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 01:07, 23 September 2018
, 5 years ago→Effects of micropores in gypsum and salt pillars in the Atacama desert
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==Effects of micropores in gypsum and salt pillars in the Atacama desert==
In experimental studies of salt pillars in the Atacama desert, microbes are able to access liquid at extremely low relative humidities due to micropores in the salt structures. They do this through spontaneous capillary condensation, at relative humidities far lower than the deliquescence point of NaCl of 75%.
These micro-organisms can survive because of numerous micro-pores in the salt, less than 0.1 micrometers in diameter in the salt. Theoretically, this reduces the limit for trapping water from the atmosphere down to relative humidities as low as 50-55% instead of the usual limit of 75%. Also once the water is trapped, it is retained for a long time, as the air gets even drier, right down to an extremely low relative humidity of 20%.
These micro-organisms can survive because of numerous micro-pores in the salt, less than 0.1 micrometers in diameter in the salt. Theoretically, this reduces the limit for trapping water from the atmosphere down to relative humidities as low as 50-55% instead of the usual limit of 75%. Also once the water is trapped, it is retained for a long time, as the air gets even drier, right down to an extremely low relative humidity of 20%.<ref name=Bortman>{{cite web|last1=Bortman|first1=Henry|title=Islands of Life, Part V|url=http://www.astrobio.net/topic/origins/extreme-life/islands-of-life-part-v/|website=Astrobiology Magazine (NASA)|date=Jul 25, 2011}}</ref>
[[File:Salt Pillars - Atacama Desert.jpg|thumb|400 px|'The Atacama desert hosts the closest analogue of what a real, live Martian might be like', in its salt rock formations.<ref>{{cite web|last1=Davies|first1=Paul|title=The key to life on Mars may well be found in Chile|url=https://www.theguardian.com/commentisfree/2012/aug/03/life-mars-chile|website=The Guardian|date=Aug 3, 2012}}</ref>]]
Micro-environmental data measured simultaneously outside and inside halite pinnacles in the Yungay region (table 2 from <ref name="WierzchosDavila2012"/>)
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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=http://www.biogeosciences.net/9/2275/2012/bg-9-2275-2012.pdf|last1=Wierzchos|first1=J.|last2=Davila|first2=A. F.|last3=Sánchez-Almazo|first3=I. M.|last4=Hajnos|first4=M.|last5=Swieboda|first5=R.|last6=Ascaso|first6=C.|title=Novel water source for endolithic life in the hyperarid core of the Atacama Desert|journal=Biogeosciences|volume=9|issue=6|year=2012|pages=2275–2286|issn=1726-4189|doi=10.5194/bg-9-2275-2012|bibcode=2012BGeo....9.2275W}}</ref>
{{quote|
===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://www.researchgate.net/profile/Alfonso_Davila/publication/45797377_Microbial_colonization_of_Ca-sulfate_crusts_in_the_hyperarid_core_of_the_Atacama_Desert_implications_for_the_search_for_life_on_Mars/links/0912f50e37831ae515000000.pdf|last1=Wierzchos|first1=J.|last2=Cámara|first2=B.|last3=De Los Ríos|first3=A.|last4=Davila|first4=A. F.|last5=Sánchez Almazo|first5=I. M.|last6=Artieda|first6=O.|last7=Wierzchos|first7=K.|last8=Gómez-Silva|first8=B.|last9=Mckay|first9=C.|last10=Ascaso|first10=C.|title=Microbial colonization of Ca-sulfate crusts in the hyperarid core of the Atacama Desert: implications for the search for life on Mars|journal=Geobiology|volume=9|issue=1|year=2011|pages=44–60|issn=1472-4677|doi=10.1111/j.1472-4669.2010.00254.x|pmid=20726901}}</ref>
===Possible relevance to Mars===
The Wierzchos et al conclude their paper by saying:<ref name="WierzchosCámara2011"/>:
{{quote|Our findings have implications for the habitability of extremely dry environments, as they suggest that salts with properties similar to halite could be the preferred habitat for life close to the dry limit on Earth and elsewhere. It is particularly tempting to speculate that the chloride-bearing evaporites recently identified on Mars may have been the last, and therefore most recently inhabited, substrate as this planet transitioned from relatively wet to extremely dry conditions}}
In another paper by Vitek et al the authors mention the possibility that these micropre results could be relevant to present day Mars as well<ref>Vítek, Petr, H. G. M. Edwards, J. Jehlička, C. Ascaso, A. De los Ríos, S. Valea, S. E. Jorge-Villar, A. F. Davila, and J. Wierzchos. [http://rsta.royalsocietypublishing.org/content/368/1922/3205 "Microbial colonization of halite from the hyper-arid Atacama Desert studied by Raman spectroscopy."] Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 368, no. 1922 (2010): 3205-3221.</ref>:
{{quote|The results presented here support the suggestion that evaporitic, chloride-bearing rocks revealed on Mars may represent a suitable habitat for life—in the past or even present—enabling photosynthetic activity and adaptation to a harsh UV and hyper-arid environment.}}
Wierzoch et al, in a section on "Implications for the search for life on Mars" write<ref name="WierzchosCámara2011"/>
{{quote|The work presented here and work conducted in deserts around the world in the past 40 years, indicate that any putative microbial life on Mars would have likely colonized the insides of rocks and crusts, as they provide natural shelter against harmful radiation and also enhance the moisture conditions on a micro scale. Sulfate and chloride evaporitic deposits have been suggested as a possible oasis for an extant biota, or the last refuge for an extinct biota on the surface of Mars). In this context, terrestrial evaporite rocks, including the Ca-sulfate crusts of the dry core of the Atacama Desert as key terrestrial analogs of Martian aqueous deposits, might prove useful for assessing the habitability of the Martian surface, and develop or improve current strategies for the search for life on Mars}}
This article uses some text developed for Touch Mars?<ref>[http://robertinventor.com/booklets/If_humans_touch_Mars.htm#salt_pillar_oases Touch Mars?]</ref> which I the author hereby release under CC by SA.
==References==
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