Definition of Deimos
: the smaller and outermost of the two satellites of Mars with an irregular shape and a diameter of approximately 9 miles (15 km) Other small bodies in the solar system may be asteroids. Phobos and Deimos, the two satellites of Mars, the eight outer moons of Jupiter and the Saturnian satellite Phoebe appear to be captured asteroids. — Richard P. Binzel et al., Scientific American, October 1991
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