The 1999 Seasonal Recession of Mars' South Polar Cap: MOC Observations

Details The 1999 Seasonal Recession of Mars' South Polar Cap: MOC Observations The 1999 Seasonal Recession of Mars' South Polar Cap: MOC Observations

Aug 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000mpse.conf...87j&link_type=abstract

International Conference on Mars Polar Science and Exploration, p. 87

Other

Mars (Planet), Mars Surface, Albedo, Frost, Mars Exploration, Polar Caps, Polar Regions, Recession, Planetary Geology, Planetary Mapping, Aerobraking, Cameras, Elevation, Irregularities, Mars Global Surveyor, Terrain

Scientific paper

The seasonal recession of the Martian South Polar cap has been observed for many years by ground-based astronomers and by spacecraft. The Viking regression in 1977 appeared to be slower than the average of ground based observations but was very similar to the especially good 1971 data set acquired by the International Planetary Patrol. Examination of all of these data sets suggests interannual variability, but no rigorous correlation with other variable phenomena on Mars, such as dust storms, has been possible. The Wide Angle (WA) cameras of the Mars Orbiter Camera (MOC) on the Mars Global Surveyor Spacecraft (MGS) have almost continuously mapped Mars since the start of the Mapping Mission in April 1999. Because the MGS orbit is inclined by about 3 degrees to the poles, images of the polar regions are acquired every two hours. Therefore MOC WA images of the entire south polar cap at low emission angles have been obtained almost every (terrestrial) day during the late winter to late summer cap recession. These data greatly augment the previous coverage of Viking, which was less complete in both space and time, and of MOC during MGS aerobraking in 1997, which was limited and provided low resolution. Accurate topographical data from the Mars Orbiter Laser Altimeter (MOLA) experiment have greatly facilitated interpretation of the numerous irregularities in the cap recession. Correlations are established both with absolute elevation, frost generally favoring lower areas, and slopes, with frost favoring south facing inclines. The regression curve for the south polar cap in 1999 is similar to the "historical average" and faster than that of 1997; the current MOC observations are very similar to the 1997 aerobraking observations. The images have been used to study the behavior of frost albedo in the cap; the new data confirm that the frost in the anomalous, early darkening regions in the cap has color (red/violet albedo) more characteristic of frost than of unfrosted terrains.

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