Obliquity-Controlled Water Vapor/Trace Gas Feedback in the Martian Greenhouse Cycle

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[0343] Atmospheric Composition And Structure / Planetary Atmospheres, [5405] Planetary Sciences: Solid Surface Planets / Atmospheres, [5450] Planetary Sciences: Solid Surface Planets / Orbital And Rotational Dynamics, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

The mechanism(s) by which the climate of early Mars was maintained in a "warm, wet" state remains unclear. The possibility that trace gases played a significant role in keeping early Mars warm suffers from some weaknesses, but is likely still an important component in an integrated climate system. Current work demonstrates that the joint effects of water vapor and volcanically derived trace gases have a more significant greenhouse effect than previously assumed. Simply, a warming "pulse" caused by injection of small amounts of volcanic gases (e.g. SO2, CH4) provides a small but sufficient increase in atmospheric temperature, allowing a greater quantity of water vapor (injected as a volcanic gas and/or available from the surface) into the atmosphere, the latter assuming the dominant greenhouse role in the warm/wet scenario. Warm temperatures can be maintained for some time even following the loss of the trace gas "trigger" by precipitation or chemical decay. The gain and loss of this water vapor in the atmosphere is further regulated by the planetary obliquity cycle, which controls the saturation abundance of atmospheric vapor. Under periods of low obliquity, the atmosphere can hold little vapor, and this feedback process will be inhibited. Only when obliquity rises above some threshold value will the amount of atmospheric vapor be capable of effectively sustaining warm temperatures (and then only when triggered by the injection of other trace gases). Multi-bar levels of CO2 are not required at any stage of the process, but are not precluded, and hence this process can take place during most of martian history. This mechanism can help explain the warm conditions during the Noachian, as well as the presence of fluvial surface features (e.g. inverted channels, valley networks) and aqueous minerals (e.g. sulfates) of Hesperian and Early Amazonian age-periods when alternate methods do not convincingly explain the presence of liquid water.

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