Christmas and winter spirit - also on Mars. Impact craters connected by a striped, coloured ribbon can be seen in the final and very wintry HRSC Mars image of this year. We wish all readers of our martian image series, published together with the European Space Agency (ESA) and Freie Universitat Berlin, happy holidays!

Image data from the High Resolution Stereo Camera (HRSC) on board ESA's Mars Express mission reveal an exciting landscape of layered deposits, frost, ice, and dark dunes near the south polar region of Mars, known as Ultimi Scopuli (from the Latin for 'the final cliffs'). The High Resolution Stereo Camera (HRSC) was developed by the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR) and has been sending images of the Martian surface to Earth since January 2004.

This amazing image shows a section of the landscape measuring approximately 215 by 65 kilometres and located 14 degrees north of the south pole. Many interesting landforms are visible - typical of regions that are permanently frozen but not covered by ice. Together with formations carved by the wind, known as aeolian landforms, and seasonal frost clouds, they complete the scenery.

The scenery appears very abstract with the strongly contrasting colour shades from the orange tones of the Martian soil and the white of water and carbon dioxide ice. Together with the curved landscape forms, it is not an easy landscape to make sense of at first glance. Nature seems to have acted as an expressionist artist on Mars too, giving the HRSC science team an aesthetic element to their processing of the colour stereo image data during the Christmas and New Year period.

These image data were acquired in the southern spring - the time when the ice retreats southward, leaving only a small ice cap at the south pole during summer in the southern hemisphere. During the seasonal cycle on Mars, carbon dioxide ice is deposited at the poles in winter. The amount of atmospheric gases trapped as ice at each pole in winter and then evaporating in spring is enormous, comprising over 10 percent of the atmosphere. This process leads to strong pressure changes in the martian gas envelope and, as a result, to very high wind speeds. These occur primarily in the autumn and are caused by this difference in atmospheric pressure in the hemispheres.

Layered deposits of water ice and fine duste
The two most eye-catching features of this image are two large impact craters that appear to be connected by a striped band. The band and craters exhibit an intense reddish-brown hue that contrasts with the grey and white of the surrounding landscape. In addition, alternating layers can be seen in the crater rims and band - especially when you zoom in. These layers are successive layers of dust and sand that have been deposited continuously and approximately horizontally on the terrain features. They consist primarily of water ice and approximately 10 percent of fine sediments.

The individual layers differ from each other in their albedo (the reflectivity of sunlight), their colour, thickness and their degree of weathering. These deposits are formed by dust and water ice dissolving from the atmosphere and sinking to the surface, and by direct frost condensation on the ground. The orange regions in the image clearly show the layered nature of these deposits.

Some regions in the image appear hazy. Clouds have formed over the scene and can be detected, particularly in the centre, above the band. Clouds in the south polar region contain not only water droplets frozen into ice crystals, but often needles of carbon dioxide ice given the extremely low temperatures of well below minus 100 degrees Celsius. Their trajectory as they sink to the ground is partly influenced by the landforms on the surface. In some regions of the image, extensive evaporation structures can be seen, making the surface appear levelled and resembling the water level of terrestrial lakes.

Mysterious dark material
Dark dunes and dune fields can be identified in numerous places, often covered by a thin layer of frost. Where they have been strung into thin lines by the wind, they resemble a formation of elongated rock ridges and wind alleys pointing in the same direction, known as yardangs. From their orientation one can read the prevailing wind direction, which can vary greatly on a local scale and is strongly influenced by the terrain formations.

There are still open questions about the origin of the dark material on Mars. It is assumed that it originates from old, buried layers of volcanic ash as well as from weathered lava. Deposits of this type are found in almost every region on Mars. While the dark dunes on the innumerable crater floors often unite to form large complex dune fields, the dunes at the north and south poles are often still present in their individual form, as can be seen here in the innumerable black dots. Presumably, in the polar regions, the frost covering prevents the material transport, which is already a rare phenomenon on Mars, and thus the mobility and 'unification' of the dunes.

In addition, the image presented here also shows individual, small dark spots from which narrow lines that resemble spider legs emerge in different directions. These may be indicative of another distribution process of dark material typical of polar latitudes on Mars: carbon dioxide jets formed by heating dark material under an ice sheet, leading to a direct transition of ice from the solid to the gaseous state, which is then ejected at high pressure in fountains mixed with dark sand. Continuous observation of these phenomena help us to understand processes that are constantly changing the surface appearance in the polar regions on Mars.

Related Links
Free University of Berlin
Mars News and Information at MarsDaily.com
Lunar Dreams and more

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Christmas craterscape
Paris (ESA) Dec 27, 2022
This beautifully crisp icy scene with a swirling ribbon of rusty red and white striped terrain connecting two large craters wraps up the year on Mars. The High Resolution Stereo Imaging camera on board ESA's Mars Express captured this frosty scene in the Ultimi Scopuli region near the south pole of Mars on 19 May 2022. While it may look like a winter wonderland, it was southern hemisphere spring at the time and ice was starting to retreat. Dark dunes are peeking through the frost and elevated terrain ap ... read more

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