Editing Viking lander biological experiments (section)

== Critiques ==

=== Failure to examine the atmosphere ===
[[James Lovelock]] argued that the Viking mission would have done better to examine the Martian atmosphere than look at the soil. He theorised that all life tends to expel waste gases into the atmosphere, and as such it would be possible to theorise the existence of life on a planet by detecting an atmosphere that was not in chemical equilibrium.<ref>{{cite web |url=http://archive.salon.com/people/feature/2000/08/17/lovelock/ |title=James Lovelock, Gaia's grand old man |last=Joseph |first=Lawrence E. | name-list-style = vanc |date=2000-08-17 |work=Salon |access-date=2009-02-10 |url-status=dead |archive-url=https://web.archive.org/web/20090408145043/http://archive.salon.com/people/feature/2000/08/17/lovelock/ |archive-date=2009-04-08 }}</ref> He concluded that there was enough information about Mars' atmosphere at that time to discount the possibility of life there. Since then, [[Natural methane on Mars|methane has been discovered in Mars]]' atmosphere at 10ppb, thus reopening this debate. Although in 2013 the Curiosity rover failed to detect methane at its location in levels exceeding 1.3ppb.<ref name="SJ-20130919">{{cite journal | vauthors = Webster CR, Mahaffy PR, Atreya SK, Flesch GJ, Farley KA | title = Low upper limit to methane abundance on Mars | journal = Science | volume = 342 | issue = 6156 | pages = 355–7 | date = October 2013 | pmid = 24051245 | doi = 10.1126/science.1242902 | bibcode = 2013Sci...342..355W | s2cid = 43194305 | url = https://authors.library.caltech.edu/42376/7/Webster.SM.pdf }}</ref> later in 2013 and in 2014, measurements by Curiosity did detect methane,<ref>NASA, [https://science.nasa.gov/science-news/science-at-nasa/2014/16dec_methanespike Curiosity Detects Methane Spike on Mars], Dec. 16, 2014 (accessed 25 Oct. 2016)</ref> suggesting a time-variable source. The [[ExoMars Trace Gas Orbiter]], launched in March 2016, implements this approach and will focus on detection, characterization of spatial and temporal variation, and localization of sources for a broad suite of atmospheric trace gases on Mars and help determine if their formation is of biological or geological origin.<ref>{{cite news |first=Paul |last=Rincon | name-list-style = vanc |title=Agencies outline Mars initiative |date=2009-07-09 |publisher=BBC |url=http://news.bbc.co.uk/2/hi/science/nature/8130393.stm |work=BBC News |access-date=2009-07-26 }}</ref><ref>{{cite news |title=NASA orbiter to hunt for source of Martian methane in 2016 |date=2009-03-06 |url=http://www.thaindian.com/newsportal/health/nasa-orbiter-to-hunt-for-source-of-martian-methane-in-2016_100163335.html |work=Thaindian News |access-date=2009-07-26 |archive-date=2018-10-05 |archive-url=https://web.archive.org/web/20181005142406/http://www.thaindian.com/newsportal/health/nasa-orbiter-to-hunt-for-source-of-martian-methane-in-2016_100163335.html |url-status=dead }}</ref> The [[Mars Orbiter Mission]] has also been attempting – since late 2014 – to detect and map methane on Mars' atmosphere. 

Studies using the Trace Gas Orbiter and Curiosity have shown that methane is only detectable at night and therefore cannot be detected by the Trace Gas Orbiter which relies on sunlight for its measurements.<ref>{{Cite web |date=2021-07-03 |title=Mars methane mystery? Depends on the time of day |url=https://earthsky.org/space/mars-methane-mystery-depends-on-the-time-of-day/ |access-date=2024-12-12 |website=earthsky.org |language=en-US}}</ref><ref>{{Cite journal |last1=Webster |first1=Christopher R. |last2=Mahaffy |first2=Paul R. |last3=Pla-Garcia |first3=Jorge |last4=Rafkin |first4=Scot C. R. |last5=Moores |first5=John E. |last6=Atreya |first6=Sushil K. |last7=Flesch |first7=Gregory J. |last8=Malespin |first8=Charles A. |last9=Teinturier |first9=Samuel M. |last10=Kalucha |first10=Hemani |last11=Smith |first11=Christina L. |last12=Viúdez-Moreiras |first12=Daniel |last13=Vasavada |first13=Ashwin R. |date=2021-06-01 |title=Day-night differences in Mars methane suggest nighttime containment at Gale crater |url=https://www.aanda.org/articles/aa/full_html/2021/06/aa40030-20/aa40030-20.html |journal=Astronomy & Astrophysics |language=en |volume=650 |pages=A166 |doi=10.1051/0004-6361/202040030 |issn=0004-6361|doi-access=free |bibcode=2021A&A...650A.166W }}</ref> 

=== Effects of landing rockets ===
A press commentary argued that, if there was life at the Viking lander sites, it may have been killed by the exhaust from the landing rockets.<ref name="viking killers">{{cite web |title=Did probes find Martian life ... or kill it off? |url=http://www.nbcnews.com/id/16516952 |archive-url=https://web.archive.org/web/20131205002852/http://www.nbcnews.com/id/16516952/ |url-status=dead |archive-date=December 5, 2013 |last=Borenstein |first=Seth | name-list-style = vanc |publisher=Associated Press via NBC News |date=2007-01-07 |access-date=2007-05-31 }}</ref>  That is not a problem for missions which land via an [[airbag]]-protected capsule, slowed by parachutes and retrorockets, and dropped from a height that allows rocket exhaust to avoid the surface.  [[Mars Pathfinder]]'s ''Sojourner'' rover and the [[Mars Exploration Rover]]s each used this landing technique successfully.  The [[Phoenix (spacecraft)|Phoenix Scout]] lander descended to the surface with retro-rockets, however, their fuel was [[hydrazine]], and the end products of the plume (water, nitrogen, and ammonia) were not found to have affected the soils at the landing site.