Editing Viking lander biological experiments (section)

=== Gas chromatograph – mass spectrometer ===
A [[Gas chromatography–mass spectrometry|gas chromatograph – mass spectrometer]] ('''GCMS''') is a device that separates vapor components chemically via a [[gas chromatograph]] and then feeds the result into a [[mass spectrometer]], which measures the [[molecular weight]] of each chemical. As a result, it can separate, identify, and quantify a large number of different chemicals. The GCMS (PI: [[Klaus Biemann]], MIT) was used to analyze the components of untreated Martian soil, and particularly those components that are released as the soil is heated to different temperatures. It could measure molecules present at a level of a few parts per billion.<ref>{{cite book |title=Mars |work=Space Science Series |publisher=University of Arizona Press |date=1992-10-01 |first1=Hugh H. |last1=Kieffer |first2=Bruce M. |last2=Jakosky |first3=Conway W. |last3=Snyder |first4=Mildred |last4=Matthews |name-list-style=vanc |isbn=978-0-8165-1257-7 |url-access=registration |url=https://archive.org/details/mars0000unse }}</ref>

The GCMS measured no significant amount of [[natural organic matter|organic molecules]] in the Martian soil. In fact, Martian soils were found to contain less carbon than lifeless lunar soils returned by the [[Apollo program]]. This result was difficult to explain if Martian bacterial metabolism was responsible for the positive results seen by the Labeled Release experiment (see below). A 2011 [[astrobiology]] textbook notes that this was the decisive factor due to which "For most of the Viking scientists, the final conclusion was that the ''Viking'' missions failed to detect life in the Martian soil."<ref name="PlaxcoGross2011">{{cite book |first1=Kevin W. |last1=Plaxco |first2=Michael |last2=Gross | name-list-style = vanc |title=Astrobiology: A Brief Introduction |url=https://books.google.com/books?id=x83omgI5pGQC&pg=PA282 |date=2011 |publisher=JHU Press |isbn=978-1-4214-0194-2 |pages=282–283 |edition=2nd }}</ref>

Experiments conducted in 2008 by the [[Phoenix (spacecraft)|''Phoenix'' lander]] discovered the presence of [[perchlorate]] in Martian soil. The 2011 astrobiology textbook discusses the importance of this finding with respect to the results obtained by ''Viking'' as "while perchlorate is too poor an oxidizer to reproduce the LR results (under the conditions of that experiment perchlorate does not oxidize organics), it does oxidize, and thus destroy, organics at the higher temperatures used in the Viking GCMS experiment. NASA astrobiologist [[Christopher McKay]] has estimated, in fact, that if ''Phoenix''-like levels of perchlorates were present in the Viking samples, the organic content of the Martian soil could have been as high as 0.1% and still would have produced the (false) negative result that the GCMS returned. Thus, while conventional wisdom regarding the ''Viking'' biology experiments still points to "no evidence of life", recent years have seen at least a small shift toward "inconclusive evidence"."<ref name="PlaxcoGross2011_2">{{cite book |first1=Kevin W. |last1=Plaxco |first2=Michael |last2=Gross | name-list-style = vanc |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 |access-date=2013-07-16 }}</ref>

According to a 2010 NASA press release: "The only organic chemicals identified when the Viking landers heated samples of Martian soil were [[chloromethane]] and [[dichloromethane]]—chlorine compounds interpreted at the time as likely contaminants from cleaning fluids." According to a paper authored by a team led by [[Rafael Navarro-González]] of the [[National Autonomous University of Mexico]], "those chemicals are exactly what [their] new study found when a little perchlorate—the surprise finding from Phoenix—was added to desert soil from Chile containing organics and analyzed in the manner of the Viking tests." However, the 2010 NASA press release also noted that: "One reason the [[chlorinated organics]] found by Viking were interpreted as contaminants from Earth was that the ratio of two isotopes of chlorine in them matched the three-to-one ratio for those isotopes on Earth. The ratio for them on Mars has not been clearly determined yet. If it is found to be much different than Earth's, that would support the 1970s interpretation."<ref name="Webster">{{cite web |last1=Webster |first1=Guy |last2=Hoover |first2=Rachel |last3=Marlaire |first3=Ruth |last4=Frias |first4=Gabriela |name-list-style=vanc |date=2010-09-03 |url=http://www.jpl.nasa.gov/news/news.cfm?release=2010-286 |title=Missing Piece Inspires New Look at Mars Puzzle |publisher=NASA Jet Propulsion Laboratory |access-date=2010-10-24 |archive-date=2010-11-03 |archive-url=https://web.archive.org/web/20101103012112/http://www.jpl.nasa.gov/news/news.cfm?release=2010-286 |url-status=dead }}</ref> Biemann has written a commentary critical of the Navarro-González and McKay paper,<ref name = "Biemann_2011">{{cite journal | vauthors = Biemann K, Bada JL |title=Comment on "Reanalysis of the Viking results suggests perchlorate and organics at midlatitudes on Mars" by Rafael Navarro-González et al. |doi=10.1029/2011JE003869 |journal=Journal of Geophysical Research |date=2011 |volume=116 |issue=E12 |pages=E12001 |bibcode=2011JGRE..11612001B |doi-access=free }}</ref> to which the latter have replied;<ref>{{cite journal | doi = 10.1029/2011JE003880 | bibcode=2011JGRE..11612002N | volume=116 | issue=E12 | pages=E12002 | title=Reply to comment by Biemann and Bada on "Reanalysis of the Viking results suggests perchlorate and organics at midlatitudes on Mars" | journal=Journal of Geophysical Research| last1=Navarro-González | first1=Rafael | last2=McKay | first2=Christopher P. | name-list-style = vanc | year=2011 | doi-access= }}</ref> the exchange was published in December 2011. In 2021 the chlorine isotope ratio on Mars was measured by the [[Trace Gas Orbiter]] and found to be almost indistinguishable from the terrestrial ratio,<ref>{{cite journal| last1=Trokhimovskiy |first1=A. |last2=Fedorova |first2=A.A. |last3=Olsen |first3=K.S. |last4=Alday |first4=J. |last5=Korablev |first5=O. |last6=Montmessin |first6=F. |last7=Lefèvre |first7=F. |last8=Patrakeev |first8=A. |last9=Belyaev |first9=D. |last10=Shakun |first10=A.V. |title=Isotopes of chlorine from HCl in the Martian atmosphere |journal=Astronomy & Astrophysics |date=July 2021| volume=651 |issue=A32 |pages=A32 |doi= 10.1051/0004-6361/202140916 |bibcode=2021A&A...651A..32T |s2cid=236336984 |doi-access=free }}</ref>  leaving the interpretation of the GCMS results inconclusive.