In certain areas the Martian surface is scored by branching networks of valleys, similar to those made by river tributary systems on Earth. Free water subsequently disappeared from the Martian surface however. Water only still occurs as ice crystals in the atmosphere, and on the surface as ice on the pole caps. In the summer months the ice caps melt partially and the Martian sky is filled with clouds. One theory is that most of this water could occur as a subterraneous layer of up to 500m thick.
Subterraneous water can also support life.
Todd Stevens and Jim McKinley of the American Pacific Northwest Laboratory in Richland, Washington, have discovered bacteria in deep aquifers in basalt formations near Washington. Life on Mars may resemble this. Certain rockets will be sent up in pairs, the one with an orbiter and the other with a lander. These robots will each conduct its own set of experiments but the orbiters will also act as relay stations transmitting data back to Earth from the landers, and vice versa. The landers will also link up electronically to do joint experiments.