Mars Mystery: Strange Spirals in Ice Caps Explained

A hypothesis for spiraling gorges in Mars' polar caps has recently been presented, giving scientists some information to work with when previously there was a great deal of confusion revolving around these odd features. The hypothesized idea states that, because the planet is tilted, one side of a crack will heat up and vaporize. This water vapor then hits the other side of the crack (which is ever-increasing in size), and freezes. It is believed that this type of spiral ice formation can only occur on Mars where the thin atmosphere, frigid climate, and planetary tilt are all present at once. The spirals are closer at the center because this is where the poles are, and therefore where the temperatures are at their lowest. Thus, the spirals grow slowly and tightly here, and more quickly and spread out further from the center. Adding to this overall explanation are computer generated models that seem to simulate the factors (excluding wind) that would appear on the Martian surface.

http://www.space.com/scienceastronomy/mars_spirals_040325.html