galilei, Galileo, 22-23, 23 See also Earth, Mars, Mercury,
gas giants, 15-16, 30, 58 Venus
gravity, 5, 13-14, 21, 28, 37, 45 Pluto, 17
Great White Spot, 36 Polydeuces, 51
Prometheus, 45
Hubble Space Telescope, 31
Huygens, Christiaan, 25, 25 Rhea, 26, 51-52, 51
rings, 6, 22-23, 24, 25-28, 30-31, 39-41, 40,
Iapetus, 26 41, 43, 51, 52, 56, 58
Roche, Edouard, 28
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