Editing Viking 2 (section)

==Results from the ''Viking 2'' mission==

===Landing site soil analysis===
The regolith, referred to often as "soil," resembled those produced from the weathering of basaltic [[lava]]s.  The tested soil contained abundant [[silicon]] and [[iron]], along with significant amounts of [[magnesium]], [[aluminum]], [[sulfur]], [[calcium]], and [[titanium]]. Trace elements, [[strontium]] and [[yttrium]], were detected.

The amount of [[potassium]] was one-fifth of the average for the Earth's crust. Some chemicals in the soil contained sulfur and [[chlorine]] that were like those remaining after the evaporation of seawater. Sulfur was more concentrated in the crust on top of the soil than in the bulk soil beneath.

The sulfur may be present as [[sulfate]]s of [[sodium]], magnesium, calcium, or iron. A [[sulfide]] of iron is also possible.<ref>Clark, B. et al.  1976.  Inorganic Analysis of Martian Samples at the Viking Landing Sites.  Science:  194. 1283–1288.</ref> The [[Spirit Rover|''Spirit'' rover]] and the [[Opportunity Rover|''Opportunity'' rover]] both found sulfates on Mars.<ref>[https://web.archive.org/web/20040626074013/http://marsrovers.nasa.gov/gallery/press/opportunity/20040625a.html Mars Exploration Rover Mission: Press Release Images: Opportunity<!-- Bot generated title -->]</ref>

Minerals typical weathering products of [[mafic]] [[igneous rocks]] were found.<ref>Baird, A.  et al.  1976.  [https://www.science.org/doi/abs/10.1126/science.194.4271.1288 Mineralogic and Petrologic Implications of Viking Geochemical Results From Mars: Interim Report.]  Science: 194. 1288–1293.</ref>  All samples heated in the [[Gas chromatography–mass spectrometry|gas chromatograph-mass spectrometer]] (GCMS) gave off water.

However, the way the samples were handled prohibited an exact measurement of the amount of water. But, it was around 1%.<ref>Arvidson, R et al.  1989.  The Martian surface as Imaged, Sampled, and Analyzed by the Viking Landers.  Reviews of Geophysics:27. 39-60.</ref> Studies with [[magnets]] aboard the landers indicated that the soil is between 3 and 7 percent magnetic materials by weight.  The magnetic chemicals could be [[magnetite]] and [[maghemite]], which could come from the weathering of [[basalt]] rock.<ref>Hargraves, R. et al. 1976.  Viking Magnetic Properties Investigation: Further Results. ''Science'': 194.  1303–1309.</ref><ref>Arvidson, R, A. Binder, and K. Jones.  The Surface of Mars. ''Scientific American''</ref>  Subsequent experiments carried out by the Mars ''Spirit'' rover (landed in 2004) suggest that magnetite could explain the magnetic nature of the dust and soil on Mars.<ref>Bertelsen, P. et al.  2004.  Magnetic Properties Experiments on the Mars Exploration rover ''Spirit'' at Gusev Crater.  ''Science'': 305. 827–829.</ref>
{{Wide image|Mars Viking 22a002.png|1500px|''Viking 2'' lander image of Utopia Planitia.}}

===Search for life===
''Viking 2'' carried a biology experiment whose purpose was to look for life.  The ''Viking 2'' biology experiment weighed {{convert|15.5|kg|lbs|abbr=on}} and consisted of three subsystems: the [[Pyrolytic Release]] experiment (PR), the Labeled Release experiment (LR), and the Gas Exchange experiment (GEX).  In addition, independent of the biology experiments, ''Viking 2'' carried a Gas Chromatograph/Mass Spectrometer (GCMS) that could measure the composition and abundance of organic compounds in the Martian soil.<ref>[http://www.msss.com/http/ps/life/life.html Life on Mars<!-- Bot generated title -->] {{webarchive |url=https://web.archive.org/web/20141020034248/http://www.msss.com/http/ps/life/life.html |date=October 20, 2014 }}</ref>

The results were unusual and conflicting: the GCMS and GEX gave negative results, while the PR and LR gave positive results.<ref>[http://www.spacedaily.com/news/mars-life-00g.html Viking Data May Hide New Evidence For Life.] Barry E. DiGregorio, July 16, 2000.</ref>  Viking scientist Patricia Straat stated in 2009, "Our (LR) experiment was a definite positive response for life, but a lot of people have claimed that it was a false positive for a variety of reasons."<ref>[http://dsc.discovery.com/news/2009/09/28/viking-lander-mars.html ''Viking 2'' Likely Came Close to Finding H2O.] {{webarchive |url=https://web.archive.org/web/20090930025048/http://dsc.discovery.com/news/2009/09/28/viking-lander-mars.html |date=September 30, 2009 }}</ref>

Many scientists believe that the data results were attributed to inorganic chemical reactions in the soil. However, this view may be changing due to a variety of discoveries and studies since Viking. These include the discovery of near-surface ice near the Viking landing zone, the possibility of perchlorate destruction of organic matter, and the reanalysis of GCMS data by scientists in 2018.<ref>{{Cite journal|last1=Guzman|first1=Melissa|last2=Mckay|first2=Christopher|last3=Quinn|first3=Richard|last4=Szopa|first4=Cyril|last5=Davila|first5=Alfonso|last6=Navarro-Gonzalez|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|url=https://hal-insu.archives-ouvertes.fr/insu-01820363|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 }}</ref> Some scientists still believe the results were due to living reactions.  The formal declaration at the time of the mission was that the discovery of organic chemicals was inconclusive.{{citation needed|date=September 2015}}

Mars has almost no ozone layer, unlike the Earth, so UV light sterilizes the surface and produces highly reactive chemicals such as peroxides that would oxidize any organic chemicals.<ref name="Hartmann, W 2003">Hartmann, W.  2003.  A Traveler's Guide to Mars.  Workman Publishing.  NY NY.</ref>  The [[Phoenix Lander|''Phoenix'' Lander]] discovered the chemical [[perchlorate]] in the Martian soil.  Perchlorate is a powerful oxidizing agent, which could have eradicated any organic material on the surface.<ref>[http://www.planetary.org/news/2008/0806_Alien_Rumors_Quelled_as_NASA_Announces.html Alien Rumors Quelled as NASA Announces Phoenix Perchlorate Discovery.] {{webarchive |url=https://web.archive.org/web/20100904132551/http://www.planetary.org/news/2008/0806_Alien_Rumors_Quelled_as_NASA_Announces.html |date=September 4, 2010 }} A.J.S. Rayl, August 6, 2008.</ref>  Perchlorate is now considered widespread on Mars, making it hard to detect any organic compounds on the Martian surface.<ref name="NYT-20131001">{{cite news |last=Chang |first=Kenneth |title=Hitting Pay Dirt on Mars |url=https://www.nytimes.com/2013/10/01/science/space/hitting-pay-dirt-on-mars.html |date=October 1, 2013 |work=[[New York Times]] |access-date=October 10, 2013 }}</ref>

===''Viking 2'' lander image gallery===
{{Wide image|Viking Lander 2 Camera 1 NOON HIGH RESOLUTION COLOR MOSAIC.jpg|1500px|align-cap=center|''Viking 2'' lander Camera 1 NOON HIGH RESOLUTION MOSAIC (With Low Resolution Color).}}
{{Wide image|22i103-104-105-109 FROST.jpg|1500px|align-cap=center|''Viking 2'' Lander Camera 2 FROST (Low Resolution Color) Sol 1028, 1030 and 1050 between 11:34 and 12:40.}}
<gallery class="center">
File:First Color Image of the Viking Lander 2 Site.jpg|First color image (''Viking 2'' lander Camera 2 sol {{age in sols|1976|09|03|1976|09|05}}, September 5, 1976) 14:36
File:22g144 netoyee.jpg|''Viking 2'' lander Camera 2 22G144 (Low Resolution Color) Sol 552 19:16
File:Mars Viking 22e169.png|Frost on Mars.
File:22i067 FROST.png|''Viking 2'' lander Camera 2 FROST (Low Resolution Color) Sol 955 12:13
File:Mars Viking 21i093.png|Frost at the landing site. (false color)
File:21i090 21i093 21d224-225-226 LOW RESOLUTION COLOR.jpg|''Viking 2'' lander Camera 1 FROST (Low Resolution Color) Sol 960 14:14
File:21i091 HIGH RESOLUTION COLOR.jpg|''Viking 2'' lander Camera 1 FROST HIGH RESOLUTION (With Low Resolution Color) Sol 959 14:39
File:SKY-AT-SUNRISE-(22b023).jpg|''Viking 2 '' lander Camera 2 SKY AT SUNRISE (Low Resolution Color) Sol 34 04:22
File:SKY-AT-SUNRISE(22h093).jpg|''Viking 2'' lander Camera 2 SKY AT SUNRISE (Low Resolution Color) Sol 631 04:00
</gallery>