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Dry Ice Blocks Slide Down Martian Grades


Scientists have puzzled over how gullies like these form on sand dunes in the southern polar region of Mars. In the winter these dunes are covered with a layer of CO2 ice (dry ice). In this image most of the ice has sublimated, but there are still bright patches sheltered behind ripples on the sand dunes. In the gullies a few small bright blocks remain, and it is the action of these blocks over the course of many Martian springs that we believe have caused the gullies. Blocks that break off higher on the dune will slide down the dune lubricated by a layer of gas that pushes sand out to the side. When the blocks reach the bottom of the channel they will come to a stop and sublimate in place, forming the pits at the end of the gully. This image cutout is from HiRISE image ESP_029408_1255, taken on the Russell Crater Dunes.  


To carry out proof-of-concept tests that blocks of dry ice could form channels on sand dunes Serina Diniega (lead author of the paper) and Candice Hansen (co-author, pictured here) purchased blocks of dry ice and took them to sand dunes in southern Utah.  Hansen carried the blocks of ice to the crest of the dune and Diniega filmed them sliding down the sand.  The gas sublimating from the bottom of the block reduced friction so much that the blocks slid even on the gently-sloped side of the dune, plowing through minor obstacles such as the ripples visible on this dune.   The two scientists also experimented with blocks of water ice, and found that the water ice, without the levitation from that layer of gas, would not slide at all, even on the steeply sloped slipface of the dune. 



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