crater mars water
© ESA/DLR/FU Berlin, CC BY-SA 3.0 IGOLooking frosty
Even Mars is getting into the festive spirit. This is the Korolev Crater near the north pole of the Red Planet, which is filled with a mound of water ice 60 kilometres across and nearly 2 kilometres thick.

The water ice is a permanent feature. It is thought that the crater traps a layer of cold air that prevents the ice melting even during the six-month-long northern summer on Mars, making this a year-long winter wonderland.

This image is based on five image strips captured by the High Resolution Stereo Camera on board the European Space Agency's Mars Express spacecraft, which has been in orbit around Mars since 2003. The image strips were taken in April this year.

ice crater mars
© ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO
The data has been processed to show what the crater might look like if viewed from the side, and with the naked eye.

There is likely some fine dust mixed in with the ice, but not enough to change the surface appearance. "The colour is the colour you see," says Ralf Jaumann of the German Aerospace Center, where the image was processed.

There is also permanent water ice at the planet's poles, mixed with frozen carbon dioxide. In the northern Martian winter, a layer of carbon dioxide ice 1 to 2 metres thick forms on the permanent ice cap.
Korolev crater
© ESA/DLR/FU Berlin, CC BY-SA 3.0 IGOA topographic map of Korolev crater.