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Thursday, January 24, 2013

Mars: Dry Ice and Dunes in Seasonal Change


Researchers using NASA's Mars Reconnaissance Orbiter see seasonal changes on far-northern Martian sand dunes caused by warming of a winter blanket of frozen carbon dioxide.

Earth has no naturally frozen carbon dioxide, though pieces of manufactured carbon-dioxide ice, called "dry ice," sublime directly from solid to gas on Earth, just as the vast blankets of dry ice do on Mars. A driving factor in the springtime changes where seasonal coverings of dry ice form on Mars is that thawing occurs at the underside of the ice sheet, where it is in contact with dark ground being warmed by early-spring sunshine through translucent ice. The trapped gas builds up pressure and breaks out in various ways.
 
Transient grooves form on dunes when gas trapped under the ice blanket finds an escape point and whooshes out, carrying out sand with it. The expelled sand forms dark fans or streaks on top of the ice layer at first, but this evidence disappears with the seasonal ice, and summer winds erase most of the grooves in the dunes before the next winter. The grooves are smaller features than the gullies that earlier research linked to carbon-dioxide sublimation on steeper dune slopes.

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