"We should go boldly where man has not gone before – fly by the comets, visit asteroids, visit the moon of Mars. There’s a monolith there. A very unusual structure on this little potato shaped object that goes around Mars once in seven hours. When people find out about that, they're going to say 'Who put that there?' Well, the universe put it there. If you choose, God put it there."
Those are the words of Buzz Aldrin, the second man to walk on the Moon, during a program commemorating the 40th anniversary of the first Moon landing. And this is the monolith he's talking about. The explanatory call-outs on the photo above were made by Efrain Palermo in his analysis of the object, which can be found on this website.