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
"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
A brief description of how the color for the Narrow Angle (High Resolution) Image was generated:
The MOC narrow angle camera only takes grayscale (black and white)
pictures. To create the color picture seen here, we have taken much
lower resolution red and blue images acquired by the MOC's wide angle
cameras, synthesized a green image by averaging red and blue, and
created a palette of colors that represent the range of colors on
Mars. We then use a relationship that correlates color and brightness
to assign a color to each gray level. This is only a crude approximation
of martian color and should only be considered representative of Mars.
It is likely the colors would not look this vivid to a human
observer at Mars.
Image Credit: NASA/JPL/Malin Space Science Systems