Life on Mars: Difference between revisions
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{{Life in the Universe}}
The possibility of '''life on [[Mars]]''' is a subject of significant interest to [[astrobiology]] due to the planet's proximity and similarities to [[Earth]]. To date no proof has been found of past or present life on Mars. However,
Scientific searches for evidence of life began in the 19th century, and they continue today via telescopic investigations and landed missions. While early work focused on phenomenology and bordered on fantasy, modern [[Models of scientific inquiry|scientific inquiry]] has emphasized the search for [[Water on Mars|water]], chemical [[biosignature]]s in the soil and rocks at the planet's surface, and [[biomarker]] gases in the atmosphere.<ref>{{cite conference|url=https://ntrs.nasa.gov/search.jsp?R=20120003707 |title=The Search for Life on Mars |last=Mumma |first=Michael J. |date=January 8, 2012 |conference=Origin of Life Gordon Research Conference |location=Galveston, TX |deadurl=no |archiveurl=https://web.archive.org/web/20160604111239/https://ntrs.nasa.gov/search.jsp?R=20120003707 |archivedate=June 4, 2016 }}</ref><ref name="NYT-20160912">{{cite news|last=Chang |first=Kenneth |title=Visions of Life on Mars in Earth’s Depths |url=https://www.nytimes.com/2016/09/13/science/south-african-mine-life-on-mars.html |date=September 12, 2016 |work=[[New York Times]] |accessdate=September 12, 2016 |deadurl=no |archiveurl=https://web.archive.org/web/20160912225220/http://www.nytimes.com/2016/09/13/science/south-african-mine-life-on-mars.html |archivedate=September 12, 2016 }}</ref> On November 22, 2016, NASA reported finding a large amount of [[Water on Mars|underground ice]] in the [[Utopia Planitia]] region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in [[Lake Superior]].<ref name="NASA-20161122">{{cite web|author=Staff |title=Scalloped Terrain Led to Finding of Buried Ice on Mars |url=http://photojournal.jpl.nasa.gov/catalog/PIA21136 |date=November 22, 2016 |work=[[NASA]] |accessdate=November 23, 2016 |deadurl=no |archiveurl=https://web.archive.org/web/20161124094205/http://photojournal.jpl.nasa.gov/catalog/PIA21136 |archivedate=November 24, 2016 }}</ref><ref name="Register-2016">{{cite web|url=https://www.theregister.co.uk/2016/11/22/nasa_finds_ice_under_martian_surface/ |title=Lake of frozen water the size of New Mexico found on Mars – NASA |publisher=The Register |date=November 22, 2016 |accessdate=November 23, 2016 |deadurl=no |archiveurl=https://web.archive.org/web/20161123120850/http://www.theregister.co.uk/2016/11/22/nasa_finds_ice_under_martian_surface/ |archivedate=November 23, 2016 }}</ref><ref name="NASA-20161122jpl">{{cite web|url=http://www.jpl.nasa.gov/news/news.php?release=2016-299 |title=Mars Ice Deposit Holds as Much Water as Lake Superior |publisher=NASA |date=November 22, 2016 |accessdate=November 23, 2016 |deadurl=no |archiveurl=https://web.archive.org/web/20161123145052/http://www.jpl.nasa.gov/news/news.php?release=2016-299 |archivedate=November 23, 2016 }}</ref>
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Mars is of particular interest for the study of the origins of life because of its similarity to the early Earth. This is especially so since Mars has a cold climate and lacks [[plate tectonics]] or [[continental drift]], so it has remained almost unchanged since the end of the [[Hesperian]] period. At least two thirds of Mars's surface is more than 3.5 billion years old, and Mars may thus hold the best record of the prebiotic conditions leading to [[abiogenesis]], even if life does not or has never existed there.<ref>{{cite journal |doi=10.1029/RG027i002p00189 |title=The early environment and its evolution on Mars: Implication for life |date=1989 |last=McKay |first=Christopher P. |last2=Stoker |first2=Carol R. |journal=Reviews of Geophysics |volume=27 |issue=2 |pages=189–214|bibcode = 1989RvGeo..27..189M }}</ref><ref name="Fromproto">{{cite journal |bibcode=2007prpl.conf..929G |arxiv=astro-ph/0602008 |title=From Protoplanets to Protolife: The Emergence and Maintenance of Life |last=Gaidos |first=Eric |last2=Selsis |first2=Franck |date=2007 |pages=929–44 |journal=Protostars and Planets V}}</ref> In May 2017, evidence of the [[Earliest known life forms|earliest known life]] [[Evolutionary history of life#Colonization of land|on land]] on Earth may have been found in 3.48-billion-year-old [[geyserite]] and other related mineral deposits (often found around [[hot spring]]s and [[geyser]]s) uncovered in the [[Pilbara Craton]] of [[Western Australia]].<ref name="PO-20170509">{{cite news|author=Staff |title=Oldest evidence of life on land found in 3.48-billion-year-old Australian rocks |url=https://phys.org/news/2017-05-oldest-evidence-life-billion-year-old-australian.html |date=May 9, 2017 |work=[[Phys.org]] |accessdate=May 13, 2017 |deadurl=no |archiveurl=https://web.archive.org/web/20170510013721/https://phys.org/news/2017-05-oldest-evidence-life-billion-year-old-australian.html |archivedate=May 10, 2017 }}</ref><ref name="NC-20170509">{{cite journal|last1=Djokic |first1=Tara |last2=Van Kranendonk |first2=Martin J. |last3=Campbell |first3=Kathleen A. |last4=Walter |first4=Malcolm R. |last5=Ward |first5=Colin R. |title=Earliest signs of life on land preserved in ca. 3.5 Ga hot spring deposits |url=https://www.nature.com/articles/ncomms15263 |date=May 9, 2017 |journal=[[Nature Communications]] |doi=10.1038/ncomms15263 |accessdate=May 13, 2017 |volume=8 |page=15263 |deadurl=no |archiveurl=https://web.archive.org/web/20170518082609/https://www.nature.com/articles/ncomms15263 |archivedate=May 18, 2017 |bibcode = 2017NatCo...815263D }}</ref> These findings may be helpful in deciding where best to search for [[Abiogenesis|early signs of life]] on the planet Mars.<ref name="PO-20170509" /><ref name="NC-20170509" />
The search for Life on Mars past and present is the first of [[NASA]]’S four science goals<ref>Hamilton, V.E., Rafkin, S., Withers, P., Ruff, S., Yingst, R.A., Whitley, R., Center, J.S., Beaty, D.W., Diniega, S., Hays, L. and Zurek, R., [https://mepag.jpl.nasa.gov/reports/MEPAG%20Goals_Document_2015_v18_FINAL.pdf Mars Science Goals, Objectives, Investigations, and Priorities: 2015 Version]</ref>:
{{quote|Goal I: determine if Mars ever supported life
* Objective A: determine if environments having high potential for prior habitability and preservation of biosignatures contain evidence of past life.
* Objective B: determine if environments with high potential for current habitability and expression of biosignatures contain evidence of extant life."
}}
This includes the search for evidence of [[Planetary habitability|habitability]], [[taphonomy]] (related to [[fossils]]), and [[organic carbon]] on the planet [[Mars]].<ref name="SCI-20140124a" />
== Early speculation ==
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The UV radiation is biocidal but can be shielded by a millimeter thickness of regolith<ref name="D.C.Golden"/>.
{| class="wikitable"
! style="align: center; background: lavender;" colspan="2" | '''Habitability factors'''<ref name="Beaty" />
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== Forward contamination ==
{{Details|Planetary protection}}
[[Planetary protection]] of Mars aims to prevent biological contamination of the planet.<ref name="strategy">{{cite book | author1=Committee on an Astrobiology Strategy for the Exploration of Mars | author2=National Research Council | date=2007 | chapter=Planetary Protection for Mars Missions | chapterurl=http://www.nap.edu/openbook.php?record_id=11937&page=95 | pages=95–98 | title=An Astrobiology Strategy for the Exploration of Mars | publisher=The National Academies Press | isbn=978-0-309-10851-5 }}</ref>
The prime concern of hardware contaminating Mars derives from incomplete spacecraft sterilization of some hardy terrestrial bacteria ([[extremophiles]]) despite best efforts.<ref name="Beaty" /><ref name="Debus">{{cite journal | bibcode=2005AdSpR..35.1648D | title=Estimation and assessment of Mars contamination | last=Debus | first=A. | volume=35 | date=2005 | pages=1648–53 | journal=Advances in Space Research | doi=10.1016/j.asr.2005.04.084 | pmid=16175730 | issue=9}}</ref> Hardware includes landers, crashed probes, end-of-mission disposal of hardware, and hard landing of entry, descent, and landing systems. This has prompted research on survival rates of [[Radioresistance|radiation-resistant microorganisms]] including the species ''[[Deinococcus radiodurans]]'' and genera ''[[Brevundimonas]]'', ''[[Rhodococcus]]'', and ''[[Pseudomonas]]'' under simulated Martian conditions.<ref name="Planetary protection – radiodurans">{{cite journal |bibcode=2010AsBio..10..717D |title=Low-Temperature Ionizing Radiation Resistance of Deinococcus radiodurans and Antarctic Dry Valley Bacteria |last=Dartnell |first=Lewis R. |last2=Hunter |first2=Stephanie J. |last3=Lovell |first3=Keith V. |last4=Coates |first4=Andrew J. |last5=Ward |first5=John M. |volume=10 |date=2010 |pages=717–32 |journal=Astrobiology |doi=10.1089/ast.2009.0439 |pmid=20950171 |issue=7}}</ref> Results from one of these experimental irradiation experiments, combined with previous radiation modeling, indicate that ''[[Brevundimonas]]'' sp. MV.7 emplaced only 30 cm deep in Martian dust could survive the cosmic radiation for up to 100,000 years before suffering 10⁶ population reduction.<ref name="Planetary protection – radiodurans" /> Surprisingly, the diurnal Mars-like cycles in temperature and relative humidity affected the viability of ''Deinococcus radiodurans'' cells quite severely.<ref name="simulation">{{cite journal |bibcode=2007AdSpR..40.1672D |title=Simulation of the environmental climate conditions on martian surface and its effect on ''Deinococcus radiodurans'' | last=de la Vega | first=U. Pogoda | last2=Rettberg | first2=P. | last3=Reitz | first3=G. |volume=40 |date=2007 |pages=1672–7 |journal=Advances in Space Research |doi=10.1016/j.asr.2007.05.022 |issue=11}}</ref> In other simulations,
</ref>
== Life under simulated Martian conditions ==
On 26 April 2012, scientists reported that an [[extremophile]] [[lichen]] survived and showed remarkable results on the [[adaptive capacity|adaptation capacity]] of [[photosynthesis|photosynthetic activity]] within the [[simulation]] time of 34 days under Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the [[German Aerospace Center]] (DLR).<ref name="lab_study">{{cite journal |bibcode=2010AsBio..10..215D |title=Survival Potential and Photosynthetic Activity of Lichens Under Mars-Like Conditions: A Laboratory Study |last=de Vera |first=Jean-Pierre |last2=Möhlmann |first2=Diedrich |last3=Butina |first3=Frederike |last4=Lorek |first4=Andreas |last5=Wernecke |first5=Roland |last6=Ott |first6=Sieglinde |volume=10 |date=2010 |pages=215–27 |journal=Astrobiology |doi=10.1089/ast.2009.0362 |pmid=20402583 |issue=2}}</ref><ref name="EGU-20120426">{{cite journal |bibcode=2012EGUGA..14.2113D |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |last=de Vera |first=J.-P. P. |last2=Schulze-Makuch |first2=D. |last3=Khan |first3=A. |last4=Lorek |first4=A. |last5=Koncz |first5=A. |last6=Möhlmann |first6=D. |last7=Spohn |first7=T. |volume=14 |date=2012 |pages=2113 |journal=EGU General Assembly 2012}}</ref><ref name="dlrMarsStudy">{{cite web|url=http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-3409/ |title=Surviving the conditions on Mars |publisher=DLR |date=April 26, 2012 |deadurl=no |archiveurl=https://web.archive.org/web/20121113081036/http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-3409/ |archivedate=November 13, 2012 }}</ref><ref name="fungal">{{cite journal |doi=10.1016/j.funeco.2012.01.008 |title=Lichens as survivors in space and on Mars |date=2012 |last=de Vera |first=Jean-Pierre |journal=Fungal Ecology |volume=5 |issue=4 |pages=472–9}}</ref><ref name="nordita_eana2012">{{cite journal | first=R. | last=de la Torre Noetzel | first2=F.J. | last2=Sanchez Inigo | first3=E. | last3=Rabbow | first4=G. | last4=Horneck | first5=J. P. | last5=de Vera | first6=L.G. | last6=Sancho | url=http://online.liebertpub.com/doi/abs/10.1089/ast.2006.0046 | format=PDF | title=Lichens Survive in Space: Results from the 2005 LICHENS Experiment | doi=10.1089/ast.2006.0046 | bibcode=2007AsBio...7..443S | volume=7 | issue=3 | journal=Astrobiology | pages=443–454 | pmid=17630840 | date=June 2007}}</ref><ref name="lichen">{{cite journal |bibcode=2012P&SS...72..102S |title=The resistance of the lichen ''Circinaria gyrosa'' (nom. Provis.) towards simulated Mars conditions—a model test for the survival capacity of an eukaryotic extremophile |last=Sánchez |first=F. J. |last2=Mateo-Martí |first2=E. |last3=Raggio |first3=J. |last4=Meeßen |first4=J. |last5=Martínez-Frías |first5=J. |last6=Sancho |first6=L. G. |last7=Ott |first7=S. |last8=de la Torre |first8=R. |volume=72 |issue=1 |date=2012 |pages=102–10 |journal=Planetary and Space Science |doi=10.1016/j.pss.2012.08.005}}</ref> However, the ability to survive in an environment is not the same as the ability to thrive, reproduce, and evolve in that same environment, necessitating further study.
The researchers are of the view that their work strongly supports the possibility that terrestrial microbes most likely can adapt physiologically to live on Mars<ref>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</ref>
{{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"}}
== Missions ==
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