Life on Venus#Phosphine

{{short description|Scientific assessments on the microbial habitability of Venus}}

File:Venuspioneeruv.jpg in 1979. The cause of the dark streaks in the clouds is not yet known.]]

The possibility of life on Venus is a subject of interest in astrobiology due to Venus's proximity and similarities to Earth. To date, no definitive evidence has been found of past or present life there. In the early 1960s, studies conducted via spacecraft demonstrated that the current Venusian environment is extreme compared to Earth's. Studies continue to question whether life could have existed on the planet's surface before a runaway greenhouse effect took hold, and whether a relict biosphere could persist high in the modern Venusian atmosphere.

With extreme surface temperatures reaching nearly {{convert|735|K|C F}} and an atmospheric pressure 92 times that of Earth, the conditions on Venus make water-based life as we know it unlikely on the surface of the planet. However, a few scientists have speculated that thermoacidophilic extremophile microorganisms might exist in the temperate, acidic upper layers of the Venusian atmosphere.{{cite news |url=https://www.newscientist.com/article/dn2843-acidic-clouds-of-venus-could-harbour-life.html |title=Acidic clouds of Venus could harbour life |work=New Scientist |first=Stuart |last=Clark |date=26 September 2003 |access-date=30 December 2015}}Redfern, Martin (25 May 2004). [http://news.bbc.co.uk/2/hi/3746583.stm "Venus clouds 'might harbour life'"]. BBC News. Retrieved 30 December 2015.{{cite journal |title=Constraints on a potential aerial biosphere on Venus: I. Cosmic rays |journal=Icarus |date=September 2015 |last1=Dartnell |first1=Lewis R. |last2=Nordheim |first2=Tom Andre |last3= Patel |first3=Manish R. |last4=Mason |first4= Jonathon P. |volume=257 |pages=396–405 |doi=10.1016/j.icarus.2015.05.006 |display-authors=etal |bibcode=2015Icar..257..396D}} In September 2020, research was published that reported the presence of phosphine in the planet's atmosphere, a potential biosignature. However, doubts have been cast on these observations.{{cite web |last1=Plait |first1=Phil |title=Update: Life Above Hell? Serious Doubt Cast on Venus Phosphine Finding |date=26 October 2020 |url=https://www.syfy.com/syfywire/update-life-above-hell-serious-doubt-cast-on-venus-phosphine-finding |access-date=26 October 2020}}{{Cite web|title=Purported phosphine on Venus more likely to be ordinary sulfur dioxide|url=https://www.sciencedaily.com/releases/2021/01/210127140147.htm|access-date=2021-02-03|website=ScienceDaily|language=en}}

As of 8 February 2021, an updated status of studies considering the possible detection of lifeforms on Venus (via phosphine) and Mars (via methane) was reported, though whether these gases are present is still unclear.{{cite news |last1=Chang |first1=Kenneth |last2=Stirone |first2=Shannon |title=Life on Venus? The Picture Gets Cloudier - Despite doubts from many scientists, a team of researchers who said they had detected an unusual gas in the planet's atmosphere were still confident of their findings. |url=https://www.nytimes.com/2021/02/08/science/venus-life-phosphine.html |date=8 February 2021 |work=The New York Times |access-date=8 February 2021 }} On 2 June 2021, NASA announced two new related missions to Venus: DAVINCI and VERITAS.{{cite news |last=Chang |first=Kenneth |title=New NASA Missions Will Study Venus, a World Overlooked for Decades - One of the spacecraft will probe the hellish planet's clouds, which could potentially help settle the debate over whether they are habitable by floating microbes. |url=https://www.nytimes.com/2021/06/02/science/nasa-neptune-venus.html |date=2 June 2021 |work=The New York Times |accessdate=2 June 2021 }}

Surface conditions

File:Venus from Mariner 10.jpg

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Because Venus is completely covered in clouds, human knowledge of surface conditions was largely speculative until the space probe era. Until the mid-20th century, the surface environment of Venus was believed to be similar to Earth, hence it was widely believed that Venus could harbor life. In 1870, the British astronomer Richard A. Proctor said the existence of life on Venus was impossible near its equator,Proctor, Richard A., Other Worlds Than Ours: The Plurality of Worlds Studied Under the Light of Recent Scientific Researches. New York : J.A. Hill and Co., 1870. s. 94. but possible near its poles.

Microwave observations published by C. Mayer et al.{{cite journal| journal =Astrophysical Journal| volume= 127| date=1958| pages =1–9 | doi=10.1086/146433| title=Observations of Venus at 3.15-CM Wave Length| first1=C. H. | last1= Mayer| first2= T. P. | last2=McCollough | first3=R. M. | last3=Sloanaker | bibcode=1958ApJ...127....1M| doi-access=free}} in 1958 indicated a high-temperature source (600 K). Strangely, millimetre-band observations made by A. D. Kuzmin indicated much lower temperatures.{{cite web |last1=Kuz'min |first1=A. D. |last2=Marov |first2=M. Y. |title=Fizika Planety Venera |trans-title=Physics of the Planet Venus |publisher="Nauka" Press |access-date=19 September 2020 |url=https://archive.org/details/nasa_techdoc_19750018887 |page=46 |date=1 June 1975 |quote=The lack of evidence that the Venusian atmosphere is transparent at 3 cm wavelength range, the difficulty of explaining such a high surface temperature, and a much lower brightness temperature measured by Kuz'min and Salmonovich [80, 81] and Gibson [310] at a shorter wavelength of 8 mm all provided a basis for a different interpretation of the radio astronomy measurement results offered by Jones [366].}} Two competing theories explained the unusual radio spectrum, one suggesting the high temperatures originated in the ionosphere, and another suggesting a hot planetary surface.

In 1962, Mariner 2, the first successful mission to Venus, measured the planet's temperature for the first time, and found it to be "about 500 degrees Celsius (900 degrees Fahrenheit)."{{Cite web|url=http://www.nasa.gov/multimedia/imagegallery/image_feature_964.html|title=Mariner 2|first=NASA Content|last=Administrator|date=6 March 2015|website=NASA}} Since then, increasingly clear evidence from various space probes showed Venus has an extreme climate, with a greenhouse effect generating a constant temperature of about {{convert|500|C|F|abbr=on}} on the surface. The atmosphere contains sulfuric acid clouds. In 1968, NASA reported that air pressure on the Venusian surface was 75 to 100 times that of Earth.{{Cite web|url=http://www.jpl.nasa.gov/news/news.php?feature=6100|title=Venus Air Pressure|website=NASA/JPL}} This was later revised to 92 bars,{{Cite web|url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html|title=Venus Fact Sheet|website=nssdc.gsfc.nasa.gov}} almost 100 times that of Earth and similar to that of more than {{cvt|1000|m|ft}} deep in Earth's oceans. In such an environment, and given the hostile characteristics of the Venusian weather, life as we know it is highly unlikely to occur.

{{Wide image|Foto de Venera 9.png|800px|align-cap=center|Venera 9 returned the first image from the surface of another planet in 1975.{{cite web |title=Venera 9's landing site |url=https://www.planetary.org/space-images/20120907_venera_9_panorama_stryk |website=The Planetary Society |access-date=16 September 2020 |language=en}}}}

Past habitability potential

Scientists have speculated that if liquid water existed on its surface before the runaway greenhouse effect heated the planet, microbial life may have formed on Venus, but it may no longer exist.Bruce Dorminey, [https://www.forbes.com/sites/brucedorminey/2016/03/28/venus-likely-had-past-life-next-step-is-finding-it/ "Venus Likely Had Past Life; Next Step Is Finding It"], Forbes, 28 March 2016. Assuming the process that delivered water to Earth was common to all the planets near the habitable zone, it has been estimated that liquid water could have existed on its surface for up to 600 million years during and shortly after the Late Heavy Bombardment, which could be enough time for simple life to form, but this figure can vary from as little as a few million years to as much as a few billion.{{cite web|url=http://www.esa.int/Our_Activities/Space_Science/Venus_Express/Was_Venus_once_a_habitable_planet |title=Was Venus once a habitable planet? |date=24 June 2010 |publisher=European Space Agency |access-date=22 May 2016}}{{cite web |url=http://www.universetoday.com/67240/was-venus-once-a-waterworld/ |title=Was Venus once a waterworld? |date=24 June 2010 |author=Nancy Atkinson |publisher=Universe Today |access-date=22 May 2016}}{{cite web |url=http://www.space.com/283-venus-alive-signs.html |title=Was Venus Alive? 'The Signs are Probably There' |date=26 August 2004 |author=Henry Bortman |publisher=Space.com |access-date=22 May 2016}}{{cite web |url=http://www.nasa.gov/feature/goddard/2016/nasa-climate-modeling-suggests-venus-may-have-been-habitable |title=NASA Climate Modeling Suggests Venus May Have Been Habitable |author= |date=11 August 2016 |website=NASA.gov |publisher=NASA |access-date=15 August 2016 }}{{Cite journal|arxiv=1608.00706 |title=Was Venus the First Habitable World of our Solar System?' |journal=Geophysical Research Letters |volume=43 |issue=16 |pages=8376–8383 |date=2 August 2016 |author=Michael J. Way |doi=10.1002/2016GL069790 |bibcode=2016GeoRL..43.8376W |pmid=28408771 |pmc=5385710 }} A study published in September 2019 concluded that Venus may have had surface water and a habitable condition for around 3 billion years and may have been in this condition until 700 to 750 million years ago. If correct, this would have been an ample amount of time for the formation of life,{{Cite web|url=http://www.sci-news.com/space/planetaryscience/habitable-venus-07619.html|title=Venus May Have Been Habitable for Three Billion Years {{!}} Planetary Science {{!}} Sci-News.com|website=Breaking Science News {{!}} Sci-News.com|date=23 September 2019 |language=en-US|access-date=2019-09-24}} and for microbial life to evolve to become aerial.{{cite web |url=http://www.dailygalaxy.com/my_weblog/2012/06/did-the-early-venus-harbor-life-weekend-feature.html |title=Did the Early Venus Harbor Life? (Weekend Feature) |date=2 June 2012 |publisher=The Daily Galaxy |access-date=22 May 2016 |archive-url=https://web.archive.org/web/20171028012143/http://www.dailygalaxy.com/my_weblog/2012/06/did-the-early-venus-harbor-life-weekend-feature.html |archive-date=28 October 2017 |url-status=dead }} Since then, there have been more studies and climate models, with different conclusions.

There has been very little analysis of Venusian surface material, so it is possible that evidence of past life, if it ever existed, could be found with a probe capable of enduring Venus's current extreme surface conditions.{{cite web |url=https://www.newscientist.com/article/dn12769-did-venuss-ancient-oceans-incubate-life/ |title=Did Venus's ancient oceans incubate life? |date=10 October 2007 |author=David Shiga |publisher=New Scientist |access-date=22 May 2016}} However, the resurfacing of the planet in the past 500 million years{{cite journal |last=Strom |first=Robert G. |author2=Schaber, Gerald G. |author3=Dawson, Douglas D. |date=25 May 1994 |title=The global resurfacing of Venus |journal=Journal of Geophysical Research |volume=99 |issue=E5 |pages=10899–10926 |doi=10.1029/94JE00388 |bibcode=1994JGR....9910899S|url=https://zenodo.org/record/1231347 }} means that it is unlikely that ancient surface rocks remain, especially those containing the mineral tremolite which, theoretically, could have encased some biosignatures.

Studies reported on 26 October 2023 suggest Venus, for the first time, may have had plate tectonics during ancient times, and, as a result, may have had a more habitable environment, and possibly one capable of life forms.{{cite news |last=Chang |first=Kenneth |title=Billions of Years Ago, Venus May Have Had a Key Earthlike Feature - A new study makes the case that the solar system's hellish second planet once may have had plate tectonics that could have made it more hospitable to life. |url=https://www.nytimes.com/2023/10/26/science/venus-plate-tectonics-life.html |date=26 October 2023 |work=The New York Times |url-status=live |archive-url=https://archive.today/20231026181052/https://www.nytimes.com/2023/10/26/science/venus-plate-tectonics-life.html |archive-date=26 October 2023 |access-date=27 October 2023 }}{{cite journal |author=Weller, Matthew B. |display-authors=et al. |title=Venus's atmospheric nitrogen explained by ancient plate tectonics |url=https://www.nature.com/articles/s41550-023-02102-w |date=26 October 2023 |journal=Nature Astronomy |volume=7 |issue=12 |pages=1436–1444 |doi=10.1038/s41550-023-02102-w |bibcode=2023NatAs...7.1436W |url-status=live |archive-url=https://archive.today/20231027132655/https://www.nature.com/articles/s41550-023-02102-w |archive-date=27 October 2023 |access-date=27 October 2023 }}

= Suggested panspermia events =

It has been speculated that life on Venus may have come to Earth through lithopanspermia, via the ejection of icy bolides that facilitated the preservation of multicellular life on long interplanetary voyages. "Current models indicate that Venus may have been habitable. Complex life may have evolved on the highly irradiated Venus, and transferred to Earth on asteroids. This model fits the pattern of pulses of highly developed life appearing, diversifying and going extinct with astonishing rapidity through the Cambrian and Ordovician periods, and also explains the extraordinary genetic variety which appeared over this period."{{Cite arXiv | eprint=1608.03074| last1=Cartwright| first1=Annabel| title=The Venus Hypothesis| year=2016| class=astro-ph.EP}} This theory, however, is a fringe one, and is seen as being unlikely.{{Cite book |last=May |first=Andrew |title=Astrobiology: The Search for Life Elsewhere in the Universe |year=2019 |isbn=978-1785783425 |location=London |publication-date=2019 |language=English |quote=Although they were part of the scientific establishment—Hoyle at Cambridge and Wickramasinghe at the University of Wales—their views on the topic were far from mainstream, and panspermia remains a fringe theory}}

= Cataclysmic events =

Between 700 and 750 million years ago, a near-global resurfacing event triggered the release of carbon dioxide from rock on the planet, which transformed its climate.{{cite web |url=https://edition.cnn.com/2019/09/20/world/venus-habitability-scn/index.html |title=Venus was potentially habitable until a mysterious event happened |website=CNN |date=20 September 2019}} In addition, according to a study from researchers at the University of California, Riverside, Venus would be able to support life if Jupiter had not altered its orbit around the Sun.{{cite web |url=https://edition.cnn.com/2020/10/01/world/venus-habitable-jupiter-scli-intl-scn/index.html |title=Venus isn't habitable -- and it could be all Jupiter's fault |website=CNN |date=1 October 2020 }}

Present habitability of its atmosphere

=Atmospheric conditions=

Although there is little possibility of existing life near the surface of Venus, the altitudes about {{convert|50|km|mi|abbr=on}} above the surface have a mild temperature, and hence there are still some opinions in favor of such a possibility in the atmosphere of Venus.[http://www.maik.ru/cgi-perl/search.pl?type=abstract&name=solsys&number=1&year=12&page=41 Venus as a Natural Laboratory for Search of Life in High Temperature Conditions: Events on the Planet on March 1, 1982] {{Webarchive|url=https://web.archive.org/web/20151107053831/http://www.maik.ru/cgi-perl/search.pl?type=abstract&name=solsys&number=1&year=12&page=41 |date=7 November 2015 }}, L. V. Ksanfomality, published in [http://www.maik.ru/contents/solsys/solsys1_12v46cont.htm Astronomicheskii Vestnik, Vol. 46, No. 1, 2012] {{webarchive|url=https://web.archive.org/web/20160304051810/http://www.maik.ru/contents/solsys/solsys1_12v46cont.htm |date=4 March 2016 }}. The idea was first brought forward by German physicist Heinz Haber in 1950.{{Cite web|url=https://archive.org/details/DTIC_AD0159052/page/n21/mode/2up|title=Epitome of Space Medicine|publisher=Defense Technical Information Center|author=Fritz Haber|date=October 1950}} In September 1967, Carl Sagan and Harold Morowitz published an analysis of the issue of life on Venus in the journal Nature.{{Cite journal|title=Life on Venus|journal=Astrobiology|volume=11|issue=9|pages=931–932|doi=10.1089/ast.2011.9270|pmid=22059693|bibcode=2011AsBio..11..931M|year=2011|last1=Morowitz|first1=Harold}}

In the analysis of mission data from the Venera, Pioneer Venus and Magellan missions, it was discovered that carbonyl sulfide, hydrogen sulfide and sulfur dioxide were present together in the upper atmosphere. Venera also detected large amounts of toxic chlorine just below the Venusian cloud cover.{{cite book|author=David Harry Grinspoon|title=Venus Revealed: A New Look Below the Clouds of Our Mysterious Twin Planet|url=https://books.google.com/books?id=Un_vAAAAMAAJ|year=1997|publisher=Addison-Wesley Pub.|isbn=978-0-201-40655-9}} Carbonyl sulfide is difficult to produce inorganically,{{cite journal| archive-url=https://web.archive.org/web/20110807004311/http://gltrs.grc.nasa.gov/reports/2003/TM-2003-212310.pdf| url=http://gltrs.grc.nasa.gov/reports/2003/TM-2003-212310.pdf| archive-date=7 August 2011| title=Astrobiology: the Case for Venus| last=Landis| first=Geoffrey A.| journal=Journal of the British Interplanetary Society| volume=56| issue=7/8| date=2003| pages=250–254| url-status=dead| bibcode = 2003JBIS...56..250L }} but it can be produced by volcanism.{{cite book | last = Seinfeld | first = J. | title = Atmospheric Chemistry and Physics | publisher = J. Wiley | location = London | year = 2006 | isbn = 978-1-60119-595-1 }} Sulfuric acid is produced in the upper atmosphere by the Sun's photochemical action on carbon dioxide, sulfur dioxide, and water vapor.{{cite web |url=http://m.esa.int/Our_Activities/Space_Science/Venus_Express/Acid_clouds_and_lightning |title=Venus Express: Acid clouds and lightning |work=European Space Agency (ESA) |access-date=8 September 2016 }} The re-analysis of Pioneer Venus data in 2020 has found part of chlorine and all of hydrogen sulfide spectral features are instead phosphine-related, meaning lower than thought concentration of chlorine and non-detection of hydrogen sulfide.

Solar radiation constrains the atmospheric habitable zone to between 51 km (65 °C) and 62 km (−20 °C) altitude, within the acidic clouds. It has been speculated that clouds in the atmosphere of Venus could contain chemicals that can initiate forms of biological activity and have zones where photophysical and chemical conditions allow for Earth-like phototrophy.{{cite web|last=David|first=Leonard|archive-url=https://web.archive.org/web/20030216063036/http://www.space.com/scienceastronomy/astrobio_venus_030211.html|url=http://www.space.com/scienceastronomy/astrobio_venus_030211.html|title=Life Zone on Venus Possible|website=Space.com|date=11 February 2003|archive-date=16 February 2003 |access-date=30 December 2015}}{{cite journal |first1=Dirk | last1=Schulze-Makuch |first2=David H. | last2=Grinspoon |first3=Ousama | last3=Abbas |first4=Louis N. | last4=Irwin |first5=Mark A. | last5=Bullock | title = A Sulfur-Based Survival Strategy for Putative Phototrophic Life in the Venusian Atmosphere. | journal = Astrobiology | volume = 4 | number = 1 | pages = 11–18 | date = March 2004 | doi= 10.1089/153110704773600203|bibcode = 2004AsBio...4...11S | pmid=15104900}}{{cite journal |last1=Mogul |first1=Rakesh |last2=Limaye |first2=Sanjay S. |last3=Lee |first3=Yeon Joo |last4=Pasillas |first4=Michael |title=Potential for Phototrophy in Venus' Clouds |journal=Astrobiology |date=1 October 2021 |volume=21 |issue=10 |pages=1237–1249 |doi=10.1089/ast.2021.0032 |pmid=34569810 |bibcode=2021AsBio..21.1237M |s2cid=237944209 |issn=1531-1074|doi-access=free }}

=Potential biomarkers=

It has been speculated that any hypothetical microorganisms inhabiting the atmosphere, if present, could employ ultraviolet light (UV) emitted by the Sun as an energy source, which could be an explanation for the dark lines (called "unknown UV absorber") observed in the UV photographs of Venus.{{cite journal |title=Reassessing the Possibility of Life on Venus: Proposal for an Astrobiology Mission |journal=Astrobiology |date=5 July 2004 |last1=Schulze-Makuch |first1=Dirk |last2=Irwin |first2=Louis N. |volume=2 |issue=2 |pages=197–202 |doi=10.1089/15311070260192264 |bibcode = 2002AsBio...2..197S |pmid=12469368}}{{Cite web|title=Could Dark Streaks in Venus' Clouds Be Microbial Life?|url=https://astrobiology.nasa.gov/news/could-dark-streaks-in-venus-clouds-be-microbial-life/|date=1 February 2017|website=astrobiology.nasa.gov|language=en-EN}} The existence of this "unknown UV absorber" prompted Carl Sagan to publish an article in 1963 proposing the hypothesis of microorganisms in the upper atmosphere as the agent absorbing the UV light.{{Cite news|url=https://astronomy.com/news/2019/08/mysterious-dark-patches-in-venus-clouds-are-affecting-the-weather-there| title=Mysterious dark patches in Venus' clouds are affecting the weather there.| author=Erica Naone| website=astronomy.com| date=29 August 2019}}

In August 2019, astronomers reported a newly discovered long-term pattern of UV light absorbance and albedo changes in the atmosphere of Venus and its weather, that is caused by "unknown absorbers" that may include unknown chemicals or even large colonies of microorganisms high up in the atmosphere.{{cite news |last=Anderson |first=Paul |title=Could microbes be affecting Venus' climate? – Unusual dark patches in Venus' atmosphere – called "unknown absorbers" – play a key role in the planet's climate and albedo, according to a new study. But what are they? That's still a mystery. |url=https://earthsky.org/space/could-microbes-be-affecting-venus-climate |date=3 September 2019 |work=Earth & Sky |access-date=3 September 2019 }}{{cite journal |author=Lee, Yeon Joo |display-authors=et al. |title=Long-term Variations of Venus's 365 nm Albedo Observed by Venus Express, Akatsuki, MESSENGER, and the Hubble Space Telescope |date=26 August 2019 |journal=The Astronomical Journal |volume=158 |issue=3 |pages=126–152 |doi=10.3847/1538-3881/ab3120|bibcode=2019AJ....158..126L |arxiv=1907.09683 |s2cid=198179774 |doi-access=free }}

In January 2020, astronomers reported evidence that suggests Venus is currently (within 2.5 million years from present) volcanically active, and the residue from such activity may be a potential source of nutrients for possible microorganisms in the Venusian atmosphere.{{cite news |last=Hall |first=Sannon |title=Volcanoes on Venus Might Still Be Smoking - Planetary science experiments on Earth suggest that the sun's second planet might have ongoing volcanic activity. |url=https://www.nytimes.com/2020/01/09/science/venus-volcanoes-active.html |date=9 January 2020 |work=The New York Times |access-date=10 January 2020 }}{{cite journal |author=Filiberto, Justin |title=Present-day volcanism on Venus as evidenced from weathering rates of olivine |date=3 January 2020 |journal=Science |volume=6 |number=1 |doi=10.1126/sciadv.aax7445 |page=eaax7445|pmid=31922004 |pmc=6941908 |bibcode=2020SciA....6.7445F |doi-access=free }}{{cite journal |author=Limaye, Sanjay S. |title=Venus' Spectral Signatures and the Potential for Life in the Clouds |date=12 September 2018 |journal=Astrobiology |volume=18 |number=9 |doi=10.1089/ast.2017.1783 |pmid=29600875 |pmc=6150942 |pages=1181–1198 |bibcode=2018AsBio..18.1181L }}

In 2021, it was suggested the color of "unknown UV absorber" match that of "red oil", a known substance comprising a mix of organic carbon compounds dissolved in concentrated sulfuric acid.

==Phosphine==

Research published in September 2020 indicated the detection of phosphine (PH₃) in Venus's atmosphere by Atacama Large Millimeter Array (ALMA) telescope that was not linked to any known abiotic method of production present or possible under Venusian conditions.{{cite news |last1=Drake |first1=Nadia |author-link=Nadia Drake |title=Possible sign of life on Venus stirs up heated debate |url=https://www.nationalgeographic.com/science/2020/09/possible-sign-of-life-found-on-venus-phosphine-gas/ |archive-url=https://web.archive.org/web/20200914153820/https://www.nationalgeographic.com/science/2020/09/possible-sign-of-life-found-on-venus-phosphine-gas/ |url-status=dead |archive-date=14 September 2020 |access-date=14 September 2020 |work=National Geographic |date=14 September 2020}}{{cite journal |author=Greaves, Jane S. |display-authors=et al. |title=Phosphine gas in the cloud decks of Venus |date=14 September 2020 |journal=Nature Astronomy |volume=5 |issue=7 |pages=655–664 |doi=10.1038/s41550-020-1174-4 |arxiv=2009.06593 |bibcode=2021NatAs...5..655G |doi-access=free }}{{cite news |last1=Stirone |first1=Shannon |last2=Chang |first2=Kenneth |last3=Overbye |first3=Dennis |title=Life on Venus? Astronomers See a Signal in Its Clouds - The detection of a gas in the planet's atmosphere could turn scientists' gaze to a planet long overlooked in the search for extraterrestrial life. |url=https://www.nytimes.com/2020/09/14/science/venus-life-clouds.html |date=14 September 2020 |work=The New York Times |access-date=14 September 2020 }} However, the claimed detection of phosphine was disputed by several subsequent studies. A molecule like phosphine is not expected to persist in the Venusian atmosphere since, under the ultraviolet radiation, it will eventually react with water and carbon dioxide. PH₃ is associated with anaerobic ecosystems on Earth, and may indicate life on anoxic planets.{{cite news |last1=Steller |first1=Luke |last2=Kranendonk |first2=Martin Van |title=Experts Explain: If There Is Life on Venus, How Could It Have Got There? |url=https://scitechdaily.com/experts-explain-if-there-is-life-on-venus-how-could-it-have-got-there/ |date=26 September 2020 |work=SciTechDaily.com |access-date=27 September 2020 }} Related studies suggested that the initially claimed concentration of phosphine (20 ppb) in the clouds of Venus indicated a "plausible amount of life," and further, that the typical predicted biomass densities were "several orders of magnitude lower than the average biomass density of Earth’s aerial biosphere.”{{cite news |last=Cimone |first=Matthew |title=How Much Life Would Be Required to Create the Phosphine Signal on Venus? |url=https://www.universetoday.com/147891/how-much-life-would-be-required-to-create-the-phosphine-signal-on-venus/ |date=20 September 2020 |work=Universe Today |access-date=22 September 2020 }}{{cite arXiv |last1=Lingam |first1=Manasvi |last2=Loeb |first2=Abraham |title=On The Biomass Required To Produce Phosphine Detected In The Cloud Decks Of Venus |date=17 September 2020 |class=astro-ph.EP |eprint=2009.07835v1}} {{as of|2019}}, no known abiotic process generates phosphine gas on terrestrial planets (as opposed to gas giants{{cite journal |title= Phosphine on Jupiter and Saturn from Cassini/CIRS |last1= Fletcher |first1=LN |last2=Orton |first2=GS |last3=Teanby |first3=NA |last4=Irwin |first4=PGJ |date= 2009 |journal= Icarus |volume= 202 |number= 2 |pages= 543–564 |doi= 10.1016/j.icarus.2009.03.023 |bibcode= 2009Icar..202..543F |url= https://www.sciencedirect.com/science/article/abs/pii/S0019103509001328 }}) in appreciable quantities. The phosphine can be generated by geological process of weathering olivine lavas containing inorganic phosphides, but this process requires an ongoing and massive volcanic activity.{{citation |arxiv=2009.11904v2 |url=https://www.universetoday.com/148094/maybe-volcanoes-could-explain-the-phosphine-in-venus-atmosphere/ |title=Hypothesis Perspectives: Might active volcanisms today contribute to the presence of phosphine in Venus's atmosphere? |year=2020 |last1=Truong |first1=Ngoc |last2=Lunine |first2=Jonathan I. }} Therefore, detectable amounts of phosphine could indicate life.{{cite journal |title= Phosphine as a Biosignature Gas in Exoplanet Atmospheres |last1= Sousa-Silva |first1=Clara|author1-link=Clara Sousa-Silva |last2=Seager |first2=Sara |last3=Ranjan |first3=Sukrit |last4=Petkowski |first4=Janusz Jurand |last5=Zhan |first5=Zhuchang |last6=Hu |first6=Renyu |last7=Bains |first7=William |publication-date= February 2020 |journal= Astrobiology |volume= 20 |number= 2 |date= 11 October 2019 |doi= 10.1089/ast.2018.1954 |bibcode= 2020AsBio..20..235S|pages= 235–268 |pmid= 31755740 |s2cid= 204401807 |arxiv= 1910.05224 }}{{cite news |title= Phosphine Could Signal Existence of Alien Anaerobic Life on Rocky Planets |url= http://www.sci-news.com/astronomy/phosphine-biosignature-gas-07957.html |date= 26 December 2019 |newspaper= Sci-News }} In July 2021, a volcanic origin was proposed for phosphine, by extrusion from the mantle.{{Cite journal |last1=Truong |first1=Ngoc |last2=Lunine |first2=Jonathan I. |date=2021-07-20 |title=Volcanically extruded phosphides as an abiotic source of Venusian phosphine |journal=Proceedings of the National Academy of Sciences |language=en |volume=118 |issue=29 |pages=e2021689118 |doi=10.1073/pnas.2021689118 |pmid=34253608 |pmc=8307446 |bibcode=2021PNAS..11821689T |issn=0027-8424 |doi-access=free }}

In a statement published on October 5, 2020, on the website of the International Astronomical Union's commission F3 on astrobiology, the authors of the September 2020 paper about phosphine were accused of unethical behaviour and criticized for being unscientific and misleading the public.{{Cite web|title=Statement from Commission F3 (Astrobiology) of the IAU on Press Reports regarding Detection of Phosphine in Venus|url=https://www.iau.org/static/science/scientific_bodies/commissions/f3/commission-f3-statement-5-october-2020.pdf|publisher=International Astronomical Union - Commission F3 Astrobiology|date=5 October 2020|website=www.iau.org|archive-url=https://web.archive.org/web/20201007184627/https://www.iau.org/static/science/scientific_bodies/commissions/f3/commission-f3-statement-5-october-2020.pdf|archive-date=7 October 2020}} Members of that commission have since distanced themselves from the IAU statement, claiming that it had been published without their knowledge or approval.{{cite tweet |user=Mike_Garrett |number=1313891539228258310 |date=7 October 2020 |title=Absolutely shocked & dismayed by this statement from the @IAU_org - as a member of IAU Com F3, I completely disagree - this is how science progresses }}{{cite tweet |user=ExoCytherean |number=1314053850765033473 |date=7 October 2020 |title=I'm also a member of F3 and I didn't even know about the letter until it was published this morning. How on Earth is the commission publishing statements that claim to represent its membership when they are not even consulted? }} The statement was removed from the IAU website shortly thereafter. The IAU's media contact Lars Lindberg Christensen stated that IAU did not agree with the content of the letter, and that it had been published by a group within the F3 commission, not IAU itself.{{cite news|title=Discovery that indicated possibility of extra-terrestrial life attacked by group of astrobiologists|url=https://indianexpress.com/article/technology/science/discovery-venus-planet-extra-terrestrial-life-attacked-astrobiologists-6715945/|author=Amitabh Sinha|website=indianexpress.com|date=8 October 2020|access-date=8 October 2020}}

By late October 2020, the review of data processing of the data collected by both ALMA used in original publication of September 2020, and later James Clerk Maxwell Telescope (JCMT) data, has revealed background calibration errors resulting in multiple spurious lines, including the spectral feature of phosphine. Re-analysis of data with a proper subtraction of background either does not result in the detection of the phosphine{{citation|arxiv=2010.09761|title=Re-analysis of the 267-GHz ALMA observations of Venus No statistically significant detection of phosphine|year=2020|last1=Snellen|first1=I. A. G.|last2=Guzman-Ramirez|first2=L.|last3=Hogerheijde|first3=M. R.|last4=Hygate|first4=A. P. S.|last5=van der Tak|first5=F. F. S.|journal=Astronomy and Astrophysics|volume=644|pages=L2|doi=10.1051/0004-6361/202039717|bibcode=2020A&A...644L...2S|s2cid=224803085}}{{citation|arxiv=2010.15188|title=The statistical reliability of 267 GHz JCMT observations of Venus: No significant evidence for phosphine absorption|year=2021|last1=Thompson|first1=M. A.|journal=Monthly Notices of the Royal Astronomical Society: Letters|volume=501|issue=1|pages=L18–L22|doi=10.1093/mnrasl/slaa187|doi-access=free |bibcode=2021MNRAS.501L..18T|s2cid=225103303}}{{citation|arxiv=2010.14305|title=No evidence of phosphine in the atmosphere of Venus from independent analyses|year=2021|last1=Villanueva|first1=Geronimo|last2=Cordiner|first2=Martin|last3=Irwin|first3=Patrick|author4=Imke de Pater|last5=Butler|first5=Bryan|last6=Gurwell|first6=Mark|last7=Milam|first7=Stefanie|last8=Nixon|first8=Conor|last9=Luszcz-Cook|first9=Statia|last10=Wilson|first10=Colin|last11=Kofman|first11=Vincent|last12=Liuzzi|first12=Giuliano|last13=Faggi|first13=Sara|last14=Fauchez|first14=Thomas|last15=Lippi|first15=Manuela|last16=Cosentino|first16=Richard|last17=Thelen|first17=Alexander|last18=Moullet|first18=Arielle|last19=Hartogh|first19=Paul|last20=Molter|first20=Edward|last21=Charnley|first21=Steve|last22=Arney|first22=Giada|last23=Mandell|first23=Avi|last24=Biver|first24=Nicolas|last25=Vandaele|first25=Ann|author26=Katherine de Kleer|last27=Kopparapu|first27=Ravi|journal=Nature Astronomy|volume=5|issue=7|pages=631–635|doi=10.1038/s41550-021-01422-z|bibcode=2021NatAs...5..631V|s2cid=236090264}} or detects it with concentration of 1ppb, 20 times below original estimate.

File:Example PH3 spectrum, from the circled region superimposed on the continuum image.png

On 16 November 2020, ALMA staff released a corrected version of the data used by the scientists of the original study published on 14 September.

On the same day, authors of this study published a re-analysis as a preprint using the new data that concludes the planet-averaged PH₃ abundance to be ~7 times lower than what they detected with data of the previous ALMA processing, to likely vary by location and to be reconcilable with the JCMT detection of ~20 times this abundance if it varies substantially in time. They also respond to points raised in a critical study by Villanueva et al. that challenged their conclusions and find that so far the presence of no other compound can explain the data.{{cite journal |last1=Witze |first1=Alexandra |title=Prospects for life on Venus fade — but aren't dead yet |url=https://www.nature.com/articles/d41586-020-03258-5 |access-date=9 December 2020 |journal=Nature |date=17 November 2020 |volume=587 |issue=7835 |pages=532 |language=en |doi=10.1038/d41586-020-03258-5|pmid=33208909 |bibcode=2020Natur.587..532W |s2cid=227067294 }}{{cite news |last1=Chan |first1=Athena |title=Life On Venus: Phosphine Signals Actually Fainter As Scientists Re-Analyze Earlier Findings |url=https://www.ibtimes.com/life-venus-phosphine-signals-actually-fainter-scientists-re-analyze-earlier-findings-3084486 |access-date=9 December 2020 |work=International Business Times |date=18 November 2020}} The authors reported that more advanced processing of the JCMT data was ongoing.

===Other measurements of phosphine===

Re-analysis of the in situ data gathered by Pioneer Venus Multiprobe in 1978 has also revealed the presence of phosphine and its dissociation products in the atmosphere of Venus.{{citation|arxiv=2009.12758|title=Is Phosphine in the Mass Spectra from Venus' Clouds?|year=2020|last1=Mogul|first1=Rakesh|last2=Limaye|first2=Sanjay S.|last3=Way|first3=M. J.|last4=Cordova, Jr|first4=Jamie A.|doi=10.1002/essoar.10504552.4|s2cid=231854943}} In 2021, a further analysis detected trace amounts of ethane, hydrogen sulfide, nitrite, nitrate, hydrogen cyanide, and possibly ammonia.{{cite journal |last1=Mogul |first1=Rakesh |last2=Limaye |first2=Sanjay S. |last3=Way |first3=M. J. |last4=Cordova |first4=Jaime A. |title=Venus' Mass Spectra Show Signs of Disequilibria in the Middle Clouds |journal=Geophysical Research Letters |date=14 April 2021 |volume=48 |issue=7 |pages=e91327 |doi=10.1029/2020GL091327 |pmid=34219837 |pmc=8244101 |arxiv=2009.12758 |bibcode=2021GeoRL..4891327M }}

The phosphine signal was also detected in data collected using the JCMT, though much weaker than that found using ALMA.

In October 2020, a reanalysis of archived infrared spectrum measurement in 2015 did not reveal any phosphine in the Venusian atmosphere, placing an upper limit of phosphine volume concentration 5 parts per billion (a quarter of value measured in radio band in 2020).{{citation|arxiv=2010.07817|title=A stringent upper limit of the PH3 abundance at the cloud top of Venus|year=2020|doi=10.1051/0004-6361/202039559|last1=Encrenaz|first1=T.|author1-link=Thérèse Encrenaz|last2=Greathouse|first2=T. K.|last3=Marcq|first3=E.|last4=Widemann|first4=T.|last5=Bézard|first5=B.|last6=Fouchet|first6=T.|last7=Giles|first7=R.|last8=Sagawa|first8=H.|last9=Greaves|first9=J.|author-link9=Jane Greaves|last10=Sousa-Silva|first10=C.|journal=Astronomy & Astrophysics|volume=643|pages=L5|bibcode=2020A&A...643L...5E|s2cid=222377688}} However, the wavelength used in these observations (10 microns) would only have detected phosphine at the very top of the clouds of the atmosphere of Venus.

BepiColombo, launched in 2018 to study Mercury, flew by Venus on October 15, 2020, and on August 10, 2021. Johannes Benkhoff, project scientist, believed BepiColombo's MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) could possibly detect phosphine, but "we do not know if our instrument is sensitive enough".{{cite news |last1=O'Callaghan |first1=Jonathan |title=In A Complete Fluke, A European Spacecraft Is About To Fly Past Venus – And Could Look For Signs Of Life |url=https://www.forbes.com/sites/jonathanocallaghan/2020/09/16/in-a-complete-fluke-a-european-spacecraft-is-about-to-fly-past-venus--and-could-look-for-signs-of-life/ |work=Forbes |date=September 16, 2020 |language=en |access-date=27 September 2020}}

In 2022, observations of Venus using the SOFIA airborne infrared telescope failed to detect phosphine, with an upper limit on the concentration of 0.8 ppb announced for Venusian altitudes 75–110 km.{{citation|arxiv=2210.13519|year=2022|title=Phosphine in the Venusian Atmosphere: A Strict Upper Limit from SOFIA GREAT Observations|doi=10.1029/2022GL101055 |last1=Cordiner |first1=M. A. |last2=Villanueva |first2=G. L. |last3=Wiesemeyer |first3=H. |last4=Milam |first4=S. N. |last5=De Pater |first5=I. |last6=Moullet |first6=A. |last7=Aladro |first7=R. |last8=Nixon |first8=C. A. |last9=Thelen |first9=A. E. |last10=Charnley |first10=S. B. |last11=Stutzki |first11=J. |last12=Kofman |first12=V. |last13=Faggi |first13=S. |last14=Liuzzi |first14=G. |last15=Cosentino |first15=R. |last16=McGuire |first16=B. A. |journal=Geophysical Research Letters |volume=49 |issue=22 |bibcode=2022GeoRL..4901055C |s2cid=253086965 }} A subsequent reanalysis of the SOFIA data using nonstandard calibration techniques resulted in a phosphine detection at the concentration level ~ 1 ppb,{{citation|arxiv=2211.09852|year=2023|title=Comment on "Phosphine in the Venusian Atmosphere: A Strict Upper Limit from SOFIA GREAT Observations" by Cordiner et al|last1=Greaves |first1=Jane S. |author1-link=Jane Greaves|last2=Petkowski |first2=Janusz J. |last3=Richards |first3=Anita M. S. |last4=Sousa-Silva |first4=Clara |last5=Seager |first5=Sara |last6=Clements |first6=David L. |journal=Geophysical Research Letters |volume=50 |issue=23 |doi=10.1029/2023GL103539 |bibcode=2023GeoRL..5003539G }} but this work is yet to be peer-reviewed and therefore remains questionable. If present, phosphine appears to be more abundant in pre-morning parts of the Venusian atmosphere.

In 2024 the existence of phosphene was confirmed.https://www.chemistryworld.com/news/controversial-phosphine-findings-on-venus-corroborated/4020063.article

===Planned measurements of phosphine levels===

ALMA restarted 17 March 2021 after a year-long shutdown in response to the COVID-19 pandemic and may enable further observations that could provide insights for the ongoing investigation.{{cite web |last1=Voosen |first1=Paul |title=Potential signs of life on Venus are fading as astronomers downgrade their original claims |url=https://www.science.org/content/article/potential-signs-life-venus-are-fading-astronomers-downgrade-their-original-claims |website=Science {{!}} AAAS |access-date=9 December 2020 |language=en |date=17 November 2020}}{{cite web |url=https://alma-telescope.jp/en/news/restart-202103 |title=ALMA science observations have re-started |date=26 March 2021 |website=alma-telescope.jp |publisher=National Astronomical Observatory of Japan |access-date=30 July 2023}}

Despite controversies, NASA is in the beginning stages of sending a future mission to Venus. The Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy mission (VERITAS) would carry radar to view through the clouds to get new images of the surface, of much higher quality than those last photographed thirty-one years ago. The other, Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging Plus (DAVINCI+) would actually go through the atmosphere, sampling the air as it descends, to hopefully detect the phosphine.{{cite web |last1=Byrne |first1=Paul |title=The detection of phosphine in Venus' clouds is a big deal – here's how we can find out if it's a sign of life |url=https://theconversation.com/the-detection-of-phosphine-in-venus-clouds-is-a-big-deal-heres-how-we-can-find-out-if-its-a-sign-of-life-146185 |website=The Conversation |date=18 September 2020 |access-date=18 September 2020}}{{cite web |url=https://www.nasa.gov/press-release/nasa-selects-four-possible-missions-to-study-the-secrets-of-the-solar-system |newspaper=NASA |access-date=23 February 2020|title=NASA Selects 4 Possible Missions to Study Secrets of the Solar System |date=13 February 2020 |last1=Brown |first1=Katherine }} In June 2021, NASA announced DAVINCI+ and VERITAS would be selected from four mission concepts picked in February 2020 as part of the NASA's Discovery 2019 competition for launch in the 2028–2030 time frame.{{cite web |url=https://www.nasa.gov/press-release/nasa-selects-2-missions-to-study-lost-habitable-world-of-venus |website=NASA |access-date=2 June 2021|title=NASA Selects 2 Missions to Study 'Lost Habitable' World of Venus |date=2 June 2021 }}

There is also an ongoing long-term monitoring campaign with JCMT to study phosphine and other molecules in Venus's atmosphere.{{cite web |title=JCMT-Venus – monitoring phosphine and other molecules in Venus's atmosphere – James Clerk Maxwell Telescope |url=https://www.eaobservatory.org/jcmt/science/large-programs/jcmt-venus-monitoring-phosphine-and-other-molecules-in-venuss-atmosphere/ |access-date=24 February 2023}}

===Confusion between phosphine and sulfur dioxide lines===

According to new research announced in January 2021, the spectral line at 266.94 GHz attributed to phosphine in the clouds of Venus was more likely to have been produced by sulfur dioxide in the mesosphere.{{cite journal|last1=Lincowski|first1=Andrew P.|last2=Meadows|first2=Victoria S.|last3=Crisp|first3=David|last4=Akins|first4=Alex B.|last5=Schwieterman|first5=Edward W.|last6=Arney|first6=Giada N.|last7=Wong|first7=Michael L.|last8=Steffes|first8=Paul G.|last9=Parenteau|first9=M. Niki|last10=Domagal-Goldman|first10=Shawn|date=2021-01-24|title=Claimed detection of PH3 in the clouds of Venus is consistent with mesospheric SO2|journal=The Astrophysical Journal|volume=908|issue=2|pages=L44|doi=10.3847/2041-8213/abde47|arxiv=2101.09837|bibcode=2021ApJ...908L..44L|s2cid=231699227 |doi-access=free }} That claim was refuted in April 2021 for being inconsistent with the available data. The detection of PH₃ in the Venusian atmosphere with ALMA was recovered to ~7 ppb.{{citation|arxiv=2104.09285|title=Reply to: No evidence of phosphine in the atmosphere of Venus from independent analyses|year=2021|last1=Greaves|first1=Jane S.|author1-link=Jane Greaves|last2=Richards|first2=Anita M. S.|last3=Bains|first3=William|last4=Rimmer|first4=Paul B.|last5=Clements|first5=David L.|last6=Seager|first6=Sara|last7=Petkowski|first7=Janusz J.|last8=Sousa-Silva|first8=Clara|author8-link=Clara Sousa-Silva|last9=Ranjan|first9=Sukrit|last10=Fraser|first10=Helen J.|journal=Nature Astronomy|volume=5|issue=7|pages=636–639|doi=10.1038/s41550-021-01424-x|bibcode=2021NatAs...5..636G|s2cid=233296859}} By August 2021 it was found the suspected contamination by sulfur dioxide was contributing only 10% to the tentative signal in phosphine spectral line band in ALMA spectra taken in 2019, and about 50% in ALMA spectra taken in 2017.{{citation|arxiv=2108.08393|year=2022|title=Low levels of sulphur dioxide contamination of Venusian phosphine spectra|last1=Greaves|first1=Jane S.|author1-link=Jane Greaves|last2=Rimmer|first2=Paul B.|last3=Richards|first3=Anita M. S.|last4=Petkowski|first4=Janusz J.|last5=Bains|first5=William|last6=Ranjan|first6=Sukrit|last7=Seager|first7=Sara|last8=Clements|first8=David L.|author9=Clara Sousa Silva|last10=Fraser|first10=Helen J.|journal=Monthly Notices of the Royal Astronomical Society |volume=514 |issue=2 |pages=2994–3001 |doi=10.1093/mnras/stac1438 |doi-access=free }}

Speculative biochemistry of Venusian life

Conventional water-based biochemistry was claimed to be impossible in Venusian conditions. In June 2021, calculations of water activity levels in Venusian clouds based on data from space probes showed these to be two magnitudes too low at the examined places for any known extremophile bacteria to survive.{{cite news |title=Scientists say there's no life on Venus — but Jupiter has potential |url=https://www.cbsnews.com/news/alien-life-venus-jupiter-water-activity-clouds-atmosphere/ |access-date=10 July 2021 |work=www.cbsnews.com}}{{cite journal |last1=Hallsworth |first1=John E. |last2=Koop |first2=Thomas |last3=Dallas |first3=Tiffany D. |last4=Zorzano |first4=María-Paz |last5=Burkhardt |first5=Juergen |last6=Golyshina |first6=Olga V. |last7=Martín-Torres |first7=Javier |last8=Dymond |first8=Marcus K. |last9=Ball |first9=Philip |last10=McKay |first10=Christopher P. |title=Water activity in Venus's uninhabitable clouds and other planetary atmospheres |journal=Nature Astronomy |date=28 June 2021 |volume=5 |issue=7 |pages=665–675 |doi=10.1038/s41550-021-01391-3 |bibcode=2021NatAs...5..665H |hdl=10261/261774 |s2cid=237820246 |url=https://www.nature.com/articles/s41550-021-01391-3 |access-date=10 July 2021 |language=en |issn=2397-3366|hdl-access=free }} Alternative calculations based on the estimation of energy costs of obtaining hydrogen in Venus conditions compared to Earth conditions indicate only minor (6.5%) additional energy expenditure during Venusian photosynthesis of glucose.

In August 2021, it was suggested that even saturated hydrocarbons are unstable in ultra-acid conditions of Venusian clouds, making cellular membranes of Venusian life concepts problematic. Instead, it was proposed that Venusian "life" may be based on self-replicating molecular components of "red oil" – a known class of substances consisting of a mixture of polycyclic carbon compounds dissolved in concentrated sulfuric acid.{{citation|arxiv=2108.02286|year=2021|title=Organic Carbon Cycle in the Atmosphere of Venus|last1=Spacek|first1=Jan}} Oppositely, in September 2024 it was reported what while short-chain fatty acids are unstable in concentrated sulfuric acid, it is possible to construct their acid-stable analogs capable of bilayer membrane formation by replacing carboxylic groups with sulfate, amine or phosphate groups.{{citation|arxiv=2409.12982|title=Simple lipids form stable higher-order structures in concentrated sulfuric acid|year=2024}} Also, 19 of the 20 protein-making amino acids (with the exception of tryptophan) and all nucleic acids are stable under Venusian cloud conditions.{{citation|arxiv=2401.01441|year=2024|title=Stability of 20 Biogenic Amino Acids in Concentrated Sulfuric Acid: Implications for the Habitability of Venus' Clouds|doi=10.1089/ast.2023.0082 |last1=Seager |first1=Maxwell D. |last2=Seager |first2=Sara |last3=Bains |first3=William |last4=Petkowski |first4=Janusz J. |journal=Astrobiology |volume=24 |issue=4 |pages=386–396 |bibcode=2024AsBio..24..386S }}{{citation|arxiv=2306.17182|year=2023|title=Stability of nucleic acid bases in concentrated sulfuric acid: Implications for the habitability of Venus' clouds|doi=10.1073/pnas.2220007120 |last1=Seager |first1=Sara |last2=Petkowski |first2=Janusz J. |last3=Seager |first3=Maxwell D. |last4=Grimes |first4=John H. |last5=Zinsli |first5=Zachary |last6=Vollmer-Snarr |first6=Heidi R. |last7=Abd El-Rahman |first7=Mohamed K. |last8=Wishart |first8=David S. |last9=Lee |first9=Brian L. |last10=Gautam |first10=Vasuk |last11=Herrington |first11=Lauren |last12=Bains |first12=William |last13=Darrow |first13=Charles |journal=Proceedings of the National Academy of Sciences |volume=120 |issue=25 |bibcode=2023PNAS..12020007S }}

In December 2021, it was suggested Venusian life – as the chemically most plausible cause – may photochemically produce ammonia from available chemicals, resulting in life-bearing droplets becoming a slurry of ammonium sulfite with a less acidic pH of 1. These droplets would deplete sulfur dioxide in upper cloud layers as they settle down, explaining the observed distribution of sulfur dioxide in the atmosphere of Venus, and may make the clouds no more acidic than some extreme terrestrial environments that harbor life.{{cite journal |last1=Bains |first1=William |last2=Petkowski |first2=Janusz J. |last3=Rimmer |first3=Paul B. |last4=Seager |first4=Sara |title=Production of ammonia makes Venusian clouds habitable and explains observed cloud-level chemical anomalies |journal=Proceedings of the National Academy of Sciences |date=28 December 2021 |volume=118 |issue=52 |pages=e2110889118 |doi=10.1073/pnas.2110889118 |pmid=34930842 |pmc=8719887 |arxiv=2112.10850 |bibcode=2021PNAS..11810889B |s2cid=245353905 |language=en |issn=0027-8424|doi-access=free }}

Speculative life cycles of Venusian life

The hypothesis paper in 2020 has suggested the microbial life of Venus may have a two-stage life cycle. The metabolically active part of such a cycle would have to happen within cloud droplets to avoid a fatal loss of liquid. After such droplets grow large enough to sink under the force of gravity, organisms would fall with them into hotter lower layers and desiccate, becoming small and light enough to be raised again to the habitable layer by gravity waves at a timescale of approximately a year.[https://www.liebertpub.com/doi/full/10.1089/ast.2020.2244 The Venusian Lower Atmosphere Haze as a Depot for Desiccated Microbial Life: A Proposed Life Cycle for Persistence of the Venusian Aerial Biosphere]

The hypothesis paper in 2021 has criticized the concept above, pointing to the large stagnancy of lower haze layers in Venus making return from the haze layer to relatively habitable clouds problematic even for small particles. Instead, an in-cloud evolution model was proposed where organisms are evolving to become maximally absorptive (dark) for the given amount of biomass and the darker, solar-heated areas of cloud are kept afloat by thermal updrafts initiated by organisms itself. Alternatively, microorganisms can be kept aloft by negative photophoresis effect.{{citation|arxiv=2306.07358|year=2024|title=Venus' Atmospheric Chemistry and Cloud Characteristics Are Compatible with Venusian Life|doi=10.1089/ast.2022.0113 |last1=Bains |first1=William |last2=Petkowski |first2=Janusz J. |last3=Seager |first3=Sara |journal=Astrobiology |volume=24 |issue=4 |pages=371–385 |pmid=37306952 |bibcode=2024AsBio..24..371B }}

References

External links

[https://www.youtube.com/watch?v=nNdy-LJWNQs PBS Space Time: Venus May Have Life!]

Category:Astrobiology

Category:Venus