Phobos (moon)

Phobos (IPA {{IPA|/?fo?b?s/}}, Greek Φόβος: "Fright"), is the larger and innermost of Mars' two moons, and is named after Phobos, son of Ares (Mars) from Greek Mythology. Phobos orbits closer to a major planet than any other moon in the solar system, less than 6000 km above the surface of Mars, and is also one of the smallest known moons in the solar system. Its systematic designation is Mars I. The adjectival form of the name is Phobian, and in fairly common usage.

Origin

Phobos and Deimos both have much in common with carbonaceous (C-type) asteroids, with very similar spectra, albedo and density to those seen in C-type asteroids. This has led to speculation that both moons could have been captured into Martian orbit from the main asteroid belt. However, both moons have very circular orbits which lie almost exactly in Mars' equatorial plane, while captured moons would be expected to have eccentric orbits in random inclinations. Some evidence suggests that Mars was once surrounded by many Phobos- and Deimos-sized bodies, perhaps ejected into orbit around it by a collision with a large planetessimal {{ref|Craddock}}.

Related Topics:
Asteroid - Spectra - Albedo - Density - Asteroid belt - Equatorial plane - Planetessimal

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