Icefield in polar crater
Icefield in polar crater
Water ice at the bottom of a crater near the Martian north pole. In the centre of the crater, which is about 35 kilometres across, white water ice stands out clearly. The impact crater is located in the northern lowland area Vastitas Borealis. Water ice can remain in the centre of the crater throughout the year, as the temperature is low enough and atmospheric pressure is sufficient to prevent sublimation (direct transition from a solid to a gaseous state). At the time of image acquisition (later summer on Mars), carbon dioxide ice had already disappeared from the entire northern polar cap, leaving only water ice. The thickness of the ice is probably only in the decimetre range. This has been confirmed by some earlier measurements. Copyright note: As a joint undertaking by DLR, ESA and FU Berlin, the Mars Express HRSC images are published under a Creative Commons licence since December 2014: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO. This licence will also apply to all HRSC images released to date.
