MESSENGER has been able to detail the planet's surface as never before. The photo, taken in 2008, shows the extensive map of craters that make up the planet's surface. MESSENGER will attempt to find some answers about key issues with the planet, such as the composition of its atmosphere. Mercury is extremely dry, very hot, and almost completely airless. As NASA reports, the sun's rays are seven times stronger on Mercury than Earth, and the sun itself appears to be two and a half times as big from the surface.