Christmas and winter spirit, also on Mars

Dec. 30 () –

In the latest and very wintry image of Mars from the HRSC camera aboard ESA’s Mars Express orbiter this year, impact craters can be seen connected by a colored striped ribbon.

Image data from the High Resolution Stereo Camera (HRSC) reveals an intricate landscape of layered deposits, frost, ice, and dark dunes near the south polar region of Mars, known as Ultimi Scopuli (Latin for “the last cliffs”) . The camera was developed by the German Aerospace Center (DLR) and It has been sending images of the Martian surface back to Earth since January 2004.

This image shows a section of the landscape that measures approximately 215 by 65 kilometers and is located 14 degrees north of the south pole. Numerous interesting shapes are seen, typical of permanently frozen but not ice-covered regions. Along with wind-sculpted formations, known as aeolian landforms, and seasonal frost clouds complete the landscape.

The landscape appears very abstract with the sharply contrasting color tones of the orange hues of the Martian soil and the white of the water and carbon dioxide ice. Coupled with the curved shapes of the landscape, it is not an easy landscape to understand at first glance, explains the DLR in a statement.

These images were taken during the austral spring, the time when the ice retreats southward, leaving only a small layer of ice at the south pole during the southern hemisphere summer. 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 evaporated in spring is enormous, accounting for more than 10% of the atmosphere. This process causes strong pressure changes in the Martian gaseous envelope and, consequently, very high wind speeds. These occur mainly in autumn and are caused by this difference in atmospheric pressure in the hemispheres.

The two most striking features in this image are two large impact craters that appear to be connected by a hatched band. The band and craters show a deep reddish-brown hue that contrasts with the gray and white of the surrounding landscape. In addition, alternating layers can be seen on the crater rims and in the band. These layers are successive layers of dust and sand that have been deposited continuously and approximately horizontally on landforms. They consist mainly of water ice and about 10 percent fine sediment.

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

Some areas of the image appear blurry. Clouds have formed over the scene and can be detected, especially in the center, above the band. Clouds in the south polar region contain not only water droplets frozen in ice crystals, but often needles of carbon dioxide ice, given the extremely low temperatures, well below 100 degrees below zero. Its trajectory as it sinks into the ground is influenced in part by the landforms on the surface. In some regions of the image there are extensive evaporation structures that make the surface appear level and resembles the water level of terrestrial lakes.

In many places dark dunes and dune fields can be identified, often covered by a thin layer of frost. Where the wind has strung them into thin lines, they resemble a formation of elongated rock ridges and wind alleys pointing in the same direction, known as yardangs. From its orientation it is possible to read the prevailing direction of the wind, which can vary greatly on a local scale and is highly influenced by landforms.

There are still open questions about the origin of the dark material on Mars. It is supposed to come from ancient buried layers of volcanic ash, as well as weathered lava. Deposits of this type are found in almost all regions of Mars. While the dark dunes of the myriad crater floors often coalesce to form large, complex dune fields, the dunes at the north and south poles often remain in their individual forms, as can be seen in the innumerable black dots.

Presumably, in the polar regions, the frost cover prevents the transport of material, which is already a rare phenomenon on Mars, and therefore the mobility and “unification” of the dunes.