Venus is one of the fourterrestrial planetsin 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".[30]Venus is close to spherical due to its slow rotation.[31]Venus has a diameter of 12,103.6 km (7,520.8 mi)—only 638.4 km (396.7 mi) less than Earth's—and its mass is 81.5% of Earth's, making it the third-smallest planet in theSolar System. Conditions on the Venusian surface differ radically from those on Earth because its denseatmosphereis 96.5% carbon dioxide, with most of the remaining 3.5% beingnitrogen.[32]The surface pressure is 9.3megapascals(93bars), and the average surface temperature is 737 K (464 °C; 867 °F), above thecritical pointsof both major constituents and making the surface atmosphere asupercritical fluidout of mainlysupercritical carbon dioxideand some supercritical nitrogen.
Atmosphere and climate
Cloud structure of the Venusian atmosphere, made visible throughultravioletimaging
Venus has a denseatmospherecomposed 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[33]—and traces of other gases includingsulphur dioxide.[34]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 1 km (5⁄8 mi) under Earth's ocean surfaces. The density at the surface is 65 kg/m3(4.1 lb/cu ft), 6.5% that of water[33]or 50 times as dense as Earth's atmosphere at 293 K (20 °C; 68 °F) at sea level. TheCO2-rich atmosphere generates the strongestgreenhouse effectin the Solar System, creating surface temperatures of at least 735 K (462 °C; 864 °F).[35][36]This makes the Venusian surface hotter thanMercury's, which has a minimum surface temperature of 53 K (−220 °C; −364 °F) and maximum surface temperature of 700 K (427 °C; 801 °F),[37][38]even though Venus is nearly twice Mercury's distance from the Sun and thus receives only 25% of Mercury's solarirradiance. Because of itsrunaway greenhouse effect, Venus has been identified by scientists such asCarl Saganas a warning and research object linked toclimate changeon Earth.[28][29]
Venus temperature[39] Type Surface
temperatureMaximum 900 °F (482 °C) Normal 847 °F (453 °C) Minimum 820 °F (438 °C) Venus's atmosphere is rich in primordialnoble gasescompared to that of Earth.[40]This enrichment indicates an early divergence from Earth in evolution. An unusually large comet impact[41]or accretion of a more massiveprimary atmospherefrom solar nebula[42]have been proposed to explain the enrichment. However, the atmosphere is depleted of radiogenic argon, a proxy for mantle degassing, suggesting an early shutdown of major magmatism.[43][44]
Studies have suggested that billions of years ago, Venus's atmosphere could have been much more like the one surrounding the early Earth, and that there may have been substantial quantities of liquid water on the surface.[45][46][47]After a period of 600 million to several billion years,[48]solar forcingfrom rising luminosity of the Sun and possiblylarge volcanic resurfacingcaused the evaporation of the original water and the current atmosphere.[49]A runaway greenhouse effect was created once a critical level of greenhouse gases (including water) was added to its atmosphere.[50]Although the surface conditions on Venus are no longer hospitable to any Earth-like life that may have formed before this event, there is speculation on the possibility that life exists in the upper cloud layers of Venus, 50 km (30 mi) up from the surface, where the atmospheric conditions are the most Earth-like in the Solar System,[51]with temperatures ranging between 303 and 353 K (30 and 80 °C; 86 and 176 °F), and the pressure and radiation being about the same as at Earth's surface, but with acidic clouds and the carbon dioxide air.[52][53][54]The putative detection of anabsorption lineofphosphinein 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.[55][56]Later research attributed the spectroscopic signal that was interpreted as phosphine to sulphur dioxide,[57]or found that in fact there was no absorption line.[58][59]
Types of cloud layers, as well as temperature and pressure change by altitude in the atmosphere
Thermal inertiaand the transfer of heat by winds in the lower atmosphere mean that the temperature of Venus's surface does not vary significantly between the planet's two hemispheres, those 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.[60]
Above the denseCO2layer are thick clouds, consisting mainly ofsulfuric acid, which is formed by sulphur dioxide and water through a chemical reaction resulting in sulfuric acid hydrate. Additionally, the clouds consist of approximately 1%ferric chloride.[61][62]Other possible constituents of the cloud particles areferric sulfate,aluminium chlorideandphosphoric anhydride. Clouds at different levels have different compositions and particle size distributions.[61]These clouds reflect, similar to thick cloud cover on Earth,[63]about 70% of the sunlight that falls on them back into space,[64]and since they cover the whole planet they 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, with only 10% of the received sunlight reaching the surface,[65]resulting in average daytime levels of illumination at the surface of 14,000lux, comparable to that on Earth "in the daytime with overcast clouds".[66]Strong 300 km/h (185 mph) winds at the cloud tops go around Venus about every four to five Earth days.[67]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.[68]
The surface of Venus is effectivelyisothermal; it retains a constant temperature not only between the two hemispheres but between the equator and the poles.[4][69]Venus's minuteaxial tilt—less than 3°, compared to 23° on Earth—also minimises seasonal temperature variation.[70]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 655 K (380 °C; 715 °F) and an atmospheric pressure of about 4.5 MPa (45 bar).[71][72]In 1995, theMagellanspacecraftimaged 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 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 elementaltelluriumto lead sulfide (galena).[73]
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-yearsunspot cycle.[74]
The existence of lightning in the atmosphere of Venus has been controversial[75]since the first suspected bursts were detected by the SovietVenera probes.[76][77][78]In 2006–07,Venus Expressclearly detectedwhistler mode waves, the signatures of lightning. Theirintermittentappearance indicates a pattern associated with weather activity. According to these measurements, the lightning rate is at least half that on Earth,[79]however other instruments have not detected lightning at all.[75]The origin of any lightning remains unclear, but could originate from clouds orVenusian volcanoes.
In 2007,Venus Expressdiscovered that a huge doubleatmospheric polar vortexexists at the south pole.[80][81]Venus Expressdiscovered, in 2011, that anozonelayer exists high in the atmosphere of Venus.[82]On 29 January 2013,ESAscientists reported that theionosphereof Venus streams outwards in a manner similar to "the ion tail seen streaming from acometunder similar conditions."[83][84]
In December 2015, and to a lesser extent in April and May 2016, researchers working on Japan'sAkatsukimission observed bow-shaped objects in the atmosphere of Venus. This was considered direct evidence of the existence of perhaps the largest stationarygravity wavesin the solar system.[85][86][87]
https://en.wikipedia.org/wiki/Venus
