Venus
Template:Short description Template:About Template:Featured article Template:Pp-move Template:Pp-semi-indef Template:Use dmy dates Template:Use Oxford spelling Template:Infobox planet
Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet, being orbital neighbours as well as Venus having the most similar mass and size to Earth among the planets of the Solar System. While both are rocky planets, Venus has an atmosphere much thicker and denser than Earth and any other rocky body in the Solar System. Its atmosphere is composed of mostly carbon dioxide (Template:Chem2), with a global sulfuric acid cloud cover and no liquid water. At the mean surface level the atmosphere reaches a temperature of Template:Convert and a pressure 92 times greater than Earth's at sea level, turning the lowest layer of the carbon dioxide atmosphere into a supercritical fluid. Venus is the third brightest object in Earth's sky, after the Moon and the Sun,<ref name="Lawrence_2005" /><ref name="Walker_2017" /> and, like Mercury, always appears relatively close to the Sun, either as a "morning star" or an "evening star", resulting from orbiting closer (inferior) to the Sun than Earth.
Venus is the destination from Earth, compared to the other planets, with the lowest delta-v needed to reach it, and is therefore often used for gravity assists and as a common waypoint for interplanetary flights from Earth. While the orbit of Venus is the next closest to Earth's, Venus and Earth stay on average the second closest planets to each other, with only the most inferior orbiting Mercury staying closer to them and all the other Solar System planets. Venus and Earth approach each other in synodic periods of 1.6 years. Venus has a very slow retrograde rotation about its axis, a result of competing forces of solar tidal locking and differential heating of Venus's massive atmosphere. A Venusian day is 116.75 Earth days long, about half a Venusian solar year, which is 224.7 Earth days long, and has no moons.
Venus has a weak magnetosphere, lacking an internal dynamo it is induced by the solar wind and the atmosphere interacting. Internally, Venus has a core, mantle, and crust. Internal heat escapes through active volcanism,<ref name="NYT-20240527">Template:Cite news</ref><ref name="NA-20240527">Template:Cite journal</ref> resulting in resurfacing instead of plate tectonics. Venus may have had liquid surface water early in its history with a habitable environment,<ref name="NYT-20231026" /><ref name="NA-20231026" /> before a runaway greenhouse effect evaporated any water and turned Venus into its present state.<ref name="Jakosky" /><ref name="Hashimoto_et_al_2008" /><ref name="Shiga_2007" /> Conditions at the cloud layer of Venus have been identified as possibly favourable for life on Venus, with possible biomarkers having been found in 2020, which has spurred new research and missions to Venus.
Throughout human history, Venus has been ascribed particular importance in the mythology, astrology, and fiction of various cultures across the world. The planet's characteristics ultimately proved crucial for the development of astronomy. The first telescopic observations of Venus in 1610 crucially proved the heliocentric model. In 1961 Venus was for the first time visited by a spacecraft (Venera 1), as a result of the very first interplanetary flight, but only the next interplanetary spacecraft, a year later, returned data (Mariner 2). Furthermore in 1967 the first atmospheric entry (Venera 4) and in 1970 the first soft landing (Venera 7) took place, the first on another planet than Earth. The study of Venus has informed the understanding of the greenhouse effect, global warming and climate change on Earth.<ref name="Newitz 2013"/> Template:As of the only active probe set to return to Venus is the Solar Orbiter performing flybys until 2030. The next planned Venus mission, the Venus Life Finder is expected to launch not earlier than summer 2026.
Physical characteristics
[edit]
Venus is one of the four terrestrial planets in the Solar System, meaning that it is a rocky body like Earth. It is similar to Earth in size and mass and is often described as Earth's "sister" or "twin".<ref name= "Lopes_Gregg_2004"/> Venus is very close to spherical due to its slow rotation.<ref name="Venus"/> It has a diameter of Template:Convert—only Template:Convert less than Earth's—and its mass is 81.5% of Earth's, making it the third-smallest planet in the Solar System. Conditions on the surface of Venus differ radically from those on Earth because its dense atmosphere is 96.5% carbon dioxide, causing an intense greenhouse effect, with most of the remaining 3.5% being nitrogen.<ref name=Darling_Venus/> The surface pressure is Template:Convert, and the average surface temperature is Template:Convert, above the critical points of both major constituents and making the surface atmosphere a supercritical fluid of mainly supercritical carbon dioxide and some supercritical nitrogen.
Geography
[edit]
The Venusian surface was a subject of speculation until some of its secrets were revealed by probes in the 20th century. Venera landers in 1975 and 1982 returned images of a surface covered in sediment and relatively angular rocks.<ref name=Mueller_2014/> The surface was mapped in detail by Magellan in 1990–91. There is evidence of extensive volcanism, and variations in the atmospheric sulphur dioxide may indicate that there are active volcanoes.<ref name=Esposito_1984/><ref name=Bullock_Grinspoon_2001/>
About 80% of the Venusian surface is covered by smooth, volcanic plains, consisting of 70% plains with wrinkle ridges and 10% smooth or lobate plains.<ref name=Basilevsky_Head_1995/> Two highland "continents" make up the rest of its surface area, one lying in the planet's northern hemisphere and the other just south of the equator. The northern continent is called Ishtar Terra after Ishtar, the Babylonian goddess of love, and is about the size of Australia. The Maxwell Montes mountain range lies on Ishtar Terra. Its peak is the highest point on Venus, Template:Convert above the Venusian average surface elevation.<ref name="planetology"/> The southern continent is called Aphrodite Terra, after the Greek mythological goddess of love, and is the larger of the two highland regions at roughly the size of South America. A network of fractures and faults covers much of this area.<ref name="Kaufmann"/>
There is recent evidence of lava flow on Venus (2024),<ref>National Geographic (2024) Venus is volcanically alive</ref> such as flows on Sif Mons, a shield volcano, and on Niobe Planitia, a flat plain.<ref>The New York Times (27 May 2024) Rivers of Lava on Venus Reveal a More Volcanically Active Planet</ref> There are visible calderas. The planet has few impact craters, demonstrating that the surface is relatively young, at 300–600Template:Spacesmillion years old.<ref name="Nimmo98" /><ref name="Strom1994" /> Venus has some unique surface features in addition to the impact craters, mountains, and valleys commonly found on rocky planets. Among these are flat-topped volcanic features called "farra", which look somewhat like pancakes and range in size from Template:Convert across, and from Template:Convert high; radial, star-like fracture systems called "novae"; features with both radial and concentric fractures resembling spider webs, known as "arachnoids"; and "coronae", circular rings of fractures sometimes surrounded by a depression. These features are volcanic in origin.<ref name="Frankel"/>
Most Venusian surface features are named after historical and mythological women.<ref name=Batson_Russell_1991/> Exceptions are Maxwell Montes, named after James Clerk Maxwell, and highland regions Alpha Regio, Beta Regio, and Ovda Regio. The last three features were named before the current system was adopted by the International Astronomical Union, the body which oversees planetary nomenclature.<ref name="jpl-magellan"/>
The longitude of physical features on Venus is expressed relative to its prime meridian. The original prime meridian passed through the radar-bright spot at the centre of the oval feature Eve, located south of Alpha Regio.<ref name="Davies_1994"/> After the Venera missions were completed, the prime meridian was redefined to pass through the central peak in the crater Ariadne on Sedna Planitia.<ref name=Seidelmann_et_al_2007/><ref name="jpl-magellan2"/>
The stratigraphically oldest tessera terrains have consistently lower thermal emissivity than the surrounding basaltic plains measured by Venus Express and Magellan, indicating a different, possibly a more felsic, mineral assemblage.<ref name="Hashimoto_et_al_2008"/><ref name=Helbert_et_al_2008/> The mechanism to generate a large amount of felsic crust usually requires the presence of a water ocean and plate tectonics, implying that habitable condition existed on early Venus, with large bodies of water at some point.<ref name="Petkowski Seager 2021">Template:Cite web</ref> However, the nature of tessera terrains is far from certain.<ref name=Gilmore_et_al_2017/>
Studies reported in 2023 suggested for the first time that Venus may have had plate tectonics during ancient times and, as a result, may have had a more habitable environment, possibly one capable of sustaining life.<ref name="NYT-20231026">Template:Cite news</ref><ref name="NA-20231026">Template:Cite journal</ref> Venus has gained interest as a case for research into the development of Earth-like planets and their habitability.
Volcanism
[edit]
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 Template:Convert across. The only volcanic complex of this size on Earth is the Big Island of Hawaii.<ref name="Frankel" />Template:Rp More than 85,000 volcanoes on Venus have been identified and mapped.<ref>Template:Cite web</ref><ref>Template:Cite journal</ref> This is not because Venus is more volcanically active than Earth, but because its crust is older and is not subject to the erosion processes active on Earth. Earth's oceanic crust is continually recycled by subduction at the boundaries of tectonic plates, and has an average age of about 100 million years,<ref name=Karttunen_et_al_2007/> whereas the Venusian surface is estimated to be 300–600Template:Spacesmillion years old.<ref name="Nimmo98" /><ref name="Frankel" />
Several lines of evidence point to ongoing volcanic activity on Venus. Sulfur dioxide concentrations in the upper atmosphere dropped by a factor of 10 between 1978 and 1986, jumped in 2006, and again declined 10-fold.<ref name="ESA_2012-12-03"/> This may mean that levels were boosted several times by large volcanic eruptions.<ref name=Glaze_1999/><ref name="Marcq2012"/> It has been suggested that Venusian lightning (discussed below) could originate from volcanic activity (i.e. volcanic lightning). In January 2020, astronomers reported evidence suggesting that Venus is currently volcanically active, specifically the detection of olivine, a volcanic product that would weather quickly on the planet's surface.<ref name="NYT-20200109"/><ref name="SCI-20200103"/>
This massive volcanic activity is fuelled by a hot interior, which models say could be explained by energetic collisions when the planet was young, as well as radioactive decay as in the case of the earth. Impacts would have had significantly higher velocity than on Earth, both because Venus moves faster due to its closer proximity to the Sun and because high-eccentricity objects colliding with the planet would have high speeds.<ref>Template:Cite web</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 Ganis Chasma,<ref name="USGS_Ganis_Chasma"/>Template:Refn 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"/><ref name="ESA_2015-06-18"/> 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 Template:Convert range, relative to a normal temperature of Template:Convert.<ref name="Shalygin2015"/> In 2023, scientists reexamined topographical images of the Maat Mons region taken by the Magellan orbiter. Using computer simulations, they determined that the topography had changed during an 8-month interval, and concluded that active volcanism was the cause.<ref>Template:Cite web</ref>
Craters
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There are almost a thousand impact craters on Venus, 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 300–600Template:Spacesmillion years ago,<ref name="Nimmo98" /><ref name="Strom1994"/> followed by a decay in volcanism.<ref name=Romeo_Turcotte_2018/> 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 100Template:Spacesmillion years, subduction occurs on an enormous scale, completely recycling the crust.<ref name="Frankel" />
Venusian craters range from Template:Convert in diameter. No craters are smaller than 3Template:Spaceskm, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy are slowed so much by the atmosphere that they do not create an impact crater.<ref name=Herrick_Phillips_1993/> Incoming projectiles less than Template:Convert in diameter will fragment and burn up in the atmosphere before reaching the ground.<ref name=Morrison_Owens_2003/>
Internal structure
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Without data from reflection seismology or knowledge of its moment of inertia, little direct information has been available about the internal structure and geochemistry of Venus.<ref name="goettel"/> The similarity in size and density between Venus and Earth suggests that they share a similar internal structure: a core, mantle, and crust. Like that of Earth, the Venusian core is most likely at least partially liquid because the two planets have been cooling at about the same rate,<ref name=Faure_Mensing_2007/> although a completely solid core cannot be ruled out.<ref name=Dumoulin2017/> The slightly smaller size of Venus means pressures are 24% lower in its deep interior than Earth's.<ref name=Aitta_2016/> The predicted values for the moment of inertia based on planetary models suggest a core radius of 2,900–3,450 km.<ref name=Dumoulin2017/> There is now an estimate of 3,500 km from the moment of inertia based on the rate of axial precession, measured between 2006 and 2020.<ref name=Margot_et_al_2021/><ref name="O'Callaghan_2021"/>
The crust of Venus is estimated to be 40 kilometers thick on average and at most 65 kilometers thick.<ref>Template:Cite journal</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 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 name=Nimmo_2002/> Instead, Venus may lose its internal heat in periodic major resurfacing events.<ref name="Nimmo98"/>
Magnetic field and core
[edit]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 name=Eroshenko_et_al_1969/><ref name=Kivelson_Russell_1995/>Template:Page needed rather than by an internal dynamo as in the Earth's core. Venus's small induced magnetosphere provides negligible protection to the atmosphere against solar and cosmic radiation.
The lack of an intrinsic magnetic field on Venus was surprising, given that it is similar to Earth in size and was expected to contain a dynamo at its core. A dynamo requires three things: a 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 name=Luhmann_Russell_2006/><ref name=Stevenson_2003/> 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 higher in temperature 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 insulating effect would cause 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 reheating the crust.<ref name="nimmo02"/>
One possibility is that Venus has no solid inner core,<ref name=Konopliv_Yoder_1996/> 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 been completely solidified. The state of the core is highly dependent on the concentration of sulphur, which is unknown at present.<ref name="nimmo02" />
Another possibility is that the absence of a large impact on Venus (contra the Earth's "Moon-forming" impact) left the core of Venus stratified from the core's incremental formation, and without the forces to initiate/sustain convection, and thus a "geodynamo".<ref name="Jacobsen2017">Template:Cite journal</ref>
The weak magnetosphere around Venus means that the solar wind interacts directly with its outer atmosphere. Here, ions of hydrogen and oxygen are being created by the dissociation of water molecules due to ultraviolet radiation. The solar wind then supplies energy that gives some of these ions sufficient speed 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 could have led to the loss of most of Venus's water during the first billion years after it formed.<ref name="nature450_7170_629"/> However, the planet may have retained a dynamo for its first 2–3 billion years, so the water loss may have occurred more recently.<ref name="O'Rourke_et_al_2019"/> 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 name=Donahue_et_al_1982/>
Atmosphere and climate
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Venus has a dense atmosphere composed of 96.5% carbon dioxide, 3.5% nitrogen—both exist as supercritical fluids at the planet's surface with a density 6.5% that of water<ref name="u3r1a"/>—and traces of other gases including sulphur dioxide.<ref name="SolarSystemEncyclopedia"/> The mass of its atmosphere is 92 times that of Earth's, whereas the pressure at its surface is about 93 times that at Earth's—a pressure equivalent to that at a depth of nearly Template:Convert under Earth's ocean surfaces. The density at the surface is Template:Convert, 6.5% that of water<ref name="u3r1a"/> or 50 times as dense as Earth's atmosphere at Template:Convert at sea level. The Template:Chem2-rich atmosphere generates the strongest greenhouse effect in the Solar System, creating surface temperatures of at least Template:Convert.<ref name="nasa_venus" /><ref name=CWRU_2006/> This makes the Venusian surface hotter than Mercury's, which has a minimum surface temperature of Template:Convert and maximum surface temperature of Template:Convert,<ref name=Lewis_2004/><ref name=Prockter_2005/> even though Venus is nearly twice Mercury's distance from the Sun and thus receives only around a quarter of Mercury's solar irradiance, of 2,600 W/m2 (double that of Earth).<ref name="fact" /> Because of its runaway greenhouse effect, Venus has been identified by scientists such as Carl Sagan as a warning and research object linked to climate change on Earth.<ref name="Newitz 2013"/> Therefore Venus has been called a greenhouse planet,<ref name="a490">Template:Cite conference</ref> a planet under a greenhouse inferno.<ref name="p181">Template:Cite web</ref>
| Type | Surface temperature |
|---|---|
| Maximum | 900 °F (482 °C) |
| Normal | 847 °F (453 °C) |
| Minimum | 820 °F (438 °C) |
Venus's atmosphere is rich in primordial noble gases compared to that of Earth.<ref name=Halliday_2020/> This enrichment indicates an early divergence from Earth in evolution. An unusually large comet impact<ref name=Owen_et_al_1992/> or accretion of a more massive primary atmosphere from the solar nebula<ref name=Pepin_1991/> have been proposed to explain the enrichment. However, the atmosphere is poor in radiogenic argon-40, a proxy for mantle degassing, suggesting an early shutdown of major magmatism.<ref name=Namiki_Solomon_1998/><ref name="O'Rurke_Korenaga_2015"/>
Studies have suggested that billions of years ago, the atmosphere of Venus may have been much more like the one surrounding the early Earth, and there may have been substantial quantities of liquid water on the surface.<ref name="Ernst 2022"/><ref name="Way Del Genio 2020 p."/><ref name="Way Del Genio Kiang Sohl 2016 pp. 8376–8383"/> After a period of 600 million to several billion years,<ref name="baas39_540"/> the rising luminosity of the Sun and possibly large volcanic resurfacing caused the evaporation of the original water.<ref name="Steigerwald 2022"/> A runaway greenhouse effect was created once a critical level of greenhouse gases (including water) was reached in the atmosphere.<ref name="Kasting"/> Although the surface conditions on Venus are no longer hospitable to any terrestrial-like life that might have formed before this event, there is speculation that life may exist in the upper cloud layers of Venus, Template:Convert above the surface, where atmospheric conditions are the most Earth-like in the Solar System,<ref name="Tillman 2018"/> with temperatures ranging between Template:Convert, and the pressure and radiation being about the same as at Earth's surface, but with acidic clouds and the carbon dioxide air.<ref name=Mullen_2002/><ref name=Landis_2003/><ref name="Cockell1999"/> More specifically, between heights of 48 and 59 km temperature and radiation conditions are suitable for life. At lower elevations water would evaporate and at higher elevation UV radiation would be too strong.<ref name="Patel Mason Nordheim Dartnell 2022 p=114796">Template:Cite journal</ref><ref name="Herbst Banjac Atri Nordheim 2019 p=A15">Template:Cite journal</ref> The putative detection of an absorption line of phosphine in Venus's atmosphere, with no known pathway for abiotic production, led to speculation in September 2020 that there could be extant life currently present in the atmosphere.<ref name=Drake_2020/><ref name=Greaves_et_al_2020/> Later research attributed the spectroscopic signal that was interpreted as phosphine to sulphur dioxide,<ref name=Lincowski_et_al_2021/> or found that in fact there was no absorption line.<ref name=Beall_2020/><ref name=Snellan_et_al_2020/>
Thermal inertia and the transfer of heat by winds in the lower atmosphere mean that the surface temperature does not vary significantly between the hemispheres facing and not facing the Sun, despite Venus's 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 without the heat, pressure, and lack of oxygen.<ref name=Moshkin_et_al_1979/>
Above the dense Template:Chem2 layer are thick clouds 45 to 70 km above the surface,<ref>Template:Cite web</ref> consisting mainly of sulphuric acid, which is formed by a reaction catalyzed by UV radiation from sulphur dioxide molecules and then water,<ref>Template:Cite web</ref> resulting in sulphuric acid hydrate.<ref>Template:Cite journal</ref> Additionally, the clouds contain approximately 1% ferric chloride.<ref name="kras006"/><ref name=Krasnopolsky_2006/> 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, like thick cloud cover on Earth, about 70% of the sunlight that falls on them back into space,<ref name="Davis 2021"/> and since they cover the whole planet they prevent visual observation of the surface. The permanent cloud cover means that although Venus is closer than Earth to the Sun, it receives less sunlight on the ground, with only 10% of the received sunlight reaching the surface,<ref name="ESA Blog Navigator – Navigator page for active ESA blogs 2012"/> resulting in average daytime levels of illumination at the surface of 14,000 lux, comparable to that on Earth "in the daytime with overcast clouds".<ref name=sci_news_1976/> Strong Template:Convert winds at the cloud tops go around Venus about every four to five Earth days.<ref name=Rossow_et_al_1990/> 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"/>
Although Venus looks featureless in visible light, there are bands or streaks in the UV, whose origin has not been pinned down. The absorption of UV may be due to a compound of oxygen and sulfur, OSSO, which has a double bond between the sulfur atoms and exists in "cis" and "trans" forms, or due to polysulfur compounds from Template:Chem2 to Template:Chem2.<ref>Template:Cite journal</ref>
The surface of Venus is effectively isothermal; it retains a constant temperature not only between the two hemispheres but between the equator and the poles.<ref name="fact"/><ref name=Lorenz_et_al_2001/> Venus's minute axial tilt—less than 3°, compared to 23° on Earth—also minimizes seasonal temperature variation.<ref name=NASA_Seasons/> Altitude is one of the few factors that affect Venusian temperatures. The highest point on Venus, Maxwell Montes, is therefore the coolest point on Venus, with a temperature of about Template:Convert and an atmospheric pressure of about Template:Convert.<ref name="Basilevsky_2003"/><ref name="McGill_2010"/> In 1995, the Magellan spacecraft imaged a highly reflective substance at the tops of the highest mountain peaks, a "Venus snow" that bore a strong resemblance to terrestrial snow. This substance likely formed by 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 name=Otten_2004/>
Although Venus has no seasons, in 2019 astronomers identified a cyclical variation in sunlight absorption by the atmosphere, possibly caused by opaque, absorbing particles suspended in the upper clouds. The variation causes observed changes in the speed of Venus's zonal winds and appears to rise and fall in time with the Sun's 11-year sunspot cycle.<ref name="TAJ-20190826"/>
The existence of lightning in the atmosphere of Venus has been controversial<ref name="Lorentz_2018"/> since the first suspected bursts were detected by the Soviet Venera probes.<ref name="Kranopol'skii_1980"/><ref name="Russell, Philips"/><ref name=Venera_12/> In 2006–07, Venus Express clearly detected 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 that on Earth,<ref name="Russell_2007"/> however other instruments have not detected lightning at all.<ref name="Lorentz_2018" /> The origin of any lightning remains unclear, but could originate from clouds or Venusian volcanoes.
In 2007, Venus Express discovered that a huge double atmospheric polar vortex exists at the south pole.<ref name=Hand_2007/><ref name=BBC_2007_11_28/> Venus Express discovered, in 2011, that an ozone layer exists high in the atmosphere of Venus.<ref name="esaozone"/> In 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"/><ref name="Space-20130130"/>
In December 2015, and to a lesser extent in April and May 2016, researchers working on Japan's Akatsuki mission observed bow-shaped objects in the atmosphere of Venus. This was considered direct evidence of the existence of perhaps the largest stationary gravity waves in the solar system.<ref name=Fukuhara_et_al_2017/><ref name=Rincon_2017/><ref name=Chang_2017/>
Orbit and rotation
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Venus orbits the Sun at an average distance of about Template:Convert, and completes an orbit every 224.7 days. It completes 13 orbits in 7.998 years, so its position in our sky almost repeats every eight years. Although all planetary orbits are elliptical, Venus's orbit is currently the closest to circular, with an eccentricity of less than 0.01.<ref name="fact" /> Simulations of the early solar system orbital dynamics have shown that the eccentricity of the Venus orbit may have been substantially larger in the past, reaching values as high as 0.31 and possibly impacting early climate evolution.<ref name="psj_1_42"/>
Venus has retrograde rotation, meaning that unlike most planets including Earth it rotates clockwise around its own axis, opposite to its anticlockwise rotation around the Sun. Therefore Venusian sidereal day, 243 Earth days, lasts longer than a Venusian year, 224.7 Earth days. If Venus where tidally locked to the Sun, it would always have the same face pointed to the Sun and its sidereal day would be 224.7 days. However, Venus's atmosphere is massive and it is close to the Sun, so differential heating of the atmosphere gives Venus a small retrograde rotation. The day length also fluctuates by up to 20 minutes for the same reason.<ref name="EarthSky Updates on your cosmos and world 2021">Template:Cite web</ref><ref>Template:Cite journal</ref> Venus's rotation period measured with Magellan spacecraft data over a 500-day period is smaller than the rotation period measured during the 16-year period between the Magellan spacecraft and Venus Express visits, with a difference of about 6.5Template:Spacesminutes.<ref name="slowing spin"/> Because of the retrograde rotation, the length of a solar day on Venus is significantly shorter than the sidereal day, at 116.75 Earth days.<ref name="planetary-facts"/> One Venusian year is about 1.92Template:SpacesVenusian solar days.<ref name="compare"/> To an observer on the surface of Venus, the Sun would rise in the west and set in the east,<ref name="compare" /> although Venus's opaque clouds prevent observing the Sun from the planet's surface.<ref name=Brunier_2002/>
Venus may have formed from the solar nebula with a different rotation period and obliquity, reaching its current state because of chaotic spin changes caused by planetary perturbations and tidal effects on its dense atmosphere, a change that would have occurred over the course of billions of years. The rotation period of Venus may represent an equilibrium state between tidal locking to the Sun's gravitation, which tends to slow rotation, and an atmospheric tide created by solar heating of the thick Venusian atmosphere.<ref name=Correia_et_al_2003/><ref name=Laskar_De_Surgy_2003/> The 584-day average interval between successive close approaches to Earth is almost exactly equal to 5Template:SpacesVenusian solar days (5.001444 to be precise),<ref name=Gold_Soter_1969/> but the hypothesis of a spin-orbit resonance with Earth has been discounted.<ref name="apj2_230_L123"/>
Venus has no natural satellites.<ref name="icarus202"/> It has several trojan asteroids: the quasi-satellite Template:Mpl<ref name=Mikkola_et_al_2004/><ref name=Carlos_De_la_Fuente_Marcos_2012/> and two other temporary trojans, Template:Mpl- and Template:Mpl.<ref name="dynamics"/> In the 17th century, Giovanni Cassini reported a moon orbiting Venus, which was named Neith and numerous sightings were reported over the following Template:Val, but most were determined to be stars in the vicinity. Alex Alemi's and David Stevenson's 2006 study of models of the early Solar System at the California Institute of Technology shows Venus likely had at least one moon created by a huge impact event billions of years ago.<ref name=Musser_2006/> About 10Template:SpacesmillionTemplate:Spacesyears later, according to the study, another impact reversed the planet's spin direction and the resulting tidal deceleration caused the Venusian moon gradually to spiral inward until it collided with Venus.<ref name=Tytell_2006/> If later impacts created moons, these were removed in the same way. An alternative explanation for the lack of satellites is the effect of strong solar tides, which can destabilize large satellites orbiting the inner terrestrial planets.<ref name="icarus202" />
The orbital space of Venus has a dust ring-cloud,<ref name="Frazier 2021"/> with a suspected origin either from Venus–trailing asteroids,<ref name="Garner 2019"/> interplanetary dust migrating in waves, or the remains of the Solar System's original circumstellar disc that formed the planetary system.<ref name="Rehm 2021"/>
Orbit in respect to Earth
[edit]
Earth and Venus have a near orbital resonance of 13:8 (Earth orbits eight times for every 13 orbits of Venus).<ref name="Bazsó">Template:Cite journal</ref> Therefore, they approach each other and reach inferior conjunction in synodic periods of 584 days, on average.<ref name="fact" /> The path that Venus makes in relation to Earth viewed geocentrically draws a pentagram over five synodic periods, shifting every period by 144°. This pentagram of Venus is sometimes referred to as the petals of Venus due to the path's visual similarity to a flower.<ref name=Ottewel_2022/>
When Venus lies between Earth and the Sun in inferior conjunction, it makes the closest approach to Earth of any planet at an average distance of Template:Convert.<ref name="fact" />Template:Refn<ref name="MoreOrLess"/> Because of the decreasing eccentricity of Earth's orbit, the minimum distances will become greater over tens of thousands of years. From the yearTemplate:Spaces1 to 5383, there are 526 approaches less than Template:Convert; then, there are none for about 60,158 years.<ref name=Solex11/>
While Venus approaches Earth the closest, Mercury is more often the closest to Earth of all planets and to any other planet.<ref name="AIP Publishing 2019 p."/><ref>Template:Cite magazine</ref> Venus has the lowest gravitational potential difference to Earth than any other planet, needing the lowest delta-v to transfer between them.<ref name="Petropoulos Longuski Bonfiglio 2000 pp. 776–783"/><ref name="Taylor 2020"/>
Tidally Venus exerts the third strongest tidal force on Earth, after the Moon and the Sun, though significantly less.<ref name="Science Mission Directorate 2000">Template:Cite web</ref>
Observability
[edit]
To the naked eye, Venus appears as a white point of light brighter than any other planet or star (apart from the Sun).<ref name=Dickinson_1998/> The planet's mean apparent magnitude is −4.14 with a standard deviation of 0.31.<ref name="Mallama_and_Hilton" /> The brightest magnitude occurs during the crescent phase about one month before or after an inferior conjunction. Venus fades to about magnitude −3 when it is backlit by the Sun, although the exact value depends on the phase angle.<ref name="n850">Template:Cite web</ref> The planet is bright enough to be seen in broad daylight,<ref name=Flanders_2011/> but is more easily visible when the Sun is low on the horizon or setting. As an inferior planet, it always lies within about 47° of the Sun.<ref name="ephemeris"/>
Venus "overtakes" Earth every 584 days as it orbits the Sun.<ref name="fact" /> As it does so, it changes from the "Evening Star", visible after sunset, to the "Morning Star", visible before sunrise. Although Mercury, the other inferior planet, reaches a maximum elongation of only 28° and is often difficult to discern in twilight, Venus is hard to miss when it is at its brightest. Its greater maximum elongation means it is visible in dark skies long after sunset. As the brightest point-like object in the sky, Venus is a commonly misreported "unidentified flying object".<ref name=ASP_2021/>
Because Venus comes close to the earth at inferior conjunction and has an orbit inclined to the plane of the earth's orbit, it can appear more than 8° north or south of the ecliptic, more than any other planet or the moon. Every eight years around March it appears this far north of the ecliptic, in Pisces (such as in mid-March 2025), and every eight years it appears this far south of the ecliptic in August or September in Virgo (as in late August 2023). Venus can thus be north of the sun and appear as a morning star and an evening star on the same day, in the northern hemisphere. The timing of these north or south excursions gets slowly earlier in the year, and over 30 cycles (240 years) the cycle is gradually replaced by another cycle offset by three years, so the situation returns close to the original situation after 243 orbits of Earth, 395 of Venus.<ref>See this JPL Horizons ephemeris calculation.</ref>
Lunar occultations of Venus, in which the moon blocks the view of Venus for observers in certain parts of the earth, occur on average about twice a year, sometimes several times in a year (though rarely).
Phases
[edit]
As it orbits the Sun, Venus displays phases like those of the Moon in a telescopic view. The planet appears as a small and "full" disc when it is on the opposite side of the Sun (at superior conjunction). Venus shows a larger disc and "quarter phase" at its maximum elongations from the Sun, and appears at its brightest in the night sky. The planet presents a much larger thin "crescent" in telescopic views as it passes along the near side between Earth and the Sun. Venus displays its largest size and "new phase" when it is between Earth and the Sun (at inferior conjunction). Its atmosphere is visible through telescopes by the halo of sunlight refracted around it.<ref name="ephemeris" /> The phases are clearly visible in a 4" telescope.<ref>Template:Cite web</ref> Although naked eye visibility of Venus's phases is disputed, records exist of observations of its crescent.<ref name="Goines_1995" />
Daylight apparitions
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When Venus is sufficiently bright with enough angular distance from the sun, it is easily observed in a clear daytime sky with the naked eye, though most people do not know to look for it.<ref>Template:Cite web</ref> Astronomer Edmund Halley calculated its maximum naked eye brightness in 1716, when many Londoners were alarmed by its appearance in the daytime. French emperor Napoleon Bonaparte once witnessed a daytime apparition of the planet while at a reception in Luxembourg.<ref name="Chatfield_2015" /> Another historical daytime observation of the planet took place during the inauguration of the American president Abraham Lincoln in Washington, D.C., on 4Template:SpacesMarch 1865.<ref name="Gaherty_2012" />
Transits
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A transit of Venus is the appearance of Venus in front of the Sun, during inferior conjunction. Since the orbit of Venus is slightly inclined relative to Earth's orbit, most inferior conjunctions with Earth, which occur every synodic period of 1.6 years, do not produce a transit of Venus. Consequently, Venus transits only occur when an inferior conjunction takes place during some days of June or December, when the orbits of Venus and Earth cross a straight line with the Sun.<ref name="NASA 2004">Template:Cite web</ref> This results in Venus transiting above Earth in a sequence currently of Template:Val, Template:Val, Template:Val and Template:Val, forming cycles of Template:Val.
Historically, transits of Venus were important, because they allowed astronomers to determine the size of the astronomical unit, and hence the size of the Solar System as shown by Jeremiah Horrocks in 1639 with the first known observation of a Venus transit (after history's first observed planetary transit in 1631, of Mercury).<ref name=Kollerstrom_1998/>
Only seven Venus transits have been observed so far, since their occurrences were calculated in the 1621 by Johannes Kepler. Captain Cook sailed to Tahiti in 1768 to record the third observed transit of Venus, which subsequently resulted in the exploration of the east coast of Australia.<ref name=Hornsby_1771/><ref name=Woolley_1969/>
The latest pair was June 8, 2004 and June 5–6, 2012. The transit could be watched live from many online outlets or observed locally with the right equipment and conditions.<ref name=Boyle_2016/> The preceding pair of transits occurred in December 1874 and December 1882.
The next transit will occur in December 2117 and December 2125.<ref name=Espenak_2004/>
Ashen light
[edit]
A long-standing mystery of Venus observations is the so-called ashen light—an apparent weak illumination of its dark side, seen when the planet is in the crescent phase. The first claimed observation of ashen light was made in 1643, but the existence of the illumination has never been reliably confirmed. Observers have speculated it may result from electrical activity in the Venusian atmosphere, but it could be illusory, resulting from the physiological effect of observing a bright, crescent-shaped object.<ref name=Baum_2000/><ref name="Russell, Philips" /> The ashen light has often been sighted when Venus is in the evening sky, when the evening terminator of the planet is towards Earth.
Observation and exploration history
[edit]Early observation
[edit]Venus is in Earth's sky bright enough to be visible without aid, making it one of the classical planets that human cultures have known and identified throughout history, particularly for being the third brightest object in Earth's sky after the Sun and the Moon. Because the movements of Venus appear to be discontinuous (it disappears due to its proximity to the sun, for many days at a time, and then reappears on the other horizon), some cultures did not recognize Venus as a single entity;<ref name="Cooley"/> instead, they assumed it to be two separate stars on each horizon: the morning and evening star.<ref name=Cooley/> Nonetheless, a cylinder seal from the Jemdet Nasr period and the Venus tablet of Ammisaduqa from the First Babylonian dynasty indicate that the ancient Sumerians already knew that the morning and evening stars were the same celestial object.<ref name=Sachs_1974/><ref name=Cooley/><ref name=Hobson_2009/>
In the Old Babylonian period, the planet Venus was known as Ninsi'anna, and later as Dilbat.<ref>Enn Kasak, Raul Veede. Understanding Planets in Ancient Mesopotamia. Folklore Vol. 16. Mare Kõiva & Andres Kuperjanov, Eds. ISSN 1406-0957</ref> The name "Ninsi'anna" translates to "divine lady, illumination of heaven", which refers to Venus as the brightest visible "star". Earlier spellings of the name were written with the cuneiform sign si4 (= SU, meaning "to be red"), and the original meaning may have been "divine lady of the redness of heaven", in reference to the colour of the morning and evening sky.<ref name=Heimpel_1982/>
The Chinese historically referred to the morning Venus as "the Great White" (Template:Transliteration Template:Lang) or "the Opener (Starter) of Brightness" (Template:Transliteration Template:Lang), and the evening Venus as "the Excellent West One" (Template:Transliteration Template:Lang).<ref name=Needham_1959/>
The ancient Greeks initially believed Venus to be two separate stars: Phosphorus, the morning star, and Hesperus, the evening star. Pliny the Elder credited the realization that they were a single object to Pythagoras in the sixth century BC,<ref name=Pliny_1991/> while Diogenes Laërtius argued that Parmenides (early fifth century) was probably responsible for this discovery.<ref name=Berkert_1972/> Though they recognized Venus as a single object, the ancient Romans continued to designate the morning aspect of Venus as Lucifer, literally "Light-Bringer", and the evening aspect as Vesper,<ref name=Dobbin_2002/> both of which are literal translations of their traditional Greek names.
In the second century, in his astronomical treatise Almagest, Ptolemy theorized that both Mercury and Venus were located between the Sun and the Earth. The 11th-century Persian astronomer Avicenna claimed to have observed a transit of Venus (although there is some doubt about it),<ref name="Goldstein"/> which later astronomers took as confirmation of Ptolemy's theory.<ref name=Enc_Irnica/> In the 12th century, the Andalusian astronomer Ibn Bajjah observed "two planets as black spots on the face of the Sun"; these were thought to be the transits of Venus and Mercury by 13th-century Maragha astronomer Qotb al-Din Shirazi, though this cannot be true as there were no Venus transits in Ibn Bajjah's lifetime.<ref name=Ansari_2002/>Template:Refn
Venus and early modern astronomy
[edit]When the Italian physicist Galileo Galilei first observed the planet with a telescope in the early 17th century, he found it showed phases like the Moon, varying from crescent to gibbous to full and vice versa. When Venus is furthest from the Sun in the sky, it shows a half-lit phase, and when it is closest to the Sun in the sky, it shows as a crescent or full phase. This could be possible only if Venus orbited the Sun, and this was among the first observations to clearly contradict the Ptolemaic geocentric model that the Solar System was concentric and centred on Earth.<ref name="palmieri"/><ref name="Fegley"/>
The 1631 transit of Venus, while not recorded, was the first one successfully predicted, by Johannes Kepler and his calculations, which he published in 1629. The following 1639 transit of Venus was accurately predicted by Jeremiah Horrocks and observed by him and his friend, William Crabtree, at each of their respective homes, on 4Template:SpacesDecember 1639 (24 November under the Julian calendar in use at that time).<ref name="Kollerstrom"/>
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The atmosphere of Venus was discovered in 1761 by Russian polymath Mikhail Lomonosov.<ref name="Marov2004"/><ref name=Britannica/> Venus's atmosphere was observed in 1790 by German astronomer Johann Schröter. Schröter found when the planet was a thin crescent, the cusps extended through more than 180°. He correctly surmised this was due to scattering of sunlight in a dense atmosphere. Later, American astronomer Chester Smith Lyman observed a complete ring around the dark side of the planet when it was at inferior conjunction, providing further evidence for an atmosphere.<ref name=Russell_1899/> The atmosphere complicated efforts to determine a rotation period for the planet, and observers such as Italian-born astronomer Giovanni Cassini and Schröter incorrectly estimated periods of about Template:Val from the motions of markings on the planet's apparent surface.<ref name=Hussey_1832/>
Early 20th century advances
[edit]Little more was discovered about Venus until the 20th century. Its almost featureless disc gave no hint what its surface might be like, and it was only with the development of spectroscopic and ultraviolet observations that more of its secrets were revealed.
Spectroscopic observations in the 1900s gave the first clues about the Venusian rotation. Vesto Slipher tried to measure the Doppler shift of light from Venus, but found he could not detect any rotation. He surmised the planet must have a much longer rotation period than had previously been thought.<ref name=Slipher_1903/>
The first ultraviolet observations were carried out in the 1920s, when Frank E. Ross found that ultraviolet photographs revealed considerable detail that was absent in visible and infrared radiation. He suggested this was due to a dense, yellow lower atmosphere with high cirrus clouds above it.<ref name=Ross_1928/>
It had been noted that Venus had no discernible oblateness in its disk, suggesting a slow rotation, and some astronomers concluded based on this that it was tidally locked like Mercury was believed to be at the time; but other researchers had detected a significant quantity of heat coming from the planet's nightside, suggesting a quick rotation (a high surface temperature was not suspected at the time), confusing the issue.<ref name=Martz_1934/> Later work in the 1950s showed the rotation was retrograde.
Space age
[edit]
The first interplanetary spaceflight attempt was in 1961 when the robotic space probe Venera 1 of the Soviet Venera programme flew to Venus. It lost contact en route.<ref name="mitchell_1"/>
The first successful interplanetary mission, also to Venus, was Mariner 2 of the United States' Mariner programme, passing on 14 December 1962 at Template:Convert above the surface of Venus and gathering data on the planet's atmosphere.<ref name=Mayer_et_al_1958/><ref name=NASA_1962/>
Additionally radar observations of Venus were first carried out in the 1960s, and provided the first measurements of the rotation period, which were close to the actual value.<ref name=Goldstein_Carpenter_1963/>
Venera 3, launched in 1966, became humanity's first probe and lander to reach and impact another celestial body other than the Moon, but could not return data as it crashed into the surface of Venus. In 1967, Venera 4 was launched and successfully deployed science experiments in the Venusian atmosphere before impacting. Venera 4 showed the surface temperature was hotter than Mariner 2 had calculated, at almost Template:Cvt, determined that the atmosphere was 95% carbon dioxide (Template:Chem), and discovered that Venus's atmosphere was considerably denser than Venera 4Template:'s designers had anticipated.<ref name="mitchell_2"/><ref name=Harvey115>Template:Cite book</ref>
In an early example of space cooperation the data of Venera 4 was joined with the 1967 Mariner 5 data, analysed by a combined Soviet–American science team in a series of colloquia over the following year.<ref name=COSPAR_Group_VII_1969/>
On 15 December 1970, Venera 7 became the first spacecraft to soft land on another planet and the first to transmit data from there back to Earth.<ref name=Time_1971/>
In 1974, Mariner 10 swung by Venus to bend its path towards Mercury and took ultraviolet photographs of the clouds, revealing the extraordinarily high wind speeds in the Venusian atmosphere. This was the first interplanetary gravity assist ever used, a technique which would be used by later probes.
Radar observations in the 1970s revealed details of the Venusian surface for the first time. Pulses of radio waves were beamed at the planet using the Template:Convert radio telescope at Arecibo Observatory, and the echoes revealed two highly reflective regions, designated the Alpha and Beta regions. The observations revealed a bright region attributed to mountains, which was called Maxwell Montes.<ref name=Campbell_et_al_1976/> These three features are now the only ones on Venus that do not have female names.<ref name="jpl-magellan"/>
In 1975, the Soviet Venera 9 and 10 landers transmitted the first images from the surface of Venus, which were in black and white. NASA obtained additional data with the Pioneer Venus project, consisting of two separate missions:<ref name=Colin_Hall_1977/> the Pioneer Venus Multiprobe and Pioneer Venus Orbiter, orbiting Venus between 1978 and 1992.<ref name=Williams_2005/> In 1982 the first colour images of the surface were obtained with the Soviet Venera 13 and 14 landers. After Venera 15 and 16 operated between 1983 and 1984 in orbit, conducting detailed mapping of 25% of Venus's terrain (from the north pole to 30°N latitude), the Soviet Venera programme came to a close.<ref name=Greeley_Batson_2007/>
In 1985 the Soviet Vega programme with its Vega 1 and Vega 2 missions carried the last entry probes and carried the first ever extraterrestrial aerobots for the first time achieving atmospheric flight outside Earth by employing inflatable balloons.
Between 1990 and 1994, Magellan operated in orbit until deorbiting, mapping the surface of Venus. Furthermore, probes like Galileo (1990),<ref name="PDS Atmospheres Node 1989">Template:Cite web</ref> Cassini–Huygens (1998/1999), and MESSENGER (2006/2007) visited Venus with flybys en route to other destinations. In April 2006, Venus Express, the first dedicated Venus mission by the European Space Agency (ESA), entered orbit around Venus. Venus Express provided unprecedented observation of Venus's atmosphere. ESA concluded the Venus Express mission in December 2014 deorbiting it in January 2015.<ref name=Howell_2014/>
In 2010, the first successful interplanetary solar sail spacecraft IKAROS travelled to Venus for a flyby.
Between 2015 and 2024 Japan's Akatsuki probe was active in orbit around Venus and BepiColombo performed flybys in 2020/2021.
Active and planned missions
[edit]
Template:As of there are no active probes at Venus, with Parker Solar Probe scheduled to return repeatedly to Venus until 2030.
Several probes are under development as well as multiple proposed missions still in their early conceptual stages. The next Venus mission scheduled is the Venus Life Finder, expected to launch not earlier than summer 2026.
Indian ISRO is working on Venus Orbiter Mission, aiming to launch it in 2028. UAE mission to asteroids, MBR Explorer, will perform a flyby of the planet. NASA approved two missions to the planet, VERITAS and DAVINCI, planned to be launched not earlier then 2031. ESA plans to launch EnVision also in 2031.
Objectives
[edit]Venus has been identified for future research as an important case for understanding:
- the origins of the solar system and Earth, and if systems and planets like ours are common or rare in the universe.
- how planetary bodies evolve from their primordial states to today's diverse objects.
- the development of conditions leading to habitable environments and life.<ref name="O'Rourke Wilson Borrelli Byrne 2023 p.">Template:Cite journal</ref>
Crewed mission concepts
[edit]Venus has been considered since the 1960s as a waypoint for crewed missions to Mars through opposition missions instead of direct conjunction missions with Venus gravity assist flybys, demonstrating that they should be quicker and safer missions to Mars, with better return or abort flight windows, and less or the same amount of radiation exposure from the flight as direct Mars flights.<ref name="Rao 2020">Template:Cite web</ref><ref name="Izenberg McNutt Runyon Byrne 2021 pp. 100–104">Template:Cite journal</ref>
Possible atmospheric habitation
[edit]
While the surface conditions of Venus are extremely hostile, the atmospheric pressure, temperature, and solar and cosmic radiation 50 km above the surface are similar to those at Earth's surface ("clement conditions").<ref name="f997">Template:Cite journal</ref><ref name="Herbst Banjac Atri Nordheim 2019 p=A15"/><ref name="Patel Mason Nordheim Dartnell 2022 p=114796"/><ref name="Taylor 2020"/> Among the many engineering challenges for any human presence in the atmosphere of Venus are the corrosive amounts of sulfuric acid in the atmosphere.<ref name="Landis2003"/> Aerostats for crewed exploration and possibly for permanent "floating cities" in the Venusian atmosphere have been proposed as an alternative to the popular idea of living on planetary surfaces such as Mars.<ref name="Landis2003" /><ref name="Архив фантастики"/><ref name="Inner Solar System 2015"/><ref name="Tickle 2015"/><ref name=Warmflash_2017/> NASA's High Altitude Venus Operational Concept was a training concept to study a crewed aerostat design.
Search for life
[edit]Speculation on the possibility of life on Venus's surface decreased significantly after the early 1960s when it became clear that conditions were extreme compared to those on Earth. Venus's extreme temperatures and atmospheric pressure make water-based life, as currently known, unlikely.
Some scientists have speculated that thermoacidophilic extremophile microorganisms might exist in the cooler, acidic upper layers of the Venusian atmosphere.<ref name=Clark_2003/><ref name=Redfern_2004/><ref name="Dartnell2015"/> Such speculations go back to 1967, when Carl Sagan and Harold J. Morowitz suggested in a Nature article that tiny objects detected in Venus's clouds might be organisms similar to Earth's bacteria (which are of approximately the same size):
- While the surface conditions of Venus make the hypothesis of life there implausible, the clouds of Venus are a different story altogether. As was pointed out some years ago, water, carbon dioxide and sunlight—the prerequisites for photosynthesis—are plentiful in the vicinity of the clouds.<ref name=Sagan_Morowitz_1967/>
In August 2019, astronomers led by Yeon Joo Lee reported that long-term pattern of absorbance and albedo changes in the atmosphere of the planet Venus caused by "unknown absorbers", which may be chemicals or even large colonies of microorganisms high up in the atmosphere of the planet, affect the climate.<ref name="TAJ-20190826"/> Their light absorbance is almost identical to that of micro-organisms in Earth's clouds. Similar conclusions have been reached by other studies.<ref name="ES-20190903"/>
In September 2020, a team of astronomers led by Jane Greaves from Cardiff University announced the likely detection of phosphine, a gas not known to be produced by any known chemical processes on the Venusian surface or atmosphere, in the upper levels of the planet's clouds.<ref name=Bains_et_al_2021/><ref name=Greaves_et_al_2020/><ref name=Drake_2020/><ref name=Perkins_2020/><ref name=Seager_et_al_2020/> One proposed source for this phosphine is living organisms.<ref name="Sample1"/> The phosphine was detected at heights of at least Template:Convert above the surface, and primarily at mid-latitudes with none detected at the poles. The discovery prompted NASA administrator Jim Bridenstine to publicly call for a new focus on the study of Venus, describing the phosphine find as "the most significant development yet in building the case for life off Earth".<ref name=Kooser_2020/><ref name=Bridenstine_2020/>
Subsequent analysis of the data-processing used to identify phosphine in the atmosphere of Venus has raised concerns that the detection-line may be an artefact. The use of a 12th-order polynomial fit may have amplified noise and generated a false reading (see Runge's phenomenon). Observations of the atmosphere of Venus at other parts of the electromagnetic spectrum in which a phosphine absorption line would be expected did not detect phosphine.<ref name="Plait1"/> By late October 2020, re-analysis of data with a proper subtraction of background did not show a statistically significant detection of phosphine.<ref name=Snellen_et_al_2020/><ref name=Thompson2020/><ref name=Cordiner_et_al_2021/>
Members of the team around Greaves, are working as part of a project by the MIT to send with the rocket company Rocket Lab the first private interplanetary space craft, to look for organics by entering the atmosphere of Venus with a probe named Venus Life Finder.<ref name="Venus Cloud Life - MIT 2023">Template:Cite web</ref>
Planetary protection
[edit]The Committee on Space Research is a scientific organization established by the International Council for Science. Among their responsibilities is the development of recommendations for avoiding interplanetary contamination. For this purpose, space missions are categorized into five groups. Due to the harsh surface environment of Venus, Venus has been under the planetary protection category two.<ref name=NRC_2006/> This indicates that there is only a remote chance that spacecraft-borne contamination could compromise investigations.
In culture
[edit]Template:Main Venus is among the most prominent features in the night sky, and has been treated as particularly important in mythology, astrology and fiction across many different cultures.
Template:Anchor Several hymns praise Inanna in her role as the goddess of the planet Venus.<ref name=Cooley/><ref name="Green1992"/><ref name="Nemet-Nejat"/> Theology professor Jeffrey Cooley has argued that, in many myths, Inanna's movements may correspond with the movements of the planet Venus in the sky.<ref name=Cooley/> The discontinuous movements of Venus relate to both mythology as well as Inanna's dual nature.<ref name=Cooley/> In Inanna's Descent to the Underworld, unlike any other deity, Inanna is able to descend into the netherworld and return to the heavens. The planet Venus appears to make a similar descent, setting in the West and then rising again in the East.<ref name=Cooley/> An introductory hymn describes Inanna leaving the heavens and heading for Kur, what could be presumed to be, the mountains, replicating the rising and setting of Inanna to the West.<ref name=Cooley/> In Inanna and Shukaletuda and Inanna's Descent into the Underworld appear to parallel the motion of the planet Venus.<ref name=Cooley/> In Inanna and Shukaletuda, Shukaletuda is described as scanning the heavens in search of Inanna, possibly searching the eastern and western horizons.<ref name="Cooley2"/> In the same myth, while searching for her attacker, Inanna herself makes several movements that correspond with the movements of Venus in the sky.<ref name=Cooley/>
Via Mesopotamian influence, it is possible that the Ancient Egyptians and Greeks knew that the morning star and the evening star were one and the same as early as the second millennium BC—or the Late Period at the latest.<ref name="Parker 1974"/><ref name="Quack 2019"/> The Egyptians knew the morning star as Template:Tlit and the evening star as Template:Tlit.<ref name=Cattermole_Moore_1997/> They depicted Venus at first as a phoenix or heron (see Bennu),<ref name="Parker 1974"/> calling it 'the crosser' or 'star with crosses',<ref name="Parker 1974"/> associating it with Osiris, and later depicting it as two-headed (with human or falcon heads), and associated it with Horus,<ref name="Quack 2019"/> son of Isis (which during the even later Hellenistic period was together with Hathor identified with Aphrodite). The Greeks used the names Template:Tlit, meaning 'light-bringer' (whence the element phosphorus; alternately Template:Tlit, meaning 'dawn-bringer'), for the morning star, and Template:Tlit, meaning 'Western one', for the evening star,<ref name="EBLCM"/> both children of dawn Eos and therefore grandchildren of Aphrodite. Though by the Roman era they were recognized as one celestial object, known as "the star of Venus", the traditional two Greek names continued to be used, though usually translated to Latin as Template:Lang and Template:Lang.<ref name="EBLCM"/><ref name=Cicero/>
Classical poets such as Homer, Sappho, Ovid and Virgil spoke of the star and its light.<ref name=Atsma/> Poets such as William Blake, Robert Frost, Letitia Elizabeth Landon, Alfred Lord Tennyson and William Wordsworth wrote odes to it.<ref name=Sobel_2005/> The composer Holst included it as the second movement of his The Planets suite.
In India, the name for Venus in Sanskrit was Template:Tlit, meaning 'the planet Shukra'—in reference to Shukra, a powerful saint. As appears in Vedic astrology,<ref name="bhalla06"/> the Sanskrit name Shukra means 'clear, pure' or 'brightness, clearness'. One of the nine Navagraha, it is held to affect wealth, pleasure and reproduction; it was the son of Bhrgu, preceptor of the Daityas, and guru of the Asuras.<ref name="behari_frawley03"/>
The English name Venus stems originally from the ancient Romans. Romans named Venus after their goddess of love, who in turn was based on the ancient Greek love goddess Aphrodite,<ref name="Getty"/> who was herself based on the similar Sumerian religion goddess Inanna (which is Ishtar in Akkadian religion), all of whom were associated with the planet.<ref name="Nemet-Nejat"/><ref name="Green1992"/> The weekday of the planet and these goddesses is Friday, named after the Germanic goddess Frigg, who has been associated with the Roman goddess Venus.
In Chinese, the planet is called Jinxing (Template:Zhi); of the five elements of traditional Chinese philosophy, Venus was historically associated with metal. These traditions are shared among modern Chinese, Japanese, Korean and Vietnamese cultures, including a name for the planet literally meaning 'metal star' (Template:Lang) in each language.<ref name=De_Groot_1912/><ref name=Crump_1992/><ref name=Hulbert_1909/><ref name=VOER/>
The Maya considered Venus to be the most important celestial body after the Sun and Moon. They called it Template:Tlit,<ref name="Volume 7 of Mayan studies"/> or Template:Tlit, 'the Great Star'.<ref name="Milbrath"/> The cycles of Venus were important to their calendar and were described in some of their books, such as the Maya Codex of Mexico and Dresden Codex. The flag of Chile (Template:Lang, 'Lone Star') depicts Venus.
Modern culture
[edit]
The impenetrable Venusian cloud cover gave science fiction writers free rein to speculate on conditions at its surface; all the more so when early observations showed that not only was it similar in size to Earth, it possessed a substantial atmosphere. Closer to the Sun than Earth, the planet was often depicted as warmer, but still habitable by humans.<ref name="miller"/> The genre reached its peak between the 1930s and 1950s, at a time when science had revealed some aspects of Venus, but not yet the harsh reality of its surface conditions. Findings from the first missions to Venus showed reality to be quite different and brought this particular genre to an end.<ref name=Dick_2001/> As scientific knowledge of Venus advanced, science fiction authors tried to keep pace, particularly by conjecturing human attempts to terraform Venus.<ref name=Seed_2005/>
Symbols
[edit].svg){kind=link}
The symbol of a circle with a small cross beneath is the so-called Venus symbol, gaining its name for being used as the astronomical symbol for Venus. The symbol is of ancient Greek origin, and represents more generally femininity, adopted by biology as gender symbol for female,<ref name="Schott 2005 pp. 1509–1510"/><ref name="stearn1961"/><ref name="stearn"/> like the Mars symbol for male and sometimes the Mercury symbol for hermaphrodite. This gendered association of Venus and Mars has been used to pair them heteronormatively, describing women and men stereotypically as being so different that they can be understood as coming from different planets, an understanding popularized in 1992 by the book titled Men Are from Mars, Women Are from Venus.<ref name="Brammer 2020"/>
The Venus symbol was also used in Western alchemy representing the element copper (like the symbol of Mercury is also the symbol of the element mercury),<ref name="stearn1961" /><ref name="stearn" /> and since polished copper has been used for mirrors from antiquity the symbol for Venus has sometimes been called Venus mirror, representing the mirror of the goddess, although this origin has been discredited as an unlikely origin.<ref name="stearn1961" /><ref name="stearn" />
Besides the Venus symbol, many other symbols have been associated with Venus, other common ones are the crescent or particularly the star, as with the Star of Ishtar.<ref>Template:Cite book</ref>
See also
[edit]Notes
[edit]References
[edit]Further reading
[edit]External links
[edit]- Venus profile at NASA's Solar System Exploration site
- Missions to Venus and Image catalogue at the National Space Science Data Center
- Soviet Exploration of Venus and Image catalogue at Mentallandscape.com
- Image catalogue from the Venera missions
- Venus page at The Nine Planets
- Transits of Venus Template:Webarchive at NASA.gov
- Geody Venus, a search engine for surface features
- Interactive 3D gravity simulation of the pentagram that the orbit of Venus traces when Earth is held fixed at the centre of the coordinate system
Cartographic resources
[edit]- Map-a-Planet: Venus by the U.S. Geological Survey
- Gazetteer of Planetary Nomenclature: Venus by the International Astronomical Union
- Venus crater database by the Lunar and Planetary Institute
- Map of Venus by Eötvös Loránd University
- Google Venus 3D, interactive map of the planet
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