Editing Extraterrestrial life (section)

===Search for basic life===
[[File:NASA-WhatBiosignaturesDoesLifeProduce-20180625.jpg|thumb|upright|Lifeforms produce a variety of biosignatures that may be detectable by telescopes.<ref name="NASA-20180625">{{cite web |url=https://www.jpl.nasa.gov/news/news.php?feature=7171 |title=NASA Asks: Will We Know Life When We See It? |publisher=[[NASA]] |last1=Cofield |first1=Calla |last2=Chou |first2=Felicia |date=25 June 2018 |access-date=26 June 2018}}</ref><ref name="EA-20180625">{{cite news |url=https://ucrtoday.ucr.edu/54211 |title=UCR Team Among Scientists Developing Guidebook for Finding Life Beyond Earth |work=UCR Today |publisher=[[University of California, Riverside]] |first=Sarah |last=Nightingale |date=25 June 2018 |access-date=26 June 2018}}</ref>]]

Scientists search for [[biosignature]]s within the [[Solar System]] by studying planetary surfaces and examining [[Meteoroid|meteorites]]. Some claim to have identified evidence that microbial life has existed on Mars.<ref name=disbelief>{{cite web |title=Experts: Little Evidence of Life on Mars |url=http://dsc.discovery.com/news/2006/08/08/marslife_spa.html?category=space&guid=20060808100030 |last=Crenson |first=Matt |publisher=[[Associated Press]] |date=6 August 2006 |access-date=8 March 2011 |archive-url=https://web.archive.org/web/20110416094930/http://dsc.discovery.com/news/2006/08/08/marslife_spa.html?category=space&guid=20060808100030 |archive-date=16 April 2011 |url-status=dead }}</ref><ref name="life">{{cite journal |title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 |journal=Science |first1=David S. |last1=McKay | first2=Everett K. Jr. |last2=Gibson |first3=Kathie L. |last3=Thomas-Keprta |first4=Hojatollah |last4=Vali |first5=Christopher S. |last5=Romanek |first6=Simon J. |last6=Clemett |first7=Xavier D. F. |last7=Chillier |first8=Claude R. |last8=Maechling |first9=Richard N. |last9=Zare |s2cid=40690489 |display-authors=5 |volume=273 |issue=5277 |pages=924–930 |date=August 1996 |doi=10.1126/science.273.5277.924 |bibcode=1996Sci...273..924M |pmid=8688069}}</ref><ref name="NASA-20140227">{{cite web |last=Webster |first=Guy |title=NASA Scientists Find Evidence of Water in Meteorite, Reviving Debate Over Life on Mars |url=http://www.jpl.nasa.gov/news/news.php?release=2014-065&1 |date=27 February 2014 |work=[[NASA]] |access-date=27 February 2014}}</ref><ref name="SP-20140228">{{cite web |last=Gannon |first=Megan |title=Mars Meteorite with Odd 'Tunnels' & 'Spheres' Revives Debate Over Ancient Martian Life |url=http://www.space.com/24834-strange-mars-meteorite-life-evidence-debate.html |date=28 February 2014 |work=[[Space.com]] |access-date=28 February 2014}}</ref> In 1996, a controversial report stated that structures resembling [[Nanobacterium|nanobacteria]] were discovered in a meteorite, [[ALH84001]], formed of [[martian meteorite|rock ejected from Mars]].<ref name=disbelief/><ref name="life"/> Although all the unusual properties of the meteorite were eventually explained as the result of inorganic processes, the controversy over its discovery laid the groundwork for the development of astrobiology.<ref name=disbelief/>

An experiment on the two [[Viking program|Viking]] Mars landers reported gas emissions from heated Martian soil samples that some scientists argue are consistent with the presence of living microorganisms.<ref name="Chambers">{{cite book |first=Paul |last=Chambers |title=Life on Mars; The Complete Story |place=London |publisher=Blandford |date=1999 |isbn=978-0-7137-2747-0 |url=https://archive.org/details/lifeonmarscomple00cham }}</ref> Lack of corroborating evidence from other experiments on the same samples suggests that a non-biological reaction is a more likely hypothesis.<ref name="Chambers"/><ref>{{cite journal |title=The Viking Biological Investigation: Preliminary Results |journal=Science |date=1 October 1976 |first1=Harold P. |last1=Klein |last2=Levin |first2=Gilbert V. |last3=Levin |first3=Gilbert V. |last4=Oyama |first4=Vance I. |last5=Lederberg |first5=Joshua |last6=Rich |first6=Alexander |last7=Hubbard |first7=Jerry S. |last8=Hobby |first8=George L. |last9=Straat |first9=Patricia A. |last10=Berdahl |first10=Bonnie J. |last11=Carle |first11=Glenn C. |last12=Brown |first12=Frederick S. |last13=Johnson |first13=Richard D. |volume=194 |issue=4260 |pages=99–105 |doi=10.1126/science.194.4260.99 |pmid=17793090 |bibcode=1976Sci...194...99K |s2cid=24957458 }}</ref><ref name="Beegle">{{cite journal |title=A Concept for NASA's Mars 2016 Astrobiology Field Laboratory |journal=Astrobiology |date=August 2007 |last1=Beegle |first1=Luther W. |last2=Wilson |first2=Michael G. |volume=7 |issue=4 |pmid=17723090 |pages=545–577 |doi=10.1089/ast.2007.0153 |bibcode=2007AsBio...7..545B |last3=Abilleira |first3=Fernando |last4=Jordan |first4=James F. |last5=Wilson |first5=Gregory R.}}</ref><ref>{{cite web |url=http://www.esa.int/SPECIALS/ExoMars/SEMK39JJX7F_0.html |title=ExoMars rover |publisher=ESA |access-date=14 April 2014 |archive-date=19 October 2012 |archive-url=https://web.archive.org/web/20121019105332/http://www.esa.int/SPECIALS/ExoMars/SEMK39JJX7F_0.html |url-status=dead }}</ref>

In February 2005 NASA scientists reported they may have found some evidence of extraterrestrial life on Mars.<ref>{{cite news |url=http://www.space.com/scienceastronomy/mars_life_050216.html |title=Exclusive: NASA Researchers Claim Evidence of Present Life on Mars |last=Berger |first=Brian |date=2005-02-16 |work=Space.com}}</ref> The two scientists, Carol Stoker and Larry Lemke of NASA's [[Ames Research Center]], based their claim on methane signatures found in Mars's atmosphere resembling the methane production of some forms of primitive life on Earth, as well as on their own study of primitive life near the [[Rio Tinto river]] in Spain. NASA officials soon distanced NASA from the scientists' claims, and Stoker herself backed off from her initial assertions.<ref>{{cite news |url=http://www.spacetoday.net/Summary/2804 |title=NASA denies Mars life reports |publisher=spacetoday.net |date=2005-02-19}}</ref>

In November 2011, NASA launched the [[Mars Science Laboratory]] that landed the ''Curiosity'' rover on Mars. It is designed to assess the past and present habitability on Mars using a variety of scientific instruments. The rover landed on Mars at [[Gale (crater)|Gale Crater]] in August 2012.<ref name="Gale Crater2">{{cite web |last1=Chow |first1=Dennis |title=NASA's Next Mars Rover to Land at Huge Gale Crater |url=http://www.space.com/12394-nasa-mars-rover-landing-site-unveiled.html |date=22 July 2011 |publisher=[[Space.com]] |access-date=22 July 2011}}</ref><ref name="Gale Crater3">{{cite news |last1=Amos |first1=Jonathan |title=Mars rover aims for deep crater |date=22 July 2011 |url=https://www.bbc.co.uk/news/science-environment-14249524 |work=[[BBC News]] |access-date=22 July 2011}}</ref>

A group of scientists at Cornell University started a catalog of microorganisms, with the way each one reacts to sunlight. The goal is to help with the search for similar organisms in exoplanets, as the starlight reflected by planets rich in such organisms would have a specific spectrum, unlike that of starlight reflected from lifeless planets. If Earth was studied from afar with this system, it would reveal a shade of green, as a result of the abundance of plants with photosynthesis.<ref name="ColorCatalog">{{cite news |last=Cofield |first=Calla |url=http://www.space.com/28906-alien-life-earth-microbe-catalog.html |title=Catalog of Earth Microbes Could Help Find Alien Life |work=Space.com |date=30 March 2015 |access-date=11 May 2015}}</ref>

In August 2011, NASA studied [[meteorite]]s found on Antarctica, finding [[adenine]], [[guanine]], [[hypoxanthine]] and [[xanthine]]. Adenine and guanine are components of DNA, and the others are used in other biological processes. The studies ruled out pollution of the meteorites on Earth, as those components would not be freely available the way they were found in the samples. This discovery suggests that several [[organic molecules]] that serve as building blocks of life may be generated within asteroids and comets.<ref name="Callahan">{{cite journal |last1=Callahan |first1=M.P. |last2=Smith |first2=K.E. |last3=Cleaves |first3=H.J. |last4=Ruzica |first4=J. |last5=Stern |first5=J.C. |last6=Glavin |first6=D.P. |last7=House |first7=C.H. |last8=Dworkin |first8=J.P. |date=11 August 2011 |title=Carbonaceous meteorites contain a wide range of extraterrestrial nucleobases |doi=10.1073/pnas.1106493108 |volume=108 |issue=34 |journal=Proceedings of the National Academy of Sciences |pages=13995–13998 |bibcode=2011PNAS..10813995C |pmid=21836052 |pmc=3161613|doi-access=free }}</ref><ref name="Steigerwald">{{cite web |last=Steigerwald |first=John |title=NASA Researchers: DNA Building Blocks Can Be Made in Space |url=http://www.nasa.gov/topics/solarsystem/features/dna-meteorites.html |publisher=[[NASA]] |date=8 August 2011 |access-date=10 August 2011 |archive-date=11 May 2020 |archive-url=https://web.archive.org/web/20200511192941/https://www.nasa.gov/topics/solarsystem/features/dna-meteorites.html |url-status=dead }}</ref> In October 2011, scientists reported that [[cosmic dust]] contains complex [[organic compound]]s ("amorphous organic solids with a mixed [[aromatic]]-[[aliphatic]] structure") that could be created naturally, and rapidly, by [[stars]].<ref name="Space-20111026">{{cite web |last=Chow |first=Denise |title=Discovery: Cosmic Dust Contains Organic Matter from Stars |url=http://www.space.com/13401-cosmic-star-dust-complex-organic-compounds.html |date=26 October 2011 |publisher=[[Space.com]] |access-date=26 October 2011}}</ref><ref name="ScienceDaily-20111026">{{cite web |title=Astronomers Discover Complex Organic Matter Exists Throughout the Universe |url=https://www.sciencedaily.com/releases/2011/10/111026143721.htm |date=26 October 2011 |website=[[ScienceDaily]] |access-date=27 October 2011}}</ref><ref name="Nature-20111026">{{cite journal |last1=Kwok |first1=Sun |last2=Zhang |first2=Yong |title=Mixed aromatic–aliphatic organic nanoparticles as carriers of unidentified infrared emission features |date=26 October 2011 |journal=[[Nature (journal)|Nature]] |doi=10.1038/nature10542 |volume=479 |issue=7371 |pages=80–3 |bibcode=2011Natur.479...80K |pmid=22031328|s2cid=4419859 }}</ref> It is still unclear if those compounds played a role in the creation of life on Earth, but Sun Kwok, of the University of Hong Kong, thinks so. "If this is the case, life on Earth may have had an easier time getting started as these organics can serve as basic ingredients for life."<ref name="Space-20111026"/>

In August 2012, and in a world first, astronomers at [[Copenhagen University]] reported the detection of a specific sugar molecule, [[glycolaldehyde]], in a distant star system. The molecule was found around the [[protostar|protostellar]] binary ''[[IRAS 16293−2422|IRAS 16293-2422]]'', which is located 400 light years from Earth.<ref>{{cite web |url= https://www.nationalgeographic.com/adventure/article/120829-sugar-space-planets-science-life|title= Sugar Found In Space: A Sign of Life?|author= Ker Than|date= August 30, 2012|publisher= National Geographic|accessdate=July 4, 2023}}</ref> Glycolaldehyde is needed to form [[ribonucleic acid]], or RNA, which is similar in function to DNA. This finding suggests that complex organic molecules may form in stellar systems prior to the formation of planets, eventually arriving on young planets early in their formation.<ref>{{cite journal |url=http://www.eso.org/public/archives/releases/sciencepapers/eso1234/eso1234a.pdf |title=Detection of the simplest sugar, glycolaldehyde, in a solar-type protostar with ALMA |journal=The Astrophysical Journal Letters |first1=Jes K. |last1=Jørgensen |first2=Cécile |last2=Favre |first3=Suzanne E. |last3=Bisschop |first4=Tyler L. |last4=Bourke |first5=Ewine F. |last5=van Dishoeck |first6=Markus |last6=Schmalzl |volume=757 |issue=1 |at=L4 |date=September 2012 |doi=10.1088/2041-8205/757/1/L4 |bibcode=2012ApJ...757L...4J |arxiv=1208.5498|s2cid=14205612 }}</ref>

In December 2023, astronomers reported the first time discovery, in the [[Plume (fluid dynamics)|plume]]s of [[Enceladus]], moon of the planet [[Saturn]], of [[hydrogen cyanide]], a possible chemical essential for [[life]]<ref name="ATL-20231205">{{cite news |last=Green |first=Jaime |title=What Is Life? - The answer matters in space exploration. But we still don't really know. |url=https://www.theatlantic.com/science/archive/2023/12/defining-life-existentialism-scientific-theory/676238/ |date=5 December 2023 |work=[[The Atlantic]] |url-status=live |archiveurl=https://archive.today/20231205121742/https://www.theatlantic.com/science/archive/2023/12/defining-life-existentialism-scientific-theory/676238/ |archivedate=5 December 2023 |accessdate=15 December 2023 }}</ref> as we know it, as well as other [[organic molecule]]s, some of which are yet to be better identified and understood. According to the researchers, "these [newly discovered] compounds could potentially support extant [[Microorganism|microbial communities]] or drive complex [[organic synthesis]] leading to the [[origin of life]]."<ref name="NYT-20231214kc">{{cite news |last=Chang |first=Kenneth |title=Poison Gas Hints at Potential for Life on an Ocean Moon of Saturn - A researcher who has studied the icy world said "the prospects for the development of life are getting better and better on Enceladus." |url=https://www.nytimes.com/2023/12/14/science/enceladus-moon-cyanide-life-saturn.html |date=14 December 2023 |work=[[The New York Times]] |url-status=live |archiveurl=https://archive.today/20231214210144/https://www.nytimes.com/2023/12/14/science/enceladus-moon-cyanide-life-saturn.html |archivedate=14 December 2023 |accessdate=15 December 2023 }}</ref><ref name="NA-20231214">{{cite journal |author=Peter, Jonah S. |display-authors=et al. |title=Detection of HCN and diverse redox chemistry in the plume of Enceladus |url=https://www.nature.com/articles/s41550-023-02160-0 |date=14 December 2023 |journal=[[Nature Astronomy]] |volume=8 |issue=2 |pages=164–173 |doi=10.1038/s41550-023-02160-0 |url-status=live |archiveurl=https://archive.today/20231215144349/https://www.nature.com/articles/s41550-023-02160-0 |archivedate=15 December 2023 |accessdate=15 December 2023 |arxiv=2301.05259 |bibcode=2024NatAs...8..164P |s2cid=255825649 }}</ref>