Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.u23e0091s&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #U23E-0091
Other
0343 Planetary Atmospheres (5210, 5405, 5704), 1610 Atmosphere (0315, 0325), 3305 Climate Change And Variability (1616, 1635, 3309, 4215, 4513), 3346 Planetary Meteorology (5445, 5739), 6225 Mars
Scientific paper
Evidence for the presence of flowing water on the Martian surface at some time in the distant past is most persuasive. The current cold, dry climate and low atmospheric pressure precludes liquid surface water for any extended period of time, and these conditions seem to have generally prevailed since 1-2 Ga after Mars" formation. Water in unknown quantities (but presumably substantial) and CO2 in relatively small amounts are well established by many observations. The considerable difficulty of producing a warm, wet Mars under present solar output pales in comparison to producing these conditions when the sun was less luminous. Attempts to model such a climate using CO2 as the main greenhouse gas lead to very high atmospheric concentrations, which should have left an obvious signature. The absence of significant carbonate mineral deposits suggests that CO2 was not likely ever present in the atmosphere at the necessary concentrations. Alternative greenhouse gases, such as methane and ammonia, have met with the same objections applied to similar discussions of the early climate of Earth, namely the instability of these gases under ultraviolet light. This may be slightly less problematical for Mars given the greater distance from the sun. However, if the major reservoir for surface carbon on Mars was as organic compounds, the resolution to the climate problem could lie in the regeneration of methane (and perhaps ammonia) by volcanically-driven hydrothermal processing of these organics in the presence of water. Maintenance of sufficiently high levels of these potent greenhouse gases would have depended on continued thermal activity, especially early in Mars history when the faint young sun required especially high levels, and when thermal sources were undoubtedly greater than at present. The climate transition from warm and wet to cold and dry (in spite of the increasing luminosity of the sun) was the result of the exponential decay of thermal activity on the relatively small Mars, and consequent reduction of atmospheric concentrations of reduced greenhouse gases.
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