Dozens of unmanned spacecraft have been sent since the 1960s to study its climate and geology.

Other proposals developed as part of the project include a 'kinetic impactor', deflecting asteroids by crashing small unmanned spacecraft into them.

The unmanned spacecraft consists of an orbiter, a lander and a rover, which together weigh more than 3.5 tonnes.

You load up an unmanned spacecraft with a heavy chunk of metal and slam it head-on into the asteroid at a speed of thousands of miles per hour.

Solar experiments included photographs of eight solar flares, and produced valuable results that scientists stated would have been impossible to obtain with unmanned spacecraft.