Mercury is the closest planet to the Sun, and the smallest planet of the solar system. Mercury has been visited by two unmanned NASA space probes, Mariner 10 and Messenger. The unmanned Messenger proble was launched by NASA in 2004 and will begin to orbit Mercury in 2011 after several flybys.
The picture on the left is a picture of Mercury that was taken by Messenger in 2008, and transmitted back to earth for scientists to study.
Mercury is 57,900,000 km away from the sun.
