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Space/Science » in reply to What are we seeing?

re: What are we seeing?
Greg Orme — (archived)

I'm not against the idea of geysers, I was pointing out there is no physical evidence of geysers, and we are not looking at actual geysers in these images. The problem here is we have dark spots and over time the streaks should remove enough material from them so the streak is gone. So that implies a mechanism to replenish the spots with dark material or at least to make new spots.
However it may not be the geyser creating the spots but the spots creating a geyser. If a small area of dark soil starts to get heat from the surface then it might sublimate more CO2 around it from this temperature increase. This is similar to the known mechanism of dark soil (as in dark Barchan dunes on the North Pole) heating up and sublimating the CO2 frost off them.
I suppose this is similar to Kieffer's model, but the sublimation rate need not be strong enough to move the dark soil very quickly. Much of the dark spot's shape might be a shadow from a hole made by the sun on dark material. The dark soil is likely very fine because all over Mars it is seen to easily form streaks. So forming a hole over a patch of dark soil, CO2 sublimating from its heat forming a gentle updraught, and the prevailing winds might then form a streak.
Another problem with the geyser model is it implies a mechanism for somehow concentrating dark material in a small area. However once the CO2 is sublimated we usually see large areas with streaks all over them or very large dark soil areas. So unless the geysers somehow remove all evidence of their mechanism the inference is that we see what is under and around the spot what was under the CO2 ice. Since this looks relatively undisturbed I believe the spots are a variation of known spots on the North pole, uncovering in small spots, sublimating the ice around them and their soil being blown by the wind.
The main difference is that on the North pole for some interesting reason the dark soil is often in dunes (as it is on other areas in the Northern hemisphere) but in the Southern Hemisphere dark dunes are much rarer and hardly seen on the South Pole. I would assume that this is related to the temperature differences on the poles stemming from the Martian orbit and axial tilt.

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