Asteroids are material left over from the formation of the solar system. One theory suggests that they are the remains of a planet that was destroyed in a massive collision long ago. More likely, asteroids are material that never coalesced into a planet. In fact, if the estimated total mass of all asteroids was gathered into a single object, the object would be less than 1,500 kilometers (932 miles) across, less than half the diameter of our Moon. The asteroid belt lies in the region between Mars and Jupiter. The Trojan asteroids lie in Jupiter's orbit, in two distinct regions in front of and behind the planet. *Image Credit*: Lunar and Planetary Institute
