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* Perchlorates, though harmful to some forms of life, are metabolized by others<ref name="Oren">{{cite journal | doi = 10.2166/wst.2009.635 | volume=60 | issue=1 | pages=75–80 | title=Molecular assessment of salt-tolerant, perchlorate- and nitrate-reducing microbial cultures | year=2009 | journal=Water Science & Technology | 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 Conley, the NASA planetary protection officer from 2006 to 2018, said of the perchlorates, ''“The environment on Mars potentially is basically one giant dinner plate for Earth organisms,”''<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>.
So far, there are no confirmed habitats for Earth life on or beneath the surface of Mars. However there are several [[#Planned and proposed missions to search for present day life on Mars | planned and proposed spacecraft missions]] to search for these potential habitats There are many [[#Instruments designed to search for present day life on Mars "in situ" | instruments designed by astrobiologists to search directly for this life on Mars]]. The [[Urey instrument]]<ref name="news8-2012" /><ref>{{cite journal |title=Development and evaluation of a microdevice for amino acid biomarker detection and analysis on Mars |journal=Proceedings of the National Academy of Sciences |first1=Alison M. |last1=Skelley |first2=James R. |last2=Scherer |first3=Andrew D. |last3=Aubrey |first4=William H. |last4=Grover |first5=Robin H. C. |last5=Ivester |first6=Pascale |last6=Ehrenfreund |first7=Frank J. |last7=Grunthaner |first8=Jeffrey L. |last8=Bada |first9=Richard A. |last9=Mathies |display-authors=5 |volume=102 |issue=4 |pages=1041–1046 |date=January 2005 |doi=10.1073/pnas.0406798102 |pmc=545824 |pmid=15657130 |bibcode=2005PNAS..102.1041S}}</ref><ref>{{cite journal |title=The Urey Instrument: An Advanced In Situ Organic and Oxidant Detector for Mars Exploration |journal=[[Astrobiology (journal)|Astrobiology]] |first1=Andrew D. |last1=Aubrey |first2=John H. |last2=Chalmers |first3=Jeffrey L. |last3=Bada |first4=Frank J. |last4=Grunthaner |first5=Xenia |last5=Amashukeli |first6=Peter |last6=Willis |first7=Alison M. |last7=Skelley |first8=Richard A. |last8=Mathies |last9=''et al.'' |first9=Richard C. |last10=Zent |first10=Aaron P. |last11=Ehrenfreund |first11=Pascale |last12=Amundson |first12=Ron |last13=Glavin |first13=Daniel P. |last14=Botta |first14=Oliver |last15=Barron |first15=Laurence |last16=Blaney |first16=Diana L. |last17=Clark |first17=Benton C. |last18=Coleman |first18=Max |last19=Hofmann |first19=Beda A. |last20=Josset |first20=Jean-Luc |last21=Rettberg |first21=Petra |last22=Ride |first22=Sally |last23=Robert |first23=François |last24=Sephton |first24=Mark A. |last25=Yen |first25=Albert |display-authors=5 |volume=8 |issue=3 |pages=583–595 |date=June 2008 |doi=10.1089/ast.2007.0169 |bibcode=2008AsBio...8..583K |pmid=18680409}}</ref> and Life Marker Chip<ref>{{cite conference |title=The life marker chip for the Exomars mission |conference=2011 ICO International Conference on Information Photonics. 18–20 May 2011. Ottawa, Ontario. |first1=A. |last1=Leinse |first2=H. |last2=Leeuwis |first3=A. |last3=Prak |first4=R. G. |last4=Heideman |first5=A. |last5=Borst |pages=1–2 |doi=10.1109/ICO-IP.2011.5953740 |isbn=978-1-61284-315-5}}</ref><ref>{{cite journal |title=In situ biomarkers and the Life Marker Chip |journal=[[Astronomy & Geophysics]] |first=Zita |last=Martins |volume=52 |issue=1 |pages=1.34–1.35 |year=2011 |doi=10.1111/j.1468-4004.2011.52134.x |bibcode=2011A&G....52a..34M}}</ref><ref>{{cite journal |title=Development status of the life marker chip instrument for ExoMars |journal=[[Planetary and Space Science]] |first1=Mark R. |last1=Sims |first2=David C. |last2=Cullen |first3=Catherine S. |last3=Rix |first4=Alan |last4=Buckley |first5=Mariliza |last5=Derveni |first6=Daniel |last6=Evans |first7=Luis Miguel |last7=García-Con |first8=Andrew |last8=Rhodes |last9=''et al.'' |first9=Carla C. |last10=Stefinovic |first10=Marijan |last11=Sephton |first11=Mark A. |last12=Court |first12=Richard W. |last13=Bulloch |first13=Christopher |last14=Kitchingman |first14=Ian |last15=Ali |first15=Zeshan |last16=Pullan |first16=Derek |last17=Holt |first17=John |last18=Blake |first18=Oliver |last19=Sykes |first19=Jonathan |last20=Samara-Ratna |first20=Piyal |last21=Canali |first21=Massimiliano |last22=Borst |first22=Guus |last23=Leeuwis |first23=Henk |last24=Prak |first24=Albert |last25=Norfini |first25=Aleandro |last26=Geraci |first26=Ennio |last27=Tavanti |first27=Marco |last28=Brucato |first28=John |last29=Holm |first29=Nils |display-authors=5 |volume=72 |issue=1 |pages=129–137 |date=November 2012 |doi=10.1016/j.pss.2012.04.007 |bibcode=2012P&SS...72..129S}}</ref> separately got into the manifest for [[ExoMars]] but were later [[ExoMars#De-scoped instruments|de-scoped]]. The first and only dedicated astrobiology missions to Mars were the two [[Viking program|Viking landers]], ''[[Viking 1]]'' and ''[[Viking 2]]'' in 1976.
This article focuses on the few places on Mars where microhabitats or deep subsurface habitats may be possible. Most features and processes on Mars are not thought to be associated with life.
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