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Ultimi Scopuli - Swirling Christmas Craterscape

» read more about the Ultimi Scopuli region

This amazing image shows a lot of interesting periglacial landforms, as well as beautiful aeolian features and seasonal frost clouds. It was taken in southern spring, the time when the ice starts to retreat, leaving only a small residual ice cap at the south pole. During the Martian seasonal cycle, carbon dioxide ice is deposited at the poles in winter. The amount of atmosphere deposited as ice at each pole in winter and then sublimating in the springtime is enormous, reaching at least 12-16% of the atmosphere of the planet. This process leads to strong pressure changes and, as a consequence, to very high wind speeds.

The main two eye-catchers in the image are two large and old impact craters, which appear connected by a striped ribbon. This ribbon and the craters display a strong reddish-brown tone, which contrasts with the grey and white of the surrounding landscape, also, alternating layers are easily recognized. These are polar layered deposits, which are characterized by continuous sub-horizontal layers, they are mostly composed of water ice and of up to 10-15% fine sediments. The individual layers often differ from each other in their albedo, color, surface morphology and erosional texture. The polar layered deposits are formed by atmospheric fallout of dust and water ice and direct frost condensation. The orange colored regions in the image also reveal the layered nature of these deposits.

Many parts of the image display a hazy appearance, and especially in the central part some clouds can be spotted. Clouds in the south polar region often contain water ice and their trajectory is partly influenced by topography. All over the image numerous large sublimation structures can be found covering the surface and resembling terrestrial lakes. A very pronounced one in the upper left image border also appears to show tiny clouds at lower elevations.

All over the image, dark dunes and dune fields can be found, in some areas covered by a thin frost layer. Interestingly, the fields follow a yardang-like morphology indicating the prevalent wind directions, influenced by the morphology of the surface. The provenance of the dark material on Mars is still poorly understood. It is believed that it derives from ancient buried layers of volcanic eruption materials. It can be found globally all over Mars. In some regions, individual dark spots can be found in the image. These spots could be a hint at another distribution process of dark material, specific to polar areas on Mars: CO2 jets formed by sublimation beneath translucent ice slabs that then eject geyser-like fountains of dark dust. Constant monitoring of these zones helps to understand the processes that steadily alter the appearance of the surface in the polar regions on Mars.