The Oxygen Balance of Primordial Mars: Oxygen Fugacity of Selected Snc Meteorites,

Martian surface can be accounted for by two methods of production; photolysis of water molecules via solar ultraviolet light, releasing hydrogen and oxidising iron, and, the residual effects of the addition of biogenic redox products. We can estimate the amount of Fe 3+ created by photodissociated oxygen by observing the primordial and current redox states of Mars. This is conducted via calculating the oxygen fugacity of selected SNC meteorites and estimating the total mass of ferric oxide deposits, respectively. Ferric phase extents on the surface are observable through Mars Global Surveyors Thermal Emission Spectrometer dataset. Indications of the oxidation state of surface environments are supplemented by results from the MERs and Pathfinder. The volume and content of deep oxidised deposits difficult to ascertain, however this is probably closely linked with the sub-surface water content (deducible from the relatively new MARSIS data) and the mechanisms by which ice forms in the regolith [5, 8]. Upon calculation of the created Fe 3+ we consider the total oxygen and water inventory of Mars in regolith, polar caps and, in further research, pre-oxidised ferric iron bearing deposits. By this we hope to place limits on, by observing their redox products, the likely types, extent and activity levels of early Martian biotic systems. This will help clarify the feasibility and likelihood of the existence of early life on Mars. Oxygen Fugacity of SNC Meteorites: Electron microprobe data of co-existing Fe-Ti oxides was measured in Dar Al Gani 476, EETA79001 A, Nakhla and Zagami. Prior estimates of fO 2 and T by [4] were used in conjunction with the Shergottites measured values of Fe 3+ / S Fe in order to calculate log(fO 2 ) using QUIlF or a fugacity curve using a reformulation of a similar program originally written for Mathematica, ‘OxideEq.m’. Application of QUILF and OxideEq: Oxygen fugacity was calculated using two models; the QUILF program of [9] and a conversion to Matlab of the OxideEq model by Dreher (2001). Neither model requires silicates to be present in order to calculate fO 2 or the crystallisation temperature, T . THE OXYGEN BALANCE OF PRIMORDIAL MARS: OXYGEN FUGACITY OF SELECTED SNC METEORITES, SUB-SURFACE H 2 O INVENTORY, THE MARTIAN Fe 3+ /Fe 2+ RATIO & THE IMPLICATIONS FOR BIOGENIC INFLUENCES E. Sefton-Nash 1 , M. Anand 2 , D. Dobson 1 , L. Vocadlo 1 & T. Williams 3 1 University College London, Gower Street, London, WC1E6BT, UK. ([email protected]) 2 Department of Earth Sciences, The Open University, Milton Keynes, MK76AA, UK. 3 Natural History Museum, Cromwell Road, London, SW75BD, UK.