The Main Asteroid Belt

The inner Solar System is defined as the four terrestrial – or rocky – planets closest to the Sun: Mercury, Venus, Earth and Mars. These inner planets are ringed by the Solar System’s main asteroid belt.

This torus-shaped band of solid, irregularly shaped bodies separates Mars from Jupiter. The total mass of the main asteroid belt is about four per cent the mass of the Moon. This mass is mostly locked up in the bodies Ceres, Vesta, Pallas and Hygiea.

Another notable occupant of the main asteroid belt is Kleopatra, a ‘dog bone’ shaped asteroid that is around 270 kilometres (168 miles) long and possesses two of its own moons.

Apophis probably originates from the main asteroid belt, and like all the bodies there is likely to be a remnant left over from the formation of the Solar System. Their unspoiled nature means that studying these bodies, which are often just loose piles of space rubble, could help astronomers understand how the Solar System evolved.