The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids or minor planets. The identified objects are of many sizes, but much smaller than planets, and, on average, are about one million kilometers apart. This asteroid belt is also called the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System.
By far the largest object within the belt is the dwarf planet Ceres. The total mass of the asteroid belt is significantly less than Pluto's, and roughly twice that of Pluto's moon Charon.
In 1596, Johannes Kepler's sense of proportion for the planetary orbits led him to believe that an invisible planet lay between the orbits of Mars and Jupiter.
Giuseppe Piazzi, discoverer of Ceres, the largest object in the asteroid belt: Ceres was known as a planet, but later reclassified as an asteroid and from 2006 as a dwarf planet.
951 Gaspra, the first asteroid imaged by a spacecraft, as viewed during Galileo's 1991 flyby; colors are exaggerated
The Solar System is the gravitationally bound system of the Sun and the objects that orbit it. It was formed 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc. The Sun is an ordinary main sequence star that maintains a balanced equilibrium by the fusion of hydrogen into helium at its core, releasing this energy from its outer photosphere.
Montage of the largest bodies in the Solar System. The asteroid belt and Kuiper belt are not added because the individual asteroids are too small to be shown.
Diagram of the early Solar System's protoplanetary disk, out of which Earth and other Solar System bodies formed
A diagram depicting the habitable zone boundaries around stars, and how the boundaries are affected by star type.
The Sun in true white color
