Mars exploration is going to experience a spectacular evolution during the next ten years, from studies on Martian soil analogs in terrestrial planetary simulation chambers to a phase global mapping of the planet and its environment by means of orbiting spacecraft, to a phase of exploration via landing probes on the surface.
The present thin Martian atmosphere with a surface pressure of 7 mbar has been one of the great puzzles of planetary science. Ancient fluvial networks on the Martian surface suggest that it was warmer and wetter three billion years ago. Surface features resembling massive outflow channels provide evidence that the Martian crust contained the equivalent of a planet wide reservoir of water several hundred meters deep. Determining the past evolution of the Martian atmosphere and searching for present and past water reservoirs is essential for the question if microbial life forms developed on Mars too.
In 2003 Europe's Mars Express spacecraft will investigate in detail how much water is on the planet in the polar caps, in form of subsurface ice and permafrost, or was lost to space by it's MARSIS and ASPERA instruments.
Mars Express' landing probe Beagle 2
will search for direct and indirect evidence of past or present
microbial life forms by investigating Martian rocks and the surface
with chemical and environmental sensors.