An Etymological Dictionary of Astronomy and Astrophysics

The smaller and outermost of Mars’ two satellites. It measures 12.6 km in size, and orbits Mars every 30.2 hours at a distance of about 23,500 km. It was discovered by the American astronomer Asaph Hall in 1877.

See also: In Gk. mythology, Deimos, meaning “fear, terror,” is one of the sons of Ares (Mars) and Aphrodite (Venus).