Between Mars and Jupiter is an area of space called the Asteroid Belt. Thousand upon thousands of tumbling chunks of rock and metal called the asteroids are trapped in an orbit around the sun. In 1596 Johann Kepler thought he would discover a planet between Mars and Jupiter. Not until 1801 did Giuseppe Piazze discover the first minor planet named Ceres. Ceres is a small body, about 600 miles (1,000 km) in diameter and its appearance lent to the alternative name these bodies are still known by: "asteroid". At present more than 35,000 minor planets are known.
Billions of asteroids, varying in size from a bus to a mountain, orbit between Mars and Jupiter. Most astronomers think that the asteroids are bits and pieces of matter left over from the time the planets were formed out of the great Suncloud matter. Jupiter's powerful gravity most likely kept a planet from forming nearby and so the asteroids came to be.