Spying Changes in Mars' South Polar Cap
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.