Deimos is one of the two moons of Mars. It was discovered by Asaph Hall on 12th August 1877 in Washington DC.

Diameter: 12.6 km
Mass: 1.48 x 1015 kg
Composition: Rock
Orbit: 23,459 km from Mars

Measuring just 15 x 12 x 15 km, Deimos is the smallest moon of Mars and is the one which orbits furthest from the planet. Phobos is Mars’s largest satellite and is closest in its orbit. Originally spelt Deimus, Deimos was discovered after Asaph Hall embarked on a search for Martian moons. Deimos is also one of the smallest moons in the whole of the Solar System.

The names Deimos and Phobos were suggested by British scholar Henry Maden and taken from Book XV of the Iliad. Deimos and Phobos are the sons of Ares and Aphrodite, which are the Greek versions of Mars, the Roman god of war and Venus, the god of love.

The composition of Deimos is carbon-rich rock, similar to that of C-type asteroids. In common with other bodies of this size, it is non-spherical and has a lumpy exterior. There are many craters visible on the outer layer of Deimos, but most are no wider than 2.5 km. The two largest craters are called Swift and Voltaire. Each is approximately 3 km wide. They were given these names because both of these writers had written about the possible existence of moons orbiting Mars prior to their actual discovery. The surface of Deimos is surprisingly smooth, particularly for a moon that is so heavily cratered. Usually when a meteorite hits, the surface is littered with the remnants of the impact. This creates bumps and ridges on the surface. On Deimos, large quantities of this material are nowhere to be seen. This is attributed to the relatively low gravity of Deimos. There is evidence of deep regolith on the surface of Deimos. Regolith is the accumulation of dust, soil and other such particles.

Deimos orbits close to Mars’s equatorial plane in 30 hours. It is the outer moon of Mars and its orbital route is circular. When viewing Deimos from Mars, it is seen to pass in front of the sun during orbit, but is not big enough to cause a total eclipse. Both Deimos and Phobos are believed to be asteroids, due in part to their compositional similarity to C-type asteroids. It is likely that while moving through space, both asteroids were drawn into Mars’s orbit, where they still remain.

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