Mars surface. Dry, rocky terrain of Mars taken by the panoramic camera on the Mars Exploration Rover Spirit on 18th January 2004. The large rock is 'Adirondack', the first target rock for geological research by Spirit. This rock was chosen by scientists because its clean, flat surface is ideally suited to grinding and close examination. Spirit will use a grinding arm to obtain samples of rock for chemical analysis by its spectrometers. The mineral composition of the rock may reveal how it was formed and whether this 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.