Mars

Mars is all flat an shiny in the north, but hilly and rugged below the equator. Why has long been a question without a good answer. New research proves that the top of Mars is actually a giant impact crater.

Pretty crazy..

http://www.nytimes.com/2008/06/26/science/space/26mars.html?em&ex=1214625600&en=e948268a678b129a&ei=5087%0A