From: Jet Propulsion Laboratory
Posted: Monday, February 11, 2002
The north polar cap of Mars is the only place on the surface of the planet that is known to have water. Of course, the water there is frozen. Unfortunately, the martian north polar cap has been a difficult place for the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) to view. Each winter, the pole spends approximately 6 months in darkness. Each spring, everything is covered with frost. In summer and through autumn, the cap is often obscured by clouds--sometimes clouds of dust from raging dust storms, and sometimes clouds of water ice crystals. However, a period of excellent viewing conditions occurred early in the MGS Extended Mission (from February through April 2001). This image, taken by MOC in April 2001, shows the layers comprising the north polar cap exposed in an arcuate scarp that occurs at one end of Chasma Boreale. MOC images acquired in 1999 showed that the polar cap has two types of layers: there is a stack of light-toned, nearly uniformly-bedded layers at the top, and a stack of darker-toned beds that form shelves and benches at the bottom. The darker, lower beds are older. Dozens of MOC images were targeted during the clear-atmosphere period in 2001 to test the MOC team's hypotheses about the polar cap layers and these images have helped in documenting the nature of these layers. The lower, dark layers of the polar cap appear to include considerable amounts of sand, while the upper layers lack sand and instead may be a mixture of ice and dust. The lower layers appear to contribute sand to the dune fields that surround the polar cap, though no dunes are present in the image shown here. This image is illuminated from the lower right and covers an area 14.5 km (9 mi.) across. The scarp slopes toward the bottom of the scene.
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