Spring on Mars. This image provided by NASA/JPL and the University of Arizona shows barchan (crescent-shaped) sand dunes in the North Polar region on Mars.
In this image, taken during the northern spring season, the dunes and ground are still covered in seasonal frost.
The speckled appearance is due to the warming of the area.
As the carbon dioxide frost and ice on the dunes warms, small areas warm and sublimate (turn from solid to gas) faster, creating small jets that expose/deposit dark sand and dust onto the surface.
Notice that there are no spots on the ground between the dunes - that is because the ground stays more uniformly cold, unlike the darker dune sand.
Picture: NASA/JPL/University of Arizona/AFP/Getty
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