Greetings from the north pole of Mars
Each winter, the Martian icecap gets an extra layer of frozen carbon dioxide.
The north pole of Mars sits on a high plain known as the Planum Boreum. It's covered all year round in a cap of water ice, but in the cold Martian winters an extra frosty blanket descends: solid carbon dioxide frozen out of the thin Martian atmosphere.
Above the pole, strong winds blow down and swirl, whipped around by the planet's rotation, creating the spiral structure of the ice cap shown above.
The image is a perspective mosaic created from several images taken by the European Space Agency's Mars Express, combined with elevation data from NASA's Mars Global Surveyor.