PHOBOS (fear) DEIMOS (panic) Mean distance from Mars (km) 9,377 23,436 Orbital period (Mars days) 0.31891 1.26244 Major axis (km) 26 16 Minor axis (km) 18 10 Mass (x 1015 kg) 10.8 1.8 Mean density (kg/m3) 1,900 1,750

Phobos and Deimos

(moons of Mars)

Mars has two small moons: Phobos and Deimos. Phobos (fear) and Deimos (panic) were named after the horses that pulled the chariot of the Greek war god Ares, the counterpart to the Roman war god Mars. Both Phobos and Deimos were discovered in 1877 by American astronomer Asaph Hall. The moons appear to have surface materials similar to many asteroids in the outer asteroid belt, which leads most scientists to believe that Phobos and Deimos are captured asteroids

Two Moons Passing in the Night





Two Moons and the Pleiades from Mars





Phobos Viewed from Mars

See the Spirit Press Release for additional information.