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Mars' Southern Polar Cap
5.12.05
 
NASA scientists have solved an age-old mystery by finding that Mars' southern polar cap is offset from its geographical south pole because of two different polar climates. The scientists found that the location of two huge craters in the southern hemisphere of Mars is the root cause of the two distinct climates. Weather generated by the two martian regional climates creates conditions that cause the red planet's southern polar ice to freeze out into a cap whose center lies about 93 miles (150 kilometers) from the actual south pole, according to a scientific paper included in the May 12, 2005 issue of the journal, Nature.

Mars Ice Cap Mars
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Mars South Pole Summer South Polar Cap, Summer 2000
This is the south polar cap of Mars as it appeared to the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) on April 17, 2000. In winter and early spring, this entire scene would be covered by frost. In summer, the cap shrinks to its minimum size, as shown here. Even though it is summer, observations made by the Viking orbiters in the 1970s showed that the south polar cap remains cold enough that the polar frost (seen here as white) consists of carbon dioxide. Carbon dioxide freezes at temperatures around -125° C (-193° F). Mid-summer afternoon sunlight illuminates this scene from the upper left from about 11.2° above the horizon. Soon the cap will experience sunsets; by June 2000, this pole will be in autumn, and the area covered by frost will begin to grow. Winter will return to the south polar region in December 2000. The polar cap from left to right is about 420 km (260 mi) across.
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Diagram Mars study
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Mars South Pole Spring Springtime on the Martian South Polar Cap
This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) wide angle view of the martian south polar region was acquired on September 12, 2001, four years to the day after MGS first began to orbit the Red Planet. The bright area at the center of the image is the permanent south polar cap---the part of the cap that will remain through the coming summer. The bright areas that surround the center make up the seasonal frost cap that was deposited during southern winter, which ended June 17, 2001. The dark area in the lower right corner results from two phenomena--the seasonal frost is subliming away much faster in this region, and the area is darker because it is closer to the night side of the planet. The fuzzy or hazy zone that covers most of the left side of the image consists of afternoon clouds and fog. The polar frosts contain both water and carbon dioxide ices. Clouds of condensing water ice crystals are common over parts of the polar cap at this time of year. For scale, the permanent cap at the center of the image is about 420 km (260 mi) across. Sunlight illuminates the scene from the upper left. For a summertime view of the cap, see http://www.msss.com/mars_images/moc/4_27_00_spcap/. Summer in the southern hemisphere will begin in mid-November 2001.
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