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Odd spiraling gorges etched deep into the polar ice caps of Mars have stumped scientists for decades. The huge arcing troughs radiate outward like arms of a pinwheel, creating an overall shape that visually and mathematically resembles hurricanes, spiral galaxies and even some seashells.
Now there is an apparent solution to the mystery, put forth by Jon Pelletier of the University of Arizona in Tucson.
The tilted planet causes ice on one side of a crack to heat and vaporize, deepening and widening the crack. Then the water vapor hits the shady, colder side of the growing canyon and refreezes.
Eventually, chasms more than a half-mile (1 kilometer) deep developed, and they cover hundreds of miles of the polar regions. But only on Mars, it seems.
Characteristics unique to the red planet -- its thin atmosphere, chilly climate and specific planetary tilt -- make it the only known place in the solar system where the ice spirals occur. They don't exist at Earth's poles, in part because temperatures are regulated somewhat by global ocean and air currents.
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