A humiliating defeat at Pubstumpers trivia two nights ago, typified by the fact that I did not know that Mars had any (let alone two) moons, led me to check out the scoop on Phobos (the moon not the quake3arena model).
Phobos is the largest and nearest orbiting moon of mars. It is messed up and lopsided and has an interesting history. Apparently Phobos has an unstable orbit if tidal forces are not accounted for. This lead to some speculation, from the US space developments advisor, as late as 1960 that Phobos could be an artificial Martian satellite or base. "Phobos had to be very light —one calculation yielded a hollow iron sphere 16 km across but less than 6 cm thick" (wikipedia on Phobos).
It is so photogenic that I have posted two pics. One shows how small and irregular it is, the other shows it passing the sun from the perspective of the Mars rover Opportunity (click on it to see animated gif action).
All this was ganked from wikipedia.