Deimos is the smaller of Mars' two moons. Named after a son of Ares (Mars) and Aphrodite (Venus) it was discovered on August 12, 1877, by American astronomer Asaph Hall, Jr. It is compsed of carbon rich rock and ice. It has no atmosphere, is cratered though smoother (the craters are partialy filled by regolith) than its companion, has a diameter of 12 kilometers and orbits at just over 20,000 kilometers above its primary. Its most prominent surface features are two large craters named Voltaire and Swift.

Phobos, the larger of Mars' two moons and also named after a son of Ares (Mars) and Aphrodite (Venus), was discovered on August 18, 1877, also by Asaph Hall, Jr. Like Deimos it is composed of carbon rich rock and ice. It also has no atmosphere (although the Soviet probe Phobus 2 detected outgassing) and is covered in a thick layer of dust, rock and debris called regolith. It has a diameter of 22 kilometers and orbits less than 6,000 kilometers above Mars' surface (closest to its primary of any satellite in the Solar System). Its most prominent surface feature is Stickney crater.

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