Space Topics: Mars
Deimos
Diameter: 15 x 12.2 x 11 kilometers, smaller than many asteroids
Orbital distance: 23,459 kilometers from the center of Mars (about 20,061 kilometers
above the surface)
Orbital period: 1.26244 days
Discovery: 1877 by Asaph Hall
Deimos is the smaller and outer of Mars’ two tiny moons. It is so
small that it appears no brighter from the surface of Mars than Venus does from
Earth. When Mars is near its vernal and autumnal equinoxes, the equatorial orbit
of Deimos carries it across the Sun in a series of daily eclipses. These
events have been observed by the Mars Exploration Rovers. Because its orbital
period is not much longer than Mars’ rotation rate, for an observer located
on Mars’ equator, it takes about 2.7 days for Deimos to set after it has
risen. Deimos is heavily cratered but smoother than Phobos. Like
Phobos, Deimos is likely a captured C-type
asteroid.
Deimos over Cassini crater, Mars
Viking Orbiter 2 caught this view of Deimos as it transited the surface of
Mars below it. Credit: NASA / JPL / O. de Goursac
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