In addition to the nine planets and their moons, the Solar System contains a wide variety of minor bodies – asteroids, comets, meteorites, and meteoroids. Although these wandering fragments of material are tiny compared with the planets, they hold many clues to the formation of the Solar System as a whole and sometimes give rise to spectacular phenomena.

ASTEROIDS

The asteroids, or minor planets, are small bodies, ranging in diameter from about 940 km down to less than 1 km, that revolve around the Sun in independent orbits. Although the first asteroid to be discovered was found by chance, a curious numerical relationship between the distances of the planets from the Sun had already led a number of astronomers to mount a search for what they thought might be a “missing planet” between the orbits of Mars and Jupiter.

In 1772, the German mathematician Johann Bode drew attention to the following relationship that had previously been noted by Johann Titius and that has generally come to be known as Bode's law or the Titius–Bode law: Take the sequence of numbers, 0, 3, 6, 12, 24, 48, 96, and so on, where each successive number after 3 is double the preceding one; add 4 to each (4, 7, 10, …), then divide by 10.