Asteroids are small, airless rocky worlds that revolve around the sun and are too small to be called planets. They are also called space rocks, planetoids or minor planets. read more
Asteroids are formed from the leftovers of the formation of our solar system from about 4.6 billion years ago. Early on, the birth of Jupiter prevented any planetary bodies from forming in the gap between Mars and Jupiter, causing the small objects that were there to collide with each other and fragment into the asteroids seen today. read more
Thus, the present structure of the solar system, including its reservoirs of asteroids and comets, reflects the manner in which it formed. The largest planetesimals became the planets and moons, while the smallest ones became the asteroids and comets. read more