Waiting for spring

A piece of Mars: These sharp-tipped hills are dunes near the north pole of Mars. At the height of summer they’re lovely dark dunes, but because it’s just barely spring here they’re still covered in white frost (mostly CO2 ice, but a little water ice). Like penguins who huddle in the dark of the polar night, these dunes are waiting for the sun to return so they can wake up and start moving with the wind. (ESP_032895_2615, NASA/JPL/Univ. of Arizona)