Frost on Mars

This animated gif shows the build up of frosts in a 73 x 41 km section of the north polar ice cap of Mars between November and December 2004.
 The images were taken by the High Resolution Stereo Camera on ESA’s Mars Express during its first year at the Red Planet. It has been orbiting Mars for over 13 years.

The north polar icecap comprises layers of water-ice that extend to a depth of around 2 km. The layers result from seasonal melting and deposition of ice mixed with dust.
 During winter the water-ice is covered by a thin layer of carbon dioxide ice that is a few centimetres to around a metre thick.
 During the warmer summer months, most of the carbon dioxide ice turns directly into vapour and escapes into the atmosphere, leaving behind the water-ice layers.