Marsgeysire, interpretation by the artist Ron Miller. (Photo: Arizona State University / Ron Miller)
Read aloud Every spring an impressive spectacle takes place at the South Pole of Mars: When the sun warms the ice cap of the polar cap for the first time after the cold winter, geysers of carbon dioxide and dark, sand-like dust begin to shoot up everywhere. This dust then falls to the ground, where it forms conspicuous dark spots and fan-shaped structures. The close astronomers around Philip Christensen of the State University of Arizona in Tempe from new data of the probe Mars Odyssey. With this discovery, researchers will be able to explain for the first time how the previously enigmatic markings are formed and why they can only be seen for a period of three to four months during the Martian spring. Every spring, in the ice cap and frozen carbon dioxide ice cap at Mars' south pole, dark spots of up to fifty meters appear, surrounded by fan-shaped structures and star-shaped canal systems. So far, scientists have assumed that these structures are areas where the sun has already thawed the ice and the darker Martian soil is visible. But the dark spots are just as cold as the surrounding ice, the new data showed. In addition, they form extremely fast: In just a few days, after the first rays of spring had fallen on the ice, already numerous spots appeared, the researchers observed.

The foundation for the staining is therefore laid in the cold Marswinter, according to the scientists, when the temperatures are so low that the carbon dioxide of the thin Martian atmosphere freezes and trickles on the permanent ice of the polar cap. During the winter, the fine dry ice forms a denser, semi-transparent layer of ice. At the same time trapped dust and sand particles sink down and deposit as a dark layer under the upper ice cover. If sunlight now falls through the ice on these dark particles, they heat up and let the carbon dioxide ice become gaseous around it. The pressure rises below the ice sheet until the material finally can not withstand it and breaks at its weakest points.

From the openings then the accumulated gas flows out at a high speed and thereby tears dust and sand in the air. The heaviest of these particles fall directly to the bottom where they form visible stains. The lighter particles, on the other hand, are caught by the wind and later deposit fan-shaped around the opening. The channel systems eventually form under the ice sheet as the gas flows toward the openings, digging into the ground. Only when the upper ice layer has completely disappeared, the fountains dry up again? until next year.

Philip Christensen (State University of Arizona, Tempe) et al .: Nature, Vol. 442, p. 793 ddp / science.de? Ilka Lehnen-Beyel advertisement

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