Identifying the Potential Biosphere of Mars
  Our current knowledge of life on Earth indicates a basic requirement for liquid water. The locations of present liquid water are therefore the logical sites to search for current life on Mars. We develop a picture of where on Mars the regions with the highest potential near-surface liquid water abundance can be found through a study of gullies. We also use rampart craters to sound the depth of water ice on Mars and where the highest concentrations of water ice occur. We estimate that low latitude gullies and rampart craters with depths greater than 100 m at 30 degrees (absolute) latitude, greater than 1.3 km at 35 degrees and greater than 2.6 km at 40 degrees latitude will give access to current liquid water environments capable of supporting microbial life. Our data is most consistent with the formation of these gullies through shallow aquifer discharge. These features should therefore be high priority targets for further study and high-resolution imaging with HiRISE. 
Eriita G. Jones, Charles H. Lineweaver