MOC View of the Martian South Polar Residual Cap
The portion of the martian south polar cap that persists through each
southern hemisphere summer is known as the residual cap. This Mars
Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a 2.9 by
4.8 km (1.8 by 3 mi) area of the south polar residual cap as it appeared
in mid-summer on 23 February 2000. The landscape of the south polar
residual cap is dominated by layered, frozen carbon dioxide
("dry ice") that has been eroded into a variety of pits,
troughs, buttes, and mesas. Commonly, the pits are circular and the
mesa scarps are arcuate. In summer, as carbon dioxide is subliming
away, the scarps bounding the pits and mesas darken. The darkened
slopes may indicate that small amounts of dust are present, mixed-in
with the ice. The ice is layered, indicating many cycles of deposition
preceded the present period of sublimation and erosion. Recent MGS
MOC images acquired in 2001 have indicated that the scarps are
retreating an average of 3 meters (3.3 yards) per martian year. These
findings, described in an accompanying release ("MOC Observes
Changes in the South Polar Cap: Evidence for Recent Climate Change
on Mars"), suggest that the martian climate may be changing
today. As more carbon dioxide is released into the atmosphere each
southern spring and summer, the atmospheric pressure of Mars may
increase such that it could double in a few hundred to a thousand
Mars years (687 Earth days = 1 Mars year). The picture shown here is
from MOC image M12-02295 and is illuminated by sunlight from the
lower right.
A version of this picture appears on the cover of the December 7, 2001,
issue of Science and accompanies a paper regarding the MGS MOC
discovery of evidence for martian climate change.
Image Credit: NASA/JPL/Malin Space Science Systems
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