Natural satellite

The common noun moon (not capitalized) is used to mean any natural satellite of the other planets. There are at least 140 moons within Earth's solar system, and presumably many others orbiting the planets of other stars.

Origin

Most moons are assumed to have been formed out of the same collapsing region of protoplanetary disk that gave rise to its primary. However, there are many exceptions and variations to this standard model of moon formation that are known or theorized. Several moons are thought to be captured asteroids; others may be fragments of larger moons shattered by impacts, or (in the case of Earth's Moon) a portion of the planet itself blasted into orbit by a large impact. As most moons are known only through a few observations via probes or telescopes, most theories about their origins are still uncertain.

Related Topics:
Protoplanetary disk - Moon - Probes - Telescope

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