What space probes have been launched to Mercury?

Mercury, being so close to the Sun, is very difficult to explore. Space probes are unable to withstand the heat of the planet. Only one space probe, Mariner 10, has visited Mercury so far. It photographed nearly half of the planet’s surface. A new probe, Messenger, is on its way to Mercury. It was launched on 3 August 2004 and is expected to return, after photographing the whole planet, in March 2012. Another space mission will begin in 2013.