Yesterday, we presented the Martian satellite Phobos (“Fear”); today, it’s Deimos’s (“Panic”) turn. Both satellites were discovered together by the American astronomer Asalph Hall; however, the names were suggested by Henry Madan (1838–1901), then Science Master of Eton, who got the idea from Book XV of the Iliad, where Ares (the Roman god Mars) summons Dread (Deimos) and Fear (Phobos).
Deimos (pronounced DEE-mos) is much smaller than Phobos, having dimensions of 15 x 12 x 10.4 kilometers, and being too small to have formed into a spherical shape. (Phobos, in contrast, is 26.8 × 21 × 18.4 kilometers in size.) Deimos is also much further away from Mars. Whereas Phobos only takes 7 hours, 39 minutes to orbit Mars, Deimos takes a little over 30 hours to complete one orbit.
The Viking 2 Orbiter took the above photo on October 5, 1977 from a distance of 1,400 kilometers.