On August 3, 2004 NASA launched the MESSENGER space probe (short for MErcury Surface, Space ENvironment, GEochemistry and Ranging, and yes they’re really stretching it with that acronym) with hopes that it would be the first spacecraft to ever orbit the planet Mercury. On March 18, 2011 orbit was successfully achieved. The last spacecraft to get even close to Mercury was Mariner 10 which performed a flyby in 1975. MESSENGER will be studying the planet’s geology, chemical composition, and magnetic fields. The probe already has made one significant discovery when it reported the presence of large amounts of water in the planet’s exosphere in July 2008. It will also look into whether or not Mercury has a liquid outer core as hinted from visual evidence of a volcanic past. NASA will conduct tests starting March 23 to make sure all systems are operating properly and MESSENGER’s mission to explore new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before will begin on April 4.
Source : NASA