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New Images Reveal Pure Water Ice On Mars
Matt_dk writes "Images of recent impact craters taken by the HiRISE Camera on the Mars Reconnaissance Orbiter have revealed sub-surface water ice halfway between the north pole and the equator on Mars. While the Phoenix lander imaged subsurface ice where the top layer of soil had been disturbed at the landing site near the north pole, these new images — taken in quick succession, detecting how the ice sublimated away — are the first to show evidence of water ice at much lower latitudes. Surprisingly, the white ice may be made from 99 percent pure water."
This is IMHO powerful evidence for recent warm wet Mars :
'The other surprising discovery is that ice exposed at the bottom of these meteorite impact craters is so pure,' Byrne said. 'The thinking before was that ice accumulates below the surface between soil grains, so there would be a 50-50 mix of dirt and ice. We were able to figure out, given how long it took that ice to fade from view, that the mixture is about one percent dirt and 99 percent ice.'
'The ice is a relic of a more humid climate not very long ago, perhaps just several thousand years ago.'
Dr. Bryne talks about making this ice through 'frost heave,' but it sounds to me like Arcadia Planitia may have been considerably warmer during the geologically recent past.
Remember, Mars has climate cycles, they cause the sublimation and freezing of both water and Carbon Dioxide, and both water vapor and Carbon Dioxide are powerful greenhouse gases on Mars. (As is methane, which is also present in the Martian atmosphere from unknown sources.) Presumably this ice dates from an earlier part of the climate cycle, when there was higher humidity. Higher humidity implies higher pressure and temperatures. Higher pressures could put the surface above the triple point of water, so that liquid water is possible.
In that case, if the temperature gets high enough, liquid water become inevitable. That would (upon the next change in the climate cycle) freeze as very pure ice.
The Europeans keep talking about sending a rover with a drill to Mars. I think we have now found a good place for it to go.