Lichens, cyanobacteria and molds growing in humidity of simulated Martian atmosphere: Difference between revisions
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Lichens, cyanobacteria and molds growing in humidity of simulated Martian atmosphere (edit)
Revision as of 23:36, 22 September 2018
, 5 years ago→Lichens relying on 75% night time humidity
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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"/>
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.▼
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"/>▼
However, when partially shaded from the UV light, as it is in its natural habitats in Antarctica, both fungus and algae survived, and the algae remained photosynthetically active throughout. Also new growth of the lichen was observed. Photosynthetic activity continued to increase for the duration of the experiment, showing that the lichen adapted to the Mars conditions.▼
▲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"/>
▲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.
▲However, when partially shaded from the UV light, as it is in its natural habitats in Antarctica, both fungus and algae survived, and the algae remained photosynthetically active throughout. Also new growth of the lichen was observed. Photosynthetic activity continued to increase for the duration of the experiment, showing that the lichen adapted to the Mars conditions.<ref name="DLRLichenHabitable"/>
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="DLRLichenHabitable">{{cite journal|url=https://core.ac.uk/download/pdf/31019036.pdf|last1=de Vera|first1=Jean-Pierre|last2=Schulze-Makuch|first2=Dirk|last3=Khan|first3=Afshin|last4=Lorek|first4=Andreas|last5=Koncz|first5=Alexander|last6=Möhlmann|first6=Diedrich|last7=Spohn|first7=Tilman|title=Adaptation of an Antarctic lichen to Martian niche conditions can occur within 34 days|journal=Planetary and Space Science|volume=98|year=2014|pages=182–190|issn=0032-0633|doi=10.1016/j.pss.2013.07.014|bibcode=2014P&SS...98..182D|quote=This work strongly supports the interconnected notions (i) that terrestrial life most likely can adapt physiologically to live on Mars (hence justifying stringent measures to prevent human activities from contaminating / infecting Mars with terrestrial organisms); (ii) that in searching for extant life on Mars we should focus on "protected putative habitats"; and (ii) that early-originating (Noachian period) indigenous Martian life might still survive in such micro-niches despite Mars' cooling and drying during the last 4 billion years|}}</ref>
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