Mercury. MESSENGER image of the cratered surface of the planet Mercury. The closest planet to the Sun, Mercury is a rocky world covered with meteorite impact craters. Its diameter (4880 kilometres) is less than half that of Earth and it has a surface area that is about the same as that of the Atlantic Ocean. The MESSENGER (Mercury Surface, Space Environment, Geochemistry and Ranging) spacecraft was launched from Earth in August 2004. After a series of flybys of Earth, Venus and Mercury, to slow the spacecraft down, it will enter orbit around Mercury in March 2011 on a year-long mission to map and study the surface. This image was obtained during the January 2008 flyby of Mercury, the first for over 30 years.