What is the asteroid belt like?
The asteroid belt is a huge, mostly empty region between Mars and Jupiter where millions of rocky bodies orbit the Sun, usually very far apart.
In films, the asteroid belt is often shown as a crowded field of rocks that spaceships must dodge. The real asteroid belt is very different.
The belt lies between the orbits of Mars and Jupiter, roughly 300 to 500 million kilometres from the Sun. It contains millions of asteroids, from the dwarf planet Ceres, about 940 kilometres across, down to boulders and pebbles. But the belt is so enormous that the asteroids are spread very thinly. On average, there are hundreds of thousands of kilometres between big ones. If you stood on an asteroid, you probably could not see another with your eyes.
Spacecraft such as Pioneer 10, Voyager, Galileo, Cassini, New Horizons and Dawn have all flown through the belt safely. Mission planners do not need to steer around asteroids unless they want to visit one.
All the asteroids in the belt together would weigh only about 3 per cent of our Moon's mass, and Ceres, Vesta, Pallas and Hygiea together make up more than half of that.
The belt is where most meteorites come from. When asteroids occasionally collide, they knock off pieces, and some of those eventually find their way to Earth.