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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If these brines do exist, they could still be outside the range of conditions that life can inhabit. Then there's also the possibility of life that survives without liquid water on Mars:
* [[#Life able to take up water from the
Some scientists continue to regard the surface of Mars as uninhabitable. <ref name="Morais" /><ref name="PlaxcoGross2011_2">{{cite book |first=Kevin W. |last=Plaxco |first2=Michael |last2=Gross |title=Astrobiology: A Brief Introduction |url=https://books.google.com/books?id=x83omgI5pGQC&pg=PA285 |date=2011-08-12 |publisher=JHU Press |isbn=978-1-4214-0194-2 |pages=285–286 |accessdate=2013-07-16 }}</ref><ref name="Quine2013" />. Others treat it it is an open question whether there are temporary habitats that could be recolonized from below,<ref name="Westall" />, or inhabited continuously on or near the surface<ref name="MorozovaMöhlmann2006" /><ref name="Crisler" /><ref name="Kilmer" /><ref name="Rummel" /><ref name="Davila" /><ref name="Fairen" /><ref name="RummelConley" />. Others say that it is likely that some parts of the Mars surface are already habitable for some lichens and [[cyanobacteria]] ("blue-green algae"), and that they can do this in the absence of liquid water, taking advantage of the night time humidity<ref name="DLRLichenHabitable" /><ref name="ZakharovaMarzban2014" />. Finally, a small minority of astrobiologists say that there is a strong possibility that present day life has already been detected on present day Mars with the Viking Labeled Release experiments<ref name="JosephMiller" /><ref name="Bianciardi-2012" /><ref name="Levin2016" />. This would mean that much of the Martian surface is not only habitable but actually inhabited by some form of life. See [[# Views on the possibility of present day life on or near the surface]].
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For details see the Dark Dune Spots section of Nilton Renno's paper<ref name="MartínezRenno2013DarkDuneSpots"/> which also has images of the two types of feature as they progress through the season.
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The lichens studied in these experiments have protection from UV light due to special pigments only found in lichens, such as parietin and antioxidants such as b-carotene in epilithic lichens. This gives them enough protection to tolerate the light levels in conditions of partial shade in the simulation chambers and make use of the light to photosynthesize. Indeed, UV protection pigments have been suggested as potential biomarkers to search for on Mars.<ref>"Solar radiation is the primary energy source for surface planetary life, so that pigments are fundamental components of any surface-dwelling organism. They may therefore have evolved in some form on Mars as they did on Earth." {{cite journal | doi = 10.1017/S1473550402001039 | volume=1 | pages=39 | title=Pigmentation as a survival strategy for ancient and modern photosynthetic microbes under high ultraviolet stress on planetary surfaces | year=2002 | journal=International Journal of Astrobiology | last1 = Wynn-Williams | first1 = D.D. | last2 = Edwards | first2 = H.G.M. | last3 = Newton | first3 = E.M. | last4 = Holder | first4 = J.M.| bibcode=2002IJAsB...1...39W }}</ref>
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An experiment on the ISS as part of [[EXPOSE#EXPOSE-E results|Expose-E]] in 2008-2009 showed that one lichen, Xanthoria elegans, retained a viability of 71% for the algae (photobiont) and 84% for the fungus (mycobiont) after 18 months in the ISS, in Mars surface simulation conditions, and the surviving cells returned to 99% photosynthetic capabilities on return to Earth. This was an experiment without the day night temperature cycles of Mars and the lichens were kept in a desiccated state so it didn't test their ability to survive in niche habitats on Mars. This greatly exceeded the post flight viability of any of the other organisms tested in the experiment.<ref name="Brandtde Vera2014">{{cite journal|url=http://elib.dlr.de/90411/1/Annette-Brandt-download.php.pdf|last1=Brandt|first1=Annette|last2=de Vera|first2=Jean-Pierre|last3=Onofri|first3=Silvano|last4=Ott|first4=Sieglinde|title=Viability of the lichen Xanthoria elegans and its symbionts after 18 months of space exposure and simulated Mars conditions on the ISS|journal=International Journal of Astrobiology|year=2014|pages=1–15|issn=1473-5504|doi=10.1017/S1473550414000214|volume=14|issue=3|bibcode=2015IJAsB..14..411B}}</ref>
Another study in 2014 by German aerospace DLR in a Mars simulation chamber used the lichen Pleopsidium chlorophanum. This lives in the most Mars like environmental conditions on Earth, at up to 2000 meters in Antarctica. It is able to cope with high UV, low temperatures and dryness. It is mainly found in cracks, where just a small amount of scattered light reaches it. This is probably adaptive behaviour to protect it from UV light and desiccation. It remains metabolically active in temperatures down to -20 C, and can absorb small amounts of liquid water in an environment with ice and snow.<ref name="DLRLichenHabitable"/>
As measured in Antarctica, the relative humidity in the lichen's niche microhabitat varies from 57 to 79% as the temperature varies from -6 to -8% and externally it varies from 23% to 46% as the external temperature varies from 8 to - 8 C.<ref name="DLRLichenHabitable"/>
In this experiment the temperature varied between +21 °C and -50 °C. Relative humidity is higher in cold air, for the same concentrations of water vapour, and as the temperature varied, the relative humidity varied between 0.1% and 75%. The atmosphere consisted of 5% CO<sub>2</sub>,4%N<sub>2</sub>, and 1% O<sub>2</sub> at 800 Pa or about 0.79% of Earth's sea level atmospheric pressure. This approximates conditions that are encountered in the equatorial and lower lattitude regions of Mars. <ref name="DLRLichenHabitable"/>
When exposed to full UV levels in a 34-day experiment in a Mars simulation chamber at DLR, the fungus component of the lichen Pleopsidium chlorophanum died, and it wasn't clear if the algae component was still photosynthesizing.<ref name="DLRLichenHabitable"/>
However, when partially shaded from the UV light, as
This is remarkable as the fungus is an aerobe, growing in an atmosphere with no appreciable amount of oxygen and 95% CO<sub>2</sub>. It seems that the algae provides it with enough oxygen to survive. The lichen was grown in Sulfatic Mars Regolith Simulant - igneous rock with composition similar to Mars meteorites, consisting of gabbro and olivine, to which quartz and anhydrous iron oxide hematite (the only thermodynamically stable iron oxide under present day Mars conditions) were added. It also contains gypsum and geothite, and was crushed to simulate the martian regolith. This was an ice free environment. They found that photosynthetic activity was strongly correlated with the beginning and the end of the simulated Martian day. Those are times when atmospheric water vapour could condense on the soil and be absorbed by it, and could probably also form cold brines with the salts in the simulated martian regolith. The pressure used for the experiment was 700 - 800 Pa, above the triple point of pure water at 600 Pa and consistent with the conditions measured by Curiosity in Gale crater.<ref name="
The experimenters concluded that it is likely that some lichens and cyanobacteria can adapt to Mars conditions, taking advantage of the night time humidity, and that it is possible that life from early Mars could have adapted to these conditions and still survive today in microniches on the surface.
In another experiment, by Kristina Zakharova et al., two species of microcolonial fungi – Cryomyces antarcticus and Knufia perforans - and a species of black yeasts–Exophiala jeanselmei were found to adapt and recover metabolic activity during exposure to a simulated Mars environment for 7 days. They depended on the temporary saturation of the atmosphere with water vapour like the lichens. The fungi didn't show any signs of stress reactions (such as creating unusual new proteins).
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There Cryomyces antarcticus is an extremophile fungi, one of several from Antarctic dry deserts. Knufia perforans is a fungi from hot arid environments, and Exophiala jeanselmei is a black yeast endolith closely related to human pathogens.
In this experiment, the temperature cycled between 21 °C and -50 and the relative humidity varied up to 70% at the lowest temperatures, with pressure 700 Pascals or about 0.69% of Earth sea level.
The experimenters concluded that these black fungi can survive in a Mars environment.<ref name="ZakharovaMarzban2014">{{cite journal|url=http://www.nature.com/srep/2014/140529/srep05114/full/srep05114.html|last1=Zakharova|first1=Kristina|last2=Marzban|first2=Gorji|last3=de Vera|first3=Jean-Pierre|last4=Lorek|first4=Andreas|last5=Sterflinger|first5=Katja|title=Protein patterns of black fungi under simulated Mars-like conditions|journal=Scientific Reports|volume=4|pages=5114|year=2014|issn=2045-2322|doi=10.1038/srep05114|pmid=24870977|pmc=4037706|quote="The results achieved from our study led to the conclusion that black microcolonial fungi can survive in Mars environment."|bibcode=2014NatSR...4E5114Z}}</ref>
==Deliquescing salts taking up moisture from the Mars atmosphere==
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Though there is little by way of water vapour in the Mars atmosphere, which is also a near vacuum - still it reaches 100% humidity at night due to the low nighttime temperatures. This effect creates the Martian morning frosts, which were observed by Viking in the extremely dry equatorial regions of Mars.
[[File:Ice on Mars Utopia Planitia (PIA00571).jpg|frame|center|600px|alt=Ice on Mars Utopia Planitia |Ice on Mars Utopia Planitia. These frosts formed every morning for about 100 days a year at the Viking location. Scientists believe dust particles in the atmosphere pick up bits of solid water. That combination is not heavy enough to settle to the ground. But carbon dioxide, which makes up 95 percent of the Martian atmosphere, freezes and adheres to the particles and they become heavy enough to sink. Warmed by the Sun, the surface evaporates the carbon dioxide and returns it to the atmosphere, leaving behind the water and dust.<br><br>The ice seen in this picture, is extremely thin, perhaps no more than one-thousandth of an inch thick. These frosts form due to the
The discovery of perchlorates raises the possibility of thin layers of salty brines that could form a short way below the surface by taking moisture from the atmosphere when the atmosphere is cooler. It is now thought that these could occur almost anywhere on Mars if the right mixtures of salts exist on the surface, even possibly in the hyper-arid equatorial regions. In the process of deliquescence, the humidity is taken directly from the atmosphere. It does not require the presence of ice on or near the surface.
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