Astronomy Picture of the Day . Mercury: A Cratered Inferno . ... 1.01.1999 . ... Credit Copyright: Mariner 10 , NASA Explanation: Mercury's surface looks similar to our Moon's. Each is heavily cratered and made of rock. ... Mercury is the closest planet to the Sun , orbiting at about 1/3 the radius of the Earth's orbit. ... The above picture was taken by the only spacecraft ever to pass Mercury: Mariner 10 in 1974. ... Publications with keywords: Mercury . Publications with words: Mercury . ...