planetesimal

Body of rock in space, smaller than a planet. Scientists, who study planetesimals using telescopes on Earth and in space, adhere to the modern theory that planetesimals were the building blocks of planets.

The Sun and the planets are thought to have formed from a rotating dust cloud formed from the remnants of a supernova explosion. On condensation, this cloud formed a central star and a rotating disc, the material of which separated into rings of dust grains that began to stick together. Larger and larger clumps formed in each ring and eventually collected into bodies the size of present-day asteroids, or planetesimals. After numerous collisions, these bodies eventually formed the nuclei of the various planets of our Solar System.