Eighteenth-century astronomers saw a pattern in the spacing of the planets, which led them to look for something orbiting between Mars and Jupiter. Several observatories joined the search and, in 1801, the first asteroid, 1 Ceres, was discovered.
knows how many asteroids there are in all, although we have probably found every object larger than 60 miles (100 km) across and about half of the 6 mile (10 km) objects. Estimates suggest there may be a million asteroids larger than 1/2 mile (1 km) in diameter.
Since that time, more than 35,000 asteroids have been identified. No one
The largest asteroid, at barely 600 miles (1,000 km) across, is Ceres, and the next biggest, Pallas and Vesta, are about half that size. Planetary scientists studying the main belt are beginning to see its current inhabitants as the remains of a much larger population. They believe that collisions—with each other and with the planets—have steadily reduced larger asteroids to smaller ones, and smaller ones to dust and fragments.