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'''Венера''' е втора [[планета]] од [[Сонце|Сонцето]], орбитирајќи на секои 224.7 [[Земја (планета)|земјини]] денови.<ref name="nasa_venus" /> Го има најдолгиот [[Вртежен период|период на ротација]] (243 дена) од сите други планети во [[Сончев систем|Сончевиот систем]] и ротира во [[Ретроградно и проградно движење|спротивна насока]] од другите планети (што значи дека Сонцето изгрева на [[Полови на астронмските тела|запад]], а заоѓа на исток).<ref>{{cite news |url=https://www.space.com/28357-how-to-live-on-venus.html |title=What Would It Be Like to Live on Venus? |work=Space.com |first=Joseph |last=Castro |date=3 February 2015 |accessdate=15 March 2018}}</ref> Нема ниту еден [[природен сателит]]. Именувана е според [[Венера (божица)|римската божица на љубовта и убавината]]. По [[Месечина]]та, таа е вториот најсјаен објект кој може да се види на ноќното [[небо]], достигнувајќи п[[Привидна ѕвездена величина|привидна магнитуда]] од −4.6 – доволно светла за да направи сенка навечер и, поретко, видлива со [[голо око]] сред бел ден. Максималната видливост планетата ја има пред [[изгрејсонце]] и малку по [[зајдисонце]]то. Затоа, често се именува како [[Деница|утринска ѕвезда]] или [[ѕвезда вечерница]].<ref>{{cite web |url=http://www.digitalsky.org.uk/venus/shadow-of-venus.html |title=In Search of the Venusian Shadow |last=Lawrence |first=Pete |date=2005 |website=Digitalsky.org.uk |accessdate=13 June 2012 |archive-url=https://web.archive.org/web/20120611003523/http://www.digitalsky.org.uk/venus/shadow-of-venus.html |archive-date=11 June 2012 |dead-url=yes}}</ref><ref>{{cite web |url=http://www.fourmilab.ch/images/venus_daytime/ |title=Viewing Venus in Broad Daylight |work=Fourmilab Switzerland |first=John |last=Walker |accessdate=19 April 2017}}</ref> Орбитирајќи во [[Земјина орбита|орбитата на Земјата]], Венера е [[Внатрешни и надворешни планети|внатрешна планета]] и никогаш не изгледа како да се оддалечува далеку од Сонцето; максималното [[аголно растојание]] од Сонцето ([[Издолжување (астрономија)|елонгација]]) е 47.8°.
Венера е [[земјовидна планета]] и понекогаш ја нарекуваат сестра на Земјата поради нивната слична големина, маса, близина до Сонцето и состав. Таа е различна од Земјата во други аспекти. Ја има најгустата [[атмосфера]] од четирите земјени планети, и се состои од повеќе од 96% [[Јаглероден диоксид|јаглерод диоксид]]. [[Атмосферски притисок|Атмносферскиот притисок]] на површината на планетата е 92 пати од оној на Земјата, или приближно притсокот што се наоѓа на {{convert|900|m|ft|abbr=on}} под водата на Земјата. Венера е најжешката планета во Сончевиот систем, со средна температура на површината од {{convert|735|K|C F|abbr=on}}, иако [[Меркур (планета)|Меркур]] е поблиску до Сонцето. Венера е обвиткана со непровиден слој од високоодбивачки облаци од [[сулфурна киселина]], спречувајќи нејзината површина да се гледа од вселената во [[Светлина|видлива светлина]]. Можно е да имало океани со вода во минатото,<ref>{{cite journal |author=Hashimoto, G. L. |author2=Roos-Serote, M. |author3=Sugita, S. |author4=Gilmore, M. S. |author5=Kamp, L. W. |author6=Carlson, R. W. |author7=Baines, K. H. |title=Felsic highland crust on Venus suggested by Galileo Near-Infrared Mapping Spectrometer data |journal=[[Journal of Geophysical Research: Planets]] |date=2008 |volume=113 |issue=E9 |doi=10.1029/2008JE003134 |pages=E00B24 |bibcode=2008JGRE..113.0B24H}}</ref><ref>{{cite web |author=David Shiga |url=https://www.newscientist.com/article/dn12769-did-venuss-ancient-oceans-incubate-life.html |title=Did Venus's ancient oceans incubate life? |work=New Scientist |date=10 October 2007}}</ref> но тие би испариле со зголемување на температурата поради [[Бесконтролиран стакленички ефект|ефектот на стаклена градина]].<ref name="Jakosky">{{cite book |last1=Jakosky |first1=Bruce M. |chapter=Atmospheres of the Terrestrial Planets |editor1-last=Beatty |editor1-first=J. Kelly |editor2-last=Petersen |editor2-first=Carolyn Collins |editor3-last=Chaikin |editor3-first=Andrew |title=The New Solar System |edition=4th |date=1999 |location=Boston |publisher=Sky Publishing |pages=175–200 |isbn=978-0-933346-86-4 |oclc=39464951}}</ref> Водата најверојатно [[Фотодисоцијација|фотодисоцирала]], а ослободениот водорот бил [[Атмосферско испарување|однесен во меѓупланетарниот простор]] од страна на [[Сончев ветер|сончевиот ветер]] поради недостатокот на [[Магнетосфера|планетарното магнетно поле]].<ref name="solarwind">{{cite web |date=28 November 2007 |title=Caught in the wind from the Sun |publisher=[[European Space Agency]] |url=http://www.esa.int/SPECIALS/Venus_Express/SEM0G373R8F_0.html |accessdate=12 July 2008}}</ref>Површината на Венера е сува пустина прошарана со камења слични на плочи и со периодично јавување на [[Вуканологија на Венера|вулканизам]].
Како планета што е најблиску до Земјата, Венера била главна мета за раното меѓупланетарно истражување. Таа била првата планета после Земјата која ја посетила вселенско летало (''[[Маринер 2]]'' во 1962), и првото кое успешно слетало (''[[Венера-7|Венера 7]]'' во 1970). Густите облаци на Венера го оневозможуваат набљудувањето на нејзината површина во видливата светлина, а првите детални карти не се појавиле се до пристигнувањето на орбитерот [[Магелан (вселенско летало)|Магелан]] во 1991 година. Предложени се планови за [[планетарни возила]] или посложени мисии, но тие се попречени од непријателските површински услови на Венера.
== Физички карактеристики ==
[[File:Venus, Earth size comparison.jpg|thumbnail|left|Големината на венера во споредба со [[Earth|Земјата.]]|alt=Venus, without its atmosphere, is placed side by side with Earth. They are nearly the same size, though Venus is slightly smaller.]]
Венера е една од четирите [[terrestrial planet|внатрешни планети]] во Соларниот Систем, што значи дека има карпесто тело како Земјата. Слична е со Земјата во големина и маса, и често ја нарекуваат "сестра" или "близначка" на Земјата.<ref>{{cite book |author=Lopes, Rosaly M. C. |author2=Gregg, Tracy K. P. |title=Volcanic worlds: exploring the Solar System's volcanoes |publisher=[[Springer Publishing]] |date=2004 |isbn=978-3-540-00431-8 |page=61}}</ref> Дијаметарот на Венера е {{convert|12103.6|km|mi|abbr=on}}—само {{convert|638.4|km|mi|abbr=on}} помалку од таа на Земјата—а нејзината маса е 81.5% од таа на Земјата. Условите на површината на Венера се радикално различни од оние на Земјата поради нејзината густа [[atmosphere|атмносфера]] која е 96.5% [[carbon dioxide|јаглерод диоксид]], а останатите 3.5% се во најголем дел [[nitrogen|азот]].<ref>{{cite web |url=http://www.daviddarling.info/encyclopedia/V/Venusatmos.html |title=Atmosphere of Venus |work=The Encyclopedia of Astrobiology, Astronomy, and Spaceflght |accessdate=29 April 2007}}</ref>
=== Географија ===
{{main|Mapping of Venus}}
Површината на Венера била предмет на шпекулации се додека некои од нејзините тајни не биле откриени од страна на [[planetary science|планетарната наука]] во 20 век. Сондите на [[Venera|Венера]] во 1975 и 1982 вратиле слики од површината покриена во седимент и камења под агол. <ref>{{cite book |last1=Mueller |first1=Nils |editor1-last=Tilman |editor1-first=Spohn |editor2-last=Breuer |editor2-first=Doris |editor3-last=Johnson |editor3-first=T. V. |title=Encyclopedia of the Solar System |date=2014 |publisher=Elsevier Science & Technology |location=Oxford |isbn=978-0-12-415845-0 |edition=3rd |chapterurl=http://literati.credoreference.com/content/entry/estsolar/venus_surface_and_interior/0 |chapter=Venus Surface and Interior}}</ref> Површината била мапирана во детали од страна на [[Magellan (spacecraft)|Магелан]] во 1990–91. Земјата покажува докази за екстензивен [[Volcanology of Venus|вулканизам]], и [[sulfur|сулфурот]] во атмносферата може да укаже на тоа дека имало во скоро време ерупции.<ref>{{cite journal |first=Larry W. |last=Esposito |authorlink=Larry W. Esposito |date=9 March 1984 |title=Sulfur Dioxide: Episodic Injection Shows Evidence for Active Venus Volcanism |journal=[[Science (journal)|Science]] |volume=223 |issue=4640 |pages=1072–1074 |doi=10.1126/science.223.4640.1072 |url=http://www.sciencemag.org/cgi/content/abstract/223/4640/1072 |accessdate=29 April 2009 |pmid=17830154 |bibcode=1984Sci...223.1072E}}</ref><ref>{{cite journal |last1=Bullock |first1=Mark A. |last2=Grinspoon |first2=David H. |authorlink2=David Grinspoon |title=The Recent Evolution of Climate on Venus |journal=[[Icarus (journal)|Icarus]] |volume=150 |issue=1 |date=March 2001 |pages=19–37 |doi=10.1006/icar.2000.6570 |bibcode=2001Icar..150...19B |url=http://www.boulder.swri.edu/~bullock/vclime.pdf |deadurl=yes |archiveurl=https://web.archive.org/web/20031023161615/http://www.boulder.swri.edu/~bullock/vclime.pdf |archivedate=23 October 2003 |df=dmy-all |citeseerx=10.1.1.22.6440 }}</ref>
Скоро 80% од површината на Венера е покриена од измазнети, вулкански рамнини, кои се состо од 70% рамнини со збрчкани гребнатини и 10% со мазни или лобуратни рамнини.<ref>{{cite journal |author=Basilevsky, Alexander T. |author2=Head, James W., III |title=Global stratigraphy of Venus: Analysis of a random sample of thirty-six test areas |date=1995 |journal=[[Earth, Moon, and Planets]] |volume=66 |issue=3 |pages=285–336 |bibcode=1995EM&P...66..285B |doi=10.1007/BF00579467}}</ref> Остатокот од површината го сочинуваат два [[highland continent|планински предели, "континенти"]], едниот лежи на северната хемисфера на планетата, а другиот јужно од екваторот. Северниот континент е наречен [[Ishtar Terra|Иштар Тера]], именуван по [[Ishtar|Иштар]], [[Babylon|Бабилонската]] божица на љубовта, и е со големина колку Австралија. [[Maxwell Montes|Максвел Монтес]], највисоката планина на Венера, се наоѓа на Иштар Тера. Вевот е {{convert|7|mi|km|order=flip|abbr=on}} над просечната надморска височина на Венера.<ref name="planetology">{{cite book |url=https://books.google.com/books?id=SL-BszT15s0C&pg=PA74 |title=Planetology: Unlocking the Secrets of the Solar System |publisher=National Geographic Society |last1=Jones |first1=Tom |last2=Stofan |first2=Ellen |page=74 |date=2008 |isbn=978-1-4262-0121-9}}</ref> Северниот континент е наречен [[Aphrodite Terra|Афродита Тера]], именуван по [[Greek mythology|Грчката]] божица на љубовта, и е поголемиот од двата планински предели, со големина колку Северна Америка. Мрежа на фрактури и грешки го опфаќа поголемиот дел од оваа област.<ref name="Kaufmann">{{cite book |last=Kaufmann |first=W. J. |date=1994 |title=Universe |publisher=[[W. H. Freeman]] |location=New York |page=204 |isbn=978-0-7167-2379-0}}</ref>
Отсуството на докази за проток на [[lava|лава]] придружени со било каква видлива [[caldera|каладера]] останува енигма. Планетата има неколку[[impact crater|ударни кратери]], покажувајќи дека површината е релативно млада, конкретно 300–600 милиони години е стара.<ref name="Nimmo98" /><ref name="Strom1994" /> Венера има неколку уникатни карактеристики на површината поради ударните кратери, планините, и долините кои најчесто се јавуваат кај карпестите планети. Покрај овие работи има и вулкански карактеристики со рамни врвови, наречени "[[Farra (Venus)|фара]]", кои имаат облик на палачинка и имаат големина од {{convert|20|to|50|km|mi|abbr=on}} во должина, и од {{convert|100|to|1000|m|ft|abbr=on}} висина; радијални системи на фрактури слични на ѕвезди наречени "нова"; карактеристики со радијални и концентрични фрактури слични на пајакови мрежи, познати како "[[arachnoid (astrogeology)|арахноиди]]"; и "корона", кружни прстени на фрактури понекогаш опкружени со вдлабнатина. Овие карактеристики по потекло се вулкански.<ref name="Frankel">{{cite book |first=Charles |last=Frankel |date=1996 |title=Volcanoes of the Solar System |publisher=Cambridge University Press |isbn=978-0-521-47770-3}}</ref>
Повеќето од карактеристиките на површината на Венера се именувани по историски и митолошки жени.<ref>{{cite conference |author=Batson, R.M. |author2=Russell J. F. |title=Naming the Newly Found Landforms on Venus |booktitle=Proceedings of the Lunar and Planetary Science Conference XXII |date=18–22 March 1991 |location=Houston, Texas |page=65 |url=http://www.lpi.usra.edu/meetings/lpsc1991/pdf/1033.pdf |format=PDF |accessdate=12 July 2009}}</ref> Исклучоци се Максвел Монтес, именувани по [[James Clerk Maxwell|Џејмс Клерк Максвел]], и планинските региони [[Alpha Regio|Алфа Регио]], [[Beta Regio|Бета Регио]], и [[Ovda Regio|Овда Регио]]. Последните три карактеристики се именувани пред сегашниот систем да биде усвоен од страна на [[International Astronomical Union|Меѓунардниот Астрономски Сојуз]], којшто ја надгледува [[planetary nomenclature|планетарната номенклатура]].<ref name="jpl-magellan">{{cite book |url=http://www2.jpl.nasa.gov/magellan/guide8.html |title=The Magellan Venus Explorer's Guide |editor=Carolynn Young |publisher=Jet Propulsion Laboratory |location=California |page=93 |date=1 August 1990 |accessdate=13 January 2016}}</ref>
Должините на физичките карактеристики на Венера се изразени во однос на нејзиниот [[prime meridian|примарен меридијан]]. Оригиналниот примарен меридијан поминува низ радарот на светла точка во центарот на овалната карактеристика Ева, лоцирана на Алфа Регио.<ref name="Davies_1994">{{cite journal |doi=10.1007/BF00693410 |last1=Davies |first1=M. E. |last2=Abalakin |first2=V. K. |last3=Bursa |first3=M. |last4=Lieske |first4=J. H. |last5=Morando |first5=B. |last6=Morrison |first6=D. |last7=Seidelmann |first7=P. K. |last8=Sinclair |first8=A. T. |last9=Yallop |first9=B.| last10=Tjuflin| first10= Y. S. |date=1994 |title=Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements of the Planets and Satellites |journal=Celestial Mechanics and Dynamical Astronomy |volume=63 |issue=2 |pages=127–148 |bibcode=1996CeMDA..63..127D}}
</ref> Откако завршиле мисиите на Венера, приматниот меридијан бил редефиниран да помине низ централниот врв во кратерот Ариадна.<ref>{{cite web |url=https://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html |title=USGS Astrogeology: Rotation and pole position for the Sun and planets (IAU WGCCRE) |publisher=[[United States Geological Survey]] |id=JPL Publication 90-24 |accessdate=22 October 2009 |archive-url=https://web.archive.org/web/20111024101856/http://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html |archive-date=24 October 2011 |dead-url=yes |df=dmy-all }}</ref><ref name="jpl-magellan2">{{cite book |url=http://www2.jpl.nasa.gov/magellan/guide8.html |title=The Magellan Venus Explorer's Guide |editor=Carolynn Young |publisher=Jet Propulsion Laboratory |location=California |pages=99–100 |date=1 August 1990 |accessdate=13 January 2016}}</ref>
=== Површинска геологија ===
{{Main|Geology of Venus|Volcanology of Venus}}
[[File:Maat Mons on Venus.jpg|thumb|False-colour image of [[Maat Mons]] with a vertical exaggeration of 22.5|alt=Image is false-colour, with Maat Mons represented in hues of gold and fiery red, against a black background]]
Much of the Venusian surface appears to have been shaped by volcanic activity. Venus has several times as many volcanoes as Earth, and it has 167 large volcanoes that are over {{convert|100|km|mi|0|abbr=on}} across. The only volcanic complex of this size on Earth is the [[Hawaii (island)|Big Island]] of Hawaii.<ref name="Frankel" />{{rp|154}} This is not because Venus is more volcanically active than Earth, but because its crust is older. Earth's [[oceanic crust]] is continually recycled by [[subduction]] at the boundaries of [[tectonic plate]]s, and has an average age of about 100 million years,<ref>{{cite book |author=Karttunen, Hannu |author2=Kroger, P. |author3=Oja, H. |author4=Poutanen, M. |author5=Donner, K. J. |title=Fundamental Astronomy |page=162 |publisher=Springer |date=2007 |isbn=978-3-540-34143-7|title-link=Fundamental Astronomy }}</ref> whereas the Venusian surface is estimated to be 300–600 million years old.<ref name="Nimmo98" /><ref name="Frankel" />
Several lines of evidence point to ongoing [[volcano|volcanic]] activity on Venus. During the Soviet [[Venera]] program, the ''[[Venera 9]]'' orbiter obtained spectroscopic evidence of [[lightning]] on Venus,<ref>{{cite journal |last1=Kranopol'skii |first1=V. A. |title=Lightning on Venus according to Information Obtained by the Satellites ''Venera 9'' and ''10'' |journal=Cosmic Research |date=1980 |volume=18 |issue=3 |pages=325–330 |bibcode=1980CosRe..18..325K}}</ref> and the ''[[Venera 12]]'' descent probe obtained additional evidence of lightning and [[thunder]].<ref name="Russell, Philips">{{cite journal |url=http://www-ssc.igpp.ucla.edu/personnel/russell/papers/ashen/ |title=The Ashen Light |journal=[[Advances in Space Research]] |last1=Russell |first1=C. T. |last2=Phillips |first2=J. L. |date=1990 |pages=137–141 |volume=10 |issue=5 |bibcode=1990AdSpR..10..137R |doi=10.1016/0273-1177(90)90174-X}}</ref><ref>{{cite web |url=http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1978-086C |title=''Venera 12'' Descent Craft |work=[[National Space Science Data Center]] |publisher=NASA |accessdate=10 September 2015}}</ref> The [[European Space Agency]]'s ''[[Venus Express]]'' in 2007 detected [[whistler (radio)|whistler waves]] further confirming the occurrence of lightning on Venus.<ref name="Russell_2007">{{cite journal |url=http://aten.igpp.ucla.edu/personnel/russell/papers/lightning_venus_whistler-mode_waves.pdf |title=Lightning on Venus inferred from whistler-mode waves in the ionosphere |journal=[[Nature (journal)|Nature]] |first1=C. T. |last1=Russell |first2=T. L. |last2=Zhang |first3=M. |last3=Delva |first4=W. |last4=Magnes |first5=R. J. |last5=Strangeway |first6=H. Y. |last6=Wei |volume=450 |issue=7170 |pages=661–662 |date=November 2007 |doi=10.1038/nature05930 |pmid=18046401 |bibcode=2007Natur.450..661R}}</ref><ref name="Venus Express">{{cite news |url=http://www.cnn.com/2007/TECH/space/11/28/venus.lightning.ap/index.html |title=Venus also zapped by lightning |work=CNN.com |date=29 November 2007 |accessdate=29 November 2007 |archiveurl=https://web.archive.org/web/20071130201237/http://www.cnn.com/2007/TECH/space/11/28/venus.lightning.ap/index.html |archivedate=30 November 2007}}</ref> One possibility is that ash from a volcanic eruption was generating the lightning. Another piece of evidence comes from measurements of [[sulfur dioxide]] concentrations in the atmosphere, which dropped by a factor of 10 between 1978 and 1986, jumped in 2006, and again declined 10-fold.<ref name = "ESA_2012-12-03">{{cite web |url=http://www.esa.int/Our_Activities/Space_Science/Venus_Express/Have_Venusian_volcanoes_been_caught_in_the_act |title=Have Venusian volcanoes been caught in the act? |publisher=European Space Agency |first=Markus |last=Bauer |date=3 December 2012 |accessdate=20 June 2015 |archiveurl=https://web.archive.org/web/20131103183610/http://www.esa.int/Our_Activities/Space_Science/Venus_Express/Have_Venusian_volcanoes_been_caught_in_the_act |archivedate=3 November 2013 |deadurl=no}}</ref> This may mean that levels had been boosted several times by large volcanic eruptions.<ref>{{cite journal |title=Transport of {{chem2|SO2}} by explosive volcanism on Venus |journal=[[Journal of Geophysical Research]] |first=Lori S. |last=Glaze |volume=104 |issue=E8 |pages=18899–18906 |date=August 1999 |doi=10.1029/1998JE000619 |bibcode=1999JGR...10418899G}}</ref><ref name="Marcq2012">{{cite journal |title=Variations of sulphur dioxide at the cloud top of Venus's dynamic atmosphere |journal=Nature Geoscience |first1=Emmanuel |last1=Marcq |first2=Jean-Loup |last2=Bertaux |first3=Franck |last3=Montmessin |first4=Denis |last4=Belyaev |volume=6 |issue=1 |pages=25–28 |date=January 2013 |doi=10.1038/ngeo1650 |bibcode=2013NatGe...6...25M}}</ref>
In 2008 and 2009, the first direct evidence for ongoing volcanism was observed by ''Venus Express'', in the form of four transient localized infrared hot spots within the rift zone [[Ganiki Chasma|Ganis Chasma]],<ref name="USGS_Ganis_Chasma">{{cite web |title=Ganis Chasma |work=Gazetteer of Planetary Nomenclature |publisher=[[USGS Astrogeology Science Center]] |url=http://planetarynames.wr.usgs.gov/Feature/2099 |accessdate=19 June 2015 |archive-url=https://web.archive.org/web/20161214115632/https://planetarynames.wr.usgs.gov/Feature/2099 |archive-date=14 December 2016 |dead-url=yes |df=dmy-all }}</ref>{{refn| Misstated as "Ganiki Chasma" in the press release and scientific publication.<ref name = "Lakdawalla2015"/>| group = n}} near the shield volcano [[Maat Mons]]. Three of the spots were observed in more than one successive orbit. These spots are thought to represent lava freshly released by volcanic eruptions.<ref name = "Lakdawalla2015">{{cite web |last=Lakdawalla |first=Emily |authorlink=Emily Lakdawalla |title=Transient hot spots on Venus: Best evidence yet for active volcanism |publisher=[[The Planetary Society]] |date=18 June 2015 |url=http://www.planetary.org/blogs/emily-lakdawalla/2015/06181637-transient-hot-spots-on-venus.html |accessdate=20 June 2015}}</ref><ref name = "ESA_2015-06-18">{{cite web |title=Hot lava flows discovered on Venus |publisher=European Space Agency |date=18 June 2015 |url=http://www.esa.int/Our_Activities/Space_Science/Venus_Express/Hot_lava_flows_discovered_on_Venus |accessdate=20 June 2015 |archivedate=19 June 2015 |archiveurl=https://web.archive.org/web/20150619071101/http://www.esa.int/Our_Activities/Space_Science/Venus_Express/Hot_lava_flows_discovered_on_Venus}}</ref> The actual temperatures are not known, because the size of the hot spots could not be measured, but are likely to have been in the {{convert|800|-|1100|K|C F}} range, relative to a normal temperature of {{convert|740|K|C F}}.<ref name="Shalygin2015">{{cite journal |last1=Shalygin |first1=E. V. |last2=Markiewicz |first2=W. J. |last3=Basilevsky |first3=A. T. |last4=Titov |first4=D. V. |last5=Ignatiev |first5=N. I. |last6=Head |first6=J. W. |title=Active volcanism on Venus in the Ganiki Chasma rift zone |journal=[[Geophysical Research Letters]] |date=17 June 2015 |pages=4762–4769 |doi=10.1002/2015GL064088 |volume=42 |issue=12 |bibcode=2015GeoRL..42.4762S}}</ref>
[[File:PIA00103 Venus - 3-D Perspective View of Lavinia Planitia.jpg|alt=The plains of Venus are outlined in red and gold, with impact craters leaving golden rings across the surface|thumb|[[Impact crater]]s on the surface of Venus (false-colour image reconstructed from radar data)]]
Almost a thousand impact craters on Venus are evenly distributed across its surface. On other cratered bodies, such as Earth and the Moon, craters show a range of states of degradation. On the Moon, degradation is caused by subsequent impacts, whereas on Earth it is caused by wind and rain erosion. On Venus, about 85% of the craters are in pristine condition. The number of craters, together with their well-preserved condition, indicates the planet underwent a global resurfacing event about 300–600 million years ago,<ref name="Nimmo98" /><ref name="Strom1994">{{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}}</ref> followed by a decay in volcanism.<ref>{{cite journal |author=Romeo, I. |author2=Turcotte, D. L. |date=2009 |title=The frequency-area distribution of volcanic units on Venus: Implications for planetary resurfacing |journal=Icarus |doi=10.1016/j.icarus.2009.03.036 |volume=203 |issue=1 |pages=13–19 |bibcode=2009Icar..203...13R|url=http://eprints.ucm.es/13279/1/Icarus_2009_1.pdf }}</ref> Whereas Earth's crust is in continuous motion, Venus is thought to be unable to sustain such a process. Without plate tectonics to dissipate heat from its mantle, Venus instead undergoes a cyclical process in which mantle temperatures rise until they reach a critical level that weakens the crust. Then, over a period of about 100 million years, subduction occurs on an enormous scale, completely recycling the crust.<ref name="Frankel" />
Venusian craters range from {{convert|3|to|280|km|mi|0|abbr=on}} in diameter. No craters are smaller than 3 km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain [[kinetic energy]] are slowed down so much by the atmosphere that they do not create an impact crater.<ref>{{cite journal |last=Herrick |first=R. R. |author2=Phillips, R. J. |date=1993 |title=Effects of the Venusian atmosphere on incoming meteoroids and the impact crater population |journal=Icarus |volume=112 |issue=1 |pages=253–281 |doi=10.1006/icar.1994.1180 |bibcode=1994Icar..112..253H}}</ref> Incoming projectiles less than {{convert|50|m|ft|abbr=on}} in diameter will fragment and burn up in the atmosphere before reaching the ground.<ref>{{cite book |title=The Planetary System |edition=3rd |publisher=[[Benjamin Cummings]] |location=San Francisco |first1=David |last1=Morrison |first2=Tobias C. |last2=Owens |date=2003 |isbn=978-0-8053-8734-6}}</ref>
=== Internal structure ===
[[File:Venus structure.jpg|thumb|The internal structure of Venus – the crust (outer layer), the mantle (middle layer) and the core (yellow inner layer)|alt=Venus is represented without its atmosphere; the mantle (red) is slightly larger than the core (yellow)]]
Without seismic data or knowledge of its [[moment of inertia]], little direct information is available about the internal structure and [[geochemistry]] of Venus.<ref name="goettel">{{cite conference |last=Goettel |first=K. A. |author2=Shields, J. A. |author3=Decker, D. A. |title=Density constraints on the composition of Venus |booktitle=Proceedings of the Lunar and Planetary Science Conference |publisher=[[Pergamon Press]] |location=Houston, TX |date=16–20 March 1981 |pages=1507–1516 |bibcode=1982LPSC...12.1507G |accessdate=}}</ref> The similarity in size and density between Venus and Earth suggests they share a similar internal structure: a [[Planetary core|core]], [[Mantle (geology)|mantle]], and [[Crust (geology)|crust]]. Like that of Earth, the Venusian core is at least partially liquid because the two planets have been cooling at about the same rate.<ref>{{cite book |author=Faure, Gunter |author2=Mensing, Teresa M. |date=2007 |title=Introduction to planetary science: the geological perspective |series=Springer eBook collection |publisher=Springer |isbn=978-1-4020-5233-0 |page=201}}</ref> The slightly smaller size of Venus means pressures are 24% lower in its deep interior than Earth's.<ref>{{citation |last1=Aitta |first1=A. |title=Venus' internal structure, temperature and core composition |journal=Icarus |volume=218 |issue=2 |pages=967–974 |date=April 2012 |doi=10.1016/j.icarus.2012.01.007 |bibcode=2012Icar..218..967A |url=https://www.researchgate.net/publication/256719725 |accessdate=17 January 2016 |postscript=.}}</ref> The principal difference between the two planets is the lack of evidence for [[plate tectonics]] on Venus, possibly because its crust is too strong to [[subduction|subduct]] without water to make it less [[viscous]]. This results in reduced heat loss from the planet, preventing it from cooling and providing a likely explanation for its lack of an internally generated [[magnetic field]].<ref>{{cite journal |author=Nimmo, F. |date=2002 |title=Crustal analysis of Venus from Magellan satellite observations at Atalanta Planitia, Beta Regio, and Thetis Regio |journal=[[Geology (journal)|Geology]] |volume=30 |issue=11 |pages=987–990 |doi=10.1130/0091-7613(2002)030<0987:WDVLAM>2.0.CO;2 |issn=0091-7613 |bibcode=2002Geo....30..987N}}</ref>
Instead, Venus may lose its internal heat in periodic major resurfacing events.<ref name="Nimmo98">{{cite journal |author=Nimmo, F. |author2=McKenzie, D. |title=Volcanism and Tectonics on Venus |journal=[[Annual Review of Earth and Planetary Sciences]] |volume=26 |issue=1 |pages=23–53 |date=1998 |doi=10.1146/annurev.earth.26.1.23 |bibcode=1998AREPS..26...23N}}</ref>
=== Atmosphere and climate ===
{{Multiple image
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|width3=158
|image3=Venuspioneeruv.jpg
|alt3=The atmosphere of Venus appears darker and lined with shadows. The shadows trace the prevailing wind direction.
|caption3=Cloud structure in [[Atmosphere of Venus|the Venusian atmosphere]] in 1979, revealed by observations in the [[ultraviolet]] band by [[Pioneer Venus Orbiter]]
|width4=170
|image4=Venus globe.jpg
|alt4=A false-colour image of Venus: ribbons of lighter colour stretch haphazardly across the surface. Plainer areas of more even colouration lie between.
|caption4=Global [[radar]] view of Venus (without the clouds) from [[Magellan (spacecraft)|''Magellan'']] between 1990 and 1994
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{{Main|Atmosphere of Venus}}
Venus has an extremely dense [[celestial body atmosphere|atmosphere]] composed of 96.5% [[carbon dioxide]], 3.5% [[nitrogen]], and traces of other gases, most notably [[sulfur dioxide]].<ref name=SolarSystemEncyclopedia>{{cite book |last1=Taylor |first1=Fredric W. |editor1-last=Tilman |editor1-first=Spohn |editor2-last=Breuer |editor2-first=Doris |editor3-last=Johnson |editor3-first=T. V. |title=Encyclopedia of the Solar System |date=2014 |publisher=[[Elsevier]] Science & Technology |location=Oxford |isbn=978-0-12-415845-0 |chapter-url=http://literati.credoreference.com/content/entry/estsolar/venus_atmosphere/0 |accessdate=12 January 2016 |chapter=Venus: Atmosphere}}</ref> The mass of its atmosphere is 93 times that of Earth's, whereas the pressure at its surface is about 92 times that at Earth's—a pressure equivalent to that at a depth of nearly {{convert|1|km|mi}} under Earth's oceans. The density at the surface is 65 kg/m<sup>3</sup>, 6.5% that of water or 50 times as dense as Earth's atmosphere at {{convert|20|C|K C F|0|order=out}} at sea level. The {{chem2|CO2}}-rich atmosphere generates the strongest [[greenhouse effect]] in the Solar System, creating surface temperatures of at least {{convert|462|C|K C F|order=out}}.<ref name="nasa_venus" /><ref>{{cite web |url=http://burro.cwru.edu/stu/advanced/venus.html |title=Venus |publisher=[[Case Western Reserve University]] |date=13 September 2006 |accessdate=21 December 2011 |archive-url=https://web.archive.org/web/20120426064658/http://burro.cwru.edu/stu/advanced/venus.html |archive-date=26 April 2012 |dead-url=yes}}</ref> This makes Venus's surface hotter than [[Mercury (planet)|Mercury]]'s, which has a minimum surface temperature of {{convert|−220|C|K C F|0|order=out|round=5}} and maximum surface temperature of {{convert|427|C|K C F|0|order=out|round=5}},<ref>{{cite book |first=John S. |last=Lewis |date=2004 |title=Physics and Chemistry of the Solar System |page=463 |edition=2nd |publisher=[[Academic Press]] |isbn=978-0-12-446744-6}}</ref><ref>{{cite book|url=http://www.jhuapl.edu/techdigest/td2602/Prockter.pdf|title=Ice in the Solar System|last=Prockter|first=Louise|date=2005|publisher=Johns Hopkins APL Technical Digest|volume=Volume 26|accessdate=July 27, 2009|archiveurl=https://web.archive.org/web/20060911205118/http://www.jhuapl.edu/techdigest/td2602/Prockter.pdf|archivedate=September 11, 2006|deadurl=bot: unknown|issue=number 2|df=}}</ref> even though Venus is nearly twice Mercury's distance from the Sun and thus receives [[Inverse square law of radiation|only 25%]] of Mercury's solar [[irradiance]]. This temperature is higher than that used for [[Sterilization (microbiology)|sterilization]].
Studies have suggested that billions of years ago Venus's atmosphere was much more like Earth's than it is now, and that there may have been substantial quantities of liquid water on the surface, but after a period of 600 million to several billion years,<ref name=baas39_540>{{Cite journal |last1=Grinspoon |first1=David H. |authorlink=David Grinspoon |last2=Bullock |first2=M. A. |title=Searching for Evidence of Past Oceans on Venus |journal=[[Bulletin of the American Astronomical Society]] |volume=39 |page=540 |date=October 2007 |bibcode=2007DPS....39.6109G}}</ref> a runaway greenhouse effect was caused by the evaporation of that original water, which generated a critical level of greenhouse gases in its atmosphere.<ref name="Kasting">{{cite journal |last=Kasting |first=J. F. |authorlink=James Kasting |date=1988 |title=Runaway and moist greenhouse atmospheres and the evolution of Earth and Venus |journal=Icarus |volume=74 |issue=3 |pages=472–494 |doi=10.1016/0019-1035(88)90116-9 |pmid=11538226 |bibcode=1988Icar...74..472K}}</ref> Although the surface conditions on Venus are no longer hospitable to any Earthlike life that may have formed before this event, there is speculation on the possibility that life exists in the upper cloud layers of Venus, {{convert|50|km|abbr=on}} up from the surface, where the temperature ranges between {{convert|30|and|80|C|K C F|order=out}} but the environment is acidic.<ref>{{cite web |url=http://www.astrobio.net/news-exclusive/venusian-cloud-colonies/ |title=Venusian Cloud Colonies |work=Astrobiology Magazine |first=Leslie |last=Mullen |date=13 November 2002 |archiveurl=https://web.archive.org/web/20140816070045/http://www.astrobio.net/news-exclusive/venusian-cloud-colonies/ |archivedate=16 August 2014}}</ref><ref>{{cite journal |url=http://gltrs.grc.nasa.gov/reports/2003/TM-2003-212310.pdf |title=Astrobiology: The Case for Venus |journal=Journal of the British Interplanetary Society |first=Geoffrey A. |last=Landis |author-link=Geoffrey A. Landis |volume=56 |issue=7–8 |pages=250–254 |date=July 2003 |id=NASA/TM—2003-212310 |archiveurl=https://web.archive.org/web/20110807004311/http://gltrs.grc.nasa.gov/reports/2003/TM-2003-212310.pdf |archivedate=7 August 2011 |bibcode=2003JBIS...56..250L}}</ref><ref name="Cockell1999">{{cite journal |title=Life on Venus |journal=[[Planetary and Space Science]] |last=Cockell |first=Charles S. |authorlink=Charles S. Cockell |volume=47 |issue=12 |pages=1487–1501 |date=December 1999 |doi=10.1016/S0032-0633(99)00036-7 |bibcode=1999P&SS...47.1487C}}</ref>
[[Thermal inertia]] and the transfer of heat by winds in the lower atmosphere mean that the temperature of Venus's surface does not vary significantly between the night and day sides, despite Venus's extremely slow rotation. Winds at the surface are slow, moving at a few kilometres per hour, but because of the high density of the atmosphere at the surface, they exert a significant amount of force against obstructions, and transport dust and small stones across the surface. This alone would make it difficult for a human to walk through, even if the heat, pressure, and lack of oxygen were not a problem.<ref>{{cite journal |title=Dust on the surface of Venus |author=Moshkin, B. E. |author2=Ekonomov, A. P. |author3=Golovin Iu. M. |journal=Kosmicheskie Issledovaniia (Cosmic Research) |volume=17 |issue=2 |pages=280–285 |date=1979 |bibcode=1979CosRe..17..232M}}</ref>
Above the dense {{chem2|CO2}} layer are thick clouds consisting mainly of [[sulfuric acid]], which is formed by [[sulfur dioxide]] and water through a chemical reaction resulting in sulfuric acid hydrate. Additionally, the atmosphere consists of approximately 1% [[ferric chloride]].<ref name="kras006">{{cite journal |title=Chemical composition of the atmosphere of Venus |last1=Krasnopolsky |first1=V. A. |last2=Parshev |first2=V. A. |journal=Nature |volume=292 |issue=5824 |pages=610–613 |date=1981 |doi=10.1038/292610a0 |bibcode=1981Natur.292..610K}}</ref><ref>{{cite journal |title=Chemical composition of Venus atmosphere and clouds: Some unsolved problems |first=Vladimir A. |last=Krasnopolsky |date=2006 |journal=[[Planetary and Space Science]] |volume=54 |issue=13–14 |pages=1352–1359 |doi=10.1016/j.pss.2006.04.019 |bibcode=2006P&SS...54.1352K}}</ref> Other possible constituents of the cloud particles are [[ferric sulfate]], [[aluminium chloride]] and [[phosphoric anhydride]]. Clouds at different levels have different compositions and particle size distributions.<ref name="kras006"/> These clouds reflect and scatter about 90% of the sunlight that falls on them back into space, and prevent visual observation of Venus's surface. The permanent cloud cover means that although Venus is closer than Earth to the Sun, it receives less sunlight on the ground. Strong {{convert|300|km/h|mph|round=5|abbr=on}} winds at the cloud tops go around Venus about every four to five Earth days.<ref>{{cite journal |title=Cloud-tracked winds from Pioneer Venus OCPP images |author=W. B. Rossow |author2=A. D. del Genio |author3=T. Eichler |journal=[[Journal of the Atmospheric Sciences]] |volume=47 |issue=17 |pages=2053–2084 |date=1990 |doi=10.1175/1520-0469(1990)047<2053:CTWFVO>2.0.CO;2 |issn=1520-0469 |bibcode=1990JAtS...47.2053R}}</ref> Winds on Venus move at up to 60 times the speed of its rotation, whereas Earth's fastest winds are only 10–20% rotation speed.<ref name="science328">{{cite journal |author=Normile, Dennis |title=Mission to probe Venus's curious winds and test solar sail for propulsion |journal=Science |page=677 |issue=5979 |volume=328 |date=7 May 2010 |pmid=20448159 |doi=10.1126/science.328.5979.677-a |bibcode=2010Sci...328..677N}}</ref>
The surface of Venus is effectively [[isothermal]]; it retains a constant temperature not only between day and night sides but between the equator and the poles.<ref name="fact">{{cite web |url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html |title=Venus Fact Sheet |publisher=NASA |last=Williams |first=David R. |date=15 April 2005 |accessdate=12 October 2007 |archive-url=https://www.webcitation.org/6ftO4K7lC?url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html |archive-date=10 March 2016 |dead-url=yes |df=dmy-all }}</ref><ref>{{cite web |title=Titan, Mars and Earth: Entropy Production by Latitudinal Heat Transport |author=Lorenz, Ralph D. |author2=Lunine, Jonathan I. |author3=Withers, Paul G. |author4=McKay, Christopher P. |publisher=[[Ames Research Center]], University of Arizona Lunar and Planetary Laboratory |url=http://sirius.bu.edu/withers/pppp/pdf/mepgrl2001.pdf |date=2001 |accessdate=21 August 2007 |format=PDF}}</ref> Venus's minute [[axial tilt]]—less than 3°, compared to 23° on Earth—also minimises seasonal temperature variation.<ref>{{cite web |title=Interplanetary Seasons |work=NASA |url=https://science.nasa.gov/headlines/y2000/interplanetaryseasons.html |accessdate=21 August 2007 |deadurl=yes |archiveurl=https://web.archive.org/web/20071016161443/https://science.nasa.gov/headlines/y2000/interplanetaryseasons.html |archivedate=16 October 2007 |df=}}</ref> The only appreciable variation in temperature occurs with altitude. The highest point on Venus, [[Maxwell Montes]], is therefore the coolest point on Venus, with a temperature of about {{convert|380|C|K C F|order=out|round=5}} and an atmospheric pressure of about {{convert|45|bar|MPa|abbr=on|order=flip}}.<ref name=Basilevsky_2003>{{cite journal |author=Basilevsky A. T. |author2=Head J. W. |title=The surface of Venus |journal=[[Reports on Progress in Physics]] |date=2003 |volume=66 |issue=10 |pages=1699–1734 |doi=10.1088/0034-4885/66/10/R04 |bibcode=2003RPPh...66.1699B}}</ref><ref name=McGill_2010>{{cite book |editor=T. R. Watters |editor2=R. A. Schultz |title=Planetary Tectonics |chapter=Venus tectonics |last1=McGill |first1=G. E. |last2=Stofan |first2=E. R. |last3=Smrekar |first3=S. E. |publisher=Cambridge University Press |date=2010 |chapter-url=https://books.google.com/books?id=9PD5hxPb6fkC&pg=PA81 |isbn=978-0-521-76573-2 |pages=81–120}}</ref> In 1995, the [[Magellan (spacecraft)|''Magellan'' spacecraft]] imaged a [[Venus snow|highly reflective substance]] at the tops of the highest mountain peaks that bore a strong resemblance to terrestrial snow. This substance likely formed from a similar process to snow, albeit at a far higher temperature. Too volatile to condense on the surface, it rose in gaseous form to higher elevations, where it is cooler and could precipitate. The identity of this substance is not known with certainty, but speculation has ranged from elemental [[tellurium]] to lead sulfide ([[galena]]).<ref>{{cite web |title="Heavy metal" snow on Venus is lead sulfide |first=Carolyn Jones |last=Otten |publisher=[[Washington University in St Louis]] |url=http://news-info.wustl.edu/news/page/normal/633.html |date=2004 |accessdate=21 August 2007}}</ref>
The clouds of Venus may be capable of producing [[lightning]].<ref name="Upadhyay, H. O. 99–108">{{cite journal |author=Upadhyay, H. O. |author2=Singh, R. N. |title=Cosmic ray Ionization of Lower Venus Atmosphere |date=April 1995 |journal=[[Advances in Space Research]] |volume=15 |issue=4 |pages=99–108 |doi=10.1016/0273-1177(94)00070-H |bibcode=1995AdSpR..15...99U}}</ref> The existence of lightning in the atmosphere of Venus has been controversial since the first suspected bursts were detected by the Soviet [[Venera|Venera probes]]. In 2006–07, ''[[Venus Express]]'' clearly detected [[Electromagnetic electron wave|whistler mode waves]], the signatures of lightning. Their [[intermittent]] appearance indicates a pattern associated with weather activity. According to these measurements, the lightning rate is at least half of that on Earth.<ref name="Russell_2007"/> In 2007, ''Venus Express'' discovered that a huge double [[Polar vortex|atmospheric vortex]] exists at the south pole.<ref>{{cite journal |first=Eric |last=Hand |date=November 2007 |title=European mission reports from Venus |journal=Nature |issue=450 |pages=633–660 |doi=10.1038/news.2007.297}}</ref><ref>{{cite news |author=Staff |url=http://news.bbc.co.uk/1/hi/sci/tech/7117303.stm |title=Venus offers Earth climate clues |accessdate=29 November 2007 |work=[[BBC News]] |date=28 November 2007}}</ref>
''Venus Express'' also discovered, in 2011, that an [[ozone]] layer exists high in the atmosphere of Venus.<ref name="esaozone">{{cite web |url=http://www.esa.int/esaCP/SEMU3N9U7TG_Life_0.html |title=ESA finds that Venus has an ozone layer too |publisher=European Space Agency |date=6 October 2011 |accessdate=25 December 2011}}</ref> On 29 January 2013, [[ESA]] scientists reported that the [[ionosphere]] of Venus streams outwards in a manner similar to "the ion tail seen streaming from a [[comet]] under similar conditions."<ref name="ESA-20130129">{{cite web |title=When A Planet Behaves Like A Comet |url=http://www.esa.int/Our_Activities/Space_Science/When_a_planet_behaves_like_a_comet |date=29 January 2013 |publisher=European Space Agency |accessdate=31 January 2013}}</ref><ref name="Space-20130130">{{cite web |last=Kramer |first=Miriam |title=Venus Can Have 'Comet-Like' Atmosphere |url=http://www.space.com/19537-venus-comet-atmosphere.html |date=30 January 2013 |work=[[Space.com]] |accessdate=31 January 2013}}</ref>
In December 2015 and to a lesser extent in April and May 2016, researchers working on Japan's ''Akatsuki'' mission observed bow shapes in the atmosphere of Venus. This was considered direct evidence of the existence of perhaps the largest stationary [[gravity wave]]s in the solar system.<ref>{{cite journal |display-authors=3 |last1=Fukuhara |first1=Tetsuya |last2=Futaguchi |first2=Masahiko |last3=Hashimoto |first3=George L. |last4=Horinouchi |first4=Takeshi |last5=Imamura |first5=Takeshi |last6=Iwagaimi |first6=Naomoto |last7=Kouyama |first7=Toru |last8=Murakami |first8=Shin-ya |last9=Nakamura |first9=Masato|last10=Ogohara|first10=Kazunori |last11=Sato |first11=Mitsuteru |last12=Sato |first12=Takao M. |last13=Suzuki |first13=Makoto |last14=Taguchi |first14=Makoto |last15=Takagi |first15=Seiko |last16=Ueno |first16=Munetaka |last17=Watanabe |first17=Shigeto |last18=Yamada |first18=Manabu |last19=Yamazaki |first19=Atsushi |title=Large stationary gravity wave in the atmosphere of Venus |journal=Nature Geoscience |date=16 January 2017 |doi=10.1038/ngeo2873 |url=http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2873.html |accessdate=17 January 2017 |volume=10 |issue=2 |pages=85–88 |bibcode=2017NatGe..10...85F}}</ref><ref>{{cite news |last1=Rincon |first1=Paul |title=Venus wave may be Solar System's biggest |url=https://www.bbc.com/news/science-environment-38638067 |accessdate=17 January 2017 |work=BBC News |date=16 January 2017}}</ref><ref>{{cite news |last1=Chang |first1=Kenneth |title=Venus Smiled, With a Mysterious Wave Across Its Atmosphere |url=https://www.nytimes.com/2017/01/16/science/venus-wave-akatsuki.html?_r=0 |accessdate=17 January 2017 |work=The New York Times |date=16 January 2017}}</ref>
{{Multiple image
|align=center
|direction=horizontal
|header=Atmospheric composition
|footer=Green colour – water vapour, red – carbon dioxide, WN – [[wavenumber]] (other colours have different meanings, lower [[wavelength]]s on the right, higher on the left).
|width1=380
|image1=Synthetic atmosphere absorption spectrum.gif
|alt1=The atmosphere of Earth is represented as a series of coloured spikes. The green of water dominates, while the red of carbon dioxide clusters near the left side.
|caption1= Absorption spectrum of a simple gas mixture corresponding to [[Atmosphere of Earth|Earth's atmosphere]]
|width2=400
|image2=Synthetic Venus atmosphere absorption spectrum.gif
|alt2=The atmosphere of Venus is represented on the same graph. Here the red of carbon dioxide is almost overwhelming, but the green of water and the purple of carbon monoxide are present.
|caption2=The composition of the [[atmosphere of Venus]] based on [[HITRAN]] data<ref name=HITRAN>{{cite web |url=http://www.cfa.harvard.edu/hitran/ |title=The HITRAN Database |publisher=Atomic and Molecular Physics Division, [[Harvard-Smithsonian Center for Astrophysics]] |accessdate=8 August 2012 |quote=HITRAN is a compilation of spectroscopic parameters that a variety of computer codes use to predict and simulate the transmission and emission of light in the atmosphere.}}</ref> created using HITRAN on the Web system.<ref name=hitraniaoru>{{cite web |url=http://hitran.iao.ru/ |title=HITRAN on the Web Information System |publisher=[[V.E. Zuev Institute of Atmospheric Optics]] |accessdate=11 August 2012}}</ref>
}}
=== Magnetic field and core ===
In 1967, ''[[Venera 4]]'' found Venus's [[magnetic field]] to be much weaker than that of Earth. This magnetic field is induced by an interaction between the [[ionosphere]] and the [[solar wind]],<ref>{{cite journal |title=Nature of the Magnetic Field in the Neighborhood of Venus |author1=Dolginov, Sh. |author2=Eroshenko, E. G. |author3=Lewis, L. |journal=[[Cosmic Research]] |volume=7 |page=675 |date=September 1969 |bibcode=1969CosRe...7..675D}}</ref><ref>{{cite book |author=Kivelson G. M. |author2=Russell, C. T. |title=Introduction to Space Physics |publisher=[[Cambridge University Press]] |date=1995 |isbn=978-0-521-45714-9}}</ref> rather than by an internal [[dynamo theory|dynamo]] as in the Earth's [[Planetary core|core]]. Venus's small [[Magnetosphere of Venus|induced magnetosphere]] provides negligible protection to the atmosphere against [[cosmic radiation]].
The lack of an intrinsic magnetic field at Venus was surprising, given that it is similar to Earth in size, and was expected also to contain a dynamo at its core. A dynamo requires three things: a [[Electrical conductor|conducting]] liquid, rotation, and [[convection]]. The core is thought to be electrically conductive and, although its rotation is often thought to be too slow, simulations show it is adequate to produce a dynamo.<ref>{{cite book |chapterurl=http://www-spc.igpp.ucla.edu/personnel/russell/papers/venus_mag/ |chapter=Venus: Magnetic Field and Magnetosphere |title=Encyclopedia of Planetary Sciences |publisher=[[Chapman and Hall]] |location=New York |author1=Luhmann, J. G. |author2=Russell, C. T. |editor1=Shirley, J. H. |editor2=Fainbridge, R. W. |pages=905–907 |date=1997 |isbn=978-1-4020-4520-2}}</ref><ref>{{cite journal |last=Stevenson |first=D. J. |title=Planetary magnetic fields |journal=[[Earth and Planetary Science Letters]] |volume=208 |issue=1–2 |pages=1–11 |doi=10.1016/S0012-821X(02)01126-3 |date=15 March 2003 |bibcode=2003E&PSL.208....1S|url=http://authors.library.caltech.edu/12373/1/STErpp83.pdf }}</ref> This implies that the dynamo is missing because of a lack of convection in Venus's core. On Earth, convection occurs in the liquid outer layer of the core because the bottom of the liquid layer is much hotter than the top. On Venus, a global resurfacing event may have shut down plate tectonics and led to a reduced heat flux through the crust. This caused the mantle temperature to increase, thereby reducing the heat flux out of the core. As a result, no internal geodynamo is available to drive a magnetic field. Instead, the heat from the core is being used to reheat the crust.<ref name="nimmo02">{{cite journal |first=Francis |last=Nimmo |date=November 2002 |title=Why does Venus lack a magnetic field? |journal=Geology |volume=30 |issue=11 |pages=987–990 |url=http://www2.ess.ucla.edu/~nimmo/website/paper25.pdf |format=PDF |accessdate=28 June 2009 |doi=10.1130/0091-7613(2002)030<0987:WDVLAM>2.0.CO;2 |issn=0091-7613 |bibcode=2002Geo....30..987N}}</ref>
One possibility is that Venus has no solid inner core,<ref>{{cite journal |author=Konopliv, A. S. |author2=Yoder, C. F. |title=Venusian ''k''<sub>2</sub> tidal Love number from Magellan and PVO tracking data |journal=[[Geophysical Research Letters]] |volume=23 |issue=14 |pages=1857–1860 |url=http://www.agu.org/pubs/crossref/1996/96GL01589.shtml |accessdate=12 July 2009 |archive-url=https://web.archive.org/web/20110512154523/http://www.agu.org/pubs/crossref/1996/96GL01589.shtml |archive-date=12 May 2011 |dead-url=yes |doi=10.1029/96GL01589 |date=1996 |bibcode=1996GeoRL..23.1857K}}</ref> or that its core is not cooling, so that the entire liquid part of the core is at approximately the same temperature. Another possibility is that its core has already completely solidified. The state of the core is highly dependent on the concentration of [[sulfur]], which is unknown at present.<ref name="nimmo02" />
The weak magnetosphere around Venus means that the [[solar wind]] is interacting directly with its outer atmosphere. Here, ions of hydrogen and oxygen are being created by the dissociation of neutral molecules from ultraviolet radiation. The solar wind then supplies energy that gives some of these ions sufficient velocity to escape Venus's gravity field. This erosion process results in a steady loss of low-mass hydrogen, helium, and oxygen ions, whereas higher-mass molecules, such as carbon dioxide, are more likely to be retained. Atmospheric erosion by the solar wind probably led to the loss of most of Venus's water during the first billion years after it formed.<ref name="nature450_7170_629">{{cite journal |doi=10.1038/nature06432 |last1=Svedhem |first1=Håkan |last2=Titov |first2=Dmitry V. |last3=Taylor |first3=Fredric W. |last4=Witasse |first4=Olivier |date=November 2007 |title=Venus as a more Earth-like planet |journal=Nature |volume=450 |issue=7170 |pages=629–632 |bibcode=2007Natur.450..629S |pmid=18046393}}
</ref> The erosion has increased the ratio of higher-mass [[deuterium]] to lower-mass hydrogen in the atmosphere 100 times compared to the rest of the solar system.<ref>{{cite journal |last1=Donahue |first1=T. M. |last2=Hoffman |first2=J. H. |last3=Hodges |first3=R. R. |last4=Watson |first4=A. J. |title=Venus Was Wet: A Measurement of the Ratio of Deuterium to Hydrogen |journal=Science |volume=216 |issue=4546 |date=1982 |pages=630–633 |issn=0036-8075 |doi=10.1126/science.216.4546.630 |bibcode=1982Sci...216..630D |pmid=17783310}}</ref>
== Структура ==
[[Податотека:Mgn_p39146.png|thumb|right|250px|Кратер на површината на Венера.]]
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