The Asteroid Belt
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Asteroids are stony or metallic lumps of matter that orbit the Sun in the vast volume of space between the orbits of Mars and Jupiter. Made of stone or metal, the known asteroids range in size from Ceres, the largest known asteroid at 923km in diameter to Aten, 1km in  diameter, and smaller. The total mass of all the known asteroids is less than that of the Moon. Even the largest asteroids on the scale of this model are so tiny as to be invisible. There are over 7000 known asteroids, with hundreds more discovered each year.
Photos courtesy NASA
Asteroid Gaspra's Best Face The spacecraft Galileo encountered and photographed two asteroids during its journey to Jupiter. This is the best color image of the asteroid Gaspra. Color variations have been added. The illuminated portion of the asteroid is about 11 miles long. Ida and Dactyl: Asteroid and Moon The second asteroid that the spacecraft Galileo photographed, called Ida, was discovered to have a moon. It appears as a small dot to the right of Ida in this picture. The tiny moon, named Dactyl, is about one mile across, while the potato shaped Ida measures about 36 miles long and 14 miles wide.
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