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K. Kossacki (Warsaw Uni., Inst. of Geophysics), W. Markiewicz (MPI for Aeronomy)
Mars Orbiter Camera (MGS) has obtained several images of polygonal features in the southern polar region. In images taken late in the southern spring, when the surrounding surface is free of the seasonal frost, CO2 ice still appears to be present within the polygonal troughs. In Earth's polar regions, polygons such as these indicate presence of subsurface water ice. We analyzed the seasonal evolution of the thermal state and the CO2 content of these features. Our model includes condensation and sublimation of the CO2 ice, a self-consistent treatment of the variations of the thermal properties of the regolith, as well as the seasonal variations of the local atmospheric conditions, which we take from the results of a general circulation model. We find that the residence time of seasonal CO2 ice in troughs depends not only on atmospheric opacity and albedo of the CO2 ice, but also and most significantly on the subsurface distribution of water ice. Our analysis quantifies the dependence of the seasonal cycle of the CO2 ice within the troughs on the assumed distribution of the water ice in the regolith. We show that presence of water ice in the ground at a depth smaller than the depth of the troughs reduces winter condensation rate of CO2 ice. This is due to higher heat flux conducted from the water ice rich regolith toward the facets of the troughs. Our model also predicts the seasonal cycle of the surface temperature. These results are compared directly to the values obtained by the Thermal Emission Spectrometer (TES).
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.