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Possible present day habitats for life on Mars (Including potential Mars special regions): Difference between revisions
Possible present day habitats for life on Mars (Including potential Mars special regions) (edit)
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Until 2008, many scientists believed that water ''"does not and cannot exist on the surface of Mars today"''<ref name="LevinMarsLifeIdea" />. There are only five regions on present day Mars where liquid fresh water could potentially form, in the Amazonis, Chryse and Elysium Planitia, and the Hellas and Argyre Basins, but even there, in those deep depressions, the water would be close to its boiling point of 10 °C. If any water formed it would soon evaporate<ref name="Hellas">{{cite web|title=Extracts from "Making a Splash on Mars"|url=http://lasp.colorado.edu/home/wp-content/uploads/2013/06/Mars_Articles_20130617.pdf}}</ref>. The equatorial regions are also expected to be ice free, as ice is not long term stable at any depth within ± 30° of the equator, unless trapped by an impervious overlying layer<ref>Schorghofer, N. and Aharonson, O., 2005. [https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2004JE002350 Stability and exchange of subsurface ice on Mars]. Journal of Geophysical Research: Planets, 110(E5)</ref>. Although salty water would be liquid at lower temperatures, most scientists had concluded that the conditions on Mars were too extreme for it to form at all. Amongst the few who continued to think Mars could be habitable was Gilbert Levin who was (and still is) of the view that his labeled release experiment on the [[Viking program|Viking landers]] may have found life on Mars in 1976<ref name="LevinMarsLifeIdea" />.
This changed in 2008 with the observations of the [[Phoenix (spacecraft) | Phoenix lander]]. It landed in what is thought to be an ancient ocean bed near the north pole, the first and so far the only spacecraft to land successfully in polar regions. It observed droplet-like features that formed on its landing legs<ref name="phoenix_droplets_2009" />. In December 2013, Nilton Renno<ref name="NiltonRennoFaculty" /> and his team using the Michigan Mars Environmental Chamber
</ref> were able to simulate the conditions at its landing site and the droplets. They formed salty brines within minutes when salt overlaid ice. The team concluded that suitable conditions for brine droplets may be widespread in the polar regions<ref name="salt_ice">[http://www.astrobio.net/news-brief/liquid-water-ice-salt-mars/ Liquid Water from Ice and Salt on Mars], Aaron L. Gronstal -Astrobiology Magazine (NASA), Jul 3, 2014</ref><ref name="salt_ice_paper">Fischer, E., Martínez, G.M., Elliott, H.M. and Rennó, N.O., 2014. [https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014GL060302 Experimental evidence for the formation of liquid saline water on Mars]. Geophysical research letters, 41(13), pp.4456-4462.</ref>. This is possible because the salts, especially perchlorates, act as an "antifreeze"<ref name="GoughChevrier2014" /> to keep the brines liquid at low temperatures. Nilton Renno talks about their results in this video
<youtube width="540" height="315">iLWv9UGwjdE</youtube>
: "Based on the results of our experiment, we expect this soft ice that can liquify perhaps a few days per year, perhaps a few hours a day, almost anywhere on Mars. --- This is a small amount of liquid water. But for a bacteria, that would be a huge swimming pool ... So, a small amount of water is enough for you to be able to create conditions for Mars to be habitable today. And we believe this is possible in the shallow subsurface, and even the surface of the Mars polar region for a few hours per day during the spring."
: transcript from 2 minutes into the video onwards
There are many other suggestions of potential surface microhabitats covered in this article, including some in the equatorial regions. If these exist, any extant life that might inhabit them faces additional challenges including:
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The [[Viking program#Viking landers|Viking landers]] (operating on Mars from 1976-1982), are the only spacecraft so far to search directly for life on Mars. They landed in the equatorial regions of Mars. With our modern understanding of Mars, this would be a surprising location to find life, as the soil there is thought to be completely ice free to a depth of at least hundred meters, and possibly for a kilometer or more. It is not totally impossible though, as some scientists have suggested ways that life could exist even in such arid conditions, using the night time humidity of the atmosphere, and possibly in some way utilizing the frosts that form frequently in the mornings in equatorial regions.<ref name=sanddunesbioreactor/><ref name=LevinMarsLifeIdea>[http://www.astrobio.net/news-exclusive/the-viking-files/ The Viking Files] Astrobiology Magazine (NASA) - May 29, 2003, astrobio.net (summary of scientific research)</ref>
The Viking results were intriguing, and inconclusive.<ref name="Levin 1976 1322–1329">{{cite journal |doi=10.1126/science.194.4271.1322 |pages=1322–1329 |title=Viking Labeled Release Biology Experiment: Interim Results |date=1976 |last=Levin |first=G. V. |last2=Straat |first2=P. A. |journal=Science |volume=194 |issue=4271 |pmid=17797094 |bibcode=1976Sci...194.1322L }}</ref> There has been much debate since then between a small number of scientists who think that the Viking missions did detect life,<ref name=VikingGasChromatograph/><ref name=JosephMiller/><ref name="Bianciardi-2012"/><ref name=Levin2016>Levin, G.V. and Straat, P.A., 2016. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6445182/ The case for extant life on Mars and its possible detection by the Viking labeled release experiment]. Astrobiology, 16(10), pp.798-810.
{{quote|"'''''It is concluded that extant life is a strong possibility, that abiotic interpretations of the LR data are not conclusive, and that, even setting our conclusion aside, biology should still be considered as an explanation for the LR experiment. Because of possible contamination of Mars by terrestrial microbes after Viking, we note that the LR data are the only data we will ever have on biologically pristine martian samples'''''"}}
</ref> and the majority of scientists who think that it did not.<ref name="PlaxcoGross2011_2"/><ref name=Quine2013/>
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Another paper published in 2012 uses cluster analysis [[cluster analysis]] and suggested once more that they may have detected biological activity.<ref name="Bianciardi-2012">{{cite journal |last=Bianciardi |first=Giorgio |last2=Miller |first2=Joseph D. |last3=Straat |first3=Patricia Ann |last4=Levin |first4=Gilbert V. |title=Complexity Analysis of the Viking Labeled Release Experiments |url=http://central.oak.go.kr/repository/journal/11315/HGJHC0_2012_v13n1_14.pdf|journal=IJASS |date=March 2012 |volume=13 |issue=1 |pages=14–26 |bibcode=2012IJASS..13...14B |doi=10.5139/IJASS.2012.13.1.14 |accessdate=2012-04-15|quote= These analyses support the interpretation that the Viking LR experiment did detect extant microbial life on Mars }}</ref><ref name="NGS-20120413">{{cite news |last=Than |first=Ker |title=Life on Mars Found by NASA's Viking Mission? |url=http://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/ |date=2012-04-13 |work=[[National Geographic (magazine)|National Geographic]] |accessdate=2013-07-16 }}</ref>
On the other hand, a paper published in 2013 by Quinn has refined the chemical explanations suggested for the labeled release observations, using radiation damaged perchlorates. By simulating the radiation environment on Mars, he was able to duplicate radioactive <sup>14</sup>CO<sub>2</sub> emission from the sample.<ref name=Quine2013>[
In short, the findings are intriguing but there is no consensus yet on whether the correct interpretation is biological or chemical. Most scientists still favour the chemical explanation, though a few scientists have recently shown renewed interest in a possible biological explanation.
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This process could melt the ice for a few hours per day in the warmest days of summer, and melt a few mms of ice around each grain. For instance, Losiak, et al., modeled dust grains of basalt (2-200 µm in diameter) if exposed to full sunlight on the surface of the ice on the warmest days in summer, on the Northern polar ice cap, and say this about their model, in 2014: "For example, for solar constant 350 W/m2, emissivity 0.80, grain size 2 um, and thermal conductivity 0.4 W/mK melting lasts for ~300 minutes [5 hours] and result in melting of 6 mm of ice."<ref>[http://www.hou.usra.edu/meetings/metsoc2014/pdf/5314.pdf ICE MELTING BY RADIANTLY HEATED DUST GRAINS ON THE MARTIAN NORTHERN POLE] A. Losiak, L. Czechowski and M.A. Velbel, 77th Annual Meteoritical Society Meeting (2014)</ref> They developed this model as a hypothesis to explain presence of extensive deposits of gypsum in the Northern polar ice cap and the dune fields around it, and concluded that, since the atmospheric pressure there is just above the triple point, this mms thin layer of liquid water could persist for a significant period of time there around grains of basalt in the middle of the day in summer.
This process has been observed in Antarctica. On Mars, there could be enough water to create conditions for physical, chemical, and biological processes.<ref>[https://www.newscientist.com/article/mg20427373.700 Watery niche may foster life on Mars]. {{Subscription required|date=August 2011}}</ref><ref>{{cite web|author=Tudor Vieru |url=http://news.softpedia.com/news/Greenhouse-Effect-on-Mars-May-Be-Allowing-for-Life-129065.shtml |title=Greenhouse Effect on Mars May Be Allowing for Life |publisher=News.softpedia.com |date=2009-12-07 |accessdate=2011-08-20}}</ref><ref>Möhlmann, D., 2010. [https://adsabs.harvard.edu/pdf/2010IJAsB...9...45M The three types of liquid water in the surface of present Mars]. International Journal of Astrobiology, 9(1), pp.45-49.</ref>
==Flow like features==
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As the salt / liquid solution cools in Mars simulation conditions, then the results can be complicated, because for instance MgSO4 releases heat in an exothermic reaction when it crystallizes. This keeps it liquid for longer than you'd expect. In their experiments, it remained liquid for twelve hours as it gradually cooled below the eutectic temperature before eventually it froze at 15.5 degrees below the eutectic temperature. In simulated Mars conditions you also have to take account of the effect of soil mixed in with the salts. Surprisingly, using Mars analogue soil, this does not reduce the supercooling and can in some cases permit more supercooling.<ref name="TonerCatling2014">{{cite journal|url=http://faculty.washington.edu/dcatling/Toner2014_SupercoolSalts.pdf|last1=Toner|first1=J.D.|last2=Catling|first2=D.C.|last3=Light|first3=B.|title=The formation of supercooled brines, viscous liquids, and low-temperature perchlorate glasses in aqueous solutions relevant to Mars|journal=Icarus|volume=233|year=2014|pages=36–47|issn=0019-1035|doi=10.1016/j.icarus.2014.01.018|bibcode=2014Icar..233...36T}}</ref><ref name="GoughChevrier2014">{{cite journal|url=https://web.archive.org/web/20160304075907/http://comp.uark.edu/~vchevrie/sub/papers/Gough%20-%202014%20-%20EPSL%20-%20perchlorate%20chloride%20mixture%20deliquescence.pdf|last1=Gough|first1=R.V.|last2=Chevrier|first2=V.F.|last3=Tolbert|first3=M.A.|title=Formation of aqueous solutions on Mars via deliquescence of chloride–perchlorate binary mixtures|journal=Earth and Planetary Science Letters|volume=393|year=2014|pages=73–82|issn=0012-821X|doi=10.1016/j.epsl.2014.02.002|bibcode=2014E&PSL.393...73G}}</ref>
With some of the salt solutions, depending on chemical composition, then the supercooling produces a glassy state instead of crystallization, and this could help to protect supercooled microbes from damage.
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Other authors also cite:
* '''''Lack of nitrogen'''''. All life on Earth requires nitrogen. Also there are theoretical reasons for expecting alien organic life to use nitrogen, as the weaker nitrogen based amide bonds are essential for the processes by which DNA is replicated. Mars, compared with Earth, has little nitrogen, either in the air or in the soil. Levels of nitrogen in the air are low, possibly too low for nitrogen fixation to be possible. But they can form in Martian conditions by non biological processes - either brought to Mars by meteorites (some carbonaceous chondrites are rich in nitrogen<ref>{{cite web|title=Meteorite with abundant nitrogen for life on Earth?|url=
Life on Mars may be limited to locations with local abundance of nitrates. Or, it may also be able to take advantage of fixation of nitrogen in monolayers of water, a process that can happen in present-day Mars conditions, and may be able to produce enough nitrates to supply a subsurface biosphere.<ref name="BoxeHand2012">{{cite journal|url=
Schuerger also mentions:
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{{quote|'''''"This presupposes that the ephemeral surface habitats could be colonized by viable life forms, that is, that a subsurface reservoir exists in which microbes could continue to metabolize and that, as noted above, the viable microbes could be transported into the short-lived habitat.... Although there are a large number of constraints on the continued survival of life in the subsurface of Mars, the astonishing biomass in the subsurface of Earth suggests that this scenario as a real possibility."'''''}}
</ref>
* '''''Possible, open question if it occurs on the surface''''' these are investigating the possibility with experiments in simulated Mars conditions, theoretical models and study of the observations from Mars, and treat it as an open question for now, whether the present day surface and near sub surface is habitable.<ref name=Kilmer>{{cite journal|pmc=3989109|last1=Kilmer|first1=Brian R.|last2=Eberl|first2=Timothy C.|last3=Cunderla|first3=Brent|last4=Chen|first4=Fei|last5=Clark|first5=Benton C.|last6=Schneegurt|first6=Mark A.|title=Molecular and phenetic characterization of the bacterial assemblage of Hot Lake, WA, an environment with high concentrations of magnesium sulphate, and its relevance to Mars|journal=International Journal of Astrobiology|volume=13|issue=1|year=2014|pages=69–80|issn=1473-5504|doi=10.1017/S1473550413000268|pmid=24748851|bibcode=2014IJAsB..13...69K}}</ref>
<ref name=RummelandConley>
Rummel, J.D. and Conley, C.A., 2017. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5655418/ Four fallacies and an oversight: searching for martian life]. Astrobiology, 17(10), pp.971-974.
{{quote|'''''"Claims that reducing planetary protection requirements wouldn't be harmful, because Earth life can't grow on Mars, may be reassuring as opinion, but the facts are that we keep discovering life growing in extreme conditions on Earth that resemble conditions on Mars. We also keep discovering conditions on Mars that are more similar—though perhaps only at microbial scales—to inhabited environments on Earth, which is where the concept of Special Regions initially came from."'''''}}
</ref><ref name=Davila>Davila, A.F., Skidmore, M., Fairén, A.G., Cockell, C. and Schulze-Makuch, D., 2010. New priorities in the robotic exploration of Mars: the case for in situ search for extant life. Astrobiology, 10(7), pp.705-710.
{{quote|'''''"We argue that the strategy for Mars exploration should center on the search for extant life. By extant life, we mean life that is active today or was active during the recent geological past and is now dormant. As we discuss below, the immediate strategy for Mars exploration cannot focus only on past life based on the result of the Viking missions, particularly given that recent analyses call for a re-evaluation of some of these results. It also cannot be based on the astsumption that the surface of Mars is uniformly prohibitive for extant life, since research contributed in the past 30 years in extreme environments on EArth has shown that life is possible under extremes of cold and dryness."'''''}}}</ref><ref name=Fairen>Fairén, A.G., Parro, V., Schulze-Makuch, D. and Whyte, L., 2017. [https://www.liebertpub.com/doi/full/10.1089/ast.2017.1703 Searching for life on Mars before it is too late]. Astrobiology, 17(10), pp.962-970.
{{quote|'''''"The case of ExoMars is particularly dramatic as the first priority of the rover is to search for signs of past and present life on Mars ... however, it has been explicitly banned to go to Special Regions because it will not comply with the minimum cleanliness requirements. As a consequence, the billion-dollar life-seeking mission ExoMars will be allowed to search for life everywhere on Mars, except in the very places where we suspect that life may exist."'''''}}</ref><ref name=
{{quote|"The observation of high survival rates of methanogens under simulated Martian conditions supports the possibility that microorganisms similar to the isolates from Siberian permafrost could also exist in the Martian permafrost"}}
Also <ref name=Crisler>{{cite journal|pmc=3277918|last1=Crisler|first1=J.D.|last2=Newville|first2=T.M.|last3=Chen|first3=F.|last4=Clark|first4=B.C.|last5=Schneegurt|first5=M.A.|title=Bacterial Growth at the High Concentrations of Magnesium Sulfate Found in Martian Soils|journal=Astrobiology|volume=12|issue=2|year=2012|pages=98–106|issn=1531-1074|doi=10.1089/ast.2011.0720|pmid=22248384|quote='''''Our results indicate that terrestrial microbes might survive under the high-salt, low-temperature, anaerobic conditions on Mars and present significant potential for forward contamination. Stringent planetary protection requirements are needed for future life-detection missions to Mars'''''|bibcode=2012AsBio..12...98C}}</ref>
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Gary M. King, PNAS March 23, 2015, {{DOI|10.1073/pnas.1424989112}}</ref> || O<sub>2</sub>: partial pressure too low
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| organics: meteoritic
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| organics: endogenous available in subsurface || ClO{{su|b=4|p=−}}: available but not shown to support life
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A candidate metabolism would use one of the electron donors in the first column paired with one of the electron acceptors on the right as a source of energy.
See also the presentations in: [http://planets.ucla.edu/meetings/past-meetings/mars-habitability-2013/program/ Redox Potentials for Martian Life]
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