The majority of asteroids that scientists have formally identified reside between the orbits of Mars and Jupiter. Scientists call this wide swath of space the asteroid belt, and though it contains millions of objects, the combined size of all of the asteroids in the belt is smaller than the Earth’s moon.
Scientists estimate that about 200 asteroids in the belt exceed 60 miles in diameter. By contrast, 750,000 asteroids of about three-fifths of a mile in diameter are thought to reside among the larger ones. One of the largest objects in the asteroid belt is classified as a dwarf planet. Named Ceres, this large asteroid is thought to represent about one-third of the total mass of the asteroid belt.
Many asteroids have moons that orbit them, although none are large enough to contain an atmosphere. As far as scientists can tell, asteroids are not capable of supporting life. Occasionally, the gravity of a large planet perturbs the orbit of an asteroid. This can cause an asteroid to crash into a planet or moon. Approximately 65 million years ago, an asteroid hit the earth with enough force to kill most of the life on the planet. Scientists scan the skies for such large meteors, hoping to spot them before they impact Earth.