Asteroids are small rocky objects that orbit the Sun. They are irregular shapes, and made from the broken fragments of larger bodies that failed to come together to form a planet. Most asteroids can be found between the orbits of Mars and Jupiter, in an area known as the "asteroid belt". This area is 180 million km in width and contains thousands of asteroids that are constantly in motion. These crash into each other at high speeds and send clouds of dust into space.
A typical asteroid
The asteroid belt was probably once far bigger than it is today and may have contained much larger bodies - some as big as planets. There are still about 100,000 asteroids greater than 1 km across, but only a few are larger than 250 km.
Despite all the activity inside it, the asteroid belt itself is relatively stable. It steadily orbits the Sun in a regular, elliptical path, in the same direction as the planets. Occasionally, asteroids are pulled from their regular path by the gravitational pull of a larger body, typically a planet.
Location of the asteroid belt
There is evidence that asteroids have hit Earth in the past. In fact, there is a theory that suggests dinosaurs were wiped off the planet, following the destructive impact of a massive asteroid.
