Potentially habitable flow-like features from Martian dry ice geyser dune spots: Difference between revisions
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Potentially habitable flow-like features from Martian dry ice geyser dune spots (edit)
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These features near the Martian southern polar region are associated with the [[Geyser (Mars)|Martian Geysers]]. Before these geysers were well understood, there was a lot of speculation about what they might be. The seasonal patterns they form resemble trees and vegetation, and in 2001 looking at the Mars Global Surveyor images, Arthur C. Clarke called them "Banyan trees"<ref name=Foulke2001>Nicole Foulke, [https://www.popsci.com/military-aviation-space/article/2001-12/banyan-trees-mars The Banyan trees of Mars], Popular science e-mail interview with Arthur C. Clarke, December 17, 2001</ref>, saying, only half joking "I'm now convinced that Mars is inhabited by a race of demented landscape gardeners,"<ref name=ClarkeSmithsonian2001>Arthur C. Clarke, speaking by teleophone for the [http://www.martianspiders.com/Sir%20Arthur%20C_%20Clarke%20at%20the%20Smithsonian,%20June%202001.htm Wernher von Braun Memorial Lecture], Smithsonian institute's National Air and Space Museum, June 6, 2001 - reported by John C. Sherwood</ref>, and a team of Hungarian scientists proposed that they might be the result of spreading colonies of overwintering photosynthetic microbial life. <ref name=Andras/>
Most of the patterns that form here are probably due to dry ice effects. Subsurface layers of dry ice are heated by the sun through the solid state greenhouse effect, and erupt as CO2 gas. The dark streaks and spots are thought to be debris from the geysers, blown by the CO2 outgassing. The dark streaks are the flow-like features and are initially formed through outgassing, not involving liquid brines at that stage. However as Renno and Martinez put it<ref name="MartínezRenno2013DarkDuneSpots"/>
{{quote|There is mounting evidence that while dark spots and FLF form by “dry” gas venting, liquid brines form temporarily on them.}}
However, later in the spring, the dark streaks from the geysers begin to extend further down the slopes, sometimes at a rate of meters per day. This is the part of the process that may be associated with liquid brines. There are streaks in both hemispheres but the details of how they form differ.▼
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In the Southern hemisphere, they form in the debris of the geysers, and both of the current models for this part of the process involve liquid water<ref name="MartínezRenno2013DarkDuneSpots"/>. In one of these models the features from initially as subsurface melt water, fresh water that forms at 0 °C below snow-ice packs, in solid state greenhouse effects - they are optically thin in visible light but opaque to thermal infrared, so trapping heat in a solid state greenhouse effect familiar in similar situations in Antarctica<ref name="MartínezRenno2013SubsurfaceMeltWater>{{cite journal|url=https://link.springer.com/article/10.1007%2Fs11214-012-9956-3/fulltext.html|last1=Martínez|first1=G. M.|last2=Renno|first2=N. O.|title=Water and Brines on Mars: Current Evidence and Implications for MSL section 2.2.2 Subsurface Melt Water|url=https://link.springer.com/article/10.1007%2Fs11214-012-9956-3#Sec6|journal=Space Science Reviews|volume=175|issue=1-4|year=2013|pages=29–51|issn=0038-6308|doi=10.1007/s11214-012-9956-3}}</ref>. The other model involves thin layers of ULI water (undercooled liquid water)<ref name="MartínezRenno2013ULIWater>{{cite journal|url=https://link.springer.com/article/10.1007%2Fs11214-012-9956-3/fulltext.html|last1=Martínez|first1=G. M.|last2=Renno|first2=N. O.|title=Water and Brines on Mars: Current Evidence and Implications for MSL section 2.2.1 Undercooled Liquid Interfacial Water|url=https://link.springer.com/article/10.1007%2Fs11214-012-9956-3#Sec5|journal=Space Science Reviews|volume=175|issue=1-4|year=2013|pages=29–51|issn=0038-6308|doi=10.1007/s11214-012-9956-3}}</ref> which form on the surface of solar heated grains, then flows downwards, supplying several litres of water per day to the features. In both cases they then pick out salts which let them remain liquid in the cold near surface conditions as they flow down the slopes.
The northern hemisphere flow like features
The southern hemisphere Richardson crater flow-like features are the ones of most interest for brines at temperatures within the range of habitability for Earth life (life based on novel biochemistry based on perchlorates or hydrogen peroxide in the place of the chloride salts of Earth life might tolerate or prefer lower temperatures<ref name=xerophilic>Schulze-Makuch, D. and Houtkooper, J.M., 2010. [https://meetingorganizer.copernicus.org/EPSC2010/EPSC2010-308.pdf A perchlorate strategy for extreme xerophilic life on Mars]. EPSC Abstracts, 5, pp.EPSC2010-308.</ref>.).
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