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10-02-2010, 04:11 AM
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About Phobos

One of a pair of irregular, small moons orbiting Mars, Phobos was discovered by the American astronomer Asaph Hall in 1877 along with its fellow satellite, Deimos. Both moons are grey in colour, cratered and generally similar in appearance to asteroids that orbit between Mars and Jupiter. One theory is that both moons were once asteroids that were captured by Mars's gravitational force, but this has not been confirmed.

Photo: Phobos taken by the Mars Global Surveyor probe (NASA/JPL/Malin Space Science Systems)

Watch and listen to clips from past programmes TV clips [3] ( ( About Phobos (

Are Mars's moons really captured asteroids? ( Phobos as rocket fuel? (

Before launch in 1988, Phillip Clark explains the ill-fated Russian Phobos missions. ( Asteroids explained (

Sir Patrick Moore describes the asteroid belt and its discovery. ( Asaph Hall discovers Phobos and Deimos (

An American astronomer discovers Mars' moons.

About Phobos

Phobos (pronounced /ˈfoʊbəs/ FOE-bəs, or as Greek Φόβος) (systematic designation: Mars I) is the larger and closer of the two moons of Mars, the other being Deimos. Both moons were discovered in 1877. With a mean radius of 11.1 km (6.9 mi), Phobos is 7.24 times as massive as Deimos. It is named after the Greek god Phobos (which means "fear"), a son of Ares (Mars).
A small, irregularly shaped object, Phobos orbits about 9,377 km (5,827 mi) from the center of Mars, closer to its primary than any other known planetary moon. Phobos is one of the least-reflective bodies in the solar system, and features a large impact crater, Stickney crater. It orbits so close to the planet that it moves around Mars faster than Mars itself rotates. As a result, from the surface of Mars it appears to rise in the west, move rapidly across the sky (in 4 h 15 min or less) and set in the east. Phobos's orbital radius is decreasing, and it will eventually either impact the surface of Mars or break up into a planetary ring.
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Discovered by

Asaph Hall (


Mars (

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Mariner 9 (
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Elsewhere on the web

The Nine Planets: Phobos (
NASA World Book: Mars (
The Planetary Society: Phobos (

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