Our Solar System LEVELED BOOK • S

Our Solar System

A Reading A–Z Level S Leveled Book
Word Count: 1,766

Written by Bruce D. Cooper

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 Our Solar
What Has System
This Tail?

Written by Bruce D. Cooper

Written by Kira Freed
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Photo Credits:
Front cover, title page, pages 4, 7, 10: courtesy of NASA/JPL; back cover:
courtesy of SDO/AIA; page 3: © Jon Christensen; page 5: courtesy of Solar
& Heliospheric Observatory/Extreme Ultraviolet Imaging Telescope/NASA/
Goddard Space Flight Center; page 6: courtesy of SOHO (ESA & NASA)/EIT
Consortium; page 8: courtesy of NASA/Johns Hopkins University Applied Physics
Laboratory/Arizona State University/Carnegie Institution of Washington. Image
reproduced courtesy of Science/AAAS; pages 9, 13: courtesy of NASA/JPL/
USGS; page 11: courtesy of NASA/GSFC/GOES/NOAA; pages 12, 17, 21:
courtesy of NASA; page 14: courtesy of NASA and The Hubble Heritage Team
(STScI/AURA); page 15: courtesy of NASA/JPL-Caltech/University of Arizona;
page 16: courtesy of NASA, ESA, and E. Karkoschka (University of Arizona);
page 18: courtesy of NASA/JPL/Space Science Institute; page 19: courtesy of
NASA, ESA, and the Hubble Heritage Team (STScI/AURA); page 20: courtesy
of Erich Karkoschka (University of Arizona) and NASA; page 22: courtesy of
NASA, ESA, and M. Buie (Southwest Research Institute); page 23: courtesy of
ESA - AOES Medialab; page 24: © WIYN/NOAO/AURA/NSF/epa/Corbis;
page 25 (center): courtesy of ESA/ LFI & HFI Consortia; page 25 (right): courtesy
of ESA – D. Ducros

Our Solar System

Level S Leveled Book
© Learning A–Z
Written by Bruce D. Cooper Correlation
Digital image manipulation LEVEL S
by Randy Gates
Fountas & Pinnell O
All rights reserved. Reading Recovery 34
www.readinga-z.com DRA 34

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 Glossary
atmosphere (n.) a layer of gases
surrounding a planet, star,
or moon (p. 12)
diameter (n.) the length of a straight line
through the center of an
object (p. 23)
fossil fuels (n.) sources of energy such as
coal, oil, and natural gas
that were made by the Table of Contents
decomposition of plants .
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 4
and animals over millions .
of years (p. 6) The Sun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
gravitational pull (n.) the force of attraction Mercury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
that tends to draw objects Venus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
together (p. 13) Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
meteor (n.) a meteoroid that enters The Moon . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Earth’s atmosphere (p. 23) Mars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
meteorite (n.) a meteoroid that actually Jupiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
lands on Earth (p. 23) Saturn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
meteoroid (n.) a comet, asteroid, or dust Uranus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
particle floating in space .
Neptune . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
(p. 23)
Pluto and Other Dwarf Planets . . . . . . . . . . . 22
orbit (n.) the path of an object
revolving around another Asteroids . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
object (p. 8) Comets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
orbits (v.) to revolve around another Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 25
object (p. 4) Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

26 Our Solar System • Level S 3

 Conclusion
Sun Saturn Neptune Humans have always wondered, “what’s
happening out there in space?” For centuries,
Jupiter
Uranus we could only guess. New rockets, space
Mars probes, satellites, and telescopes show us what’s
Pluto happening in our Solar System every day.
Earth These tools have helped scientists to discover
new planets, re-count moons, and see stars
Venus
Moon being born and being swallowed. The have also
Mercury
given us the first full-sky survey map of our
universe and a direct view at the Sun. What
Introduction will they show us next about our Solar System
Our Solar System is made up of the Sun, and beyond?
eight official planets, several dwarf planets, .
and hundreds of planetary satellites, or moons.
It also contains comets, asteroids, and clouds
of gas. The Sun is the center of the Solar
System. Everything else in the Solar System
goes around, or orbits, the Sun. Mercury,
Venus, Earth, and Mars are the inner, rocky
planets. They are made of hard materials. The
In July 2010, after a year-long mapping mission, the orbiting
outer planets are Jupiter, Saturn, Uranus, and Planck Telescope of the European Space Agency (ESA) delivered
its first full-sky survey of our universe. Planck’s mission is to
Neptune. They are known as the gas giants and measure radiation left over from the ancient beginnings of our
are made mostly of gases. The outer planets universe so that scientists can study how it was formed. As Planck
sweeps the sky, it also measures the temperatures, density of
are hundreds of times larger than Earth. matter, speed, and movement of galaxies.

4 Our Solar System • Level S 25

 To get an idea of the size of things in our
Solar System, imagine that Earth is a grape. .
If the Earth were the size of a grape, the Moon
would be the size of a green pea. The Sun
would be as big as a ball that an adult man
could stand in. Jupiter, the largest planet,
would be the size of a grapefruit, while Saturn,
the second largest planet, would be the size of
an orange. Uranus and Neptune would be the
size of lemons.
The comet NEAT, photographed by the WIYN telescope at Kitt
Peak National Observatory in Arizona, was discovered in 2001
by the Near Earth Asteroid Tracking system.

Comets
Comets are composed of ice and dust and
are like large dirty snowballs in space. They
have very oval-shaped orbits. For part of that Approximate
size of
orbit, they come close to the Sun, and then they Earth for
swing far out into space. Some comets orbit the comparison

Sun in less than 200 years. The most famous

of these is Halley’s Comet. It returns every
seventy-six years. Other comets take thousands
of years to complete an orbit. Comet Hyakutake, The Sun is approximately 110 times larger than Earth. The
which passed close to the Earth in 1996, will diameter of Earth is approximately 13,000 kilometers (8,100
miles). The Sun’s diameter is approximately 1.4 million kilometers
return in about 9,000 years. (870,000 miles).

24 Our Solar System • Level S 5

 Satellites monitor impact tests during research into ways to
prevent asteroids from colliding with Earth.

The temperature of the Sun’s surface is approximately 6,000

degrees Celsius (10,832 degrees Fahrenheit). The Sun’s core is
approximately 15,000,000 degrees Celsius (27,000,032
Asteroids
degrees Fahrenheit).
Asteroids are rocky, metallic objects orbiting
the Sun. They range in size from a few feet .
The Sun in diameter to hundreds of miles in diameter.
The Sun is a huge ball of burning gas that Most asteroids are found between Mars and
sends energy far out into the Solar System. Jupiter. Some have orbits that cross the Earth’s
The Sun plays a very important part in our path, and in the past, some have even crashed
daily lives, providing energy that supports all into Earth. Asteroids and other smaller objects
life on Earth. The Sun causes seasons, climate, that enter Earth’s atmosphere are called
ocean currents, air circulation, and weather. meteoroids. If they survive the trip and land
Without the Sun’s energy, plants could not on the ground, they are called meteorites. If
grow and make food. Also, there would be no they burn up before landing, they are called
gas, oil, or coal, which are Earth’s fossil fuels. meteors. Among the best evidence of an
Fossil fuels are formed over millions of years asteroid hitting Earth is the Barringer Crater
from dead plant and animal life. near Winslow, Arizona.

6 Our Solar System • Level S 23

 Pluto and Other Dwarf Planets The Sun is just one of billions of stars. It
has been around for about 4.6 billion years. .
Before 2006, the space object
It will keep producing energy for another .
called Pluto was the ninth planet
5 billion years. Before it dies, it will swell up
of our Solar System. But scientists
and swallow many of the inner planets. Then .
debated and voted to create a new
it will shrink into a much smaller ball.
category called dwarf planets for space objects
like Pluto. Dwarf planets orbit the Sun, have
nearly round shapes, produce a minimum Relative sizes of
the objects in our
level of brightness, and are not moons. They Sun Solar System
also do not have enough gravitational pull to
sweep other space objects from their orbit.
Scientists began by identifying six official
dwarf planets, but Mercury Venus

some scientists What Would You Weigh? Earth

wanted to classify Gravity is different on each Mars

planet, and gravity determines
dozens of similar how much you weigh.
Jupiter
space objects as If you weigh 70 lbs. on Earth,
dwarf planets. then you would weigh:

Many more space On Mercury 27 lbs.

On Venus 63 lbs. Saturn
objects could be On the Moon 12 lbs.
counted among On Mars 27 lbs.
the dwarf planets On Jupiter 165 lbs.
Uranus
On Saturn 65 lbs.
as technology On Uranus 62 lbs. Neptune
makes it easier . On Neptune 79 lbs.
Pluto
to identify them. On Pluto 5 lbs.
In outer space, you’d weigh
nothing!
22 Our Solar System • Level S 7
 A close-up image
from the NASA Toward the
Discovery flight top is the
in 2008, shows “backward”
the huge Caloris storm that
Impact Basin scientists have
on Mercury. named Dark
Spot One
and lower is,
Dark Spot
Two. Their
cyclonelike
winds spin
counter to
the direction
of Neptune’s
orbit.

Mercury
Mercury is the closest planet to the Sun. Neptune
It is the second smallest planet in our Solar Neptune is the eighth planet from the Sun.
System. It takes only 88 Earth days for Mercury Neptune and Uranus are sometimes called
to make a complete orbit around the Sun. (For the twin giants because they are so much
comparison, it takes Earth 365 days, or one alike. They are about the same size and color
year, to orbit the Sun.) Like all other planets, and both are covered with thick clouds. But
Mercury spins like a top as it goes around the Neptune’s winds are the fastest in the Solar
Sun. It spins very slowly. Each spin of a planet System—reaching 2,000 kilometers per hour
is a day on that planet. A day on Mercury is (over 1,242 mph). Neptune has one large
59 times longer than an Earth day. Because moon and many smaller moons, plus several
Mercury spins, or rotates, so slowly, it gets . visible dust rings. It takes Neptune about 165
very hot during the day and very cold at night. Earth years to go around the Sun.

8 Our Solar System • Level S 21

 Some of Uranus’s
moons and rings
can be seen very
clearly in this
Hubble Telescope
image. The bright
spots on the far
right of the planet
are high clouds.

Uranus In addition to having air too heavy to breathe, scientists found

that Venus rotates backward. This means that on Venus the
Sun rises in the west and sets in the east. The colors used on
Uranus is the seventh planet of the Solar this Magellan-mission image represent different elevations on the
System and the third largest. It looks blue- surface of Venus.

green in color because of methane gas in its

atmosphere. Uranus seems to roll around the Venus
Sun because it is very tilted. Scientists think Venus and Earth are similar in size. But
this might be because it bumped into another Earth and Venus are very different. Venus is
planet-sized object long ago. Uranus has at covered by layers of clouds that are much
least twenty-seven moons, five of which are thicker than clouds on Earth. These clouds
large. Scientists have also counted at least trap most of the Sun’s heat. The temperature
thirteen rings. It takes Uranus eighty-one Earth on Venus gets very, very hot—more than four
years to go around the Sun. times hotter than boiling water.

20 Our Solar System • Level S 9

 As well as trapping in heat, the clouds of Saturn is also unique for another reason.
Venus reflect sunlight. This makes Venus one of It weighs little compared to how large it is.
the brightest objects in the sky. The air pressure Saturn would float if a swimming pool could
on Venus is ninety times greater than that on be made big enough to hold it. Saturn spins
Earth. For this reason, space probes that land very fast, making one day on Saturn ten and .
on Venus stop working within a few hours. one-half hours long.
Venus rotates even more slowly than Mercury.
One day on Venus is equal to 243 Earth days.
moon
moon shadow
shadow moon

moon

Four moons of Saturn pass in front of the planet. Enceladus and

Maat Mons, a volcano on Venus, is 8 km (5 mi.) high. Dione on the far left cast shadows while the larger Titan and the
It is very similar to the types of volcanoes found in Hawaii. small Mimas at the far right do not.

10 Our Solar System • Level S 19

Saturn’s spectacular rings are mostly made of water ice. Each
ring averages about 30 feet in depth but some bumps and points
Earth
are more than two miles high.
Earth is a very special planet because it
is our home and also because it is the only
Saturn planet in our Solar System that can support
Saturn is the sixth planet of the Solar life. The most important difference between
System. It is easy to recognize because of its Earth and other planets is the abundance of
large, visible system of rings. The rings are liquid water. Water covers nearly 70 percent .
made up of millions of pieces of ice and frozen of the Earth. Earth rotates about once every .
gases. Saturn also has dozens of small moons 24 hours (one day). It completes one orbit of
that orbit it. the Sun about once every 365 days (one year).

18 Our Solar System • Level S 11

 Earth’s atmosphere is made up of gases In some ways, Jupiter is like a mini-solar
that living things need to stay alive. The system because it is so big and has four large
atmosphere protects us from most of the moons and dozens of smaller moons orbiting
Sun’s harmful rays. It also helps to protect around it. It also has several thin rings at its
us from meteors by causing them to burn up equator. Scientists believe that if Jupiter had
before reaching Earth’s surface. Earth has one become larger during its development, it could
natural satellite, the Moon. have become a star instead of a planet. Jupiter
spins quite fast for such a large planet. One
day on Jupiter is roughly ten hours. It takes
Do You Know? Jupiter almost twelve Earth years to complete
Earth’s atmosphere is very thin. its orbit around the Sun.
If Earth were an apple, the
atmosphere would only be as
thick as the apple’s skin.

Jupiter’s constant dust storm, the Big Red Spot, is highly visible.
Shown in their approximate size relationship, Jupiter’s four moons
are named, top to bottom: Io, Europa, Ganymede and Callisto.

12 Our Solar System • Level S 17

Jupiter and its moon, Ganymede, photographed April 9, 2007,
by the Hubble Space Telescope

Jupiter
Jupiter is the largest planet in our Solar
System. It is like a star in many ways because
it is made up mostly of gas clouds. The
clouds of Jupiter form bands that have very
high winds and are always very stormy. One
The Moon
gigantic storm rotates counterclockwise at a The Moon is about one-fourth the size
constant speed of 360 kilometers per hour of Earth. It reflects light from the Sun onto
(225 mph), and acts much like a hurricane. It’s us. Many scientists believe the Moon was
called the Great Red Spot. Easily visible, it can originally a part of Earth and was broken off
be as wide as three times the size of Earth. in an enormous space collision. Tests have
Jupiter’s temperature is very cold at the tops shown that there is water ice on the Moon’s
of the clouds. At its core, it is hotter than the surface. Earth’s ocean tides are caused by the
surface of the Sun. gravitational pull of the Moon.

16 Our Solar System • Level S 13

 Mars often has
winds that blow up
to 200 kilometers per
hour (120 mph). These
winds cause great dust
storms that color the
planet’s atmosphere
pink. There are ice
caps on both poles of
Mars. The northern one
is made up mostly of
water that never melts,
while the southern
Mars
pole is made up of
Mars is the fourth planet from the Sun. It carbon dioxide, which
is known as the red planet because of large changes from solid to
amounts of rust-colored dust on its surface. gas during the Martian
Mars is the most Earth-like of all the planets summer. Mars has two
of our Solar System. Mars has seasons similar small moons, Phobos
to our own, and the soil there is similar to the and Deimos. A year on
soil on Earth. But there is very little oxygen or Mars is almost as long
water vapor in Mars’s atmosphere. The climate as two Earth years. A
on Mars changes widely between seasons. day on Mars lasts only Scientists are studying the
Temperatures on its surface can range from one-half hour longer gullies at Mars Hale Crater
30° Celsius (86°F) in the summer, to –130° to discover if their changing
than a day on Earth. surface shapes are created by
Celsius (–202°F) in the winter. the movement of liquid water.

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