PLANNING FOR EXPLORATION OF THE SHALLOW MARTIAN SUBSURFACE

For several reasons, interest in exploring the martian subsurface has been steadily increasing. First, understanding the present distribution of water, and its cycling between reservoirs, is important for many of the highest priority questions related to Mars. It is now abundantly clear from orbital imaging that that there is presently no liquid water at the martian surface. However, several arguments suggest that there may be substantial amounts of water, in both liquid and solid form, in the martian subsurface. Second, there is evidence that water existed on the martian surface in the geologic past. Understanding the aqueous history will require documenting and interpreting the sedimentary record. Third, the surface of Mars is oxidizing. Interpreting the biological potential of Mars will require assessing samples from below the depth of action of this oxidant.

In order to explore the shallow martian subsurface, the Mars Program is planning or considering a series of investigations which will span multiple missions. These investigations will involve geophysics, drilling, and subsurface geology/geochemistry. In 2003, the Mars Express orbiter will include a ground penetrating radar sounding instrument (MARSIS) which has the potential to detect liquid water at depths up to 5 km. A second orbital GPR in 2005 will be optimized to detect water in the 0.3-1.0 km depth range. A rover-based landed GPR is being seriously considered for the 2007 mission, and 1-D GPR is planned for the French Netlander mission. These data sets will increase our understanding of the 3D distribution and state of water in the upper martian crust. Physical access to this region is being planned through the development of robotic martian drills. Drills with depth ranges of 1-3m, 10-20m, 200m, and 2km are under development by several different engineering teams. These drills will be considered for flight as early as 2007, and extending into the next decade. As on Earth, there are valuable opportunities to integrate drilling and geophysics into a coherent exploration package.