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Evolution of the Martian Atmosphere

Publication Date
DOI: 10.1006/icar.1994.1146
  • Chemistry


Abstract Carbon dioxide, nitrogen, and the nonradiogenic and radiogenic noble gases are tracked from primordial inventories to their present states in a revised model of atmospheric evolution on Mars. Elemental and isotopic abundances evolve by hydrodynamic escape, impact erosion, outgassing, sputtering, photochemical escape of nitrogen, and carbonate formation and recycling. Atmospheric history is divided into early and late evolutionary periods, the first characterized by high CO 2 pressures and a possible greenhouse and the second by a low pressure cap-regolith buffered system initiated by polar CO 2 condensation ∼3.7 Gyr ago. During early evolution the Xe isotopes are fractionated to their present composition by hydrodynamic escape, and CO 2 pressure and isotopic history are dictated by the interplay of losses to erosion, sputtering, and carbonate precipitation, additions by outgassing and carbonate recycling, and perhaps also by feedback stabilization under green-house conditions. Atmospheric collapse near 3.7 Gyr leads to abrupt increases in the mixing ratios of preexisting Ar, Ne, and N 2 at the exobase and their rapid removal by sputtering. Current abundances and isotopic compositions of these light species are therefore entirely determined by the action of sputtering and photo-chemical escape on gases supplied by outgassing during the late evolutionary epoch. The present atmospheric Kr inventory also derives almost completely from solar-like Kr degassed during this period. Consequently, among current observables, only the Xe isotopes and δ 13C survive as isotopic tracers of atmospheric history prior to its transition to low pressure.

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