Stabilizing the Early Martian Climate: Effects of Airborne Dust, CO2 Ice Cap Albedo, and Orbital Obliquity on Atmospheric Collapse

Details Stabilizing the Early Martian Climate: Effects of Airborne Dust, CO2 Ice Cap Albedo, and Orbital Obliquity on Atmospheric Collapse Stabilizing the Early Martian Climate: Effects of Airborne Dust, CO2 Ice Cap Albedo, and Orbital Obliquity on Atmospheric Collapse

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p21a1656k&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P21A-1656

Physics

[5405] Planetary Sciences: Solid Surface Planets / Atmospheres, [5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

The stability of the early Martian atmosphere against collapse into permanent surface CO2 ice reservoirs is fundamentally important for understanding the evolution of Mars' atmosphere and surface throughout its history. A clear, thick (~80 mb) CO2 atmosphere early in Mars' history is not stable against collapse in the presence of a faint young sun. However, an active dust cycle may provide a mechanism to stave off atmospheric collapse by directly affecting the thermal and dynamical state of the atmosphere and by modifying the albedo of the polar ice caps. The goal of this work is to develop an understanding of the importance of the dust cycle in determining the stability of early Martian atmospheres. The NASA Ames Mars General Circulation Model (MGCM) is used to explore the effects of atmospheric dust loading, polar cap albedo, and orbital obliquity on atmospheric collapse. Results of this parameter study indicate that 80 mbar CO2 atmospheres are difficult to maintain, especially in the presence of a faint young sun. Of the 36 simulations conducted, only 6 predicted a stable atmosphere (i.e., did not lead to the formation of permanent CO2 ice caps). Increasing the albedo of the polar CO2 ice cap accelerates atmospheric collapse at all dust loadings and obliquities. The energy absorbed by the surface during local spring decreases as albedo increases, making it more difficult for the seasonal CO2 ice to completely sublimate each year. If any CO2 ice survives through the summer season, permanent CO2 caps form and the atmosphere collapses. Increasing the orbital obliquity increases atmospheric stability. All but two of the stable cases were at the highest obliquity (i.e., 60°). The annually averaged insolation received at the poles increases as obliquity increases. This increased energy delivered to the poles works to stave off atmospheric collapse. Increasing atmospheric dust loading does not have a monotonic effect on the stability of the atmosphere. At all obliquities, when the CO2 ice cap albedo is at or below ~0.5, increasing atmospheric dust accelerates atmospheric collapse. Conversely, when the CO2 ice cap albedo is above 0.5, increasing atmospheric dust decelerates atmospheric collapse. Understanding these effects through the analysis of atmosphere/surface energy balance and heat transport is a primary focus of the work presented.

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