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Semimajor Axis of Orbit 9,378 km
Siderial Revolution Period 7h 39m
Orbit Eccentricity 0.015
Orbital Inclination 1.1
Radius 14 x 11 x 9 km
Visual Magnitude 11.8

Phobos, the innermost of the two martian satellites, was discovered in 1877 by Asaph Hall. Its name means fear, the name of one of the dogs of the god Mars. The satellites small size and irregular shape leads scientists to believe that it is an asteroid that was captured by mars long ago. Little is known about it except what could be gathered by pictures taken by the Viking I spacecraft as it passed in 1975.