Brochure on PHOBOS and Deimos

The rotation of Phobos and Deimos is synchronous with the planet, i.e., they always face Mars with the same side. The orbits of the Martian satellites are almost circular; the eccentricity being .015 + or - .001 for Phobos and .0005 + or - .0003 for Deimos. They are also practically in the same plane as Mars' equator, that of Phobos being tilted at 1.02 deg and Deimos 1.82 deg. Semi-major axes of the orbits are 9378.5 and 23,459 km and orbital periods 7h 39 min and 30h 21 min, respectively. Thus, Phobos, while revolving around Mars, moves faster than the daily rotation of the planet, and for a Martian observer it would rise in the west and set in the east.