The Planets and Space Exploration
The four rocky planets at the center of the solar system Mercury, Venus, Earth, Mars, are known as the inner planets. Jupiter, Saturn, Uranus, and Neptune are all composed primarily of gas and are known as the outer planets. Pluto,a small solid icy body smaller than the Earth's Moon, is usually the outermost planet. The asteroid belt, between Mars and Jupiter, is made of thousands of chunks of rock which travel around the Sun. Comets are small icy bodies that travel past the Sun and give off gas and dust each time they pass by.
Unmanned spacecraft have travelled to all the planets in the solar system (except Pluto) and taken pictures of the planets and many of their moons. They have also taken measurements that tell us what the planets are like inside.
A Solar System Model Builders Guide
Last modified April 10, 1997 by the Windows Team
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