From: Jet Propulsion Laboratory
Posted: Monday, February 11, 2002
Extended mission operations for the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) has provided thousands of opportunities to image sites previously seen by the camera. Often, these are chances to see if anything on the planet has changed. The most surprising changes were documented starting in August 2001, when the south polar cap emerged from winter darkness. In 1999 MOC found that the south polar cap exhibits an array of bizarre layers, arcuate scarps, and "swiss cheese" holes and pits. How these formed was unknown. Once MOC began to re-image these areas in 2001, however, the team discovered that the polar scarps had changed. They had retreated approximately 3 meters (about 3 yards) in less than 1 Mars year (a Mars year is 687 Earth days long). In some places, small buttes completely disappeared (e.g., see arrow). In December 2001, MOC scientists reported that such rapid change could only have occurred if the south polar cap is composed mainly of frozen carbon dioxide. The image on the left, above,tleAwas taken on November 28, 1999. The picture on the right was obtained nearly 1 Mars year later on October 9, 2001. Both images are illuminated from the upper right and each covers an area 2 km (1.2 mi.) wide by 6.9 km (4.3 mi.) long.
Since the initial discovery of scarp retreat in the south polar cap in August 2001, MOC Extended Mission operations have included observation of many changes that occurred since 1999, and acquisition of new data to see how the cap changes from Spring in late 2001 through Summer in early 2002. Additional images have been obtained to help document changes when the polar cap returns to Spring in 2003.
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