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Spying Changes in Mars' South Polar Cap

July 13, 2005

This is a black and white animated image that highlights the recession of the carbon dioxide layers at Mars' south polar cap over the last six years.  The images move in a time-lapse fashion, making it appear that holes and pits are becoming larger as the viewer watches.

+ Larger Animation

Image Credit: NASA/JPL/MSSS

This animated image shows Mars in motion over the last six years. Images from the Mars Orbiter Camera aboard the Mars Global Surveyor spacecraft have documented dramatic changes in the planet's south polar cap.

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 (arc-shaped slopes), 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 (nearly 10 feet) 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 (26 feet), in others, only 1 meter (3.3 feet) 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 November 21, 1999. The second image, a sub-frame of S06-00973, was obtained on May 11, 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.

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