Artist's impression of two astronauts on the surface of Mars. They are depicted on the edge of Noctis Labyrinthus, part of the Valles Marineris system, just after dawn. Early morning clouds may be seen covering the valley miles below, and patches of frost are on the ground. These will quickly disappear as the Sun rises in the sky. The astronauts have used a six-wheeled buggy (right) to visit this spot. The astronaut on the left is a planetary geologist, studying the strata in the canyon wall. His companion is setting up a weather monitoring station. Such manned exploration of the surface of Mars is unlikely to occur before 2015.