Seasonal and Annual Change in the Martian Polar Regions

Details Seasonal and Annual Change in the Martian Polar Regions Seasonal and Annual Change in the Martian Polar Regions

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p21d..04c&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P21D-04

Physics

[5462] Planetary Sciences: Solid Surface Planets / Polar Regions, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing

Scientific paper

The polar caps have a long established dichotomy in visual appearance, relative elevations, and surface composition. Observations using the Mars Reconnaissance Orbiter (MRO) instruments MARCI, CTX and CRISM have shown unique styles of seasonal frost retreat as well as fine scale variations in the composition of various units. With MRO we have observations for three Martian Years (MY) 28, 29 and 30 from November of 2006 to the present. We have observed the seasonal cap recessions in both the north and south using MARCI daily global images and have examined the composition of selected units of the polar layered deposits exposed in summer. Observation over multiple Mars years allows us to compare changes between years as well as longer term evolution of the high albedo deposits at the poles. North Cap Recession and Change: The northern seasonal cap recession was observed in both MY 29 and 30. Past work had noted large scale loss of bright deposits up to Ls 95 and the rugged terrain of the Gemini Scopuli darkens up to ~Ls 100 and then subsequently brightens. The patterns observed in MY 29 and 30 are similar. Significant variability in the early season is noted in both years and the retreating seasonal cap edge is extremely dynamic. Additional retreat of high albedo deposits are noted in MY 30. A new high albedo deposit appears off a reentrant in Olympia Planum in MY 29 and later disappears. In MY30, portions of Olympia Planitia have larger areas of high albedo. In both years sustained bright patches appear along the cap margins and while some are persistent between years, they are also variable over the northern summer. It is still uncertain if these albedo changes represent volatile "refrosting" or the removal of low albedo material to expose higher albedo material underneath and whether or not longer term loss of volatiles is implied. South Cap Recession and Change: The southern seasonal cap recession is fundamentally different than the north, and persistence of outliers have long been observed. Seasonal frost remains long past the summer solstice and removal of residual CO2 ice is not complete until ~ Ls 330. MRO has observed the southern seasonal retreat in all three martian years, but the peak of the summer season was not monitored in MY 29 due to spacecraft software changes. MY 28 was unusual due to the onset of a planet encircling dust storm, that becomes evident at Ls 265. Analysis suggests more rapid retreat of the seasonal deposits in MY 28 due to this event. A water ice outlier previously noted in THEMIS and OMEGA data has been associated with the persistence of seasonal frost. This outlier is gone by Ls 316 in MY 28 but observed to retain seasonal frost as late as Ls 334 in MY 30. The spatial coverage and timing of changes varies among the three MY observed to date and this outlier brightens somewhat with the approach of fall equinox in MY 28.

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