Mars surface. Dry, rocky terrain of Mars taken by the panoramic camera on the Mars Exploration Rover Spirit in January 2004. The large rock at centre is 'Sashimi', and the smaller one (far right) is 'Sushi'. These rocks were considered by scientists as targets for geological research by Spirit, but were not chosen because their surfaces were too rough and dusty. Spirit will investigate the mineral composition of other rocks to reveal how they were formed and whether the Gusev crater area was once covered in water. An identical rover called Opportunity is due to land on the other side of Mars on 24th January 2004.