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P.B. James, B.A. Cantor (University of Toledo), K. Edgett, M.C. Malin (Malin Space Science Systems)
The Mars Orbiter Cameras on Mars Global Surveyor observed the south polar cap of Mars during its spring recession in 1997. The images acquired by the Wide Angle Cameras reveal a pattern of recession that is qualitatively similar to that observed by Viking in 1977 but that does differ in at least two respects. The 1977 recession in the 0° to 120°-longitude sector was accelerated relative to the 1997 observations after LS = 240°; the Mountains of Mitchel also detached from the main cap earlier in 1997. Comparison of the MOC images with MOLA data shows that the Mountains of Mitchel feature is controlled by local topography. Relatively dark, low albedo regions well within the boundaries of the seasonal cap were observed to have red to violet ratios that characterize them as frost units rather than unfrosted or partially frosted ground; this suggests the possibility of regions covered by CO2 frost having different grain sizes.