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Image above: Scientifically, perhaps the most important result from use of the Mars Orbiter Camera on NASA's Mars Global Surveyor during that spacecraft's extended mission has been the discovery and documentation of a fossil delta. The feature is located in a crater northeast of Holden Crater, near 24.0 degrees south latitude, 33.7 degrees west longitude. Since the announcement of the discovery of the delta in November 2003, the International Astronomical Union has provided a provisional name (pending final approval) for the crater in which the landforms occur. The crater has been named Eberswalde, for a town in Germany. This image offers a higher-resolution view of a portion of the fossil delta than any seen earlier. North is up. At the bottom of the frame, the image includes the north end of a looping, inverted, meandering channel. The image covers an area of about 3 by 3 kilometers (1.9 x 1.9 miles). It was produced using a technique called "compensated pitch and roll targeted observation," in which the rotation rate of the spacecraft is adjusted to match the ground speed under the camera. At full resolution, this map-projected image is at 50 centimeters (20 inches) per pixel.
Image credit: NASA/JPL/MSSS/ASU
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Four Mars Years of South Polar Changes
Image above: One of the most profound discoveries that would not have been possible if NASA's Mars Global Surveyor mission had not been extended beyond its primary mission of one Mars year (687 Earth days) is that of dramatic changes that take place in the south polar residual ice cap each martian year. To make this discovery, the Mars Orbiter Camera on the spacecraft had to be employed during a second Mars year to repeat images of sites on the south polar cap that had been imaged during the primary mission.
The initial discovery was made in 2001, when the camera team repeated images of portions of the south polar cap that had already been imaged in 1999. The goal of these images was to obtain stereo views, which would allow investigators to see the topography of the cap in three dimensions and to measure the thickness of the polar ice layers.
It was not possible to produce the desired 3-D views. To the team's surprise, the landforms of the south polar cap had changed.
Image below: Animated GIF showing changes in south polar scarp positions, as they evolved from 1999 to 2001 to 2003 to 2005. + View a larger animation 1.24MB
The south polar residual cap - that is, the portion of the ice cap that remains bright and retains ice throughout the southern summer season - was seen in 1997 and 1999 images to have a complex terrain of broad, relatively flat mesas, small buttes, and many pits and troughs. Pits are generally circular and in some areas visually resemble a stack of thin slices of Swiss cheese. Very early in the Mars Global Surveyor mission, the Mars Orbiter Camera team speculated that these landforms must be carved into frozen carbon dioxide, because they look so unfamiliar and because Viking orbiter infrared measurements indicated that the south polar cap is cold enough consist of frozen carbon dioxide, even in summer.
The observations made by Mars Orbiter Camera in 2001, during the first part of the extended mission, showed that the scarps and pit walls of the south polar cap had retreated at an average rate of about 3 meters (10 feet) since 1999. In other words, they were retreating 3 meters per Mars year (and, of course, most of that retreat takes place during the summer). In some places on the cap, the scarps retreat less than 3 meters a Mars year, and in others it can retreat as much as 8 meters (26 feet) per martian year.
Of the two volatile materials one is likely to find in a frozen state on Mars - water and carbon dioxide - it is carbon dioxide that is volatile enough to permit scarp retreat rates like those observed by the Mars Orbiter Camera.
Image Credit: NASA/JPL/MSSS
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