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Our Solar SystemA Reading A–Z Level S Leveled Reader

Word Count: 1,660

LLEEVVEELLEEDD RREEAADDEERR •• SS

Our Solar System

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Our Solar System Level S Leveled Reader© 2002 Learning Page, Inc.Written by Bruce D. CooperDigital image manipulationby Randy Gates

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Written by Bruce D. Cooper

Our Solar SystemPhoto Credits:Front cover, title page, pages 4, 7: Composite illustrations using NASA-NSSDC and SOHO (ESA & NASA) source material; back cover, pages16, 17, 18, 19: NASA-NSSDC—The Voyagers are managed forNASA by the Jet Propulsion Laboratory/California Institute ofTechnology; table of contents: NASA-NSSDC—NEAR was built andmanaged by The Johns Hopkins University Applied Physics Laboratory,Laurel, Maryland; page 5: SOHO (ESA & NASA); page 6: The SOHO-EIT Consortium— SOHO is an ESA-NASA program of internationalcooperation; pages 8, 11, 12, 13, 20: Illustrations based on NASA-NSSDC material; pages 9, 21: NASA-NSSDC, page 10: NASA-NSSDC—Created by the JPL Multimission Image Processing Laboratory;page 14: NASA-NSSDC—David Crisp and the WFPC2 Science Team(Jet Propulsion Laboratory/California Institute of Technology); page 15:NASA-NSSDC—Mary A. Dale-Bannister, Washington University in St.Louis; page 22: Pluto and Charon—NASA-NSSDC—Dr. R. Albrecht,ESA/ESO Space Telescope European Coordinating Facility; NASAPluto’s Surface—Alan Stern (Southwest Research Institute), Marc Buie(Lowell Observatory), NASA and ESA; page 23: NASA-NSSDC—TheGalileo project is managed for NASA’s Office of Space Science by theJet Propulsion Laboratory; page 24: NASA-NSSDC—Photographed byW. Liller, Easter Island, part of the International Halley Watch (IHW)Large Scale Phenomena Network; page 25: NASA-NSSDC—HubbleHeritage Team (AURA/STScI/NASA).

CorrelationLEVEL S

Fountas & Pinnell OReading Recovery 22

DRA 34

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Table of ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . .4

The Sun . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Mercury . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Venus . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

The Moon . . . . . . . . . . . . . . . . . . . . . . . . .13

Mars . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Jupiter . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Saturn . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Uranus . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Neptune . . . . . . . . . . . . . . . . . . . . . . . . . .21

Pluto . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Asteroids . . . . . . . . . . . . . . . . . . . . . . . . . .23

Comets . . . . . . . . . . . . . . . . . . . . . . . . . . .24

Conclusion . . . . . . . . . . . . . . . . . . . . . . . .25

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . .26

Introduction

Our solar system is made up of the Sun,nine planets, and 69 moons. It also containscomets, asteroids, and clouds of gas. The Sunis the center of the solar system. Everythingelse in the solar system goes around, or orbits,the Sun. Mercury, Venus, Earth, and Mars arethe inner, rocky planets. They are made ofrocky materials. The outer planets are Jupiter,Saturn, Uranus, and Neptune. They are knownas the gas giants and are made mostly ofgases. The outer planets are hundreds of times larger than Earth. The last planet, Pluto, is more like a frozen moon.

SunJupiter

Saturn

Uranus

Neptune

Pluto

Mercury Venus Earth Mars

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The Sun

The Sun is a huge ball of burning gas thatsends energy far out into the solar system. The Sun plays a very important part in ourdaily lives, providing energy that supports alllife on Earth. The Sun causes seasons, climate,ocean currents, wind, and weather. Withoutthe Sun’s energy, plants could not grow andmake food. And there would be no gas, oil, or coal. These things are called fossil fuels,and they come from dead plants.

To get an idea of the size of things in oursolar system, imagine that Earth is a grape. If Earth were the size of a grape, the Moonwould be the size of a green pea. The Sunwould be as big as a ball that an adult mancould 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.

Approximate size of Earthfor comparison

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Mercury

Mercury is the closest planet to the Sun. It is the second smallest planet in our solarsystem. It takes only 88 Earth days forMercury to make a complete orbit around the Sun. (For comparison, it takes Earth 365days, or one year, to orbit the Sun.) Like allother planets, Mercury spins like a top as itgoes around the Sun. It spins very slowly. Eachspin of a planet is a day on that planet. A dayon Mercury is 59 times longer than an Earthday. Because it spins so slowly, Mercury getsvery hot during the day and very cold at night.

The Sun is just one of billions of stars. It has been around for about 4.6 billion years.And it will keep producing energy for another5 billion years. Before it dies, it will swell upand swallow many of the inner planets. Thenit will shrink into a much smaller ball.

Do You Know?Gravity is different on each planet, andgravity determines howmuch you weigh. If youweigh 32 kg (70 lbs.) onEarth, you weigh 12 kg(27 lbs.) on Mercury.

Relative sizes ofthe objects in oursolar system

Sun

Jupiter

Saturn

UranusNeptune

Pluto

Mercury

EarthVenus

Mars

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As well as trapping in heat, the clouds ofVenus reflect sunlight. This makes Venus one of the brightest objects in the sky. The airpressure on Venus is 90 times greater than onEarth. For this reason, space probes that landon Venus stop working within a few hours.Venus rotates even more slowly than Mercury.One day on Venus is equal to 243 Earth days.

Venus

Venus and Earth are similar in size. ButEarth and Venus are very different. Venus is covered by layers of clouds that are muchthicker than clouds on Earth. These clouds trap most of the Sun’s heat. The temperatureon Venus gets very, very hot—more than fourtimes hotter than boiling water.

Do You Know?If you weigh 32 kg (70 lbs.)on Earth, you weigh 29 kg(63 lbs.) on Venus.

Gula Mons, a volcano on Venus, is almost 3.2 km (2 mi.) high.

Earth’s atmosphere is made up of gasesthat living things need to stay alive. Theatmosphere protects us from most of the Sun’s harmful rays. It also helps protect usfrom meteors by causing them to burn upbefore reaching Earth’s surface. Earth has onenatural satellite, the Moon.

Earth

Earth is a very special planet because it is our home and also because it is the onlyplanet in our solar system that can supportlife. The most important difference betweenEarth and other planets is the presence ofwater. Water covers nearly 70 percent of Earth.Earth spins around approximately once every24 hours (one day). It completes one orbit ofthe Sun about every 365 days (one year).

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Do You Know?Earth’s atmosphere isvery thin. If Earth werean apple, the atmospherewould only be as thick asthe apple’s skin.

A meteorenteringEarth’satmosphere

Mars

Mars is the fourth planet from the Sun. It is known as the red planet because of largeamounts of rust on its surface. Mars is themost Earth-like of all the planets of our solarsystem. Mars has seasons similar to our own,and the soil there is similar to the soil onEarth. But there is very little oxygen or watervapor in Mars’s atmosphere. The climate on Mars changes widely between seasons.Temperatures on its surface can range from 30°Celsius (86°F) in the summer to –130°Celsius (–202°F) in the winter.

The Moon

The Moon is about one-fourth the size of Earth. The origin of the Moon is unknown.Most scientists believe that it came from Earth when Earth was hit by an enormousobject from space. The gravitational pullof the Moon causes Earth’s ocean tides.

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Do You Know?If you weigh 32 kg (70 lbs.) on Earth, youweigh 5 kg (12 lbs.) on the Moon.

Jupiter

Jupiter is the largest planet in our solarsystem. It is like a star in many ways becauseit is made up mostly of gas clouds andproduces its own heat. The clouds of Jupiterform bands that have very high winds and are always very stormy. Scientists believe onestorm is like a huge hurricane. It is called theGreat Red Spot. This storm is about threetimes the size of Earth. Jupiter’s temperature is very cold at the tops of the clouds. Beneaththe upper layer of clouds, it is much hotter.

Mars often has winds that blow up to 200 kilometers per hour (120 mph). Thesewinds cause great dust storms that color theplanet’s atmosphere pink. There are ice capson both poles of Mars. The northern one ismade up mostly of ice that never melts, whilethe southern pole is made of carbon dioxide,which melts during the Martian summer. Marshas two small moons, Phobos and Deimos. A year on Mars is almost as long as two Earthyears. A day on Mars lasts only thirty minuteslonger than a day on Earth.

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Do You Know?If you weigh 32 kg (70 lbs.)on Earth, you weigh 12 kg(27 lbs.) on Mars.

Do You Know?If you weigh 32 kg (70 lbs.)on Earth, you weigh 75 kg(165 lbs.) on Jupiter.

A panorama of the Martian surface

Saturn

Saturn is the sixth planet of the solarsystem. It is easy to recognize because of its large, visible system of rings. The rings are made up of millions of pieces of ice andfrozen gases. Saturn has the most moons of any planet, approximately 23.

In some ways, Jupiter is like a “mini-solarsystem” because it is so big and has 16 moonsand several thin rings around it. Scientistsbelieve that if Jupiter had become larger during its development, it could have becomea star instead of a planet. Jupiter spins quitefast for such a large planet. One day on Jupiteris roughly 10 hours. It takes Jupiter almost 12 Earth years to complete its orbit around the Sun.

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Do You Know?If you weigh 32 kg(70 lbs.) on Earth,you weigh 29 kg(65 lbs.) on Saturn.

Uranus

Uranus is the seventh planet of the solar system and the third largest. It looksblue-green in color because of methane gas in its atmosphere. Uranus seems to roll aroundthe Sun because it is very tilted. Scientiststhink this might be because it bumped intoanother planet-sized object long ago. Uranushas 18 moons and 11 known rings. It takesUranus 81 Earth years to go around the sun.

2019

Saturn is also unique for other reasons. It isnot as dense as the other planets. It is the onlyplanet less dense than water. Saturn wouldfloat in a swimming pool if there were one big enough to hold it. Saturn spins very fast,making one day on Saturn ten and one-halfhours long.

Do You Know?If you weigh 32 kg(70 lbs.) on Earth,you weigh 28 kg(62 lbs.) on Uranus.

Pluto

Pluto is the smallest planet. It is evensmaller than seven of the moons in our solarsystem. Pluto is more like a moon than a planet. Some scientists think at one time it may have been one of Neptune’s moons.Pluto’s orbit is more oval than the orbits of the other planets. For this reason, it sometimescomes closer to the Sun than Neptune does.Pluto has one moon, which is half its size. It takes Pluto about 248 Earth years to orbitthe Sun.

Neptune

Neptune is the eighth planet from the Sun.Neptune and Uranus are sometimes called the twin giants because they are so muchalike. They are about the same size, and theyboth glow with the same blue-green color. And like Uranus, Neptune is covered with thick clouds. Neptune has at least 8 moonsand 5 dust rings. It takes Neptune about 165 Earth years to go around the Sun.

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Do You Know?If you weigh 32 kg(70 lbs.) on Earth,you weigh 2 kg (5 lbs.) on Pluto.

Do You Know?If you weigh 32 kg (70 lbs.)on Earth, you weigh 36 kg(79 lbs.) on Neptune.

Pluto and its moon, Charon

A closeup of Pluto

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 orbit, they come close to the Sun, and then they swing far out into space. Somecomets orbit the Sun in less than 200 years.The most famous of these is Halley’s comet. It returns every 76 years. Other comets takethousands of years to complete an orbit.Comet Hyakutake, which passed close to theEarth in 1996, will return in about 9,000 years.

Asteroids

Asteroids are rocky, metallic objects orbiting the Sun. They are too small to becalled planets. They range in size from a fewfeet in diameter to hundreds of miles indiameter. Most asteroids are found betweenMars and Jupiter. Some have orbits that crossEarth’s path, and in the past, some have evencrashed into Earth. Asteroids and other smallerobjects called meteoroids that float in spaceand enter Earth’s atmosphere are calledmeteors. Most burn up in the atmosphere. If they survive the trip and land on the ground,they are called meteorites. Among the bestevidence of an asteroid hitting Earth is theBarringer Crater near Winslow, Arizona.

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Asteroid Ida and its moon

Halley’s comet

Glossaryatmosphere a layer of gases surrounding a

planet, star, or moon (p. 12)

diameter the length of a straight linethrough an object (p. 23)

fossil fuels sources of energy such ascoal, oil, and natural gas thatwere made by thedecomposition of plants and animals over millions of years (p. 6)

gravitational pull the force of attraction thattends to draw objects together(p. 13)

meteor a meteoroid that entersEarth’s atmosphere (p. 23)

meteorite a meteoroid that actuallylands on Earth (p. 23)

meteoroid a comet, asteroid, or dustparticle floating in space (p. 23)

orbit (noun) the path of an objectrevolving around anotherobject (p. 8)

(verb) to revolve aroundanother object (p. 8)

Conclusion

Humans are fascinated with outer space.There are thousands of books and hundreds of television programs and movies devoted to space travel. We wonder about other solarsystems in space. Humans are curious aboutthe universe, and we like going in search ofnew adventures. As technology continues toadvance, many of the space adventures thatare now only fantasy may become real.

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A spiral galaxy much like our own