World Book at NASA for Students
A planet is a large object that travels around the sun. Earth is one of the planets in our solar system. Planets are much smaller than the sun and the stars.
Planets do not produce their own light the way the sun and other stars do. The planets can be seen only because light from the sun shines on them. Going outward from the sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Other stars also have planets around them.
Image to left: Planets travel around the sun. Earth is the third planet from the sun. Credit: World Book illustration
The Planets of the Solar System
The planets of the solar system are different from one another in a number of ways. These differences include how warm it is on a planet, what kinds of gases surround it, and what it looks like.
The planets nearest the sun receive more heat that those farther away from it. Mercury, the planet closest to the sun, is dry and very, very hot. During the day, the temperature rises to about 800 degrees F (427 degrees C). That is almost twice as hot as the hottest setting on an oven. Neptune is the farthest planet from the sun. On Neptune, the temperature is probably lower than -300 degrees F (-184 degrees C). It is one of the coldest places in our solar system.
Each planet has a different atmosphere. An atmosphere is the mixture of gases that surrounds a planet. No other planet in the solar system has an atmosphere like Earth's. Earth is the only planet with a large amount of a gas called oxygen in its air. People and animals need oxygen to live.
Some of the planets are mostly made of rock and metal. Others are mostly made of gas with a rocky center. Mercury, Venus, Earth, and Mars are made mostly of iron and rock. These planets have mountains, valleys, flat areas, and bowl-shaped holes called craters. Earth also has lakes and rivers.
Jupiter, Saturn, Uranus, and Neptune are the largest planets. They are called the giant planets. They are made mainly of gases, and they probably have hard, rocky cores. These gases can give them beautiful colors. Jupiter has a swirling spot of gases that looks red. Scientists call it the Great Red Spot. It is probably a huge storm.
The giant planets also have rings around them. The rings may be made of dust or chunks of ice.
Most of the planets have moons. Some have more than one moon. Scientists have counted 18 moons around Saturn*, more than any other planet. Only Mercury and Venus do not have moons.
How to cite this article: To cite this article, World Book recommends the following format: "Planet." The World Book Student Discovery Encyclopedia. Chicago: World Book, Inc., 2005.
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Image to left: Planets travel around the sun. Earth is the third planet from the sun. Credit: World Book illustration
The Planets of the Solar System
The planets of the solar system are different from one another in a number of ways. These differences include how warm it is on a planet, what kinds of gases surround it, and what it looks like.
The planets nearest the sun receive more heat that those farther away from it. Mercury, the planet closest to the sun, is dry and very, very hot. During the day, the temperature rises to about 800 degrees F (427 degrees C). That is almost twice as hot as the hottest setting on an oven. Neptune is the farthest planet from the sun. On Neptune, the temperature is probably lower than -300 degrees F (-184 degrees C). It is one of the coldest places in our solar system.
Each planet has a different atmosphere. An atmosphere is the mixture of gases that surrounds a planet. No other planet in the solar system has an atmosphere like Earth's. Earth is the only planet with a large amount of a gas called oxygen in its air. People and animals need oxygen to live.
Some of the planets are mostly made of rock and metal. Others are mostly made of gas with a rocky center. Mercury, Venus, Earth, and Mars are made mostly of iron and rock. These planets have mountains, valleys, flat areas, and bowl-shaped holes called craters. Earth also has lakes and rivers.
Jupiter, Saturn, Uranus, and Neptune are the largest planets. They are called the giant planets. They are made mainly of gases, and they probably have hard, rocky cores. These gases can give them beautiful colors. Jupiter has a swirling spot of gases that looks red. Scientists call it the Great Red Spot. It is probably a huge storm.
The giant planets also have rings around them. The rings may be made of dust or chunks of ice.
Most of the planets have moons. Some have more than one moon. Scientists have counted 18 moons around Saturn*, more than any other planet. Only Mercury and Venus do not have moons.
How to cite this article: To cite this article, World Book recommends the following format: "Planet." The World Book Student Discovery Encyclopedia. Chicago: World Book, Inc., 2005.
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* Note from editor: Sixty-three moons have been discovered around Jupiter. Saturn has 59 known moons. |
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