Image: Martian sand dunes in spring

(Phys.org) —Mars' northern-most sand dunes are beginning to emerge from their winter cover of seasonal carbon dioxide (dry) ice. Dark, bare south-facing slopes are soaking up the warmth of the sun.

The steep lee sides of the dunes are also ice-free along the crest, allowing sand to slide down the dune.

Dark splotches are places where ice cracked earlier in spring, releasing sand. Soon the dunes will be completely bare and all signs of spring activity will be gone.

This image was acquired by the HiRISE camera aboard NASA's Mars Reconnaissance Orbiter on Jan. 16, 2014.