World Book at NASA for Students
Satellites are natural objects that orbit, or move around, a planet or an asteroid. An asteroid is a chunk of rock that moves around the sun. Satellites are also called moons. All the planets except Mercury and Venus have moons. Jupiter, Saturn, Uranus, and Neptune have many moons. At least one asteroid, called Ida, has a moon.
Satellites come in many different sizes. The smallest known satellite is Ida's moon Dactyl. The largest is Jupiter's moon Ganymede.
Satellites are made up of different materials, depending on their distance from the sun. The satellites closest to the sun are made up of a kind of rock called silicate. This is the same material that makes up most of Earth's crust. The other satellites are made up of silicate and ice. In general, the farther a satellite is from the sun, the more ice it has. Most satellites are made up mostly of ice. Most of the ice on satellites is water ice, like the ice we see on Earth.
Image to right: An artist painted this view of what Jupiter might look like from Europa, one of its larger satellites. Another moon is traveling between Jupiter and Europa. Credit: World Book illustration by Alex Ebel
Many satellites seem to have a rough surface with many craters, or large hollows shaped like a bowl. Some satellites have changed since they first came into existence. These moons have many kinds of surface features, including active volcanoes.
How Satellites Form
Many scientists believe that satellites formed at about the same time as planets did, and in the same way. According to this theory, or idea, a huge cloud of gas and dust spun slowly in space almost 5 billion years ago. Pieces of the dust bumped into each other, forming small chunks of material. These chunks, in turn, bumped into each other and formed larger objects. As each object grew in size, its gravity also increased.
Gravity is a natural force that draws objects toward each other. Once an object is about 6 mils (10 kilometers) wide, it has enough gravity to pull other materials toward it. As the object grows larger, its gravity increases, and the build-up of materials becomes very fast. The object quickly pulls all nearby materials into itself.
How Scientists Study Satellites
Scientists use telescopes and spacecraft to study satellites and their planets. Spacecraft missions provide the best information about satellites. Spacecraft have flown close to all the planets. Human beings have set foot on only one satellite, Earth's moon.
Image to left: Jupiter's satellite Io has active volcanoes. The volcanoes shoot out sulfur and other minerals that give Io its yellow color. Credit: NASA
Most telescopes study satellites from Earth's surface. The others are attached to artificial, or human-made, satellites that move around Earth, or they are placed in spacecraft. Scientists use light gathered by these telescopes in two ways. One way is called imaging, or creating pictures. Scientists then study the pictures. The other method is called spectroscopy. In spectroscopy scientists study the light reflected from a satellite. They can then identity its chemical elements and learn what the satellite is made of.
How to cite this article: To cite this article, World Book recommends the following format: "Satellite." The World Book Student Discovery Encyclopedia. Chicago: World Book, Inc., 2005.
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Satellites are made up of different materials, depending on their distance from the sun. The satellites closest to the sun are made up of a kind of rock called silicate. This is the same material that makes up most of Earth's crust. The other satellites are made up of silicate and ice. In general, the farther a satellite is from the sun, the more ice it has. Most satellites are made up mostly of ice. Most of the ice on satellites is water ice, like the ice we see on Earth.
Image to right: An artist painted this view of what Jupiter might look like from Europa, one of its larger satellites. Another moon is traveling between Jupiter and Europa. Credit: World Book illustration by Alex Ebel
Many satellites seem to have a rough surface with many craters, or large hollows shaped like a bowl. Some satellites have changed since they first came into existence. These moons have many kinds of surface features, including active volcanoes.
How Satellites Form
Many scientists believe that satellites formed at about the same time as planets did, and in the same way. According to this theory, or idea, a huge cloud of gas and dust spun slowly in space almost 5 billion years ago. Pieces of the dust bumped into each other, forming small chunks of material. These chunks, in turn, bumped into each other and formed larger objects. As each object grew in size, its gravity also increased.
Gravity is a natural force that draws objects toward each other. Once an object is about 6 mils (10 kilometers) wide, it has enough gravity to pull other materials toward it. As the object grows larger, its gravity increases, and the build-up of materials becomes very fast. The object quickly pulls all nearby materials into itself.
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Scientists use telescopes and spacecraft to study satellites and their planets. Spacecraft missions provide the best information about satellites. Spacecraft have flown close to all the planets. Human beings have set foot on only one satellite, Earth's moon.
Image to left: Jupiter's satellite Io has active volcanoes. The volcanoes shoot out sulfur and other minerals that give Io its yellow color. Credit: NASA
Most telescopes study satellites from Earth's surface. The others are attached to artificial, or human-made, satellites that move around Earth, or they are placed in spacecraft. Scientists use light gathered by these telescopes in two ways. One way is called imaging, or creating pictures. Scientists then study the pictures. The other method is called spectroscopy. In spectroscopy scientists study the light reflected from a satellite. They can then identity its chemical elements and learn what the satellite is made of.
How to cite this article: To cite this article, World Book recommends the following format: "Satellite." The World Book Student Discovery Encyclopedia. Chicago: World Book, Inc., 2005.
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