The TES has been monitoring changes in the south polar ice cap during
the spring season. During this time, the cap has been shrinking as the
sun warms the surface and sublimates the CO2 ice. The cap
location is easily detected using surface temperature measurements because
CO2 ice has a temperature near -190 F, while the ice-free
surface is 20-30 degrees warmer. The cap was approximately 2,600 miles
in diameter on 19 September, and has shrunk by over 600 miles during the
past two months. The MGS polar orbit provides the first opportunity to
observe the polar caps of Mars on a daily basis. Throughout the aerobraking
phase of the mission, a temperature image of the cap will be collected on each
orbit, allowing the retreat of the cap edge to be tracked in spectacular
detail. Variations in the retreat of the polar cap from year to year will
provide insight into yearly changes in the martian climate.
This figure shows the 25 micron temperature of the martian southern
hemisphere as measured by the TES during orbits 5 (19 September 1997)
and 29 (27 October 1997). The dark violet regions are the coldest, and
the red-pink regions are the warmest. In September, the cap was
approximately 3000 miles in diameter, roughly the size of the United
States. By October, a significant decrease in the extent of the polar
cap is observed, concurrent with the onset of summer in the southern
hemisphere.
