This picture was taken by the HiRISE camera on the Mars Reconnaissance Orbiter last January. It shows Mars’s northern-most sand dunes beginning to emerge from their winter cover of seasonal dry ice (frozen CO2). The dark, bare south-facing slopes are soaking up the warmth of the sun. The steep downwind sides of the dunes are also ice-free along the crest, allowing sand to slide down the dune. The dark areas are places where ice cracked earlier in the spring, releasing sand. Eventually, the dunes will be completely bare and all signs of spring activity will be gone.
Image Credit: NASA