Scientists from Germany and Switzerland presented the new theory of Martian dunes formation, which origin was a riddle for a long time.
The riddle for scientists was in that, that externally Martian dunes look as terrestrial ones which are formed as a result of influence of a wind, however the atmosphere of the fourth planet is quiet and rarefied for such simple explanation.
Also experts have never earlier fixed movings of dunes on the surface of the Mars; therefore they made a conclusion, that the Martian atmosphere was much more dense, than it is now.
But, having done a computer modeling, Eric Partely from University of Stuttgart and Hans Herman from the Swiss federal institute of technology in Zurich, have seen, that formation of dunes is possible even in a rarefied Martian atmosphere.
They managed to simulate formation of two types of dunes: arrow-shaped barkhans which are formed when the wind blows in one direction, and so-called exotic dunes which are formed under influence of various winds.
Scientists have assumed that the Martian dune is exposed to the influence of a wind only for 40 seconds during five years that approximately corresponds to the Martian conditions. Then they have calculated that formation of an exotic barkhan demands 50 thousand years, and moving of a dune on a meter will take four thousand years.

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