Lichens, cyanobacteria and molds growing in humidity of simulated Martian atmosphere: Difference between revisions
Lichens, cyanobacteria and molds growing in humidity of simulated Martian atmosphere (edit)
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[[Image:Martian conditions in miniature (7494313830) (2).jpg|thumb|Martian conditions in miniature - In the Mars simulation chamber, DLR researchers recreated the atmospheric composition and pressure, the planet's surface, the temperature cycles and the solar radiation incident on the surface. The activity of polar and alpine lichen was investigated under these conditions.]]
A series of experiments by DLR (German aerospace company) in Mars simulation chambers and on the ISS show that some Earth life (Lichens and strains of
Though the absolute humidity is low, the relative humidity at night in winter reaches over 70% even in regions close to the equator, as measured directly in Gale Crater by Curiosity, because of the large day / night swings in atmospheric pressure and temperature. It may well reach much closer to 100% in regions where frosts are seen (including the [[Viking 2]] lander site) and where ground hugging mists form, including equatorial regions in Valles Marineres and the Hellas basin<ref name=Martínez2017/>.
This is relevant to the search for native life on Mars. It is also relevant to planetary protection, the need to protect Mars from Earth life if we wish to study native life in the habitats in its original state.
==Lichens surviving in Mars surface conditions==
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==Lichens relying on 75% night time humidity to metabolize, photosynthesize, and develop new growth==
[[Image:Pleopsidium chlorophanum in Antarctica.jpg |thumb|
[[Image:Pleopsidium chlorophanum.jpg|thumb|The same lichen showing its spreading habit in more usual conditions]]
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 from the atmosphere in an environment
As measured in Antarctica, the relative humidity in the lichen's niche microhabitat varies from 57% to 79% as the temperature varies from -6 °C to -8
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"/>
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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
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.<ref name="DLRLichenHabitable"/>
{{quote|This work strongly supports the interconnected notions (i) thatterrestrial life most likely can adapt physiologically to live on Mars (hence justifying stringent measures to prevent human activitiesf rom contaminating/infecting Mars with terrestrial organisms);(ii) that in searching for extant life on Mars we should focus on“protected putative habitats”; and (iii) 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}}
==Black fungi and black yeast relying on 70% night time humidity==
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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).
The three organisms they used were
* Cryomyces antarcticus, an extremophile fungi, one of several from Antarctic dry deserts.
* Knufia perforans, a fungi from hot arid environments
* 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 and that an unknown metabolic pathway may be responsible.<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}}
{{quote|The results achieved from our study led to the conclusion that black microcolonial fungi can survive in Mars environment.
...
We can conclude that an unknown metabolic pathway might be discovered, which enables the fungi to live in a quasi-anaerobic Mars-like environment.}}</ref>
==Locations of landers and rovers on Mars==
Note the higher latitude of [[Viking 2]] which observed the seasonal frosts. Mists in Valles Marineres suggest high humidity there<ref name=Martínez2017/>. Curiosity observed humidites of up to 70% in winter.
{{Features and artificial objects on Mars}}
==Effects of micropores in gypsum and salt pillars in the Atacama desert==
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===Brines still present down to 30% external humidity in micropores in salt pillars===
The researchers, Wierzchos et al., did detailed studies with scanning electron microscopes. At 75% relative humidity then brine was abundant inside the salt pillars. As the humidity was reduced, even at 30% RH, the cyanobacteria aggregates shrunk due to water loss, but still there were small pockets of brine in the salt pillars.<ref name="WierzchosDavila2012">{{cite journal|url=
{{quote|Endolithic communities inside halite pinnacles in the Atacama Desert take advantage of the moist conditions that are created by the halite substrate in the absence of rain, fog or dew. The tendency of the halite to condense and retain liquid water is enhanced by the presence of a nano-porous phase with a smooth surface skin, which covers large crystals and fills the larger pore spaces inside the pinnacles... Endolithic microbial communities were observed as intimately associated with this hypothetical nano-porous phase. While halite endoliths must still be adapted to stress conditions inside the pinnacles (i.e. low water activity due to high salinity), these observations show that hygroscopic salts such as halite become oasis for life in extremely dry environments, when all other survival strategies fail.}}
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===Microbes imbibe water down to 60% external humidity in micropores in gypsum pillars===
Microbes also inhabit Gypsum deposits (CaSO<sub>4</sub>.2H<sub>2</sub>O), however Gypsum doesn't deliquesce. Researchers found that the regions of the desert that had microbial colonies within the gypsum correlated with regions with over 60% relative humidity for a significant part of the year. They also found that the microbes imbibed water whenever the humidity increased above 60% and gradually became desiccated when it was below that figure.<ref name="WierzchosCámara2011">{{cite journal|url=https://
===Possible relevance to Mars===
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This section is based on the survey article by Martinez et al, "The modern near-surface martian climate: A review of in-situ meteorological data from Viking to Curiosity."<ref name=Martínez2017>Martínez, G. M., C. N. Newman, A. De Vicente-Retortillo, E. Fischer, N. O. Renno, M. I. Richardson, A. G. Fairén et al. [https://link.springer.com/article/10.1007/s11214-017-0360-x "The modern near-surface martian climate: A review of in-situ meteorological data from Viking to Curiosity."] Space Science Reviews 212, no. 1-2 (2017): 295-338.</ref>
In short, Curiosity measured humidity directly 70% humidity at a height of 1.6 meters above ground level in winter, ground temperature
The humidity variations on Mars are mainly due to the daily and seasonal variations of temperature of the air. Colder air has a higher relative humidity for the same water content.
The amount of water vapour can be measured as the volume mixing ratio of water vapour (VMR). This varies between around 10 ppm in winter and 70 ppm in summer at the Curiosity site. You might expect the highest relative
So, it's 10ppm (approx) for 70% RH in winter, and 70 ppm for 10% RH in summer (by a strange coincidence the numbers are reversed).
The Viking landers didn't have humidity sensors. But the humidity can be estimated indirectly, with maximum
The Viking 2 observed frosts for 250 sols of the year (frost usually suggests a high relative humidity close to 100%).
Viking 1 and Curiosity didn't observe them directly. But there is indirect evidence that frosts may form at times at lower latitudes, including imaging of mists in the Valles Marineres, and possible observation of frost on the deck and calibration target of Opportunity.
== See also==
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