Apparent retrograde motion notable on Mars which has two natural satellites, Phobos and Deimos. Both moons orbit Mars in an eastward (prograde) direction, however Deimos has an orbital period of 1.23 Martian sidereal days, making it supersynchronous, whereas Phobos has an orbital period of 0.31 Martian sidereal days making it subsynchronous. Consequently, although both moons are travelling in an eastward (prograde) direction, they appear to be travelling in opposite directions when viewed from the surface of Mars due to their orbital periods in relation to the rotational period of the planet. All other planetary bodies in the Solar System also appear to periodically
Phobos (audio drama) Phobos (audio drama) Phobos is an audio drama based on the long-running British science fiction television series "Doctor Who". This audio drama was produced by Big Finish Productions and was broadcast on BBC 7 on 28 January 2007. The Doctor and Lucie land on Phobos, the moon of Mars, which has become popular with extreme sports fans in the future, due to a wormhole on the surface which is used for bungee jumping. The Doctor and Lucie listen to Kai Tobias's stories of monsters on the surface, although no-one takes him seriously. Later the monsters from Tobias's stories appear and