Department of Earth Sciences

This HRSC image shows the scarps demarking the boundary between the layered deposits covering the north polar region of Mars and the lower surrounding terrain exhibiting large dune fields. The North Polar layered deposits represent a up to 3-kilometer thick stack of dusty water ice layers, about 1000 kilometers across. The layers record information about the climate, stretching back a few million years into Martian history. The deposits are formed by atmospheric fallout of dust and water ice and direct frost condensation. They are characterized by continuous sub-horizontal layers, mostly composed of water ice and of up to 10-15% fine dust sediments. It is important to mention, that the north polar ice cap of Mars also shows a thin, 1 to 2 m thick seasonal cap of dry ice (CO₂) which in summer completely sublimates into the atmosphere.

The right part of the image shows a smooth and pristine appearing surface with some visible layering, but untouched by impact cratering processes. This means, that the surface is very young, probably rejuvenating every Martian year. Two large semicircular cliffs, the larger one measuring 20 km in diameter can be found. They are located at a so-called polar trough, a morphologic feature created by the erosional force of the wind. These clockwise oriented troughs create the characteristic spiral pattern of the polar plateau. The cliffs presented in this HRSC observation display a vertical wall of layered ice, in some places more than a kilometer high. Very well visible are the sharp shadows underlining the steepness of the cliffs. This becomes strikingly clear by looking at the anaglyph image. At the base of the cliffs, erosional features can be spotted exposing more layers and also large frost covered dune fields. In summer, these dunes will show a very dark to black color. The left part of the image is dominated by a giant elongated dune field, stretching for more than 150 km within this image. It looks as if the sands building up this dune field could originate from erosion of the polar deposits at the large scarp visible here.

Surrounding the north polar region at greater distance are the so-called Olympia Undae, a vast dune field covering an area of 470 000 km² from 78° to 83°N latitude (larger than Sweden, about the size of the whole Balkan peninsula). Already in 2005, shortly after the arrival at Mars of the Mars Express orbiter, the OMEGA instrument detected high gypsum concentrations on the dunes of Olympia Undae. These dunes are intriguing due to their unique gypsum composition, proximity to the polar ice deposits, and seasonal variations.