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Although the Modern Mars atmosphere is far too thin for fresh liquid water to be stable on its surface, except briefly in the depths of the Hellas Basin<ref name=Hellas/>. Salty percholrate brines, however, may be stable in Mars surface or near surface conditions. Modern Earth life is able to survive extreme conditions including extremes of aridity, and salinity. The surface of Mars is bathed in UV radiation which is sterilizing for microbial life, however this is easily blocked out by a shadow or a thin layer of dust.


== Do these habitats exist? ==
The Mars' surface is exposed to much more ultraviolet radiation than Earth's, and this is lethal to most forms of microbial life. However, this radiation is blocked by shadows or a layer of dust a fraction of a millimeter thick. The levels of ionizing radiation are such that 500 years of exposure would kill only 90% of even highly radiosensitive microbes. At only 0.6% of the pressure of Earth's atmosphere at the surface on average (0.01139 to 0.00030 atm), the Mars' current atmosphere is too thin for fresh water to exist in liquid form anywhere on the planet's surface except the Hellas Basin, and there, only for a short while, as it is close to boiling point<ref name=Hellas/>. Salty perchlorate brines, however, may remain stable under surface conditions or near-surface conditions, and depending on the composition, may be stable at temperatures warm enough to support Earth based life. <ref name="RummelBeaty2014SpecialRegionsConclusion"/>
There's a wide range of views on whether these habitats exist, especially so when it comes to potential surface microhabitats. Some astrobiologists consider that though these brines do exist, they are likely to be uninhabitable<ref name="Morais">[https://books.google.com/books?id=TZKeBQAAQBAJ&pg=PA153 Planetary Exploration and Science: Recent Results and Advances], Antonio de Morais M. Teles, page 153, 27 Nov 2014</ref><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">[http://www.astrobio.net/news-exclusive/how-habitable-is-mars-a-new-view-of-the-viking-experiments/ How Habitable Is Mars? A New View of the Viking Experiments] By Elizabeth Howell -Astrobiology Magazine (NASA) Nov 21, 2013</ref>. Others treat it it is an open question whether there are temporary habitats that could be recolonized from below,<ref name="Westall">[https://books.google.com/books?id=VYjEBAAAQBAJ&pg=PA192 Habitability of other planets and satellites - Habitability and Survival], Francis Westall, page 192, 30 Jul 2013{{quote|'''''"This presupposes that the ephemeral surface habitats could be colonized by viable life forms, that is, that a subsurface reservoir exists in which microbes could continue to metabolize and that, as noted above, the viable microbes could be transported into the short-lived habitat.... Although there are a large number of constraints on the continued survival of life in the subsurface of Mars, the astonishing biomass in the subsurface of Earth suggests that this scenario as a real possibility."'''''}}</ref>, or inhabited continuously on or near the surface<ref name="MorozovaMöhlmann2006">{{cite journal|url=http://epic.awi.de/14473/1/Mor2006e.pdf|last1=Morozova|first1=Daria|last2=Möhlmann|first2=Diedrich|last3=Wagner|first3=Dirk|title=Survival of Methanogenic 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|pmid=17160628|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="Crisler">{{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|pmid=22248384|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 name="Kilmer">{{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=1|year=2014|pages=69–80|issn=1473-5504|doi=10.1017/S1473550413000268|pmid=24748851|bibcode=2014IJAsB..13...69K}}</ref><ref name="Rummel">Rummel, J.D., Beaty, D.W., Jones, M.A., Bakermans, C., Barlow, N.G., Boston, P.J., Chevrier, V.F., Clark, B.C., de Vera, J.P.P., Gough, R.V. and Hallsworth, J.E., 2014. A new analysis of Mars “special regions”: findings of the second MEPAG Special Regions Science Analysis Group (SR-SAG2).{{quote|'''''"Claims that reducing planetary protection requirements wouldn't be harmful, because Earth life can't grow on Mars, may be reassuring as opinion, but the facts are that we keep discovering life growing in extreme conditions on Earth that resemble conditions on Mars. We also keep discovering conditions on Mars that are more similar—though perhaps only at microbial scales—to inhabited environments on Earth, which is where the concept of Special Regions initially came from."'''''}}</ref><ref name="Davila">Davila, A.F., Skidmore, M., Fairén, A.G., Cockell, C. and Schulze-Makuch, D., 2010. New priorities in the robotic exploration of Mars: the case for in situ search for extant life. Astrobiology, 10(7), pp.705-710.{{quote|'''''"We argue that the strategy for Mars exploration should center on the search for extant life. By extant life, we mean life that is active today or was active during the recent geological past and is now dormant. As we discuss below, the immediate strategy for Mars exploration cannot focus only on past life based on the result of the Viking missions, particularly given that recent analyses call for a re-evaluation of some of these results. It also cannot be based on the astsumption that the surface of Mars is uniformly prohibitive for extant life, since research contributed in the past 30 years in extreme environments on EArth has shown that life is possible under extremes of cold and dryness."'''''}}}</ref><ref name="Fairen">Fairén, A.G., Parro, V., Schulze-Makuch, D. and Whyte, L., 2017. [https://www.liebertpub.com/doi/full/10.1089/ast.2017.1703 Searching for life on Mars before it is too late]. Astrobiology, 17(10), pp.962-970.{{quote|'''''"The case of ExoMars is particularly dramatic as the first priority of the rover is to search for signs of past and present life on Mars ... however, it has been explicitly banned to go to Special Regions because it will not comply with the minimum cleanliness requirements. As a consequence, the billion-dollar life-seeking mission ExoMars will be allowed to search for life everywhere on Mars, except in the very places where we suspect that life may exist."'''''}}</ref><ref name="RummelConley">Rummel, J. D., Conley C. A, 2017,.[http://online.liebertpub.com/doi/full/10.1089/ast.2017.1749 Four fallacies and an oversight: searching for martian life] Astrobiology, 17(10), pp. 971-974.</ref>. 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">{{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">{{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>. 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">[http://www.gillevin.com/Mars/Reprint119-Miller-Straat-Levin-FINAL_files/Reprint119-Miller-Straat-Levin-FINAL.htm Periodic Analysis of the Viking Lander Labeled Release Experiment], [http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=894168 Proc. SPIE 4495, Instruments, Methods, and Missions for Astrobiology IV, 96 (February 6, 2002)]; {{DOI|10.1117/12.454748}}{{quote|"Did Viking Lander biology experiments detect life on Mars? ... Recent observations of circadian rhythmicity in microorganisms and entrainment of terrestrial circadian rhythms by low amplitude temperature cycles argue that a Martian circadian rhythm in the LR experiment may constitute a biosignature."}}</ref><ref name="Bianciardi-2012">{{cite journal |last=Bianciardi |first=Giorgio |last2=Miller |first2=Joseph D. |last3=Straat |first3=Patricia Ann |last4=Levin |first4=Gilbert V. |title=Complexity Analysis of the Viking Labeled Release Experiments |url=http://central.oak.go.kr/repository/journal/11315/HGJHC0_2012_v13n1_14.pdf|journal=IJASS |date=March 2012 |volume=13 |issue=1 |pages=14–26 |bibcode=2012IJASS..13...14B |doi=10.5139/IJASS.2012.13.1.14 |accessdate=2012-04-15|quote= These analyses support the interpretation that the Viking LR experiment did detect extant microbial life on Mars }}</ref><ref name="Levin2016">Levin, G.V. and Straat, P.A., 2016. The case for extant life on Mars and its possible detection by the Viking labeled release experiment. Astrobiology, 16(10), pp.798-810.{{quote|"'''''It is concluded that extant life is a strong possibility, that abiotic interpretations of the LR data are not conclusive, and that, even setting our conclusion aside, biology should still be considered as an explanation for the LR experiment. Because of possible contamination of Mars by terrestrial microbes after Viking, we note that the LR data are the only data we will ever have on biologically pristine martian samples'''''"}}</ref>. This would mean that much of the Martian surface is not only habitable but actually inhabited by some form of life. See [[Possible Present Day Habitats For Life On Mars# Views on the possibility of present day life on or near the surface|# Views on the possibility of present day life on or near the surface]].


Mars is the fourth planet from the Sun, after Mercury, Venus, and Earth. During the formation of the solar system, it cooled down before Earth did. There is some evidence that Mars once had a large body of water in its northern hemisphere, although it may have been covered with ice for much of the time. This evidence includes fossil [[River delta|deltas]] , with seventeen of them found at the altitude of a proposed shoreline for a Martian ocean<ref>{{cite journal | last1 = DiAchille | first1 = G | last2 = Hynek | first2 = B. | year = 2010 | title = Ancient ocean on Mars supported by global distribution of deltas and valleys. nat | url = | journal = Geosci | volume = 3 | issue = 7| pages = 459–463 | doi = 10.1038/ngeo891 | bibcode=2010NatGe...3..459D}}</ref> This is what would be expected if the deltas were all next to a large body of water.<ref>{{cite journal | last1 = DiBiasse | first1 = | last2 = Limaye | first2 = A. | last3 = Scheingross | first3 = J. | last4 = Fischer | first4 = W. | last5 = Lamb | first5 = M. | year = 2013 | title = Deltic deposits at Aeolis Dorsa: Sedimentary evidence for a standing body of water on the northern plains of Mars | url = | journal = [[Journal Of Geophysical Research: Planets]] | volume = 118 | issue = | pages = 1285–1302 }}</ref>, see [[Mars ocean hypothesis]]. In a press conference on December 8, 2014, Curiosity scientists presented evidence that Crater Lake once contained a huge lake that was filled and evaporated many times.<ref name="NASA-20141208">{{cite web |last=Brown |first=Dwayne |last2=Webster |first2=Guy |title=Release 14-326 - NASA’s Curiosity Rover Finds Clues to How Water Helped Shape Martian Landscape |url=http://www.nasa.gov/press/2014/december/nasa-s-curiosity-rover-finds-clues-to-how-water-helped-shape-martian-landscape/ |date=8 December 2014 |work=[[NASA]] |accessdate=8 December 2014}}</ref><ref name="NYT-20141208">{{cite news |last=Kaufmann |first=Marc |title=(Stronger) Signs of Life on Mars |url=https://www.nytimes.com/2014/12/09/science/-stronger-signs-of-life-on-mars.html |date=8 December 2014 |work=[[New York Times]] |accessdate=8 December 2014}}</ref><ref name="sciencedaily2">{{cite web|url=https://www.sciencedaily.com/releases/2014/12/141208122903.htm|archive-url=https://web.archive.org/web/20141213204457/https://www.sciencedaily.com/releases/2014/12/141208122903.htm |archive-date=2014-12-13 |dead-url=yes|title=NASA's Curiosity rover finds clues to how water helped shape Martian landscape -- ScienceDaily|accessdate=4 July 2015}}</ref><ref name="nasa">{{cite web|url=http://www.jpl.nasa.gov/video/details.php?id=1346|title=JPL &#124; Videos &#124; The Making of Mount Sharp|publisher=jpl.nasa.gov|accessdate=4 July 2015}}</ref><ref name="nasa2">{{cite web|url=http://www.jpl.nasa.gov/news/news.php?feature=4398|title=JPL &#124; News &#124; NASA&#039;s Curiosity Rover Finds Clues to How Water Helped Shape Martian Landscape|publisher=jpl.nasa.gov|accessdate=4 July 2015}}</ref><ref name="usgs">{{cite web|url=https://pubs.er.usgs.gov/publication/70047207|title=Martian fluvial conglomerates at Gale Crater|publisher=pubs.er.usgs.gov|accessdate=4 July 2015}}</ref><ref>{{cite journal |last1=Williams |first1=R. |display-authors=etal |year=2013 |title=Martian fluvial conglomerates at Gale Crater |url=|journal=Science |volume= 340| issue=|pages= 1068–1072| doi=10.1126/science.1237317 |pmid=23723230|bibcode=2013Sci...340.1068W}}</ref>, about 3 billion years ago. See [[Lakes on Mars#Gale Crater]]. From this, researchers have inferred that the thick atmosphere of early [[Noachian]] period Mars continued through to the intermediate [[Hesperian]] period (although it may have been intermittent, possibly released by volcanic activity [cite]). This created conditions that may have been suitable for life to evolve there in the past, or for life to be transferred from early Earth to inhabit early Mars during the large impacts of the Late Heavy Bombardment. The atmosphere almost vanished, however as it transitioned through to the [[Amazonian (Mars|Amazonian]] period which continues to the present day.
If these habitats do exist they could be inhabited. Life could have evolved on Mars in the past, as there is evidence that it was far more habitable in the past. There is evidence of an early [[Mars ocean hypothesis| Mars ocean]] covering most of the northern hemisphere<ref>{{cite journal | last1 = DiAchille | first1 = G | last2 = Hynek | first2 = B. | year = 2010 | title = Ancient ocean on Mars supported by global distribution of deltas and valleys. nat | url = | journal = Geosci | volume = 3 | issue = 7| pages = 459–463 | doi = 10.1038/ngeo891 | bibcode=2010NatGe...3..459D}}</ref><ref>{{cite journal | last1 = DiBiasse | first1 = | last2 = Limaye | first2 = A. | last3 = Scheingross | first3 = J. | last4 = Fischer | first4 = W. | last5 = Lamb | first5 = M. | year = 2013 | title = Deltic deposits at Aeolis Dorsa: Sedimentary evidence for a standing body of water on the northern plains of Mars | url = | journal = [[Journal Of Geophysical Research: Planets]] | volume = 118 | issue = | pages = 1285–1302 }}</ref>, and in December 2014, Curiosity scientists presented evidence that [[Lakes on Mars#Gale Crater|Gale Crater]] once contained a huge lake that was filled and evaporated many times.<ref name="NASA-20141208">{{cite web |last=Brown |first=Dwayne |last2=Webster |first2=Guy |title=Release 14-326 - NASA’s Curiosity Rover Finds Clues to How Water Helped Shape Martian Landscape |url=http://www.nasa.gov/press/2014/december/nasa-s-curiosity-rover-finds-clues-to-how-water-helped-shape-martian-landscape/ |date=8 December 2014 |work=[[NASA]] |accessdate=8 December 2014}}</ref><ref name="NYT-20141208">{{cite news |last=Kaufmann |first=Marc |title=(Stronger) Signs of Life on Mars |url=https://www.nytimes.com/2014/12/09/science/-stronger-signs-of-life-on-mars.html |date=8 December 2014 |work=[[New York Times]] |accessdate=8 December 2014}}</ref><ref name="sciencedaily2">{{cite web|url=https://www.sciencedaily.com/releases/2014/12/141208122903.htm|archive-url=https://web.archive.org/web/20141213204457/https://www.sciencedaily.com/releases/2014/12/141208122903.htm |archive-date=2014-12-13 |dead-url=yes|title=NASA's Curiosity rover finds clues to how water helped shape Martian landscape -- ScienceDaily|accessdate=4 July 2015}}</ref><ref name="nasa">{{cite web|url=http://www.jpl.nasa.gov/video/details.php?id=1346|title=JPL &#124; Videos &#124; The Making of Mount Sharp|publisher=jpl.nasa.gov|accessdate=4 July 2015}}</ref><ref name="nasa2">{{cite web|url=http://www.jpl.nasa.gov/news/news.php?feature=4398|title=JPL &#124; News &#124; NASA&#039;s Curiosity Rover Finds Clues to How Water Helped Shape Martian Landscape|publisher=jpl.nasa.gov|accessdate=4 July 2015}}</ref><ref name="usgs">{{cite web|url=https://pubs.er.usgs.gov/publication/70047207|title=Martian fluvial conglomerates at Gale Crater|publisher=pubs.er.usgs.gov|accessdate=4 July 2015}}</ref><ref>{{cite journal |last1=Williams |first1=R. |display-authors=etal |year=2013 |title=Martian fluvial conglomerates at Gale Crater |url=|journal=Science |volume= 340| issue=6136|pages= 1068–1072| doi=10.1126/science.1237317 |pmid=23723230|bibcode=2013Sci...340.1068W}}</ref>. This lake may have been habitable for life<ref>{{cite web |last1=Doyle - |first1=Amanda |title=Ancient Lake On Mars Was Hospitable Enough To Support Life |url=https://www.astrobio.net/news-exclusive/ancient-lake-mars-hospitable-enough-support-life/ |website=NASA Astrobiology Magazine |date=Sep 18, 2017}}</ref>. For more on this see [[Life on Mars]].


The habitats could also exist and be uninhabited, a possibility investigated by Charles Cockell in a series of papers. See [[#Uninhabited habitats|Uninhabited habitats]]
Most of the search for life on modern Mars has focused on microorganisms, although lichens are also possible there. On Earth, there are many life forms that can survive under extreme conditions, such as very arid, very salty, very acidic, and very hot and cold environments, and most of them are microbial. The Mars' surface is exposed to much more ultraviolet radiation than Earth's, and this is lethal to most forms of microbial life. However, this radiation is blocked by shadows or a layer of dust a fraction of a millimeter thick. The levels of ionizing radiation are such that 500 years of exposure would kill only 90% of even highly radiosensitive microbes. At only 0.6% of the pressure of Earth's atmosphere at the surface on average (0.01139 to 0.00030 atm), the Mars' current atmosphere is too thin for fresh water to exist in liquid form anywhere on the planet's surface except the Hellas Basin, and there, only for a short while, as it is close to boiling point<ref name=Hellas/>. Salty perchlorate brines, however, may remain stable under surface conditions or near-surface conditions, and depending on the composition, may be stable at temperatures warm enough to support Earth based life. <ref name="RummelBeaty2014SpecialRegionsConclusion"/> It is also possible that Mars has life adapted to lower temperatures than Earth microbes, with perchlorates and hydrogen peroxide in place of the chlorides of Earth life, as an "antifreeze"

The Modern Mars atmosphere is far too thin for fresh liquid water to be stable on its surface, except briefly in the depths of the Hellas Basin<ref name=Hellas/>. Salty percholrate brines, however, may be stable in Mars surface or near surface conditions. Modern Earth life is able to survive extreme conditions including extremes of aridity, and salinity. The surface of Mars is bathed in UV radiation which is sterilizing for microbial life, however this is easily blocked out by a shadow or a thin layer of dust. The ionizing radiation at the surface has been found to be attenuated to the levels where 500 years of radiation would kill only 90% of even the most radiosensitive microbes<ref name="RummelBeaty2014SpecialRegionsConclusion"/>. The perchlorate salts themselves are harmful to some forms of life but they serve as an oxidant, as part of their metabolic processes for others, in essence, a form of "food".<ref name=Oren>{{cite journal | doi = 10.2166/wst.2009.635 | volume=60 | title=Molecular assessment of salt-tolerant, perchlorate- and nitrate-reducing microbial cultures | year=2009 | journal=Water Science & Technology | page=1745 | last1 = Zuo | first1 = G. | last2 = Roberts | first2 = D. J. | last3 = Lehman | first3 = S. G. | last4 = Jackson | first4 = G. W. | last5 = Fox | first5 = G. E. | last6 = Willson | first6 = R. C.|pmid=24150694}}</ref>. Cassie Connley, planetary protection officer for NASA from 2006 to 2018, put it like this, when interviewed by the New York Times:<ref>{{cite news|last1=Chang|first1=Kenneth|title=Mars Is Pretty Clean. Her Job at NASA Is to Keep It That Way.|url=https://www.nytimes.com/2015/10/06/science/mars-catharine-conley-nasa-planetary-protection-officer.html|agency=New York Times|date=October 5, 2015}}</ref>:
== Conferences on the topic of present day habitats for life on Mars ==
{{quote|"The salts known as perchlorates that lower the freezing temperature of water at the R.S.L.s, keeping it liquid, can be consumed by some Earth microbes. “The environment on Mars potentially is basically one giant dinner plate for Earth organisms,” Dr. Conley said."}}
* 2013, February 4-6, conference on the ''Present Day Habitability of Mars'' was held in 2013 in UCLA.<ref>{{cite web|last1=David Paige and Charles Cockell|title=Report to MEPAG on The Present-Day Habitability of Mars Workshop|url=https://mepag.jpl.nasa.gov/meeting/2013-02/present_day_habitability_mepag_report.pdf}}</ref><ref>{{cite web|last1=CASE|first1=ELIZABETH|title=UCLA holds Mars habitability conference|url=http://dailybruin.com/2013/02/07/ucla-holds-mars-habitability-conference/|website=Daily Bruin}}</ref><ref name="PresentDayHabitability">{{cite web|author1=UCLA Institute for Planets and Exoplanets, The UK Center for Astrobiology and the NASA Astrobiology Institute|title=The Present-Day Habitability of Mars 2013 - Includes link to video recordings of the talks which you can stream online|url=http://planets.ucla.edu/meetings/past-meetings/pdhm2013/|website=UCLA Institute for Planets and Exoplanets|date=February 4–6, 2013}}</ref>.
This leads to the question of whether there are any habitats for life on Mars. If there are then there may be life there that has survived since the times of early Mars when it was far more habitable than it is now.{{cn|date=August 2018}}<!--will be adding cites-->
* 2017, April 24-29 conference sub session on ''Modern Mars Habitability'', Mesa, Arizona, organized by the NASA Ames Research Center, and LPL, University of Arizona, as part of the Astrobiology Science Conference 2017 <ref name="ModernMarsHabitability">{{cite web|title=Astrobiology Science Conference Session on Modern Mars Habitability|url=http://www.lpi.usra.edu/planetary_news/2016/12/28/astrobiology-science-conference-session-on-the-modern-mars-habitability/|website=Lunar and Planetary Institute}} organized by Carol Stoker, NASA Ames Research Center, and Alfred McEwen, LPI, University of Arizona, April 24–28, 2017, [https://www.hou.usra.edu/meetings/abscicon2017/program-abstracts/topics/ Session details: one subsession on Modern Mars Habitability and three on biomarkers]</ref>.
* 2019, January 20 - February 1: ''Mars Extant Life: What’s Next?''" to discuss the "numerous extant life hypotheses that have been advanced over the years and that have evolved in response to discoveries by on-going Mars missions."<ref>[https://www.hou.usra.edu/meetings/lifeonmars2019/ Mars Extant Life: What’s Next? scheduled for January 29–February 1, 2019] at the National Cave and Karst Research Institute, 400-1 Cascades Ave., Carlsbad, New Mexico.</ref>

==Mars surface conditions simulation chambers==
These chambers simulate the Martian day night cycle and other conditions of the Martian surface, with the goal to investigate the present day habitability of Mars. It's especially important to simulate the temperature and pressure variations because, though the amount of water vapour in the Mars atmosphere is low, at night the atmosphere becomes so cold that the relative humidity approaches 100%, which is of significance for any life that may be there. The chambers also have to simulate the Martian sunlight which has much less UV light filtered out than Earth sunlight. This is sterilizing over short timescales to any unprotected life directly exposed to the sunlight.

The Michigan Mars Environmental Chamber<ref name="MicheganMars2">https://www.researchgate.net/publication/283504377_The_Michigan_Mars_Environmental_Chamber_Preliminary_Results_and_Capabilities</ref> is run by Nilton Renno<ref name="NiltonRennoFaculty2">[http://clasp.engin.umich.edu/people/nrenno/FACULTY Nilton Renno - Faculty page], Mitchigen State University - Honors, Awards and Accomplishments, and Publications, etc</ref> and his team:{{quote|1=Introduction: We have developed the Michigan Mars Environmental Chamber (MMEC) to simulate the entire range of Martian surface and shallow subsurface conditions with respect to temperature, pressure, relative humidity, solar radiation and soil wetness. Our goal is to simulate the Martian diurnal cycle for equatorial as well as polar Martian conditions and test the hypothesis that salts known to exist in the Martian regolith can deliquesce and form brine pockets or layers by freeze-thaw cycles. Motivation: Liquid water is one of the necessary ingredients for the development of life as we know it. ... It has been shown that liquid brines are ubiquitous in the Martian polar regions and microbial communities have been seen to survive under similar conditions in Antarctica's Dry Valleys.|sign=|source=}}The Mars Simulation Facility-Laboratory at the German Aerospace facilities (DLR) in Berlin<ref name="DLRMarsSimuulationFacilityLaboratory">[https://www.dlr.de/pf/en/desktopdefault.aspx/tabid-178/327_read-37506/ The Mars Simulation Facility-Laboratory], German Aerospace Center (DLR), Berlin</ref> is run by Jean-Pierre de Vera<ref name="deVeraProfile">[https://www.researchgate.net/profile/Jean-Pierre_de_Vera Jean-Pierre de Vera] profile at research gate</ref> used for numerous astrobiological Mars habitability studies<ref name=":0">Google scholar search for: [https://scholar.google.co.uk/scholar?hl=en&as_sdt=0%2C5&q=Mars+Simulation+Facility+Laboratory+dlr+mars+habitability&btnG= Mars Simulation Facility Laboratory DLR Mars habitability] for some of the many experiments in modern Mars habitability using the DLR facilities</ref>. as part of HOME (Habitability of Mars Environments)<ref name="HOME">[https://www.dlr.de/pf/en/desktopdefault.aspx/tabid-10881/19035_read-44438/ HOME: Habitability of Martian Environments: Exploring the Physiological and Environmental Limits of Life] Mars Simulation Facility-Laboratory at the German Aerospace faciliites (DLR) in Berlin run by Jean-Pierre de Vera</ref>

"used for different astrobiological and physical experiments to simulate the key environmental conditions like pressure, temperature, radiation, gas composition, and primarily also the diurnally varying atmospheric humidity in a range from earth conditions to similar to those at the near-surface atmosphere of Martian mid- and low latitude" run by Jean-Pierre de Vera<ref name="deVeraProfile" /> used for numerous astrobiological Mars habitability studies<ref name=":0" />.

Latest revision as of 00:27, 15 January 2019

Do these habitats exist?[edit | hide | hide all]

There's a wide range of views on whether these habitats exist, especially so when it comes to potential surface microhabitats. Some astrobiologists consider that though these brines do exist, they are likely to be uninhabitable[1][2][3]. Others treat it it is an open question whether there are temporary habitats that could be recolonized from below,[4], or inhabited continuously on or near the surface[5][6][7][8][9][10][11]. 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[12][13]. 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[14][15][16]. 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.

If these habitats do exist they could be inhabited. Life could have evolved on Mars in the past, as there is evidence that it was far more habitable in the past. There is evidence of an early Mars ocean covering most of the northern hemisphere[17][18], and in December 2014, Curiosity scientists presented evidence that Gale Crater once contained a huge lake that was filled and evaporated many times.[19][20][21][22][23][24][25]. This lake may have been habitable for life[26]. For more on this see Life on Mars.

The habitats could also exist and be uninhabited, a possibility investigated by Charles Cockell in a series of papers. See Uninhabited habitats

Conferences on the topic of present day habitats for life on Mars[edit | hide]

  • 2013, February 4-6, conference on the Present Day Habitability of Mars was held in 2013 in UCLA.[27][28][29].
  • 2017, April 24-29 conference sub session on Modern Mars Habitability, Mesa, Arizona, organized by the NASA Ames Research Center, and LPL, University of Arizona, as part of the Astrobiology Science Conference 2017 [30].
  • 2019, January 20 - February 1: Mars Extant Life: What’s Next?" to discuss the "numerous extant life hypotheses that have been advanced over the years and that have evolved in response to discoveries by on-going Mars missions."[31]

Mars surface conditions simulation chambers[edit | hide]

These chambers simulate the Martian day night cycle and other conditions of the Martian surface, with the goal to investigate the present day habitability of Mars. It's especially important to simulate the temperature and pressure variations because, though the amount of water vapour in the Mars atmosphere is low, at night the atmosphere becomes so cold that the relative humidity approaches 100%, which is of significance for any life that may be there. The chambers also have to simulate the Martian sunlight which has much less UV light filtered out than Earth sunlight. This is sterilizing over short timescales to any unprotected life directly exposed to the sunlight.

The Michigan Mars Environmental Chamber[32] is run by Nilton Renno[33] and his team:

Introduction: We have developed the Michigan Mars Environmental Chamber (MMEC) to simulate the entire range of Martian surface and shallow subsurface conditions with respect to temperature, pressure, relative humidity, solar radiation and soil wetness. Our goal is to simulate the Martian diurnal cycle for equatorial as well as polar Martian conditions and test the hypothesis that salts known to exist in the Martian regolith can deliquesce and form brine pockets or layers by freeze-thaw cycles. Motivation: Liquid water is one of the necessary ingredients for the development of life as we know it. ... It has been shown that liquid brines are ubiquitous in the Martian polar regions and microbial communities have been seen to survive under similar conditions in Antarctica's Dry Valleys.

The Mars Simulation Facility-Laboratory at the German Aerospace facilities (DLR) in Berlin[34] is run by Jean-Pierre de Vera[35] used for numerous astrobiological Mars habitability studies[36]. as part of HOME (Habitability of Mars Environments)[37]

"used for different astrobiological and physical experiments to simulate the key environmental conditions like pressure, temperature, radiation, gas composition, and primarily also the diurnally varying atmospheric humidity in a range from earth conditions to similar to those at the near-surface atmosphere of Martian mid- and low latitude" run by Jean-Pierre de Vera[35] used for numerous astrobiological Mars habitability studies[36].

  1. ↑ Planetary Exploration and Science: Recent Results and Advances, Antonio de Morais M. Teles, page 153, 27 Nov 2014
  2. ↑ Plaxco, Kevin W.; Gross, Michael (2011-08-12). Astrobiology: A Brief Introduction. JHU Press. pp. 285–286. ISBN 978-1-4214-0194-2. Retrieved 2013-07-16. 
  3. ↑ How Habitable Is Mars? A New View of the Viking Experiments By Elizabeth Howell -Astrobiology Magazine (NASA) Nov 21, 2013
  4. ↑ Habitability of other planets and satellites - Habitability and Survival, Francis Westall, page 192, 30 Jul 2013

    "This presupposes that the ephemeral surface habitats could be colonized by viable life forms, that is, that a subsurface reservoir exists in which microbes could continue to metabolize and that, as noted above, the viable microbes could be transported into the short-lived habitat.... Although there are a large number of constraints on the continued survival of life in the subsurface of Mars, the astonishing biomass in the subsurface of Earth suggests that this scenario as a real possibility."

  5. ↑ Morozova, Daria; Möhlmann, Diedrich; Wagner, Dirk (2006). "Survival of Methanogenic Archaea from Siberian Permafrost under Simulated Martian Thermal Conditions" (PDF). Origins of Life and Evolution of Biospheres. 37 (2): 189–200. Bibcode:2007OLEB...37..189M. doi:10.1007/s11084-006-9024-7. ISSN 0169-6149. PMID 17160628. 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. 
  6. ↑ Crisler, J.D.; Newville, T.M.; Chen, F.; Clark, B.C.; Schneegurt, M.A. (2012). "Bacterial Growth at the High Concentrations of Magnesium Sulfate Found in Martian Soils". Astrobiology. 12 (2): 98–106. Bibcode:2012AsBio..12...98C. doi:10.1089/ast.2011.0720. ISSN 1531-1074. PMC 3277918 Freely accessible. PMID 22248384. 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 
  7. ↑ Kilmer, Brian R.; Eberl, Timothy C.; Cunderla, Brent; Chen, Fei; Clark, Benton C.; Schneegurt, Mark A. (2014). "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". International Journal of Astrobiology. 13 (1): 69–80. Bibcode:2014IJAsB..13...69K. doi:10.1017/S1473550413000268. ISSN 1473-5504. PMC 3989109 Freely accessible. PMID 24748851. 
  8. ↑ Rummel, J.D., Beaty, D.W., Jones, M.A., Bakermans, C., Barlow, N.G., Boston, P.J., Chevrier, V.F., Clark, B.C., de Vera, J.P.P., Gough, R.V. and Hallsworth, J.E., 2014. A new analysis of Mars “special regions”: findings of the second MEPAG Special Regions Science Analysis Group (SR-SAG2).

    "Claims that reducing planetary protection requirements wouldn't be harmful, because Earth life can't grow on Mars, may be reassuring as opinion, but the facts are that we keep discovering life growing in extreme conditions on Earth that resemble conditions on Mars. We also keep discovering conditions on Mars that are more similar—though perhaps only at microbial scales—to inhabited environments on Earth, which is where the concept of Special Regions initially came from."

  9. ↑ Davila, A.F., Skidmore, M., Fairén, A.G., Cockell, C. and Schulze-Makuch, D., 2010. New priorities in the robotic exploration of Mars: the case for in situ search for extant life. Astrobiology, 10(7), pp.705-710.

    "We argue that the strategy for Mars exploration should center on the search for extant life. By extant life, we mean life that is active today or was active during the recent geological past and is now dormant. As we discuss below, the immediate strategy for Mars exploration cannot focus only on past life based on the result of the Viking missions, particularly given that recent analyses call for a re-evaluation of some of these results. It also cannot be based on the astsumption that the surface of Mars is uniformly prohibitive for extant life, since research contributed in the past 30 years in extreme environments on EArth has shown that life is possible under extremes of cold and dryness."

    }
  10. ↑ Fairén, A.G., Parro, V., Schulze-Makuch, D. and Whyte, L., 2017. Searching for life on Mars before it is too late. Astrobiology, 17(10), pp.962-970.

    "The case of ExoMars is particularly dramatic as the first priority of the rover is to search for signs of past and present life on Mars ... however, it has been explicitly banned to go to Special Regions because it will not comply with the minimum cleanliness requirements. As a consequence, the billion-dollar life-seeking mission ExoMars will be allowed to search for life everywhere on Mars, except in the very places where we suspect that life may exist."

  11. ↑ Rummel, J. D., Conley C. A, 2017,.Four fallacies and an oversight: searching for martian life Astrobiology, 17(10), pp. 971-974.
  12. ↑ de Vera, Jean-Pierre; Schulze-Makuch, Dirk; Khan, Afshin; Lorek, Andreas; Koncz, Alexander; Möhlmann, Diedrich; Spohn, Tilman (2014). "Adaptation of an Antarctic lichen to Martian niche conditions can occur within 34 days". Planetary and Space Science. 98: 182–190. Bibcode:2014P&SS...98..182D. doi:10.1016/j.pss.2013.07.014. ISSN 0032-0633. 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 
  13. ↑ Zakharova, Kristina; Marzban, Gorji; de Vera, Jean-Pierre; Lorek, Andreas; Sterflinger, Katja (2014). "Protein patterns of black fungi under simulated Mars-like conditions". Scientific Reports. 4: 5114. Bibcode:2014NatSR...4E5114Z. doi:10.1038/srep05114. ISSN 2045-2322. PMC 4037706 Freely accessible. PMID 24870977. The results achieved from our study led to the conclusion that black microcolonial fungi can survive in Mars environment. 
  14. ↑ Periodic Analysis of the Viking Lander Labeled Release Experiment, Proc. SPIE 4495, Instruments, Methods, and Missions for Astrobiology IV, 96 (February 6, 2002); doi:10.1117/12.454748

    "Did Viking Lander biology experiments detect life on Mars? ... Recent observations of circadian rhythmicity in microorganisms and entrainment of terrestrial circadian rhythms by low amplitude temperature cycles argue that a Martian circadian rhythm in the LR experiment may constitute a biosignature."

  15. ↑ Bianciardi, Giorgio; Miller, Joseph D.; Straat, Patricia Ann; Levin, Gilbert V. (March 2012). "Complexity Analysis of the Viking Labeled Release Experiments" (PDF). IJASS. 13 (1): 14–26. Bibcode:2012IJASS..13...14B. doi:10.5139/IJASS.2012.13.1.14. Retrieved 2012-04-15. These analyses support the interpretation that the Viking LR experiment did detect extant microbial life on Mars 
  16. ↑ Levin, G.V. and Straat, P.A., 2016. The case for extant life on Mars and its possible detection by the Viking labeled release experiment. Astrobiology, 16(10), pp.798-810.

    "It is concluded that extant life is a strong possibility, that abiotic interpretations of the LR data are not conclusive, and that, even setting our conclusion aside, biology should still be considered as an explanation for the LR experiment. Because of possible contamination of Mars by terrestrial microbes after Viking, we note that the LR data are the only data we will ever have on biologically pristine martian samples"

  17. ↑ DiAchille, G; Hynek, B. (2010). "Ancient ocean on Mars supported by global distribution of deltas and valleys. nat". Geosci. 3 (7): 459–463. Bibcode:2010NatGe...3..459D. doi:10.1038/ngeo891. 
  18. ↑ DiBiasse; Limaye, A.; Scheingross, J.; Fischer, W.; Lamb, M. (2013). "Deltic deposits at Aeolis Dorsa: Sedimentary evidence for a standing body of water on the northern plains of Mars". Journal Of Geophysical Research: Planets. 118: 1285–1302. 
  19. ↑ Brown, Dwayne; Webster, Guy (8 December 2014). "Release 14-326 - NASA's Curiosity Rover Finds Clues to How Water Helped Shape Martian Landscape". NASA. Retrieved 8 December 2014. 
  20. ↑ Kaufmann, Marc (8 December 2014). "(Stronger) Signs of Life on Mars". New York Times. Retrieved 8 December 2014. 
  21. ↑ "NASA's Curiosity rover finds clues to how water helped shape Martian landscape -- ScienceDaily". Archived from the original on 2014-12-13. Retrieved 4 July 2015. 
  22. ↑ "JPL | Videos | The Making of Mount Sharp". jpl.nasa.gov. Retrieved 4 July 2015. 
  23. ↑ "JPL | News | NASA's Curiosity Rover Finds Clues to How Water Helped Shape Martian Landscape". jpl.nasa.gov. Retrieved 4 July 2015. 
  24. ↑ "Martian fluvial conglomerates at Gale Crater". pubs.er.usgs.gov. Retrieved 4 July 2015. 
  25. ↑ Williams, R.; et al. (2013). "Martian fluvial conglomerates at Gale Crater". Science. 340 (6136): 1068–1072. Bibcode:2013Sci...340.1068W. doi:10.1126/science.1237317. PMID 23723230. 
  26. ↑ Doyle -, Amanda (Sep 18, 2017). "Ancient Lake On Mars Was Hospitable Enough To Support Life". NASA Astrobiology Magazine. 
  27. ↑ David Paige and Charles Cockell. "Report to MEPAG on The Present-Day Habitability of Mars Workshop" (PDF). 
  28. ↑ CASE, ELIZABETH. "UCLA holds Mars habitability conference". Daily Bruin. 
  29. ↑ UCLA Institute for Planets and Exoplanets, The UK Center for Astrobiology and the NASA Astrobiology Institute (February 4–6, 2013). "The Present-Day Habitability of Mars 2013 - Includes link to video recordings of the talks which you can stream online". UCLA Institute for Planets and Exoplanets. 
  30. ↑ "Astrobiology Science Conference Session on Modern Mars Habitability". Lunar and Planetary Institute.  organized by Carol Stoker, NASA Ames Research Center, and Alfred McEwen, LPI, University of Arizona, April 24–28, 2017, Session details: one subsession on Modern Mars Habitability and three on biomarkers
  31. ↑ Mars Extant Life: What’s Next? scheduled for January 29–February 1, 2019 at the National Cave and Karst Research Institute, 400-1 Cascades Ave., Carlsbad, New Mexico.
  32. ↑ https://www.researchgate.net/publication/283504377_The_Michigan_Mars_Environmental_Chamber_Preliminary_Results_and_Capabilities
  33. ↑ Nilton Renno - Faculty page, Mitchigen State University - Honors, Awards and Accomplishments, and Publications, etc
  34. ↑ The Mars Simulation Facility-Laboratory, German Aerospace Center (DLR), Berlin
  35. ↑ 35.0 35.1 Jean-Pierre de Vera profile at research gate
  36. ↑ 36.0 36.1 Google scholar search for: Mars Simulation Facility Laboratory DLR Mars habitability for some of the many experiments in modern Mars habitability using the DLR facilities
  37. ↑ HOME: Habitability of Martian Environments: Exploring the Physiological and Environmental Limits of Life Mars Simulation Facility-Laboratory at the German Aerospace faciliites (DLR) in Berlin run by Jean-Pierre de Vera
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