An asteroid is a predominantly rocky body that orbits around its star. In our solar system, asteroids are the best known class of minor planet (or planetoid). They are much smaller than even the small major planets such as Mercury or Mars.
The vast majority of the asteroids are found within the main asteroid belt, with elliptical orbits between those of Mars and Jupiter. It is thought that asteroids are remnants of the protoplanetary disc, and in this region the incorporation of protoplanetary remnants into the planets was prevented by large gravitational perturbations induced by Jupiter during the formative period of the solar system. Some asteroids have moons.