Potentially habitable flow-like features from Martian dry ice geyser dune spots: Difference between revisions
Potentially habitable flow-like features from Martian dry ice geyser dune spots (edit)
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[[File:Flow-like-features.gif|thumb|Flow-like-features|Larger region
These features near the Martian southern polar
{{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 year dark streaks gradually extend down the slopes from the dark spots, sometimes at a rate of meters per day. These are the "flow-like features" that may be associated with liquid brines. There are streaks in both hemispheres but the details of how they form differ.▼
▲
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 modelsfresh water that forms as subsurface meltwater, insulated from the surface temperatures and pressures at 0°C below snow-ice packs. These are optically thin in visible light but opaque to thermal infrared, so trapping heat from one day to the next 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 up salts from the debris from the geysers, which let them remain liquid in the cold near surface conditions as they flow down the slopes.
The northern hemisphere flow like features form at much lower surface temperatures and if they involve brines the temperatures are around -90 °C, too low in temperature to be habitable for Earth life, at least. Also, though most of the models for the northern hemisphere features involve water, they can also be explained with dry ice and cascading dust. ▼
▲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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==Southern hemisphere flow-like features==
The process starts with the dark dune spots which form in early spring. Here are some examples in
▲The process starts with the dark dune spots which form in early spring. Here are some examples in [[Richardson (Martian crater)|Richardson Crater]] in the Martian southern hemisphere- one of the places where the Flow Like Features (FLFs) have been observed.
{{Wide image |WikirichardsonPSP_002885_1080.jpg|800px|Dark dune spots in Richardson crater}}
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The debris from these geysers form the dark spots, and the "flow like features".
Then, as local summer approaches, the flow like features start to extend down the slope. These are small features only a few tens of meters in scale, and grow at a rate of a meter or a few meters per Martian sol through the late Martian spring and summer. This is the part of the process that is thought to be due to liquid water, in nearly all the models proposed for them so far.<ref name=Kereszturi2008/><ref name="
A different mechanism is proposed for them in the Northern and in the Southern hemispheres.
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===Solid state greenhouse effect model===
Möhlmann uses a solid state greenhouse effect in his model, similarly to the process that forms the geysers, but with translucent ice or snow-ice packs, rather than dry ice as the solid state greenhouse layer.<ref name="LiquidWaterSnowIce">{{cite journal|url=http://www.sciencedirect.com/science/article/pii/S0019103509004539|last1=Möhlmann|first1=Diedrich T.F.|title=Temporary liquid water in upper snow/ice sub-surfaces on Mars?|journal=Icarus|volume=207|issue=1|year=2010|pages=140–148|issn=0019-1035|doi=10.1016/j.icarus.2009.11.013|bibcode=2010Icar..207..140M}}</ref>
[[File:JoekullsarlonBlueBlockOfIce.jpg|thumb|JoekullsarlonBlueBlockOfIce|
In his model, first the ice forms a translucent layer - then as summer approaches, the solid state greenhouse effect raises the temperature of a layer below the surface to 0 °C, so melting it. This is a process familiar on the Earth for instance in Antarctica. On Earth, in similar conditions, the surface ice remains frozen, but a layer of liquid water forms from 0.1 to 1 meters below the surface. It forms preferentially in "blue ice".<ref>Nl, K., and T. SAND. [http://www.igsoc.org:8080/journal/42/141/igs_journal_vol42_issue141_pg271-278.pdf "Melting, runoff and the formation of frozen lakes in a mixed snow and blue-ice field in Dronning Maud Land, Antarctica."], Journal of Glaciology, T'ol. 42, .\"0.141, 1996</ref>
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===Interfacial liquid layers model===
Another model for these southern hemisphere features involves ULI water (undercooled liquid water) which forms as a thin layer over surfaces and can melt at well below the usual melting point of ice. In Mohlmann's sandwich model, then the interfacial water layer forms on the surfaces of solar heated grains in the ice, which then flows together down the slope. Calculations of downward flow of water shows that several litres a day of water could be supplied to the seepage flows in this way.<ref name="MartínezRenno2013DarkDuneSpots">{{cite journal|last1=Martínez|first1=G. M.|last2=Renno|first2=N. O.|title=Water and Brines on Mars: Current Evidence and Implications for MSL - section 3.1.2 Dune Dark Spots and Flow-like Features|url=https://link.springer.com/article/10.1007%2Fs11214-012-9956-3#Sec12|journal=Space Science Reviews|volume=175|issue=1–4|year=2013|pages=29–51|issn=0038-6308|doi=10.1007/s11214-012-9956-3|bibcode=2013SSRv..175...29M}}</ref><ref name=Kereszturi2008/>
The idea then is that this ULI water would be the water source for liquid brines which then flow down the surface to form the features.
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===Northern Hemisphere flow like features===
[[File:Seasonal processes in the Northern polar dunes with Flow Like Features.gif
The
{{quote|"They show a characteristic sequence of changes: first only wind-blown features emanate from them, while later a bright circular and elevated ring forms, and dark seepage-features start from the spots. These streaks grow with a speed between 0.3 meters per day and 7 meters per day, first only from the spots, later from all along the dune crest." <ref name=Kereszturi/>}}
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Then, as with the model for the Martian geysers, shortwave radiation can penetrate translucent CO<sub>2</sub> ice layer, and heat the subsurface through the solid state greenhouse effect.
The models suggest that both subsurface melt water layers, and interfacial water could form with surface temperatures as low as 180°K (-90 °C). Salts in contact with them could then form liquid brines.<ref name=Kereszturi/><ref name="
An alternative mechanism for the Northern hemisphere involves dry ice and sand cascading down the slope.
==Earlier hypotheses==
[[Image:DDS MSO.jpg|thumb|right
In 2003 a team of Hungarian scientists proposed that the dark dune spots and channels may be colonies of [[photosynthesis|photosynthetic]] Martian microorganisms, which over-winter beneath the ice cap, and as the [[sunlight]] returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesise and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. As this ice layer thins, the microorganisms show through grey. When it has completely melted, they rapidly desiccate and turn black surrounded by a grey aureole.<ref name=Andras >{{cite journal|title=Probable Evidences of Recent Biological Activity on Mars: Appearance and Growing of Dark Dune Spots in the South Polar Region|journal=32nd Annual Lunar and Planetary Science Conference, Houston, Texas, abstract no.1543|date=12–16 March 2001|first=Tibor|last=Gánti |author2=András Horváth |author3=Szaniszló Bérczi |author4=Albert Gesztesi |author5=Eörs Szathmáry|url=http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1543.pdf|format=PDF|accessdate=20 November 2008}}</ref><ref>{{Cite book| author=Pócs, T. |author2=A. Horváth |author3=T. Gánti |author4=Sz. Bérczi |author5=E. Szathmáry |title=ESA SP-545 - Possible crypto-biotic-crust on Mars?| publisher=European Space Agency| date=2003| url=http://adsabs.harvard.edu/full/2004esasp.545..265p| format=PDF| accessdate=24 November 2008 }}</ref><ref>{{cite journal|title=Dark Dune Spots: Possible Biomarkers on Mars?|journal=Origins of Life and Evolution of Biospheres|date=31 October 2003 |first=Tibor|last=Gánti|author2=András Horváth |author3=Szaniszló Bérczi |author4=Albert Gesztesi |author5=Eörs Szathmáry |volume= 33|issue=s 4–5|pages=515–557|doi=10.1023/A:1025705828948|url=http://www.springerlink.com/content/ut8r78131173254n/|accessdate=18 November 2008 }}</ref><ref>{{Cite journal|author=Pócs, T. |author2=A. Horváth |author3=T. Gánti |author4=S. Bérczi |author5=E. Szathmáry |title=38th Vernadsky-Brown Microsymposium on Comparative Planetology - Are the dark dune spots remnants of the crypto-biotic-crust of Mars? |place=Moscow, Russia |date=27–29 October 2003 |url=http://www.colbud.hu/esa/publications/26MosCBC10color.pdf |format=[[PDF]] |accessdate=7 September 2009 |deadurl=yes |archiveurl=https://web.archive.org/web/20110721104952/http://www.colbud.hu/esa/publications/26MosCBC10color.pdf |archivedate=21 July 2011 |df=dmy }}</ref> The Hungarian scientists suggested that that even a complex sublimation process was insufficient to explain the formation and evolution of the dark dune spots in space and time.<ref name=Planetary >{{Cite journal |title=Lunar and Planetary Science XXXIII - Morphological Analysis of the Dark Dune Spots on Mars: New Aspects in Biological Interpretation| editors=A. Horváth, T. Gánti, Sz. Bérczi, A. Gesztesi, E. Szathmáry| date=2002| url=http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1108.pdf| format=PDF| accessdate=24 November 2008 }}</ref><ref>{{cite web|url=http://www.monochrom.at/dark-dune-spots/ |title=Dark Dune Spots – Could it be that it’s alive? |accessdate=4 September 2009 |author=András Sik |author2=Ákos Kereszturi |publisher=Monochrom }} (Audio interview, MP3 6 min.)</ref>
[[File:High resolution image of Arthur C. Clarke's "Banyam tress of Mars".jpg|
Science fiction writer [[Arthur C. Clarke]] promoted these formations as deserving of study from an [[astrobiology|astrobiological]] perspective.<ref name=Orme>{{cite journal|title=Marsbugs |journal=The Electronic Astrobiology Newsletter |date=9 June 2003 |first=Greg M. |last=Orme |author2=Peter K. Ness |volume=10 |issue=23 |page=5 |url=http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |accessdate=6 September 2009 |deadurl=yes |archiveurl=https://web.archive.org/web/20090327135109/http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |archivedate=27 March 2009 }}</ref><ref name=ClarkeSmithsonian2001/><ref name=Foulke2001/>[[File:BanyanTreesMarsGallery.jpg.638x0 q80 crop-smart.jpg|thumb|The original lower resolution images that looked like banyan trees to Arthur C. Clarke]]
In 2009 a multinational European team suggested that if liquid water is present in the spiders' channels during their annual defrost cycle, the structures might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from [[Ultraviolet|UV]] solar radiation.<ref name=Manrubia>{{cite journal |title=Comparative Analysis of Geological Features and Seasonal Processes in Inca City and PittyUSA Patera Regions on Mars |journal=European Space Agency Publications (ESA SP) |date=2004 |first=S. C. |last=Manrubia |author2=O. Prieto Ballesteros |author3=C. González Kessler |author4=D. Fernández Remolar |author5=C. Córdoba-Jabonero |author6=F. Selsis |author7=S. Bérczi |author8=T. Gánti |author9=A. Horváth |author10=A. Sik |author11=E. Szathmáry |page=545 |url=http://www.colbud.hu/esa/publications/29ProcCAB-3ESASP-545pp77-80.pdf |deadurl=yes |archiveurl=https://web.archive.org/web/20110721105008/http://www.colbud.hu/esa/publications/29ProcCAB-3ESASP-545pp77-80.pdf |archivedate=21 July 2011 |df=dmy-all }}</ref> British and German teams also consider the possibility that [[organic matter]], [[microbe]]s, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a [[Geothermal gradient|geothermal]] energy source.<ref name=Ness /><ref>{{cite journal|title=Temporary liquid water in upper snow/ice sub-surfaces on Mars? |journal=Icarus|date=13 November 2009 |last1=Möhlmann |first=Diedrich T.F. |doi=10.1016/j.icarus.2009.11.013 |url=https://www.sciencedirect.com/science/article/pii/S0019103509004539|volume=207 |pages=140 |bibcode=2010Icar..207..140M}}</ref> However, they also remarked that the majority of geological structures may be accounted for without invoking any organic "life on Mars" hypothesis<ref name=Ness >{{cite journal|title=Spider-Ravine Models and Plant-like Features on Mars – Possible Geophysical and Biogeophysical Modes of Origin|journal=[[Journal of the British Interplanetary Society]] (JBIS) |date=2002 |first=Peter K.|last=Ness |author2=Greg M. Orme |volume=55|pages= 85–108|url=http://spsr.utsi.edu/articles/ness.pdf |accessdate=3 September 2009 }}</ref> (See also: [[Life on Mars]].)
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