The asteroid belt is a region of the solar system between Mars and Jupiter where the majority of the asteroids in the solar system are found. Millions of asteroids are believed to be located in this region.
The asteroid belt may have been created by material that almost formed a planet between Mars and Jupiter. Jupiter's gravity stopped the planet's formation and swept up much of the original material in the asteroid belt. Scientists believe the asteroid belt originally contained enough material to form a planet four times the size of Earth. Today, however, if all the material in the asteroid belt somehow formed a planet, it would only be about half the size of the moon.
Although there may be millions of asteroids, they are spread out over a very large area. In "Star Wars," the asteroid field is densely packed with asteroids. In our solar system, however, someone standing on an asteroid in the asteroid belt would have a hard time seeing another one without a telescope. Asteroids can range in size from pebbles to the largest asteroid, Ceres, which is about one-quarter the size of the Earth's moon. Ceres is so large compared to other asteroids that it is considered a dwarf planet and holds about one-third of the asteroid belt's mass.