Giant ice spirals found on the Martian polar caps are the result of an unusual combination of the temperature of the planet, tilt of its axis and the rarefied atmosphere, showed a new computer model. These concentric swirls of hundreds of kilometers long, were first spotted "Viking" in 1976, but until now scientists did not know how they were formed. John Pelletier, geomorphology from the University of Arizona, has developed a surprisingly simple model that accurately reproduces these curls "at the right distance from each other, and with the right bend in the correct orientation relative to each other."
• Left — real ice spirals on Mars, on the right — the model Pelletier
The average annual temperature on the Martian poles is somewhere around 40 degrees, but a few days of summer it rises so that the ice begins to evaporate. Pelletier's model ignores the wind and shifting ice, paying attention only to the way the sun's heat warms and turns into steam small cracks in the ice. Since the rotation axis of Mars is tilted, sunlight is almost always falls on one side of the crack, melting the ice. Some of this water vapor then freezes on the shaded side of the crack. The overall effect is that the crack over time, expanding and deepening — and importantly — migrates to the pole, blending in its movement to other similar.
In the model, Pelletier cracks begin as randomly distributed points, which are extended in some spirals and piles of forms. Some modeled for five million years — a period roughly estimated to have spirals on Mars — they have merged into one giant spiral. It is estimated that the spiral arms extend about one kilometer per million years.
And do not spiral would be formed, if not thin Martian atmosphere. Because it is very little heat is transferred to the planet airflows, resulting in localized melting of one side of the crack is the dominant mechanism.