Solar System: Other Orbiting Bodies
The asteroids are small rocky bodies that move in orbits primarily between the orbits of Mars and Jupiter. Numbering in the thousands, asteroids range in size from Ceres, which has a diameter of 1,003 km (623 mi), to microscopic grains. Some asteroids are perturbed, or pulled by forces other than their attraction to the Sun, into eccentric orbits that can bring them closer to the Sun. If the orbits of such bodies intersect that of Earth, they are called meteoroids. When they appear in the night sky as streaks of light, they are known as meteors, and recovered fragments are termed meteorites. Laboratory studies of meteorites have revealed much information about primitive conditions in our solar system. The surfaces of Mercury, Mars, and several satellites of the planets (including Earth’s Moon) show the effects of an intense bombardment by asteroidal objects early in the history of the solar system. On Earth that record has eroded away, except for a few recently found impact craters. S