Round Thing Near South Pole Options

[antoniseb]

Here is an image which I think is from Mars Odyssey, but I'm not certain. It is from one of the orbiters. Thanks to a friend in another forum for pointing it out.

It shows a dark, very close to circular, ring near the extremities of the polar cap.

http://www.msss.com/moc_gallery/e13_e18/me...14/E1401276.jpg
http://www.msss.com/moc_gallery/e13_e18/im...4/E1401276.html

It may be that this feature has already been discussed here, if so can someone please point me to the discussion. Otherwise, I am curious to know what you think may have caused this.

[Guest_Richard Trigaux_*]

I think you should not be excited you all: patterns of parallel straight lines are common in Martian ice caps. The more common explanation is that these ice caps are formed of layers of water ice, dust, carbon dioxid ice... When an ice cap evaporates (and not melt, it is impossible in today Mars conditions) evaporating starts from the border of the ice cap, while lefting the top untouched (because the redish soil around is hotter than the white ice). So the ice cap erodes in a way to cut through all its layers (like in Colorado Canyon) showing, from above, sets of numerous parallel lines. It is most probably what hapened here. Why is it circular? probably because it started from a spot, a meteorite impact, or an underlying crater.

By the way if an impact makes ice melt, the resulting water will stlle in hollow in a matter of some minutes and freeze in some hours, far after any wave is dissipated: it is impossible to freeze a wave.