Asteroids are smaller than any of planets and only a few have a diameter of over 30 km (1.6 m). Asteroids are small rocky or icy bodies that orbit the sun. They are sometimes called minor planets. Most asteroids are found in an orbit between mars and Jupiter, and more than 7,000 of them have been identified.
The term asteroid is usually applied to objects that are larger than 1.6km (0.9m) in diameter. One asteroid, called Ida, has a tiny moon all of its own. This is that smallest known satellite in the solar system. Asteroids were probably formed at the same time as the planets.