“Life on Venus”的意思、由来-开放百科全书

The speculation of life currently existing on Venus decreased significantly since the early 1960s, when spacecraft began studying Venus and it became clear that the conditions on Venus are extreme compared to those on Earth.

Venus's location closer to the Sun than Earth and the extreme greenhouse effect raising temperatures on the surface to nearly {{convert|735|K|C}}, and the atmospheric pressure 90 times that of Earth, 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 lower-temperature, acidic upper layers of the Venusian atmosphere.^[1]^[2]^[3]

Historical views

Until the mid 20th century, the surface environment of Venus was believed to be similar to Earth, and hence it was widely believed that Venus could harbor life.

In 1870, the British astronomer Richard Proctor said the existence of life on Venus was impossible near its equator,^[4] but possible near its poles.

Since the 1960s, increasingly clear evidence from various space probes showed Venus has an extreme climate, with a greenhouse effect generating a constant temperature of about 500 °C on the surface. The atmosphere contains sulfuric acid clouds and the atmospheric pressure at the surface is 90 bar, almost 100 times that of Earth and similar to that of more than {{convert|1000|m|ft|abbr=on}} deep in Earth's oceans. In such environment, and given the increasingly hostile characteristics of the Venusian weather, the chances of life as we know it are excluded from the surface of Venus.

In September 1967, Carl Sagan and Harold Morowitz published an analysis of the issue of life on Venus to the journal Nature.^[5]

Habitability of its atmosphere

Although there is little possibility of existing life near the surface of Venus, the altitudes about 50 km 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.^[6]^[7]

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.^[7] Carbonyl sulfide is difficult to produce inorganically,^[8] but it can be produced by volcanism.^[9] Sulfuric acid is produced in the upper atmosphere by the Sun's photochemical action on carbon dioxide, sulfur dioxide, and water vapour.^[10]

Solar radiation constrains the atmospheric habitable zone to between 51 km (65 °C) and 62 km (−20 °C) altitude, within the acidic clouds.^[3] It has been speculated that clouds in the atmosphere of Venus could contain chemicals that can initiate forms of biological activity.^[11]^[12] 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 observed in the UV photographs of Venus.^[13]^[14]

Past habitability potential

It is plausible that microbial life originated on Venus if liquid water existed on its surface prior to the heating of the planet by the runaway greenhouse effect, but no longer exists.^[15] 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 few billion.^[16]^[17]^[18]^[19]^[20] This might also have given enough time for microbial life to evolve to be aerial.^[21] 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,^[5]^[22] although the resurfacing of the planet in the past 500 million years^[23] means that it is unlikely that ancient surface rocks remain, especially those containing the mineral tremolite which, theoretically, could have encased some biosignatures.^[22]

See also

References

1. ^{{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|accessdate=30 December 2015}}
2. ^Redfern, Martin (25 May 2004). "Venus clouds 'might harbour life'". BBC News. Retrieved 30 December 2015.
3. ^¹{{cite journal |title=Constraints on a potential aerial biosphere on Venus: I. Cosmic rays |journal=Icarus |date=September 2015 |last=Dartnell |first=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 |url=http://www.sciencedirect.com/science/article/pii/S0019103515002080 |accessdate=20 August 2015 |display-authors=etal|bibcode = 2015Icar..257..396D }}
4. ^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.
5. ^¹{{Cite journal|title=Life on Venus|journal=Astrobiology|volume=11|issue=9|pages=931–932|via=Academic OneFile|doi=10.1089/ast.2011.9270|pmid=22059693|bibcode=2011AsBio..11..931M|year=2011|last1=Morowitz|first1=Harold}}
6. ^Venus as a Natural Laboratory for Search of Life in High Temperature Conditions: Events on the Planet on March 1, 1982, L. V. Ksanfomality, published in 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 }}.
7. ^[https://www.amazon.com/dp/0201328399/ Venus Revealed: A New Look Below the Clouds of Our Mysterious Twin Planet], David Grinspoon, {{ISBN|978-0-201-32839-4}}
8. ^¹{{cite journal| archiveurl=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| archivedate=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| bibcode = 2003JBIS...56..250L }}
9. ^{{cite book | last = Seinfeld | first = J. | title = Atmospheric Chemistry and Physics | publisher = J. Wiley | location = London | year = 2006 | isbn = 978-1-60119-595-1 }}
10. ^{{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) |accessdate=2016-09-08 }}
11. ^{{cite web|last=David|first=Leonard|archiveurl=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|archivedate=16 February 2003 |accessdate=30 December 2015}}
12. ^{{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}}
13. ^{{cite news|url=http://www.abc.net.au/cgi-bin/common/printfriendly.pl?/news/scitech/2002/09/item20020926135029_1.htm|title=Venus could be a haven for life|work=ABC News|date=28 September 2002|accessdate=30 December 2015}}
14. ^{{cite journal |title=Reassessing the Possibility of Life on Venus: Proposal for an Astrobiology Mission |journal=Astrobiology |date=5 July 2004 |last=Schulze-Makuch |first=Dirk |last2=Irwin |first2=Louis N. |volume=2 |issue=2 |pages=197–202 |doi=10.1089/15311070260192264 |bibcode = 2002AsBio...2..197S |pmid=12469368}}
15. ^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, Mar 28, 2016.
16. ^{{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 |accessdate=22 May 2016}}
17. ^{{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 |accessdate=22 May 2016}}
18. ^{{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 |accessdate=22 May 2016}}
19. ^{{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=August 11, 2016 |website=NASA.gov |publisher=NASA |access-date=August 15, 2016 |quote=}}
20. ^{{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 }}
21. ^{{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|accessdate=22 May 2016}}
22. ^¹{{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 |accessdate=22 May 2016}}
23. ^{{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}}