Difference between revisions 796681596 and 799453806 on enwiki

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{{AFC comment|1=Fix reference errors. [[User:Robert McClenon|Robert McClenon]] ([[User talk:Robert McClenon|talk]]) 02:52, 21 April 2016 (UTC)}}

(contracted; show full)ASA's Jet Propulsion Laboratory | September 9, 2010</ref><ref name="NilesBoynton2010">{{cite journal|url=https://www.sciencemag.org/content/329/5997/1334.full.pdf|last1=Niles|first1=P. B.|last2=Boynton|first2=W. V.|last3=Hoffman|first3=J. H.|last4=Ming|first4=D. W.|last5=Hamara|first5=D.|title=Stable Isotope Measurements of Martian Atmospheric CO2 at the Phoenix Landing Site|journal=Science|volume=329|issue=5997|year=2010|pages=1334–1337|issn=0036-8075|doi=10.1126/science.1192863
|bibcode = 2010Sci...329.1334N }}</ref> This gives indirect but strong evidence that liquid water exists on the surface or has existed, in the very recent geological past.

In detail, first they found that the ratio of isotopes for <sup>13</sup>C to <sup>12</sup>C in the atmosphere is similar to Earth. Mars should be enriched in <sup>13</sup>C because the lighter <sup>12</sup>C is lost to space, but isn't. So this shows that the CO<sub>2</sub> must be continually repl(contracted; show full)ef><ref>[http://www.sciencedaily.com/releases/2010/10/101029135505.htm NASA/Jet Propulsion Laboratory. "Study links fresh Mars gullies to carbon dioxide." ScienceDaily 30 October 2010. 10 March 2011]</ref><ref>{{cite journal|last1=Diniega|first1=S.|last2=Byrne|first2=S.|last3=Bridges|first3=N. T.|last4=Dundas|first4=C. M.|last5=McEwen|first5=A. S.|title=Seasonality of present-day Martian dune-gully activity|journal=Geology|volume=38|pages=1047|date=2010| doi=10.1130/G31287.1 
|bibcode = 2010Geo....38.1047D }}
</ref><ref name="Dundas 2015">Dundas, C., S. Diniega, A. McEwen. 2015. Long-term monitoring of martian gully formation and evolution with MRO/HiRISE.  Icarus: 251, 244–263</ref>

(contracted; show full)s that is thought to be due to liquid water, in nearly all the models proposed for them so far.<ref name=Kereszturi2008/><ref name="MartínezRenno2013">{{cite journal|url=http://link.springer.com/article/10.1007%2Fs11214-012-9956-3/fulltext.html|last1=Martínez|first1=G. M.|last2=Renno|first2=N. O.|title=Water and Brines on Mars: Current Evidence and Implications for MSL|journal=Space Science Reviews|volume=175|issue=1-4|year=2013|pages=29–51|issn=0038-6308|doi=10.1007/s11214-012-9956-3
|bibcode = 2013SSRv..175...29M }}</ref>

A different mechanism is proposed for them in the Northern and in the Southern hemispheres.

===Southern hemisphere flow like features===

The southern hemisphere features grow at a rate of around 1.4 meters per Martian sol.
[[File:Flow-like-features detail.gif|thumb|400 px|Flow-like features on Dunes in Richardson Crater, Mars.  - detail. This flow moves approximately 39 meters in 26 days between the last two frames in the sequence]]

All the models for these features, to date, involve some form of water.

====Solid state greenhouse effect model====

Möhlmann uses a solid state greenhouse effect in his model, similarly to the process that forms the geysers, but with translucent ice rather than dry ice as the solid state greenhouse layer.<ref name="Möhlmann2010">{{cite journal|url=http://www.sciencedirect.com/science/article/pii/S0019103509004539|last1=Möhlmann|first1=Diedrich T.F.|title=Temporary liquid water in upper snow/ice sub-surfaces on Mars?|journal=Icarus|volume=207|issue=1|year=2010|pages=140–148|issn=00191035|doi=10.1016/j.icarus.2009.11.013|bibcode = 2010Icar..207..140M }}</ref>
[[File:JoekullsarlonBlueBlockOfIce.jpg|thumb|JoekullsarlonBlueBlockOfIce| 400px|  Blue wall of an Iceberg on [[Jökulsárlón]], Iceland. On the Earth, [[Blue ice (glacial)| Blue ice]] like this forms as a result of air bubbles squeezed out of glacier ice. This has the right optical and thermal properties to act as a solid state greenhouse, trapping a layer of liquid water that forms 0.1 to 1 meters below the surface. In Möhlmann's model, if ice with similar optical and thermal properties f(contracted; show full)ut there is nothing to rule it out either. Then, the other open question is whether their assumption of low thermal conductivity of the ice, preventing escape of the heat to the surface, is valid on Mars. <ref>{{cite journal|url=http://www.sciencedirect.com/science/article/pii/S0019103509004539|last1=Möhlmann|first1=Diedrich T.F.|title=Temporary liquid water in upper snow/ice sub-surfaces on Mars?|journal=Icarus|volume=207|issue=1|year=2010|pages=140–148|issn=00191035|doi=10.1016/j.icarus.2009.11.013
|bibcode = 2010Icar..207..140M }} '''"The results described above make bare and optically transparent ice fields on Mars, analogous to terrestrial porous ‘‘blue-ice fields” of frozen snow with bluish meltwater at depths around 10 cm and more (cf. Liston and Winther, 2005), to be candidate sites where sub-surface melting might be possible. The thickness of the ice at these sites with translucent ice must be of several cenyimetres at least. The question is yet open as to whether bare and translucent water ice can have e(contracted; show full)iciently penetrate the translucent CO<sub>2</sub> ice layer. Thus, both the underlying surface and the dark ejecta can reach temperatures much higher than those measured by TES and THEMIS (Martinez et al. 2012). Also, subsurface melt water and ULI water can form in the shallow subsurface at temperatures as low as 180 K (see Sect. 2). Salts in contact with these types of liquid water could form liquid brines, and thus help explain the evolution of dune dark spots and FLF."'''
|bibcode = 2013SSRv..175...29M }}</ref>

An alternative mechanism for the Northern hemisphere involves dry ice and sand cascading down the slope but most of the models involve liquid brines for the seepage stages of the features. .<ref name="MartínezRenno2013"/>

(contracted; show full) 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
|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's 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 tempe(contracted; show full)rctic_lichen_to_Martian_niche_conditions_can_occur_within_34_days/links/00b4952e11f3088291000000.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=00320633|doi=10.1016/j.pss.2013.07.014
|bibcode = 2014P&SS...98..182D }}</ref>

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/>

====Black fungi and black yeast relying on 100% night time humidity====

(contracted; show full)//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|year=2014|issn=2045-2322|doi=10.1038/srep05114|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==

Mars is rich in perchlorates - a discovery made by Phoenix, and later confirmed by Curiosity and by analysis of Martian meteorites on Earth. It now seems that perchlorates probably occur over much of the surface of Mars<ref>[http://www.astrobio.net/news-exclusive/salty-martian-meteorite-offers-clues-habitability/ A Salty, Martian Meteorite Offers Clues to Habitability]
(contracted; show full)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=00191035|doi=10.1016/j.icarus.2014.01.018
|bibcode = 2014Icar..233...36T }}</ref><ref name="GoughChevrier2014">{{cite journal|url=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=0012821X|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.

===Effects of micropores in salt pillars===

(contracted; show full) 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|"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 associat(contracted; show full)d need to be perchlorate tolerant, and ideally, able to use it as a source of energy as well.<ref name=Oren/>.<ref name="ElsenousyHanley2015">{{cite journal|last1=Elsenousy|first1=Amira|last2=Hanley|first2=Jennifer|last3=Chevrier|first3=Vincent F.|title=Effect of evaporation and freezing on the salt paragenesis and habitability of brines at the Phoenix landing site|journal=Earth and Planetary Science Letters|volume=421|year=2015|pages=39–46|issn=0012821X|doi=10.1016/j.epsl.2015.03.047
|bibcode = 2015E&PSL.421...39E }}</ref>

The conditions for these liquid layers to form may include regions where there is no ice present on the surface such as the arid equatorial regions of Mars.<ref>{{cite web|last1=Matson|first1=John|title=The New Way to Look for Mars Life: Follow the Salt|url=http://blogs.scientificamerican.com/observations/2013/02/06/the-new-way-to-look-for-mars-life-follow-the-salt/|publisher=Scientific American|date=February 6, 2013}}</ref>. 

(contracted; show full)no|first14=Nilton|last15=Chevrier|first15=Vincent F.|last16=Mischna|first16=Michael|last17=Navarro-González|first17=Rafael|last18=Martínez-Frías|first18=Jesús|last19=Conrad|first19=Pamela|last20=McConnochie|first20=Tim|last21=Cockell|first21=Charles|last22=Berger|first22=Gilles|last23=R. Vasavada|first23=Ashwin|last24=Sumner|first24=Dawn|last25=Vaniman|first25=David|title=Transient liquid water and water activity at Gale crater on Mars|journal=Nature Geoscience|year=2015|issn=1752-0894|doi=10.1038/ngeo2412
|bibcode = 2015NatGe...8..357M }}</ref>

==Advancing sand dunes bioreactor==

The idea behind this proposal is that the constantly moving sand dunes of Mars may be able to create a potential environment for life. Raw materials can be replenished, and the chemical disequilibrium needed for life maintained through churning of the sand by the winds.<ref name=sanddunesbioreactor/>

(contracted; show full)easured dunes with clear lee edges to measure) and the ripples move on average 0.1 meters per year. <ref name="BridgesAyoub2012">{{cite journal|url=ftp://ftp.seti.org/lfenton/Papers/bridgesetal2012_sandfluxes.pdfA|last1=Bridges|first1=N. T.|last2=Ayoub|first2=F.|last3=Avouac|first3=J-P.|last4=Leprince|first4=S.|last5=Lucas|first5=A.|last6=Mattson|first6=S.|title=Earth-like sand fluxes on Mars|journal=Nature|volume=485|issue=7398|year=2012|pages=339–342|issn=0028-0836|doi=10.1038/nature11022
|bibcode = 2012Natur.485..339B }}</ref>.<br><br>The idea of the advancing sand dunes bioreactor is that this movement of the sand dunes could "mix oxidants, reductants, water, nutrients, and possibly organic carbon in what could be considered bioreactors"<ref name=sanddunesbioreactor/>|bibcode = 2012Natur.485..339B }}

The sources of carbon would come from space - it's supplied at a steady rate of 5 nanograms per square meter per sol from micrometeorites. At the equator it has a mean lifetime of 300 years - but lasts longer if buried. 

On the leeward side of transgressing dunes, then the sand can be buried at the rate of centimeters per year. Since the UV light only penetrates the top centimeter of the soil, then the interplanetary carbon would be buried, beyond reach of UV, within a year. 

(contracted; show full)

In the academic paper about this research he writes:<ref name="FischerMartínez2014">{{cite journal|url=http://onlinelibrary.wiley.com/doi/10.1002/2014GL060302/full|last1=Fischer|first1=Erik|last2=Martínez|first2=Germán M.|last3=Elliott|first3=Harvey M.|last4=Rennó|first4=Nilton O.|title=Experimental evidence for the formation of liquid saline water on Mars|journal=Geophysical Research Letters|year=2014|pages=n/a–n/a|issn=00948276|doi=10.1002/2014GL060302
|bibcode = 2014GeoRL..41.4456F }}</ref>

{{quote|"The results of our experiments suggest that the spheroids observed on a strut of the Phoenix lander formed on water ice splashed during landing [Smith et al., 2009; Rennó et al., 2009]. They also support the hypothesis that “soft ice” found in one of the trenches dug by Phoenix was likely frozen brine that had been formed previously by perchlorates on icy soil. Finally, our results indicate that liquid water could form on the surface during the spring where snow has been deposi(contracted; show full) spend most of their time in survival mode.<ref name="JepsenPriscu2007">{{cite journal|url=http://www.montana.edu/priscu/DOCS/Publications/JepsenEtAl2007LifeOnMars.pdf|last1=Jepsen|first1=Steven M.|last2=Priscu|first2=John C.|last3=Grimm|first3=Robert E.|last4=Bullock|first4=Mark A.|title=The Potential for Lithoautotrophic Life on Mars: Application to Shallow Interfacial Water Environments|journal=Astrobiology|volume=7|issue=2|year=2007|pages=342–354|issn=1531-1074|doi=10.1089/ast.2007.0124
|bibcode = 2007AsBio...7..342J }}</ref><ref name="PriceSowers2004"/>. Models show that interfacial water should form in some regions of Mars, for instance in Richardson crater.<ref name="KereszturiRivera-Valentin2012">{{cite journal|url=http://www.planetary.brown.edu/pdfs/4591.pdf|last1=Kereszturi|first1=Akos|last2=Rivera-Valentin|first2=Edgard G.|title=Locations of thin liquid water layers on present-day Mars|journal=Icarus|volume=221|issue=1|year=2012|pages=289–295|issn=00191035|doi=10.1016/j.icarus.2012.08.004|bibcode = 2012Icar..221..289K }}</ref>

==Ice covered lakes that form in polar regions after large impacts==

This is a possibility that was highlighted recently with the close flyby of Mars by the comet Siding Spring in 2014 [[C/2013_A1#Predicted_effects | C/2013 A1 Siding Spring]]. Before its trajectory was known in detail, there remained a small chance that it could hit Mars. Calculations showed it could create a crater of many km in diameter and perhaps a couple of km deep. If a comet like that was to hit polar regions or high(contracted; show full)ofile/Justin_Simon2/publication/269393996_Meteoritic_evidence_for_a_previously_unrecognized_hydrogen_reservoir_on_Mars/links/54887e000cf268d28f08f75c.pdf|last1=Usui|first1=Tomohiro|last2=Alexander|first2=Conel M. O'D.|last3=Wang|first3=Jianhua|last4=Simon|first4=Justin I.|last5=Jones|first5=John H.|title=Meteoritic evidence for a previously unrecognized hydrogen reservoir on Mars|journal=Earth and Planetary Science Letters|volume=410|year=2015|pages=140–151|issn=0012821X|doi=10.1016/j.epsl.2014.11.022
|bibcode = 2015E&PSL.410..140U }}</ref>
{{Wide image| Illustration of Martian Water Reservoirs.jpg | 600px | Research in 2014 into the deuterium / hydrogen isotope ratios in the water in martian meteorites gives evidence of a subsurface reservoir with a ratio in between the composition of the mantle and the composition of the water mixing with its current atmosphere. This supports the hypothesis that Mars has a deep cryosphere which may contain much of the original water from Mars."}}

(contracted; show full)pdf|publisher=Under ESA contract: 4000104716/11/NL/AF|date=5 December 2012}}</ref><ref name="PrestonDartnell2014">{{cite journal|url=http://lewisdartnell.com/en-gb/wp-content/uploads/2014/01/18-Preston-Dartnell2014_IJA.pdf|last1=Preston|first1=Louisa J.|last2=Dartnell|first2=Lewis R.|title=Planetary habitability: lessons learned from terrestrial analogues|journal=International Journal of Astrobiology|volume=13|issue=01|year=2014|pages=81–98|issn=1473-5504|doi=10.1017/S1473550413000396
|bibcode = 2014IJAsB..13...81P }}</ref>

This section is for analogues of conditions that could prevail on present day Mars. This includes analogues of deep subsurface habitats, and temporary habitats that can form after volcanic eruptions and large meteorite impacts. However, it leaves out sites that are thought to be analogues only of conditions on early Mars. Also, it leaves out geological analogues, or analogues used only for testing engineering details for landing systems and rovers<ref name=PlanetaryAnalogues/>. For ana(contracted; show full)mposition of the organics by non biological processes. The samples had trace elements of organics, no DNA was recovered, and extremely low levels of culturable bacteria<ref name="Navarro-Gonzalez2003">{{cite journal|url=http://www.sciencemag.org/content/302/5647/1018|last1=Navarro-Gonzalez|first1=R.|title=Mars-Like Soils in the Atacama Desert, Chile, and the Dry Limit of Microbial Life|journal=Science|volume=302|issue=5647|year=2003|pages=1018–1021|issn=0036-8075|doi=10.1126/science.1089143
|bibcode = 2003Sci...302.1018N }}</ref>This lead to increased interest in the site as a Mars analogue.<ref name="Azua-BustosUrrejola2012">{{cite journal|url=http://www.sciencedirect.com/science/article/pii/S0014579312005935|last1=Azua-Bustos|first1=Armando|last2=Urrejola|first2=Catalina|last3=Vicuña|first3=Rafael|title=Life at the dry edge: Microorganisms of the Atacama Desert|journal=FEBS Letters|volume=586|issue=18|year=2012|pages=2939–2945|issn=00145793|doi=10.1016/j.febslet.2012.07.025}}</ref>

(contracted; show full)rría|first12=Alex|last13=Urtuvia|first13=Viviana N.|last14=Ruiz-Bermejo|first14=Marta|last15=García-Villadangos|first15=Miriam|last16=Postigo|first16=Marina|last17=Sánchez-Román|first17=Mónica|last18=Chong-Díaz|first18=Guillermo|last19=Gómez-Elvira|first19=Javier|title=A Microbial Oasis in the Hypersaline Atacama Subsurface Discovered by a Life Detector Chip: Implications for the Search for Life on Mars|journal=Astrobiology|volume=11|issue=10|year=2011|pages=969–996|issn=1531-1074|doi=10.1089/ast.2011.0654
|bibcode = 2011AsBio..11..969P }}</ref><ref name=PlanetaryAnalogues2>{{cite web|last1=The Planetary and Space Sciences Research Institute, The Open University|title=TN2: The Catalogue of Planetary Analogues, section 2.6.1|url=http://esamultimedia.esa.int/docs/gsp/The_Catalogue_of_Planetary_Analogues.pdf|publisher=Under ESA contract: 4000104716/11/NL/AF|date=5 December 2012|quote= '''Very little active biological material can be recovered from the soils of the hyperarid zone. Plant activity is zero and only limi(contracted; show full)esses that form the RSLs on Mars.<ref name="DicksonHead2013">{{cite journal|url=http://www.nature.com/srep/2013/130130/srep01166/full/srep01166.html#supplementary-information|last1=Dickson|first1=James L.|last2=Head|first2=James W.|last3=Levy|first3=Joseph S.|last4=Marchant|first4=David R.|title=Don Juan Pond, Antarctica: Near-surface CaCl2-brine feeding Earth's most saline lake and implications for Mars|journal=Scientific Reports|volume=3|year=2013|issn=2045-2322|doi=10.1038/srep01166
|bibcode = 2013NatSR...3E1166D }}</ref><ref>{{cite web|last1=Stacey|first1=Kevin|title=How the world’s saltiest pond gets its salt - describing the research of Jay Dickson and Jim Head|url=https://news.brown.edu/articles/2013/02/antarctica|date=February 7, 2013}}</ref>

(contracted; show full)cki2014">{{cite journal|last1=Dachwald|first1=Bernd|last2=Mikucki|first2=Jill|last3=Tulaczyk|first3=Slawek|last4=Digel|first4=Ilya|last5=Espe|first5=Clemens|last6=Feldmann|first6=Marco|last7=Francke|first7=Gero|last8=Kowalski|first8=Julia|last9=Xu|first9=Changsheng|title=IceMole: a maneuverable probe for clean in situ analysis and sampling of subsurface ice and subglacial aquatic ecosystems|journal=Annals of Glaciology|volume=55|issue=65|year=2014|pages=14–22|issn=02603055|doi=10.3189/2014AoG65A004
|bibcode = 2014AnGla..55...14D }}</ref><ref>{{cite web|last1=ANDERSON|first1=PAUL SCOTT|title=Exciting New ‘Enceladus Explorer’ Mission Proposed to Search for Life|url=http://www.universetoday.com/93879/exciting-new-enceladus-explorer-mission-proposed-to-search-for-life/|website=Universe Today|date=February 29, 2012}}</ref>

===Qaidam Basin in Tibet===

(contracted; show full)urnal|url=http://journals.cambridge.org/download.php?file=%2FIJA%2FIJA10_04%2FS1473550411000206a.pdf&code=3f230f16d8dc8a0991802b67ab63f032|last1=Bishop|first1=Janice L.|last2=Schelble|first2=Rachel T.|last3=McKay|first3=Christopher P.|last4=Brown|first4=Adrian J.|last5=Perry|first5=Kaysea A.|title=Carbonate rocks in the Mojave Desert as an analogue for Martian carbonates|journal=International Journal of Astrobiology|volume=10|issue=04|year=2011|pages=349–358|issn=1473-5504|doi=10.1017/S1473550411000206
|bibcode = 2011IJAsB..10..349B }}</ref>

===Other deserts of astrobiological interest for present day Mars===

* [[Namib Desert]] - oldest desert, life with limited water and high temperatures, large dunes and wind features<ref name="PrestonDartnell2014"/>
(contracted; show full)=http://www.researchgate.net/publication/256719821_Mineralogy_of_saline_perennial_cold_springs_on_Axel_Heiberg_Island_Nunavut_Canada_and_implications_for_spring_deposits_on_Mars |last1=Battler|first1=Melissa M.|last2=Osinski|first2=Gordon R.|last3=Banerjee|first3=Neil R.|title=Mineralogy of saline perennial cold springs on Axel Heiberg Island, Nunavut, Canada and implications for spring deposits on Mars|journal=Icarus|volume=224|issue=2|year=2013|pages=364–381|issn=00191035|doi=10.1016/j.icarus.2012.08.031
}}</ref>|bibcode = 2013Icar..224..364B }}</ref>|bibcode = 2013Icar..224..364B }}

Some of the extremophiles from these two sites have been cultured in simulated Martian environment, and it is thought that they may be able to survive in a Martian cold saline spring, if such exist.<ref>{{cite web|last1=The Planetary and Space Sciences Research Institute, The Open University|title=TN2: The Catalogue of Planetary Analogues|url=http://esamultimedia.esa.int/docs/gsp/The_Catalogue_of_Planetary_Analogues.pdf|publisher=Under ESA contract: 4000104716/11/NL/AF|date=5 December 2012|quote=B(contracted; show full)

It's thought that ice caves may exist on Mars - ice preserved under the surface in cave systems protected from the surface conditions.<ref name="WilliamsMcKay2010">{{cite journal|url=http://www.planetary.brown.edu/pdfs/3933.pdf|last1=Williams|first1=K.E.|last2=McKay|first2=Christopher P.|last3=Toon|first3=O.B.|last4=Head|first4=James W.|title=Do ice caves exist on Mars?|journal=Icarus|volume=209|issue=2|year=2010|pages=358–368|issn=00191035|doi=10.1016/j.icarus.2010.03.039
|bibcode = 2010Icar..209..358W }}</ref>

The ice caves near the summit of Mt. Erebus (Antarctica) associated with the fumaroles are dark, in a polar alpine environments starved in organics and with oxygenated hydrothermal circulation in highly reducing host rock.<ref name="TeboDavis2015">{{cite journal|url=http://journal.frontiersin.org/article/10.3389/fmicb.2015.00179/full|last1=Tebo|first1=Bradley M.|last2=Davis|first2=Richard E.|last3=Anitori|first3=Roberto P.|last4=Connell|first4=Laurie B.|last5=Schiffman|first5(contracted; show full)rnal|pmc=3176350|last1=Northup|first1=D.E.|last2=Melim|first2=L.A.|last3=Spilde|first3=M.N.|last4=Hathaway|first4=J.J.M.|last5=Garcia|first5=M.G.|last6=Moya|first6=M.|last7=Stone|first7=F.D.|last8=Boston|first8=P.J.|last9=Dapkevicius|first9=M.L.N.E.|last10=Riquelme|first10=C.|title=Lava Cave Microbial Communities Within Mats and Secondary Mineral Deposits: Implications for Life Detection on Other Planets|journal=Astrobiology|volume=11|issue=7|year=2011|pages=601–618|issn=1531-1074|doi=10.1089/ast.2010.0562
|bibcode = 2011AsBio..11..601N }}</ref><ref>Northup, Diana E., et al. [https://books.google.co.uk/books?id=9xxdhs29fnIC&pg=PA465 "Life In Earth’s lava caves: Implications for life detection on other planets."] Life on Earth and other Planetary Bodies. Springer Netherlands, 2012. 459-484.</ref>

====[[Lechuguilla Cave]]====

(contracted; show full)i</ref><ref name="HosePalmer2000">{{cite journal|url=http://bioannexlabs.unm.edu/BIOL/HoseChemGeol2000.pdf|last1=Hose|first1=Louise D.|last2=Palmer|first2=Arthur N.|last3=Palmer|first3=Margaret V.|last4=Northup|first4=Diana E.|last5=Boston|first5=Penelope J.|last6=DuChene|first6=Harvey R.|title=Microbiology and geochemistry in a hydrogen-sulphide-rich karst environment|journal=Chemical Geology|volume=169|issue=3-4|year=2000|pages=399–423|issn=00092541|doi=10.1016/S0009-2541(00)00217-5
|bibcode = 2000ChGeo.169..399H }}</ref>

====[[Movile Cave]], Romania<ref name="AertsRöling2014"/>====

* Isolated from the atmosphere and sunlight for 5.5 million years.
* Atmosphere rich in H<sub>2</sub>S and CO<sub>2</sub> with 1% - 2% methane 
* It does have some oxygen, 7-10% O<sub>2</sub> in the cave atmosphere, compared to 21% O<sub>2</sub> in air
* Microbes rely mainly on sulfide and methane oxidation.
* Has 33 vertebrates and a wide range of indigenous microbes.

===Magnesium Sulfate lakes===

[[File:Meridianiite Crystals.jpg|thumb|400 px| Crystals of [[Meridianiite]], formula [[Magnesium]] [[sulfate]] 11 [[hydrate]] MgSO<sub>4</sub>•11H<sub>2</sub>O. Evidence from orbital measurements show that this is the phase of Magnesium sulfate which would be in equilibrium with the ice in the Martian polar and sub polar regions<ref name="PetersonNelson2007">{{cite journal|last1=Peterson|first1=R.C.|last2=Nelson|first2=W.|last3=Madu|first3=B.|last4=Shurvell|first4=H.F.|title=Meridianiite: A new mineral species observed on Earth and predicted to exist on Mars|journal=American Mineralogist|volume=92|issue=10|year=2007|pages=1756–1759|issn=0003-004X|doi=10.2138/am.2007.2668|bibcode = 2007AmMin..92.1756P }}</ref>  It also occurs on the Earth, for instance in Basque Lake 2 in Western Columbia, which may give an analogue for Mars habitats]]
[[File:Voids on bedrock on Mars.jpg|thumb|Vugs on Mars which may be voids left by [[Meridianiite]] when it dissolved or dehydrated]]
(contracted; show full)=E.|last26=Léveillé|first26=R.|last27=McLennan|first27=S.|last28=Maurice|first28=S.|last29=Meslin|first29=P.-Y.|last30=Rapin|first30=W.|last31=Rice|first31=M.|last32=Squyres|first32=S. W.|last33=Stack|first33=K.|last34=Sumner|first34=D. Y.|last35=Vaniman|first35=D.|last36=Wellington|first36=D.|title=Calcium sulfate veins characterized by ChemCam/Curiosity at Gale crater, Mars|journal=Journal of Geophysical Research: Planets|volume=119|issue=9|year=2014|pages=1991–2016|issn=21699097|doi=10.1002/2013JE004588
|bibcode = 2014JGRE..119.1991N }}</ref>. (Curiosity is currently exploring ancient deposits at the base of Mount Sharp. It won't reach the youngest Magnesium Sulfate deposits towards the summit of Mt. Sharp until towards the end of its extended mission if that goes ahead<ref>{{cite web|last1=Erickson|first1=Jim|title=Mission to Mt. Sharp - Senior Review Proposal (for extended mission)|url=http://mars.nasa.gov/files/msl/2014-MSL-extended-mission-plan.pdf|website=NASA|date=April 2014}}</ref>). Orbital maps also sugge(contracted; show full)ear subsurface.<ref name="FosterKing2010">{{cite journal|url=http://www.sciencedirect.com/science/article/pii/S0032063309002463|last1=Foster|first1=Ian S.|last2=King|first2=Penelope L.|last3=Hyde|first3=Brendt C.|last4=Southam|first4=Gordon|title=Characterization of halophiles in natural MgSO4 salts and laboratory enrichment samples: Astrobiological implications for Mars|journal=Planetary and Space Science|volume=58|issue=4|year=2010|pages=599–615|issn=00320633|doi=10.1016/j.pss.2009.08.009
|bibcode = 2010P&SS...58..599F }}</ref>. With the abundance of algae and bacteria, in alkaline hypersaline conditions, they are of astrobiological interest for both past and present life on Mars.

These lakes are most common in Western Canada, and the northern part of Washington state, USA. One of the examples, is Basque Lake 2 in Western Columbia, which is highly concentrated in magnesium sulfate. In summer it deposits epsomite ("Epsom salts"). In winter, it deposits [[Meridianiite| meridianiite]]. This is named after [[Meridiani Planum]] where Opportunity rover found crystal molds in sulfate deposits ([[Vugs]]) which are thought to be remains of this mineral which have since been dissolved or dehydrated. It is preferentially formed at subzero temperatures, and is only stable below 2°C<ref>{{cite web|title=An Earth and Mars mineral – Meridianiite MgSO4.11H2O|url=https://crystallography365.wordpress.com/2014/07/30/an-earth-and-mars-mineral-meridianiite-mgso4-11h2o/|website=Crystallography 365|date=July 30, 2014}}</ref>, while  Epsomite (MgSO <sub>4</sub>·7H <sub>2</sub>O) is favored at higher temperatures .<ref name="MarionCatling2010">{{cite journal|last1=Marion|first1=G.M.|last2=Catling|first2=D.C.|last3=Zahnle|first3=K.J.|last4=Claire|first4=M.W.|title=Modeling aqueous perchlorate chemistries with applications to Mars|journal=Icarus|volume=207|issue=2|year=2010|pages=675–685|issn=00191035|doi=10.1016/j.icarus.2009.12.003|bibcode = 2010Icar..207..675M }}</ref><ref name=Webmin>[http://webmineral.com/data/Meridianiite.shtml Webmineral.com]</ref>  <ref>{{cite web|title=Analogue Environments|url=https://www.ucl.ac.uk/silva/earth-sciences/research/ices/research/analogue-environments|website=UCL Planetary Ices Group}}</ref>

Another example is [[Spotted Lake]], which shows a wide variety of minerals, most of them sulfates, with sodium, magnesium and calcium as cations.

(contracted; show full)gt;{{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=01|year=2014|pages=69–80|issn=1473-5504|doi=10.1017/S1473550413000268
|bibcode = 2014IJAsB..13...69K }}</ref>. <ref name="CrislerNewville2012">{{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|bibcode = 2012AsBio..12...98C }}</ref><ref name="KilmerEberl2014">{{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=01|year=2014|pages=69–80|issn=1473-5504|doi=10.1017/S1473550413000268|bibcode = 2014IJAsB..13...69K }}</ref><ref>{{cite web|title=Searching salt for answers about life on Earth, Mars|url=http://www.sciencedaily.com/releases/2012/08/120809151324.htm|website=Science Daily - press release from Wichita State University|date=August 9, 2012}}</ref>

(contracted; show full)ive in Lake Vostok.<ref name="DuxburyZotikov2001">{{cite journal|url=http://onlinelibrary.wiley.com/doi/10.1029/2000JE001254/pdf|last1=Duxbury|first1=N. S.|last2=Zotikov|first2=I. A.|last3=Nealson|first3=K. H.|last4=Romanovsky|first4=V. E.|last5=Carsey|first5=F. D.|title=A numerical model for an alternative origin of Lake Vostok and its exobiological implications for Mars|journal=Journal of Geophysical Research|volume=106|issue=E1|year=2001|pages=1453|issn=0148-0227|doi=10.1029/2000JE001254
|bibcode = 2001JGR...106.1453D }}</ref>

=== Subsurface life kilometers below the surface===

Investigations of life in deep mines, and drilling beneath the ocean depths may give an insight into possibilities for life in the Mars Hydrosphere and other deep subsurface habitats, if they exist.

====[[Boulby Mine]] on the edge of the Yorkshire moors<ref name="AertsRöling2014"/>====

(contracted; show full) 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=00320633|doi=10.1016/j.pss.2013.07.014|quote=We studied the psychrophilic lichen Pleopsidium chlorophanum , because it lives in Earth's most Mars-like environmental conditions (low temperatures, high UV fluxes, dryness). P. chlorophanum preferentially colonizes granaites and volcanic rocks of North Victoria Land (Atarctica), at up to 2000 meters altitude.
|bibcode = 2014P&SS...98..182D }}</ref>

==Habitability factors for life on Mars==

This section is organized around the listing of the main factors limiting surface and near surface life on Mars, according to Schuerger<ref name=Schuerger>[http://plantpath.ifas.ufl.edu/faculty/statewide/schuerger/Schuerger_2012_PSS-3371.pdf Biotoxicity of Mars soils: 1. Dry deposition of analog soils on microbial olonies and survival under Martian conditions], Andrew C. Schuerger, D.C. Golden, Doug W. Ming, Planetary and Space Science,  20 Ju(contracted; show full)he thin atmosphere, this is hardly filtered at all, and is a major challenge for any life exposed to the light. It is easily blocked by about 0.3 mm of surface soil<ref name="Mateo-Marti2014">{{cite journal|url=http://www.mdpi.com/2078-1547/5/2/213/htm|last1=Mateo-Marti|first1=Eva|title=Planetary Atmosphere and Surfaces Chamber (PASC): A Platform to Address Various Challenges in Astrobiology|journal=Challenges|volume=5|issue=2|year=2014|pages=213–223|issn=2078-1547|doi=10.3390/challe5020213
|bibcode = 2014Chall...5..213M }}''' "It was found that the UV transmittance value drops to nearly zero for a basalt-dust thickness of ~300 µm, and therefore, microorganisms living at deeper layers than this would be protected from damaging UV irradiation on Mars."'''<sup>Superscript text</sup></ref> or in the shadow of a rock. Mars conditions are likely to favour lifeforms that can tolerate high levels of UV radiation, at least, if they are exposed to direct unfiltered sunlight a(contracted; show full)pply a subsurface biosphere.<ref name="BoxeHand2012">{{cite journal|url=http://yly-mac.gps.caltech.edu/Reprintsyly/A_RecentPapers/Boxe%20et%20al%202012.pdf|last1=Boxe|first1=C.S.|last2=Hand|first2=K.P.|last3=Nealson|first3=K.H.|last4=Yung|first4=Y.L.|last5=Saiz-Lopez|first5=A.|title=An active nitrogen cycle on Mars sufficient to support a subsurface biosphere|journal=International Journal of Astrobiology|volume=11|issue=02|year=2012|pages=109–115|issn=1473-5504|doi=10.1017/S1473550411000401
|bibcode = 2012IJAsB..11..109B }}</ref>

Schuerger also mentions:

* Cosmic radiation - this is not limiting of surface life in the short term (similar to the levels inside the ISS) but prevents it from reviving if kept dormant for periods of order of hundreds of thousands of years.<ref>"Solar particle events and galactic cosmic rays are considered external factors that occur infrequently or at low dosage, respectively" [http://plantpath.ifas.ufl.edu/faculty/statewide/schuerger/Schuerger_2012_PSS-3371.pdf Biotoxicit(contracted; show full)in glaciers down to -40°C, at a very low metabolic rate of ten turnovers of cellular carbon per billion years<ref name="PriceSowers2004short">{{cite journal|url=http://www.pnas.org/content/101/13/4631.short|last1=Price|first1=P. B.|last2=Sowers|first2=T.|title=Temperature dependence of metabolic rates for microbial growth, maintenance, and survival|journal=Proceedings of the National Academy of Sciences|volume=101|issue=13|year=2004|pages=4631–4636|issn=0027-8424|doi=10.1073/pnas.0400522101
|bibcode = 2004PNAS..101.4631P }}</ref>. 

There can be some activity at even lower temperatures. In an experiment to test incorporation of the amino acid Leucine, Karen Junge et all used two controls at -80°C and -196°C, well below the eutectic freezing point of salt, and to their surprise, they found that the  Colwellia psychrerythraea strain 34H  was able to continue to incorporate low levels of Leucine right down to -196°C. They  hypothesize that the Leucine enters the cell boundaries at higher temperatures in the first few seconds of the experiment, then gets incorporated into the cell at lower temperatures (it doesn't get incorporated right away as they proved through zero time controls).<ref name="JungeEicken2006"/><ref name="JepsenPriscu2007LifeOnMars">{{cite journal|url=http://www.montana.edu/priscu/DOCS/Publications/JepsenEtAl2007LifeOnMars.pdf|last1=Jepsen|first1=Steven M.|last2=Priscu|first2=John C.|last3=Grimm|first3=Robert E.|last4=Bullock|first4=Mark A.|title=The Potential for Lithoautotrophic Life on Mars: Application to Shallow Interfacial Water Environments|journal=Astrobiology|volume=7|issue=2|year=2007|pages=342–354|issn=1531-1074|doi=10.1089/ast.2007.0124|bibcode = 2007AsBio...7..342J }}</ref>

Price et al did a review of the literature to date, in 2004, and came to the conclusion that there is no evidence of a fixed lowest temperature limit to metabolism, in the presence of impurities and thin films of water to supply liquid to microbes.<ref name="PriceSowers2004">{{cite journal|url=http://www.pnas.org/content/101/13/4631.full|last1=Price|first1=P. B.|last2=Sowers|first2=T.|title=Temperature dependence of metabolic rates for microbial growth, maintenance, and survival|journal=Proceedings of the National Academy of Sciences|volume=101|issue=13|year=2004|pages=4631–4636|issn=0027-8424|doi=10.1073/pnas.0400522101|bibcode = 2004PNAS..101.4631P }}</ref>

{{quote|"Our results disprove the view that the lowest temperature at which life is possible is ≈-17°C in an aqueous environment, as well as the remark that “the lowest temperature at which terrestrial and presumably martian life can function is probably near -20°C. Our data show no evidence of a threshold or cutoff in metabolic rate at temperatures down to -40°C. A cell resists freezing, due to the “structured” water in its cytoplasm. Ionic impurities prevent freezing of veins in ice a(contracted; show full)document-martian-climate-cycles/|website=Astrobiology Magazine (NASA)|date=Jan 29, 2015}}</ref><ref name="DicksonHead2015">{{cite journal|last1=Dickson|first1=James L.|last2=Head|first2=James W.|last3=Goudge|first3=Timothy A.|last4=Barbieri|first4=Lindsay|title=Recent climate cycles on Mars: Stratigraphic relationships between multiple generations of gullies and the latitude dependent mantle|journal=Icarus|volume=252|year=2015|pages=83–94|issn=00191035|doi=10.1016/j.icarus.2014.12.035
|bibcode = 2015Icar..252...83D }}</ref>

That's still challenging for life with a maximum of around 500,000 years dormancy on the surface. However the cosmic radiation only penetrates a few meters into the ground, with most of the effects shielded in the top 1.5 meters (400 grams per cm<sup>2</sup> of material, at 2.6 grams per cm<sup>3</sup> typical regolith density) and significant shielding at a depth of half a meter.<ref name="KminekBada2006">{{cite journal|last1=Kminek|first1=G|last2=Bada|first2=J|title=The effect of ionizing radiation on the preservation of amino acids on Mars|journal=Earth and Planetary Science Letters|volume=245|issue=1-2|year=2006|pages=1–5|issn=0012821X|doi=10.1016/j.epsl.2006.03.008|bibcode = 2006E&PSL.245....1K }}</ref> Below that depth, there could be dormant microbes that have survived for longer periods. Depending on the depth below the surface they could remain dormant for millions of years. Some microbes on Earth have lasted for many millions of years in ice and salt, and have been revived. So some of these on Mars also may still be viable today. Such microbes could also survive in caves on Mars in dormancy, or in subsurface locations kept habitable by geothermal hot spots, until times when Mars is more(contracted; show full)year=2014|pages=887–968|issn=1531-1074|doi=10.1089/ast.2014.1227|quote='''''From MSL RAD measurements, ionizing radiation from GCRs [Galactic Cosmic Rays] at Mars is so low as to be negligible. Intermittent SPEs [Solar Particle Events] can increase the atmospheric ionization down to ground level and increase the total dose, but these events are sporadic and last at most a few (2–5) days. . These facts are not used to distinguish Special Regions on Mars'''''
|bibcode = 2014AsBio..14..887R }}</ref>

==Views on the possibility of present day life on or near the surface==

It is a challenge for life to survive on the surface, or the near subsurface, because of the hyper arid conditions, combined with low temperatures. Often when the temperature is high enough for cellular division, the humidity is too low and vice versa. <ref name="RummelBeaty2014SpecialRegionsConclusion">{{cite journal|last1=Rummel|first1=John D.|last2=Beaty|first2=David W.|last3=Jones|first3=Melissa A.|l(contracted; show full)ngle sol, but it is unknown whether terrestrial organisms can use resources in this discontinuous fashion. No regions have been definitively identified where these parameters are attained simultaneously, but a classification of landforms on Mars leads to RSL, certain types of gullies, and caves being named Uncertain Regions, which will be treated as if they were Special Regions until further data are gathered to properly classify them as Special Regions or Non-Special Regions.'''''
|bibcode = 2014AsBio..14..887R }}</ref>. Also in surface conditions, it's not possible for microbes to remain in dormancy through the changes in axial tilt when the Mars atmosphere becomes thicker and more habitable (as it does from time to time).

Authors in recent publications present a variety of views on the possibility of present day life on the surface of Mars or in the near subsurface.

(contracted; show full)nic Archaea from Siberian Permafrost under Simulated Martian Thermal Conditions|journal=Origins of Life and Evolution of Biospheres|volume=37|issue=2|year=2006|pages=189–200|issn=0169-6149|doi=10.1007/s11084-006-9024-7|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.'''''
|bibcode = 2007OLEB...37..189M }}</ref><ref name=Carnobacterium/><ref>{{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|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><ref>{{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=01|year=2014|pages=69–80|issn=1473-5504|doi=10.1(contracted; show full)duced through deliquescence. Brines of perchlorate salts may be present in north polar regions (McKay et al. 2013). Initial screening of bacterial isolates from Hot Lake and the GSP have shown considerable tolerance to perchlorates, in some cases, growing at 15% sodium or magnesium perchlorate (Mai et al. 2012). A better understanding of terrestrial microbes growing under these conditions will impact life detection and sample return missions to Mars and other celestial bodies.'''''
|bibcode = 2014IJAsB..13...69K }}</ref> and many others).

* '''''Likely''''' Some researchers, particularly the researchers at DLR consider that their experiments have already shown a high likelihood that the surface of Mars is habitable, for some lichens and cyanobacteria, taking advantage of the night time humidity, and even in equatorial regions such as Gale crater. <ref name=DLRLichenHabitable>{{cite journal|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=00320633|doi=10.1016/j.pss.2013.07.014|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|bibcode = 2014P&SS...98..182D }}</ref><ref name="ZakharovaMarzban2014"/>. See [[#Life able to take up water from the 100% night time humidity of the Mars atmosphere]]
* '''''Already detected on the surface''''' A small minority of authors believe that their reanalysis of the Viking Labeled Release experiments already indicates presence of life on present day Mars, see [[#Viking observations]]

(contracted; show full)gsb-gga&ct=res&cd=1&ei=M2AqVeLzG-fq0AG5xYGACA&scisig=AAGBfm1aHrkKehQaYpPYGQ9mjRxVTxPS0Q|last1=Billi|first1=Daniela|last2=Viaggiu|first2=Emanuela|last3=Cockell|first3=Charles S.|last4=Rabbow|first4=Elke|last5=Horneck|first5=Gerda|last6=Onofri|first6=Silvano|title=Damage Escape and Repair in DriedChroococcidiopsisspp. from Hot and Cold Deserts Exposed to Simulated Space and Martian Conditions|journal=Astrobiology|volume=11|issue=1|year=2011|pages=65–73|issn=1531-1074|doi=10.1089/ast.2009.0430
|bibcode = 2011AsBio..11...65B }}</ref>
* '''''[[Halobacteria]]''''' - UV and radioresistant, photosynthetic (using a different mechanism), can form single species ecosystems, and highly salt tolerant. Some are tolerant of perchlorates and even use them as an energy source, examples include Haloferax mediterranei, Haloferax denitrificans, Haloferax gibbonsii, Haloarcula marismortui, and Haloarcula vallismortis <ref name=Oren/> 
(contracted; show full)==See also==
* [[Life on Mars]]

==References==
{{reflist}}

==External links==
* Three days long conference on the subject in 2013 [http://planets.ucla.edu/meetings/past-meetings/mars-habitability-2013/program/ The Present-Day Habitability of Mars 2013] under the auspices of the UCLA Institute for Planets and Exoplanets - with video archived for all the talks.