PerspectivePlanetary Science

Cold-Trapping Mars' Atmosphere

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Science  13 May 2011:
Vol. 332, Issue 6031, pp. 797-798
DOI: 10.1126/science.1205169

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Earth's climate is buffered by massive oceans of liquid water and by gases, such as carbon dioxide (CO2), which cycle through the atmosphere and through biologic and geologic reservoirs. Mars has no oceans to buffer its temperatures, and the thin atmosphere (95% CO2) provides little thermal buffering. The surface pressure is close to that in equilibrium with solid CO2 at Mars' polar temperatures, and early space probes explored whether large CO2-ice deposits might buffer the atmospheric pressure of Mars (1). Subsequent investigations found reservoirs of frozen water in thick polar layered deposits, but revealed only thin perennial deposits of CO2 at the south pole (termed “residual cap”) in addition to the ∼30% of atmospheric CO2 that is cycled through the seasonal caps. On page 838 of this issue, Phillips et al. (2) report the discovery of thick deposits in the south polar region that are most likely composed of solid CO2 and comparable in mass to the present Mars atmosphere.