The pictured permanent north polar ice cap of Mars is composed of water ice and dust and covers an area of approximately 1x106 km². The volume of the permanent cap is estimated to be 1.2x106 km³, about half the size of the Greenland ice cap on Earth. The ice cap has an average thickness of approximately two kilometres. Temperatures fall to below -125 degrees Celsius during the Martian winter, which is twice as long as Earth's due to Mars' two-year orbital period and is characterised by long polar nights due to the tilt of its rotational axis. Only in the Martian winter season, temperatures are cold enough for carbon dioxide to precipitate from the atmosphere, forming an additional seasonal cap of carbon dioxide ice.
Characteristic features of the north polar cap are the dark troughs that spiral outward from the pole in counterclockwise direction, and a prominent trench at about 300°E with a length of 500 km and a width of up to 100 km, termed Chasma Boreale.
Radar investigations of the north polar cap were performed by MARSIS on Mars Express and by SHARAD on Mars Reconnaissance Orbiter. They show that the ice cap is made up of many individual layers that are considered a valuable archive for the climate of Mars during the past millions of years. Some radar data hint to wind transport and atmospheric deposition as dominant processes for the formation of the spiral troughs and trenches.
Image processing and the HRSC experiment on Mars Express
The mosaic consists of 32 orbit stripes (1154, 1177, 1219, 1291, 1394, 1745, 3663, 3681, 3685, 3695, 5483, 5775, 5784, 5796, 5808, 5810, 5818, 5824, 5827, 5838, 5853, 5864, 5867, 5900, 5904, 5963, 6007, 6229, 8042, 8080, 8153, 8160) and covers a region 0°-360° East and approximately 78° to 90° North. The images were acquired mainly during the summer seasons, since images of the winter ice cap suffer from CO2 cloud covering and dust, and are thus unsuitable for mosaic production. The color mosaic was created using data from the nadir channel, the field of view of which is aligned perpendicular to the surface of Mars, and the color channels of the HRSC. The oblique perspective views were generated using elevation data from the Mars Orbiter Laser Altimeter (MOLA) experiment on board the NASA Mars Global Surveyor mission. The context map is in stereographic projection and uses a Mars sphere as reference body for elevation values.
HRSC image in top view: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO
Perspective views: ESA/DLR/FU Berlin, NASA MGS MOLA Science Team
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The High Resolution Stereo Camera was developed at the German Aerospace Center (DLR) and built in collaboration with partners in industry (EADS Astrium, Lewicki Microelectronic GmbH and Jena-Optronik GmbH). The science team, which is headed by Principal Investigator (PI) Ralf Jaumann, consists of 52 co-investigators from 34 institutions and 11 countries. The camera is operated by the DLR Institute of Planetary Research in Berlin-Adlershof.