Asteroid belt

The asteroid belt was discovered by Astronomers after the invention of the telescope. Ancient Astronomers were aware of seven objects they recognized as planets, that regularly moved against the background of the fixed stars. In the geocentric systems they recognized, Sol, our sun, and Luna, our moon, were considered planets, like Mercury, Venus, Mars, Jupiter and Saturn.

Ancient Astronomers also monitored comets, but did not classify them as planets, because their movements weren't regular.

Telescopic observation enabled the discover of Uranus, and several smaller bodies, like Ceres, Juno and Vesta. Initially, Ceres, Juno and Vesta were also considered planets, until it became obvious that there was a belt of a large number of smaller bodies, all with similar orbits. So Ceres, Juno and Vesta were demoted, and recognized as new object, asteroids.

Ceres is by far the largest asteroid in the asteroid belt, accounting for approximately 40 percent of the mass of the entire belt. It is the only asteroid with enough mass to be spherical.

As of 2026 over 1.4 million asteroids have been catalogues in the asteroid belt.

The objects in the asteroid belt circle roughly between the orbits of Mars and Jupiter, although exceptional objects, like Icarus, whose orbit approaches Sol closer than Mercuury is also considered an asteroid, as are the Trojan asteroids, which share the same orbit as Jupiter.

Several hundred years after the discovery of the asteroid belt Astronomers realized there was a larger belt of object beyond the orbit of Neptune Neptune, called the Kuiper Belt. It contains many objects larger than Ceres, and is estimated to be 20 to 200 times more massive than the asteroid belt.