Deimos
Deimos is the smaller, outer moon of Mars, about 12 kilometres across and smoothed by dust.
Deimos is the outer and smaller of Mars's two moons, discovered by Asaph Hall in August 1877, a few days before Phobos. Its name means dread in Greek. It measures roughly 15 by 12 by 11 kilometres and orbits about 23,000 kilometres above Mars, taking about 30 hours to go round.
Deimos looks smoother than Phobos, because its craters are partly filled with a layer of loose dust and rubble. Like Phobos, it is dark and has a spectrum similar to some carbon-rich asteroids, but its origin is uncertain. It may be a captured asteroid, or it may have formed from a disc of debris created by a giant impact on early Mars.
In March 2025, the European Hera spacecraft photographed Deimos during a Mars flyby on its way to the Didymos asteroids, capturing views of the far side seldom seen. Japan's MMX mission will also study it.
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Level: Explorer Ages 10 and up