What is the asteroid belt?
The asteroid belt is a ring-shaped region between the orbits of Mars and Jupiter that contains millions of rocky objects called asteroids, left over from the formation of the solar system.
The asteroid belt formed about 4.6 billion years ago, when the planets were forming. Jupiter's powerful gravity stirred up the material in this region and prevented it from coming together into a planet. Instead, it remained as countless separate bodies, ranging from dust to objects hundreds of kilometers wide.
The largest object in the belt is Ceres, about 940 kilometers across, which is classed as a dwarf planet. Other large asteroids include Vesta, Pallas and Hygiea. NASA's Dawn spacecraft orbited both Vesta and Ceres between 2011 and 2018, sending back detailed images and data.
Mostly empty space
Movies often show asteroid belts as crowded fields of rocks, but the real belt is mostly empty. Asteroids are typically hundreds of thousands of kilometers apart. Spacecraft such as Pioneer, Voyager and New Horizons have passed through without any trouble. All its asteroids together have less mass than our Moon.
Did You Know?
NASA's Psyche spacecraft, launched in 2023, is traveling to a metal-rich asteroid called 16 Psyche, which may be the exposed core of an early planet.