13 July 2005
The south polar residual cap of Mars is composed of
layered, frozen carbon dioxide. In 1999, the Mars Global Surveyor (MGS)
Mars Orbiter Camera (MOC) showed that the carbon dioxide layers have been
eroded to form a variety of circular pits, arcuate scarps, troughs,
buttes, and mesas. In 2001, MOC images designed to provide repeated views
of the areas imaged in 1999 -- with the hope of creating stereo (3-D)
images, so that the height of scarps and depth of pits could be measured
-- showed that the scarps had retreated, pits enlarged, and buttes and
mesas shrank. Only carbon dioxide is volatile enough in the martian
environment to have caused such dramatic changes -- the scarps were seen
to retreat at an average rate of 3 meters (about 3 yards) per Mars year.
Most of the scarp retreat occurs during the southern summer season; in
some areas the scarps move as much as 8 meters, in others, only 1 meter
per Mars year.
Three Mars years have now elapsed since MOC first surveyed the south polar
cap in 1999. Over the past several months, MGS MOC has been re-imaging
areas that were seen in 1999, 2001, and 2003, to develop a detailed look
at how the landscape has been changing. This animated GIF provides an
example of the dramatic changes that have occurred during the past three
martian years. The first image, a sub-frame of M09-05244, was acquired on
21 November 1999. The second image, a sub-frame of S06-00973, was obtained
on 11 May 2005. The animation shows the changes that have occurred between
1999 and 2005. Each summer, the cap has lost more carbon dioxide. This may
mean that the carbon dioxide content of the martian atmosphere has been
increasing, bit by very tiny little bit, each of the years that MGS has
been orbiting the red planet. These observations also imply that there was
once a time, in the not-too-distant past (because there are no impact
craters on the polar cap), when the atmosphere was somewhat thinner and
colder, to permit the layers of carbon dioxide to form in the first place. Just as
Earth's environment is very different today than it was just 11,000 or so years
ago, the martian environment has also been changing on a similar time scale.
Location near: 88.9°S, 25.7°W
Image width: width: ~0.6 km (~0.4 mi)
Illumination from: upper left
Season: Southern Spring