THE EXPLORATION OF MARS IS MOTIVATED IN LARGE PART BY THE POSSIBILITY THAT MARS MAY HAVE HARBORED LIFE EARLY IN ITS HISTORY OR MAY HAVE EXTANT LIFE IN THE SUBSURFACE. BECAUSE WATER IS AN ESSENTIAL INGREDIENT FOR LIFE RESEARCH ON THE PROCESSES THAT FORM LIQUID WATER IS CRITICAL FOR UNDERSTANDING THE HABITABILITY OF MARS. TO INVESTIGATE THE POSSIBLE FORMATION OF NEAR-SURFACE LIQUID WATER ON MARS WE PROPOSE A COMBINATION OF (1) FIELD RESEARCH ON SHALLOW GROUNDWATER FEATURES IN A MARS ANALOG ENVIRONMENT THE ANTARCTIC DRY VALLEYS (ADV) AND (2) THEORETICAL MODELING OF BRINE AND VAPOR TRANSPORT IN PERMAFROST SOILS. THE FIELD WORK COMPONENT OF THIS PROPOSAL WILL INVESTIGATE THE CHEMICAL MINERALOGICAL AND ISOTOPIC COMPOSITION OF WIDE-SPREAD SHALLOW GROUNDWATERS IN THE ADV AND SOILS ASSOCIATED WITH THESE FEATURES. TO COMPLEMENT OUR FIELD WORK WE WILL DEVELOP AND APPLY A NOVEL THERMAL-REACTIVE-TRANSPORT MODEL USING DATA COLLECTED FROM THE FIELD TO CONSTRAIN THE MODEL INPUTS AND GROUND-TRUTH THE MODEL OUTPUTS. AT THE CONCLUSION OF OUR RESEARCH WE WILL HAVE RIGOROUSLY TESTED IF MECHANISMS OF GROUNDWATER FORMATION IN THE ADV CAN PRODUCE WIDE-SPREAD SHALLOW GROUNDWATERS ON MARS AND WHAT THE PROPERTIES OF PUTATIVE MARTIAN GROUNDWATERS WOULD BE (E.G. COMPOSITION TEMPERATURE AND WATER ACTIVITY). THIS RESEARCH IS CRITICAL FOR TESTING HYPOTHESES ABOUT APPARENT AQUEOUS FLOWS SUCH AS RECURRING SLOPE LINEAE (RSL). THE OUTCOMES OF THIS RESEARCH WILL ADDRESS FUNDAMENTAL QUESTIONS ABOUT THE FORMATION AND PROPERTIES OF POTENTIALLY HABITABLE AQUEOUS ENVIRONMENTS ON MARS INCLUDING: (1) HOW DO SHALLOW GROUNDWATERS FORM IN THE ADV A MARS ANALOG ENVIRONMENT? COULD SIMILAR PROCESSES OCCUR ON MARS? (2) WHAT IS THE CHEMICAL COMPOSITION OF SHALLOW GROUNDWATER BRINES IN THE ADV AND MARS? UNDER WHAT CONDITIONS OF TEMPERATURE AND SALINITY CAN SUCH BRINES REMAIN LIQUID? (3) WHAT SECONDARY MINERALS FORM AS A RESULT OF LOWTEMPERATURE WATER-ROCK INTERACTIONS? HOW DO THESE REACTIONS INFLUENCE BRINE CHEMISTRY? (4) WHAT IS THE HABITABILITY OF BRINES IN TERMS OF WATER ACTIVITY SALINITY AND TEMPERATURE IN SHALLOW GROUNDWATER SYSTEMS?