NASA said today new data show carbon dioxide-based snow, or what's more commonly known as dry ice, falls on the Red Planet's south pole -the only known such weather in our solar system.
Frozen carbon dioxide requires temperatures of about minus 193 degrees Fahrenheit (minus 125 Celsius) and the new analysis is based on data from observations in the south polar region during southern Mars winter in 2006-2007, identifying a tall carbon dioxide cloud about 300 miles (500 kilometers) in diameter persisting over the pole and smaller, shorter-lived, lower-altitude carbon dioxide ice clouds at latitudes from 70 to 80 degrees south.
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Instruments on NASA's Mars Reconnaissance Orbiter (MRO) in orbit around Mars detected the snow for this latest study, NASA said. The presence of carbon dioxide ice in Mars' southern polar caps isn't a surprise, NASA said, for example, the Phoenix Lander mission in 2008 observed falling water-ice snow on northern Mars.
NASA said Mars' south polar ice cap is the only place on Mars where frozen carbon dioxide persists on the surface year-round. Just how the carbon dioxide from Mars' atmosphere gets deposited has been in question. It is unclear whether it occurs as snow or by freezing out at ground level as frost. These results show snowfall is especially vigorous on top of the residual cap.
"These are the first definitive detections of carbon dioxide snow clouds," said Paul Hayne of NASA's Jet Propulsion Laboratory in a statement. "We firmly establish the clouds are composed of carbon dioxide -- flakes of Martian air -- and they are thick enough to result in snowfall accumulation at the surface."
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