Asteroids, sometimes called minor planets, are rocky remnants left over from the early formation of the solar system about 4.6 billion years ago. Most of this ancient space rubble can be found orbiting the Sun between Mars and Jupiter within the main asteroid belt. Asteroids range in size from Ceres - the largest at about 950 kilometers (590 miles) in diameter and also identified as a dwarf planet - to bodies that are less than 1 kilometer (0.6 mile) across. The total mass of all the asteroids combined is less than that of Earth's Moon.
Note: This lithograph was revised in September 2013.
For the most recent planetary science developments, visit our Planets section.