Editing Viking program (section)

===Biological experiments===
{{Main|Viking biological experiments}}
The Viking landers conducted [[Viking biological experiments|biological experiments]] designed to detect [[life on Mars (planet)|life in the Martian soil]] (if it existed) with experiments designed by three separate teams, under the direction of chief scientist [[Gerald Soffen]] of NASA. One experiment turned positive for the detection of [[metabolism]] (current life), but based on the results of the other two experiments that failed to reveal any [[Organic matter|organic molecules]] in the soil, most scientists became convinced that the positive results were likely caused by non-biological chemical reactions from highly oxidizing soil conditions.<ref name=Beegle >{{Cite journal|title=A Concept for NASA's Mars 2016 Astrobiology Field Laboratory|journal=Astrobiology|date=August 2007|first=LUTHER W.|last=BEEGLE|display-authors=etal |volume=7 | issue = 4|pmid=17723090 |pages=545–577|doi=10.1089/ast.2007.0153|bibcode=2007AsBio...7..545B}}</ref>

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|image1=Mars Viking 11a097.png
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|caption1=Dust dunes and a large boulder taken by the ''Viking 1'' lander.
|caption2=Trenches dug by the soil sampler of the  ''Viking 1'' lander.
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Although there was a pronouncement by NASA during the mission saying that the Viking lander results did not demonstrate conclusive [[biosignature]]s in soils at the two landing sites, the test results and their limitations are still under assessment. The validity of the positive 'Labeled Release' (LR) results hinged entirely on the absence of an oxidative agent in the Martian soil, but one was later discovered by the [[Phoenix lander|''Phoenix'' lander]] in the form of [[perchlorate]] salts.<ref name="latimes-20080806">{{Cite web |last=Johnson |first=John |date=August 6, 2008 |title=Perchlorate found in Martian soil |url=https://www.latimes.com/la-sci-phoenix6-2008aug06-story.html |url-status=live |archive-url=https://web.archive.org/web/20230419020853/https://www.latimes.com/la-sci-phoenix6-2008aug06-story.html |archive-date=April 19, 2023 |work=[[Los Angeles Times]] }}</ref><ref name="sciencedaily-20080806">{{Cite news |date=August 6, 2008 |title=Martian Life Or Not? NASA's Phoenix Team Analyzes Results |work=Science Daily |url=https://www.sciencedaily.com/releases/2008/08/080805192122.htm |url-status=live |archive-url=https://web.archive.org/web/20231118165426/http://www.sciencedaily.com/releases/2008/08/080805192122.htm |archive-date=November 18, 2023 }}</ref> It has been proposed that organic compounds could have been present in the soil analyzed by both ''Viking 1'' and ''Viking 2'', but remained unnoticed due to the presence of perchlorate, as detected by Phoenix in 2008.<ref>{{Cite news |url=http://www.agu.org/pubs/crossref/2010/2010JE003599.shtml |title=Reanalysis of the Viking results suggests perchlorate and organics at midlatitudes on Mars |journal=Journal of Geophysical Research: Planets |volume=115 |issue=E12010 |date=December 15, 2010 |access-date=January 7, 2011 |first=Rafael |last=Navarro–Gonzáles |author2=Edgar Vargas |author3=José de la Rosa |author4=Alejandro C. Raga |author5=Christopher P. McKay |archive-date=January 9, 2011 |archive-url=https://web.archive.org/web/20110109102058/http://www.agu.org/pubs/crossref/2010/2010JE003599.shtml |url-status=dead }}</ref>  Researchers found that perchlorate will destroy organics when heated and will produce [[chloromethane]] and [[dichloromethane]], the identical chlorine compounds discovered by both Viking landers when they performed the same tests on Mars.<ref>{{cite magazine| url=https://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/| archive-url=https://web.archive.org/web/20120415072431/http://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/| url-status=dead| archive-date=April 15, 2012| magazine=National Geographic| title=Life on Mars Found by NASA's Viking Mission| first=Ker| last=Than| date=April 15, 2012| access-date=April 13, 2018}}</ref>

The question of microbial life on Mars remains unresolved. Nonetheless, on April 12, 2012, an international team of scientists reported studies, based on mathematical speculation through [[complexity analysis]] of the [[Viking biological experiments#Labeled release|Labeled Release experiments]] of the 1976 Viking Mission, that may suggest the detection of "extant microbial life on Mars."<ref name="Bianciardi-2012">{{cite journal |last1=Bianciardi |first1=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 |journal=IJASS |date=March 2012 |volume=13 |issue=1 |pages=14–26 |doi=10.5139/IJASS.2012.13.1.14 |bibcode=2012IJASS..13...14B |df=mdy-all |doi-access=free }}</ref><ref name="Discovery-20120412">{{cite web |last=Klotz |first=Irene |title=Mars Viking Robots 'Found Life' |url=http://news.discovery.com/space/mars-life-viking-landers-discovery-120412.html |date=April 12, 2012 |publisher=[[Discovery Channel|DiscoveryNews]] |access-date=April 16, 2012 }}</ref> In addition, new findings from re-examination of the Gas Chromatograph Mass Spectrometer (GCMS) results were published in 2018.<ref>{{Cite journal|last1=Guzman|first1=Melissa|last2=McKay|first2=Christopher P.|last3=Quinn|first3=Richard C.|last4=Szopa|first4=Cyril|last5=Davila|first5=Alfonso F.|last6=Navarro-González|first6=Rafael|last7=Freissinet|first7=Caroline|date=2018|title=Identification of Chlorobenzene in the Viking Gas Chromatograph-Mass Spectrometer Data Sets: Reanalysis of Viking Mission Data Consistent With Aromatic Organic Compounds on Mars|journal=Journal of Geophysical Research: Planets|language=en|volume=123|issue=7|pages=1674–1683|doi=10.1029/2018JE005544|bibcode=2018JGRE..123.1674G|s2cid=133854625 |issn=2169-9100|url=https://hal-insu.archives-ouvertes.fr/insu-01820363/file/2018JE005544.pdf |archive-url=https://web.archive.org/web/20201103090059/https://hal-insu.archives-ouvertes.fr/insu-01820363/file/2018JE005544.pdf |archive-date=2020-11-03 |url-status=live}}</ref>