10¹² meters = 1,000,000,000 kilometers

You can see more of those asteroids now. Most of them cruise in a ring called the Main Belt flanked by the orbits of Mars and Jupiter.

The Main Belt lies between 2 and 3.5 AU from the sun (that's between two and three-and-a-half times Earth's average distance from the sun).

Astronomers once thought that the Main Belt was the debris from a destroyed planet. This turns out not to be the case. Scientists now think that Jupiter's gravity prevented a planet from forming out of the initial clump of matter in this region of the solar system.