The closest planet to our sun carries its share of impact scars. NASA’s MESSENGER space flyer took this image of a previously unseen portion Mercury's surface on Jan. 14, 2008. NASA has been using the information compiled by MESSENGER to understand Mercury's geological history. According to NASA, “In this image alone, 763 craters have been identified and measured (shown in green) along with 189 hills (shown in yellow).” Scientists are using the number of craters to date the surface of the planet. In other words, the more craters they can count in one area, the older the geological age of that area.