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Venus

May 11, 2023

This article is about the planet. For the deity, see Venus (mythology). For other uses, see Venus (disambiguation).

Venus is the second planet from the Sun. It is a rocky planet with a mass and size narrowly second in the Solar System to Earth, and with an atmosphere, which is the thickest of all four rocky planets of the Solar System and substantially thicker than Earth's. Its orbit is the next closest to Earth's, orbiting the Sun inferior inside of Earth's orbit, appearing (like Mercury) in Earth's sky always close to the Sun as either a "morning star" or "evening star". In Earth's sky it is also the natural object with the third highest maximum apparent brightness, after the Sun and the Moon, due to its proximity to Earth and the Sun, its size, and its highly reflective global cloud cover.[19][20] Because of these prominent appearances in Earth's sky, Venus has been, particularly among the other four star-like classical planets, a common and important object for humans, their cultures and astronomy.

Venus
Near-global view of Venus in natural colour, taken by the MESSENGER space probe
Designations
Pronunciation/ˈviːnəs/ (listen)
Named after
Roman goddess of love (see goddess Venus)
AdjectivesVenusian /vɪˈnjuːziən, -ʒən/,[1] rarely Cytherean /sɪθəˈriːən/[2] or Venerean / Venerian /vɪˈnɪəriən/[3]
Orbital characteristics[5][7]
Epoch J2000
Aphelion
  • 0.728213 AU
  • 108,939,000 km
Perihelion
  • 0.718440 AU
  • 107,477,000 km
  • 0.723332 AU
  • 108,208,000 km
Eccentricity0.006772[4]
583.92 days[5]
35.02 km/s
50.115°
Inclination
76.680°[4]
54.884°
SatellitesNone
Physical characteristics
Mean radius
  • 6,051.8±1.0 km[8]
  • 0.9499 Earths
Flattening0[8]
  • 4.6023×108 km2
  • 0.902 Earths
Volume
  • 9.2843×1011 km3
  • 0.857 Earths
Mass
  • 4.8675×1024 kg[9]
  • 0.815 Earths
Mean density
5.243 g/cm3
  • 8.87 m/s2
  • 0.904 g
10.36 km/s (6.44 mi/s)[10]
−116.75 d (retrograde)[11]
1 Venus solar day
−243.0226 d (retrograde)[12]
Equatorial rotation velocity
6.52 km/h (1.81 m/s)
2.64° (for retrograde rotation)
177.36° (to orbit)[5][note 1]
North pole right ascension
  • 18h 11m 2s
  • 272.76°[13]
North pole declination
67.16°
Albedo
Temperature232 K (−41 °C) (blackbody temperature)[16]
Surface temp. min mean max
Kelvin 737 K[5]
Celsius 464 °C
Fahrenheit 867 °F
Surface absorbed dose rate2.1×10−6 μGy/h[18]
Surface equivalent dose rate2.2×10−6 μSv/h
0.092–22 μSv/h at habitable altitudes[18]
−4.92 to −2.98[17]
9.7″–66.0″[5]
Atmosphere[5]
Surface pressure
93 bar (9.3 MPa)
92 atm
Composition by volume
  1. ^ Defining the rotation as retrograde, as done by NASA space missions and the USGS, puts Ishtar Terra in the northern hemisphere and makes the axial tilt 2.64°. Following the right-hand rule for prograde rotation puts Ishtar Terra in the southern hemisphere and makes the axial tilt 177.36°.

Venus retains, despite having only a weak induced magnetosphere, an especially thick atmosphere of mainly carbon dioxide, creating an extreme greenhouse effect together with its global sulfuric acid cloud cover. Consequently the atmosphere reaches at its bottom an intense mean temperature of 737 K (464 °C; 867 °F) and an atmospheric pressure of 92 times that of Earth at sea level, turning the air into a supercritical fluid. Internally Venus is thought to consist of a core, mantle, and crust. The surface was most likely shaped by volcanic resurfacing and has active volcanism, though it lacks more active geology like plate tectonics. Venus might have had water and maybe even oceans in its early history, if so this water probably evaporated when greenhouse effects cascaded and subsequently taken into space by the solar wind.[21][22][23] The possibility of life on Venus has long been a topic of speculation, particularly in its clouds and atmospheric layers at roughly 50 km (30 mi) altitude with conditions closest among any other in the Solar System to the ones at the surface of Earth. Despite recent indicative research, no convincing evidence has been found thus far.

Venus has no moon (like Mercury).[24] It rotates retrograde (like Uranus), against its orbital direction, and having been slowed by the strong currents and drag of the atmosphere it completes a sidreal rotation, relative to the stars, in 243 Earth days. Therefore it rotates slower than it is orbiting, having a solar year of 224.7 Earth days,[25] this results together with the retrograde rotation in having a solar day of 117 Earth days.[26] Venus and Earth approach each other in synodic periods of 1.6 years, while coming closer to each other at inferior conjunction than any other pair of planets, both stay on average closer to Mercury than to any other planet.[27] That said the gravitational potential between Earth and Venus and the needed speed to transfer between them is the lowest than between any other planet from Earth. This and its proximity to Earth has allowed Venus to be the most accessible destination and attractive gravity assist waypoint for interplanetary flights.

In 1961, Venus became the target of the first interplanetary flight in human history, followed by many essential interplanetary firsts, confirming in 1970 Venus' inhospitable surface conditions with the first soft landing on another planet. Venus as a place for humans to be was a popular topic in early science fiction. Actual proposals have suggested to send crews particularly on flybys, used as gravity assists for crewed missions to Mars, while some have suggested crews to enter the atmosphere, benefiting from Earth-like pressure, temperature, radiation and gravitation at cloud levels. Currently robotic probes are studying and will be sent to study Venus, having been providing crucial knowledge particularly about greenhouse effects, informing predictions about global warming on Earth.[28][29]

Physical characteristics

 
Venus to scale among the terrestrial planets of the Solar System, which are arranged by the order of their Inner Solar System orbits outward from the Sun (from left: Mercury, Venus, Earth and Mars)

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".[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. Conditions on the Venusian surface differ radically from those on Earth because its dense atmosphere is 96.5% carbon dioxide, with most of the remaining 3.5% being nitrogen.[32] The surface pressure is 9.3 megapascals (93 bars), and the average surface temperature is 737 K (464 °C; 867 °F), above the critical points of both major constituents and making the surface atmosphere a supercritical fluid out of mainly supercritical carbon dioxide and some supercritical nitrogen.

Atmosphere and climate

Main article: Atmosphere of Venus
 
Cloud structure of the Venusian atmosphere, made visible through ultraviolet imaging

Venus has a dense atmosphere composed of 96.5% carbon dioxide, 3.5% nitrogen—both exist as supercritical fluids at the planet's surface—and traces of other gases including sulfur dioxide.[33] 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 oceans. The density at the surface is 65 kg/m3 (4.1 lb/cu ft), 6.5% that of water or 50 times as dense as Earth's atmosphere at 293 K (20 °C; 68 °F) at sea level. The CO2-rich atmosphere generates the strongest greenhouse effect in the Solar System, creating surface temperatures of at least 735 K (462 °C; 864 °F).[25][34] This makes the Venusian surface hotter than Mercury'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),[35][36] even though Venus is nearly twice Mercury's distance from the Sun and thus receives only 25% of Mercury's solar irradiance. 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.[28][29]

Venus Temperature[37]
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.[38] This enrichment indicates an early divergence from Earth in evolution. An unusually large comet impact[39] or accretion of a more massive primary atmosphere from solar nebula[40] have been proposed to explain the enrichment. However, the atmosphere is depleted of radiogenic argon, a proxy to mantle degassing, suggesting an early shutdown of major magmatism.[41][42]

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.[43][44][45] After a period of 600 million to several billion years,[46] solar forcing from rising luminosity of the Sun and possibly large volcanic resurfacing caused the evaporation of the original water and the current atmosphere.[47] A runaway greenhouse effect was created once a critical level of greenhouse gases (including water) was added to its atmosphere.[48] 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,[49] witht 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 carbondioxide air.[50][51][52] 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.[53][54] Later research attributed the spectroscopic signal that was interpreted as phosphine to sulfur dioxide,[55] or found that in fact there was no absorption line.[56][57]

 
Temperature and pressure change by altitude in the atmosphere

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 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.[58]

Above the dense 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 clouds consist of approximately 1% ferric chloride.[59][60] 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.[59] 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 300 km/h (185 mph) winds at the cloud tops go around Venus about every four to five Earth days.[61] 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.[62]

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.[5][63] Venus's minute axial tilt—less than 3°, compared to 23° on Earth—also minimises seasonal temperature variation.[64] Altitude is one of the few factors that affect Venusian temperature. 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).[65][66] 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 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).[67]

Although Venus has no seasons as such, 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.[68]

The existence of lightning in the atmosphere of Venus has been controversial[69] since the first suspected bursts were detected by the Soviet Venera probes.[70][71][72] 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 of that on Earth,[73] however other instruments have not detected lightning at all.[69] The origin of any lightning remains unclear, but could originate from the clouds or Venusian volcanoes.

In 2007, Venus Express discovered that a huge double atmospheric polar vortex exists at the south pole.[74][75] Venus Express discovered, in 2011, that an ozone layer exists high in the atmosphere of Venus.[76] 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."[77][78]

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 waves in the solar system.[79][80][81]

Geography

Main articles: Mapping of Venus, Geology of Venus, and Surface features of Venus
 
Color-coded elevation map, showing the elevated terrae "continents" in yellow and minor features of Venus.

The Venusian surface was a subject of speculation until some of its secrets were revealed by planetary science in the 20th century. Venera landers in 1975 and 1982 returned images of a surface covered in sediment and relatively angular rocks.[82] The surface was mapped in detail by Magellan in 1990–91. The ground shows evidence of extensive volcanism, and the sulfur in the atmosphere may indicate that there have been recent eruptions.[83][84]

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.[85] 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. Maxwell Montes, the highest mountain on Venus, lies on Ishtar Terra. Its peak is 11 km (7 mi) above the Venusian average surface elevation.[86] 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.[87]

The absence of evidence of lava flow accompanying any of the visible calderas remains an enigma. The planet has few impact craters, demonstrating that the surface is relatively young, at 300–600 million years old.[88][89] 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 20 to 50 km (12 to 31 mi) across, and from 100 to 1,000 m (330 to 3,280 ft) 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.[90]

Most Venusian surface features are named after historical and mythological women.[91] 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.[92]

The longitude of physical features on Venus are 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.[93] After the Venera missions were completed, the prime meridian was redefined to pass through the central peak in the crater Ariadne on Sedna Planitia.[94][95]

 
Rectified and colourized surface image, Venera 10 (1975)

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.[22][96] The mechanism to generate a large amount of felsic crust usually requires the presence of water ocean and plate tectonics, implying that habitable condition had existed on early Venus with large bodies of water at some point.[97] However, the nature of tessera terrains is far from certain.[98]

Volcanism

Main article: Volcanism on Venus
 
Radar mosaic of two 65 km (40 mi) wide (and less than 1 km (0.62 mi) high) pancake domes in Venus's Eistla region

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 100 km (60 mi) across. The only volcanic complex of this size on Earth is the Big Island of Hawaii.[90]: 154  More than 85,000 volcanoes on Venus were identified and mapped.[99][100] This is not because Venus is more volcanically active than Earth, but because its crust is older and is not subject to the same erosion process. 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,[101] whereas the Venusian surface is estimated to be 300–600 million years old.[88][90]

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.[102] This may mean that levels had been boosted several times by large volcanic eruptions.[103][104] It has been suggested that Venusian lightning (discussed below) could originate from volcanic activity (i.e. volcanic lightning). In January 2020, astronomers reported evidence that suggests that Venus is currently volcanically active, specifically the detection of olivine, a volcanic product that would weather quickly on the planet's surface.[105][106]

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,[107][note 1] 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.[108][109] 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 800–1,100 K (527–827 °C; 980–1,520 °F) range, relative to a normal temperature of 740 K (467 °C; 872 °F).[110] 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 have concluded that active volcanism was the cause.[111]

Craters

 
Impact craters 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 300–600 million years ago,[88][89] followed by a decay in volcanism.[112] 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.[90]

Venusian craters range from 3 to 280 km (2 to 174 mi) 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 so much by the atmosphere that they do not create an impact crater.[113] Incoming projectiles less than 50 m (160 ft) in diameter will fragment and burn up in the atmosphere before reaching the ground.[114]

Internal structure

 
The differentiated structure of Venus

Without data from reflection seismology or knowledge of its moment of inertia, little direct information is available about the internal structure and geochemistry of Venus.[115] The similarity in size and density between Venus and Earth suggests 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,[116] although a completely solid core cannot be ruled out.[117] The slightly smaller size of Venus means pressures are 24% lower in its deep interior than Earth's.[118] The predicted values for the moment of inertia based on planetary models suggest a core radius of 2,900–3,450 km.[117] This is in line with the first observation-based estimate of 3,500 km.[119]

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.[120] Instead, Venus may lose its internal heat in periodic major resurfacing events.[88]

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,[121][122][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, reaching at elevations of 54 to 48 km Earth-like levels.[123][124]

The lack of an intrinsic magnetic field at 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.[125][126] 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.[127]

One possibility is that Venus has no solid inner core,[128] 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.[127]

Another possibility [129]is that the absence of a late, 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".

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 water 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 could have led to the loss of most of Venus's water during the first billion years after it formed.[130] However, the planet may have retained a dynamo for its first 2–3 billion years, so the water loss may have occurred more recently.[131] 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.[132]

Orbit and rotation

Main article: Orbit of Venus
 
Venus is the second planet from the Sun, making a full orbit in about 224 days

Venus orbits the Sun at an average distance of about 0.72 AU (108 million km; 67 million mi), and completes an orbit every 224.7 days. Although all planetary orbits are elliptical, Venus's orbit is currently the closest to circular, with an eccentricity of less than 0.01.[5] 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 the early climate evolution.[133] The current near-circular orbit of Venus means that 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 41 million km (25 million mi).[5][note 2][134] The planet has a near orbital resonance of 8 Earth orbits to 13 Venus orbits,[135] with inferior conjunctions occurring with a synodic period of 584 days, on average.[5]

Because of the decreasing eccentricity of Earth's orbit, the minimum distances will become greater over tens of thousands of years. From the year 1 to 5383, there are 526 approaches less than 40 million km (25 million mi); then, there are none for about 60,158 years.[136] While Venus approaches Earth the closest, Mercury is more frequently the closest to Earth of all planets.[137] Venus has the lowest gravitational potential difference to Earth than any other planet, needing the lowest delta-v to transfer between them.[138][139]

All planets in the Solar System orbit the Sun in an anticlockwise direction as viewed from above Earth's north pole. Most planets rotate on their axes in an anticlockwise direction, but Venus rotates clockwise in retrograde rotation once every 243 Earth days—the slowest rotation of any planet. This Venusian sidereal day lasts therefore longer than a Venusian year (243 versus 224.7 Earth days). Slowed by its strong atmospheric current the length of the day also fluctuates by up to 20 minutes.[140] Venus's equator rotates at 6.52 km/h (4.05 mph), whereas Earth's rotates at 1,674.4 km/h (1,040.4 mph).[note 3][144] 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 6.5 minutes.[145] 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 (making the Venusian solar day shorter than Mercury's 176 Earth days — the 116-day figure is close to the average number of days it takes Mercury to slip underneath the Earth in its orbit).[11] One Venusian year is about 1.92 Venusian solar days.[146] To an observer on the surface of Venus, the Sun would rise in the west and set in the east,[146] although Venus's opaque clouds prevent observing the Sun from the planet's surface.[147]

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.[148][149] The 584-day average interval between successive close approaches to Earth is almost exactly equal to 5 Venusian solar days (5.001444 to be precise),[150] but the hypothesis of a spin-orbit resonance with Earth has been discounted.[151]

Venus has no natural satellites.[152] It has several trojan asteroids: the quasi-satellite 2002 VE68[153][154] and two other temporary trojans, 2001 CK32 and 2012 XE133.[155] In the 17th century, Giovanni Cassini reported a moon orbiting Venus, which was named Neith and numerous sightings were reported over the following 200 years, 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.[156] About 10 million years 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.[157] 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.[152]

The orbital space of Venus has a dust ring-cloud,[158] with a suspected origin either from Venus–trailing asteroids,[159] interplanetary dust migrating in waves, or the remains of the Solar System's original circumstellar disc that formed the planetary system.[160]

Observability

 
Venus, pictured center-right, is always brighter than all other planets or stars at their maximal brightness, as seen from Earth. Jupiter is visible at the top of the image.

To the naked eye, Venus appears as a white point of light brighter than any other planet or star (apart from the Sun).[161] The planet's mean apparent magnitude is −4.14 with a standard deviation of 0.31.[17] The brightest magnitude occurs during crescent phase about one month before or after inferior conjunction. Venus fades to about magnitude −3 when it is backlit by the Sun.[162] The planet is bright enough to be seen in broad daylight,[163] 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.[164]

Venus "overtakes" Earth every 584 days as it orbits the Sun.[5] 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".[165]

Phases

Main article: Phases of Venus
 
The phases of Venus and evolution of its apparent diameter

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 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.[164] The phases are clearly visible in a 4" telescope.[citation needed]

Daylight apparitions

Naked-eye observations of Venus during daylight hours exist in several anecdotes and records. 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.[166] Another historical daytime observation of the planet took place during the inauguration of the American president Abraham Lincoln in Washington, D.C., on 4 March 1865.[167] Although naked eye visibility of Venus's phases is disputed, records exist of observations of its crescent.[168]

Transits

Main article: Transit of Venus
 
2012 transit of Venus, projected to a white card by a telescope

A transit of Venus is the appearance of Venus infront 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 above Earth. Consequently Venus transits above Earth only occur when an inferior conjunction takes place during some days of June or December, the time where the orbits of Venus and Earth cross a straight line with the Sun.[169] This results in Venus transiting above Earth in a sequence of currently 8 years, 105.5 years, 8 years and 121.5 years, forming cycles of 243 years.

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).[170]

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.[171][172]

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.[173] The preceding pair of transits occurred in December 1874 and December 1882.

The next transit will occur in December 2117 and December 2125.[174]

Pentagram of Venus

 
The pentagram of Venus. Earth is positioned at the centre of the diagram, and the curve represents the direction and distance of Venus as a function of time.

The pentagram of Venus is the path that Venus makes as observed from Earth. Successive inferior conjunctions of Venus repeat with a orbital resonance of 13:8 (Earth orbits eight times for every 13 orbits of Venus), shifting 144° upon sequential inferior conjunctions. The 13:8 ratio is approximate. 8/13 is approximately 0.61538 while Venus orbits the Sun in 0.61519 years.[citation needed] The pentagram of Venus is sometimes referred to as the petals of Venus due to the path's visual similarity to a flower.[175]

Ashen light

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.[176][71] The ashen light has often been sighted when Venus is in the evening sky, when the evening terminator of the planet is towards to Earth.

Observation and exploration history

Main article: Observations and explorations of Venus

Early observation

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;[177] instead, they assumed it to be two separate stars on each horizon: the morning and evening star.[177] 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.[178][177][179] In the Old Babylonian period, the planet Venus was known as Ninsi'anna, and later as Dilbat.[180] 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.[181]

The Chinese historically referred to the morning Venus as "the Great White" (Tàibái 太白) or "the Opener (Starter) of Brightness" (Qǐmíng 啟明), and the evening Venus as "the Excellent West One" (Chánggēng 長庚).[182]

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,[183] while Diogenes Laërtius argued that Parmenides was probably responsible for this discovery.[184] 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,[185] 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 are located between the Sun and the Earth. The 11th-century Persian astronomer Avicenna claimed to have observed the transit of Venus,[186] which later astronomers took as confirmation of Ptolemy's theory.[187] 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.[188][note 4]

Venus and early modern astronomy

 
 
In 1610 Galileo Galilei observed with his telescope that Venus showed phases, despite remaining near the Sun in Earth's sky (first image). This proved that it orbits the Sun and not Earth, as predicted by Copernicus's heliocentric model and disproved the then conventional geocentric model (second image).

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.[191][192]

The 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 4 December 1639 (24 November under the Julian calendar in use at that time).[193]

 
The "black drop effect" as recorded during the 1769 transit

The atmosphere of Venus was discovered in 1761 by Russian polymath Mikhail Lomonosov.[194][195] 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.[196] 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 24 h from the motions of markings on the planet's apparent surface.[197]

Early 20th century advances

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.[198]

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.[199]

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 wasn't suspected at the time), confusing the issue.[200] Later work in the 1950s showed the rotation was retrograde.

Space age

Further information: List of missions to Venus

Humanity's first interplanetary spaceflight was achieved in 1961 with the robotic space probe Venera 1 of the Soviet Venera program flying to Venus, though it lost contact en route.[201]

Therefore the first successful interplanetary mission was the Mariner 2 mission to Venus of the United States' Mariner program, passing on 14 December 1962 at 34,833 km (21,644 mi) above the surface of Venus and gathering data on the planet's atmosphere.[202][203]

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.[204]

After Venera 3 in 1966, humanity's first probe and lander to reach and impact another celestial body other than the Moon, couldn't return data, Venera 4 in 1967, successfully for the first time at location deployed science experiments before impacting. Venera 4 showed the surface temperature was hotter than Mariner 2 had calculated, at almost 500 °C (932 °F), determined that the atmosphere was 95% carbon dioxide (CO
2), and discovered that Venus's atmosphere was considerably denser than Venera 4's designers had anticipated.[205]

In an early example of space cooperation the data of Venera 4 was joint with the 1967 Mariner 5 data, analysed by a combined Soviet–American science team in a series of colloquia over the following year.[206]

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.[207]

In 1974, Mariner 10 swung by Venus to bend its path toward 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 300 m (1,000 ft) 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.[208] These three features are now the only ones on Venus that do not have female names.[92]

 
First view and first clear 180-degree panorama of Venus's surface as well as any other planet than Earth (1975, Soviet Venera 9 lander). Black-and-white image of barren, black, slate-like rocks against a flat sky. The ground and the probe are the focus.

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 that consisted of two separate missions:[209] the Pioneer Venus Multiprobe and Pioneer Venus Orbiter, orbiting Venus between 1978 and 1992.[210] 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 successful Soviet Venera program came to a close.[211]

 
Global topographic map of Venus, with all probe landings marked

In 1985 the Vega program with its Vega 1 and Vega 2 missions carried the last entry probes and carried the first ever extraterrestrial aerobots for the first time achiving atmospheric flight outside Earth by employing inflatable baloons.

Between 1990 and 1994 Magellan operated in orbit until deorbiting, mapping the surface of Venus. Furthermore probes like Galileo (1990),[212] Cassini–Huygens (1998/1999), and MESSENGER (2006/2007) visited Venus with flybys flying 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.[213]

2010 the first successful interplanetary solar sail spacecraft IKAROS traveled to Venus for a flyby.

Active and future missions

Further information: List of missions to Venus § Future missions
 
WISPR visible light footage (2021) of the nightside, showing the hot faintly glowing surface, and its Aphrodite Terra as large dark patch, through the clouds, which prohibit such observations on the dayside when they are illuminated.[214][215]

As of 2020, Japan's Akatsuki is since its orbital insertion on 7 December 2015 the only probe in orbit around Venus. Additionally flybys by other probes have been performed studying Venus on their way, as with the Parker Solar Probe and the Solar Orbiter.

There are several probing proposals under study by Roscosmos, NASA, ISRO, ESA, and the private sector (e.g. by Rocketlab).

Search for life

Main article: Life on Venus

Speculation on the possibility of life on Venus's surface decreased significantly after the early 1960s when it became clear that the conditions are extreme compared to those on Earth. Venus's extreme temperature 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).[216][217][218] 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.[219]

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.[68] Their light absorbance is almost identical to that of micro-organisms in Earth's clouds. Similar conclusions have been reached by other studies.[220]

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.[221][54][53][222][223] One proposed source for this phosphine is living organisms.[224] The phosphine was detected at heights of at least 30 miles 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".[225][226]

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.[227] By late October 2020, re-analysis of data with a proper subtraction of background did not show a statistically significant detection of phosphine.[228][229][230]

Planetary protection

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.[231] This indicates that there is only a remote chance that spacecraft-borne contamination could compromise investigations.

Human presence

Main article: List of missions to Venus

Venus is the place of the first interplanetary human presence, mediated through robotic missions, with the first successful landings on another planet and extraterrestrial body other than the Moon. Currently in orbit is Akatsuki, and other probes routinely use Venus for gravity assist maneuvers capturing some data about Venus on the way.[232]

The only nation that has sent lander probes to the surface of Venus has been the Soviet Union,[note 5] which has been used by Russian officials to call Venus a "Russian planet".[233][234]

Crewed flight

Studies of routes for crewed missions to Mars have since the 1960s proposed 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.[235][236]

Early in the space age the Soviet Union and the United States proposed the TMK-MAVR and Manned Venus flyby crewed flyby missions to Venus, though they were never realized.

Habitation

See also: Colonization of Venus and Floating cities and islands in fiction § Venus
 
Artist's rendering of a NASA High Altitude Venus Operational Concept (HAVOC) crewed floating outpost on Venus

While the surface conditions of Venus are inhospitable, the atmospheric pressure, temperature, or solar and cosmic radiation 50 km above the surface are similar to those at Earth's surface.[124][123] With this in mind, Soviet engineer Sergey Zhitomirskiy (Сергей Житомирский, 1929–2004) in 1971[237][238] and NASA aerospace engineer Geoffrey A. Landis in 2003[239] suggested the use of aerostats for crewed exploration and possibly for permanent "floating cities" in the Venusian atmosphere, an alternative to the popular idea of living on planetary surfaces such as Mars.[240][241] Among the many engineering challenges for any human presence in the atmosphere of Venus are the corrosive amounts of sulfuric acid in the atmosphere.[239]

NASA's High Altitude Venus Operational Concept is a mission concept that proposed a crewed aerostat design.

In culture

Main article: Venus in culture

Venus is a primary feature of the night sky, and so has been of remarkable importance in mythology, astrology and fiction throughout history and in different cultures.

The English name of Venus was originally the ancient Roman name for it. Romans named Venus after their goddess of love, who in turn was based on the ancient Greek goddess of love Aphrodite,[242] 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.[243][244] 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.

 
The eight-pointed star a symbol used in some cultures for Venus, and sometimes combined into a star and crescent arrangement. Here the eight pointed star is the Star of Ishtar, the Babylonian Venus goddess, alongside the solar disk of her brother Shamash and the crescent moon of their father Sin on a boundary stone of Meli-Shipak II, dating to the twelfth century BC.

Several hymns praise Inanna in her role as the goddess of the planet Venus.[177][244][243] 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.[177] The discontinuous movements of Venus relate to both mythology as well as Inanna's dual nature.[177] 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.[177] 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.[177] In Inanna and Shukaletuda and Inanna's Descent into the Underworld appear to parallel the motion of the planet Venus.[177] In Inanna and Shukaletuda, Shukaletuda is described as scanning the heavens in search of Inanna, possibly searching the eastern and western horizons.[245] In the same myth, while searching for her attacker, Inanna herself makes several movements that correspond with the movements of Venus in the sky.[177]

The Ancient Egyptians and ancient Greeks at first believed Venus to be two separate bodies, a morning star and an evening star. The Egyptians knew the morning star as Tioumoutiri and the evening star as Ouaiti.[246] The Greeks used the names Phōsphoros (Φωσϕόρος), meaning "light-bringer" (whence the element phosphorus; alternately Ēōsphoros (Ἠωσϕόρος), meaning "dawn-bringer"), for the morning star, and Hesperos (Ἕσπερος), meaning "Western one", for the evening star.[247] 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 Lūcifer and Vesper.[247][248]

Classical poets such as Homer, Sappho, Ovid and Virgil spoke of the star and its light.[249] Poets such as William Blake, Robert Frost, Letitia Elizabeth Landon, Alfred Lord Tennyson and William Wordsworth wrote odes to it.[250]

In India Shukra Graha ("the planet Shukra") is named after the powerful saint Shukra. Shukra which is used in Indian Vedic astrology[251] means "clear, pure" or "brightness, clearness" in Sanskrit. 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.[252] The word Shukra is also associated with semen, or generation.

Venus is known as Kejora in Indonesian and Malaysian Malay.

In Chinese the planet is called Jīn-xīng (金星), the golden planet of the metal element. Modern Chinese, Japanese, Korean and Vietnamese cultures refer to the planet literally as the "metal star" (金星), based on the Five elements.[253][254][255][256]

The Maya considered Venus to be the most important celestial body after the Sun and Moon. They called it Chac ek,[257] or Noh Ek', "the Great Star".[258] The cycles of Venus were important to their calendar and were described in some of their books such as Maya Codex of Mexico and Dresden Codex.

Modern culture

See also: Venus in fiction
 
The Hidden Planet an anthology of short stories from 1959, depicting in its cover the tropical and exotic vision of Venus at the time caused by still being a hidden planet with the means not available yet to study what lies below its planetwide cloud cover.

With the invention of the telescope, the idea that Venus was a physical world and possible destination began to take form.

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 frequently depicted as warmer, but still habitable by humans.[259] 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 the reality to be quite different and brought this particular genre to an end.[260] As scientific knowledge of Venus advanced, science fiction authors tried to keep pace, particularly by conjecturing human attempts to terraform Venus.[261]

Symbols

Main article: Venus symbol
 

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,[262][263][264] 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.[265][266]

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),[263][264] 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.[263][264]

Beside 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.

See also

Notes

  1. ^ Misstated as "Ganiki Chasma" in the press release and scientific publication.[108]
  2. ^ It is important to be clear about the meaning of "closeness". In the astronomical literature, the term "closest planets" often refers to the two planets that approach each other the most closely. In other words, the orbits of the two planets approach each other most closely. However, this does not mean that the two planets are closest over time. Essentially because Mercury is closer to the Sun than Venus, Mercury spends more time in proximity to Earth; it could, therefore, be said that Mercury is the planet that is "closest to Earth when averaged over time". However, using this time-average definition of "closeness", it turns out that Mercury is the closest planet to all other planets in the solar system. For that reason, arguably, the proximity-definition is not particularly helpful. An episode of the BBC Radio 4 programme "More or Less" explains the different notions of proximity well.[134]
  3. ^ The equatorial speed of Earth is given as both about 1674.4 km/h and 1669.8 km/h by reliable sources. The simplest way to determine the correct figure is to multiply Earth's radius of 6378137 m (WGS84) and Earth's angular speed, 7.2921150×10−5 rad/s,[141] yielding 465.1011 m/s = 1674.364 km/h. The incorrect figure of 1669.8 km/h is obtained by dividing Earth's equatorial circumference by 24 h. But the correct speed must be relative to inertial space, so the stellar day of 86164.098903691 s/3600 = 23.934472 h (23 h 56 m 4.0989 s) must be used.[142] Thus 2π(6378.137 km)/23.934472 h = 1674.364 km/h.[143]
  4. ^ Several claims of transit observations made by medieval Islamic astronomers have been shown to be sunspots.[189] Avicenna did not record the date of his observation. There was a transit of Venus within his lifetime, on 24 May 1032, although it is questionable whether it would have been visible from his location.[190]
  5. ^ The American Pioneer Venus Multiprobe has brought the only non-Soviet probes to enter the atmosphere, as atmospheric entry probes only briefly signals were received from the surface.

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May 11, 2023
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This article is about the planet For the deity see Venus mythology For other uses see Venus disambiguation Venus is the second planet from the Sun It is a rocky planet with a mass and size narrowly second in the Solar System to Earth and with an atmosphere which is the thickest of all four rocky planets of the Solar System and substantially thicker than Earth s Its orbit is the next closest to Earth s orbiting the Sun inferior inside of Earth s orbit appearing like Mercury in Earth s sky always close to the Sun as either a morning star or evening star In Earth s sky it is also the natural object with the third highest maximum apparent brightness after the Sun and the Moon due to its proximity to Earth and the Sun its size and its highly reflective global cloud cover 19 20 Because of these prominent appearances in Earth s sky Venus has been particularly among the other four star like classical planets a common and important object for humans their cultures and astronomy VenusNear global view of Venus in natural colour taken by the MESSENGER space probeDesignationsPronunciation ˈ v iː n e s listen Named afterRoman goddess of love see goddess Venus AdjectivesVenusian v ɪ ˈ nj uː z i e n ʒ e n 1 rarely Cytherean s ɪ 8 e ˈ r iː e n 2 or Venerean Venerian v ɪ ˈ n ɪer i e n 3 Orbital characteristics 5 7 Epoch J2000Aphelion0 728213 AU 108 939 000 kmPerihelion0 718440 AU 107 477 000 kmSemi major axis0 723332 AU 108 208 000 kmEccentricity0 006772 4 Orbital period sidereal 224 701 d 5 0 615198 yr 1 92 Venus solar dayOrbital period synodic 583 92 days 5 Average orbital speed35 02 km sMean anomaly50 115 Inclination3 39458 to ecliptic 3 86 to Sun s equator 2 15 to invariable plane 6 Longitude of ascending node76 680 4 Argument of perihelion54 884 SatellitesNonePhysical characteristicsMean radius6 051 8 1 0 km 8 0 9499 EarthsFlattening0 8 Surface area4 6023 108 km2 0 902 EarthsVolume9 2843 1011 km3 0 857 EarthsMass4 8675 1024 kg 9 0 815 EarthsMean density5 243 g cm3Surface gravity8 87 m s2 0 904 gEscape velocity10 36 km s 6 44 mi s 10 Synodic rotation period 116 75 d retrograde 11 1 Venus solar daySidereal rotation period 243 0226 d retrograde 12 Equatorial rotation velocity6 52 km h 1 81 m s Axial tilt2 64 for retrograde rotation 177 36 to orbit 5 note 1 North pole right ascension18h 11m 2s 272 76 13 North pole declination67 16 Albedo0 689 geometric 14 0 76 Bond 15 Temperature232 K 41 C blackbody temperature 16 Surface temp min mean maxKelvin 737 K 5 Celsius 464 CFahrenheit 867 FSurface absorbed dose rate2 1 10 6 mGy h 18 Surface equivalent dose rate2 2 10 6 mSv h0 092 22 mSv h at habitable altitudes 18 Apparent magnitude 4 92 to 2 98 17 Angular diameter9 7 66 0 5 Atmosphere 5 Surface pressure93 bar 9 3 MPa 92 atmComposition by volume96 5 carbon dioxide 3 5 nitrogen 0 015 sulfur dioxide 0 0070 argon 0 0020 water vapour 0 0017 carbon monoxide 0 0012 helium 0 0007 neon Trace carbonyl sulfide Trace hydrogen chloride Trace hydrogen fluoride Defining the rotation as retrograde as done by NASA space missions and the USGS puts Ishtar Terra in the northern hemisphere and makes the axial tilt 2 64 Following the right hand rule for prograde rotation puts Ishtar Terra in the southern hemisphere and makes the axial tilt 177 36 Venus retains despite having only a weak induced magnetosphere an especially thick atmosphere of mainly carbon dioxide creating an extreme greenhouse effect together with its global sulfuric acid cloud cover Consequently the atmosphere reaches at its bottom an intense mean temperature of 737 K 464 C 867 F and an atmospheric pressure of 92 times that of Earth at sea level turning the air into a supercritical fluid Internally Venus is thought to consist of a core mantle and crust The surface was most likely shaped by volcanic resurfacing and has active volcanism though it lacks more active geology like plate tectonics Venus might have had water and maybe even oceans in its early history if so this water probably evaporated when greenhouse effects cascaded and subsequently taken into space by the solar wind 21 22 23 The possibility of life on Venus has long been a topic of speculation particularly in its clouds and atmospheric layers at roughly 50 km 30 mi altitude with conditions closest among any other in the Solar System to the ones at the surface of Earth Despite recent indicative research no convincing evidence has been found thus far Venus has no moon like Mercury 24 It rotates retrograde like Uranus against its orbital direction and having been slowed by the strong currents and drag of the atmosphere it completes a sidreal rotation relative to the stars in 243 Earth days Therefore it rotates slower than it is orbiting having a solar year of 224 7 Earth days 25 this results together with the retrograde rotation in having a solar day of 117 Earth days 26 Venus and Earth approach each other in synodic periods of 1 6 years while coming closer to each other at inferior conjunction than any other pair of planets both stay on average closer to Mercury than to any other planet 27 That said the gravitational potential between Earth and Venus and the needed speed to transfer between them is the lowest than between any other planet from Earth This and its proximity to Earth has allowed Venus to be the most accessible destination and attractive gravity assist waypoint for interplanetary flights In 1961 Venus became the target of the first interplanetary flight in human history followed by many essential interplanetary firsts confirming in 1970 Venus inhospitable surface conditions with the first soft landing on another planet Venus as a place for humans to be was a popular topic in early science fiction Actual proposals have suggested to send crews particularly on flybys used as gravity assists for crewed missions to Mars while some have suggested crews to enter the atmosphere benefiting from Earth like pressure temperature radiation and gravitation at cloud levels Currently robotic probes are studying and will be sent to study Venus having been providing crucial knowledge particularly about greenhouse effects informing predictions about global warming on Earth 28 29 Contents 1 Physical characteristics 1 1 Atmosphere and climate 1 2 Geography 1 2 1 Volcanism 1 2 2 Craters 1 3 Internal structure 1 4 Magnetic field and core 2 Orbit and rotation 3 Observability 3 1 Phases 3 2 Daylight apparitions 3 3 Transits 3 4 Pentagram of Venus 3 5 Ashen light 4 Observation and exploration history 4 1 Early observation 4 2 Venus and early modern astronomy 4 3 Early 20th century advances 4 4 Space age 4 5 Active and future missions 5 Search for life 5 1 Planetary protection 6 Human presence 6 1 Crewed flight 6 2 Habitation 7 In culture 7 1 Modern culture 7 2 Symbols 8 See also 9 Notes 10 References 11 External links 11 1 Cartographic resourcesPhysical characteristics Venus to scale among the terrestrial planets of the Solar System which are arranged by the order of their Inner Solar System orbits outward from the Sun from left Mercury Venus Earth and Mars 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 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 Conditions on the Venusian surface differ radically from those on Earth because its dense atmosphere is 96 5 carbon dioxide with most of the remaining 3 5 being nitrogen 32 The surface pressure is 9 3 megapascals 93 bars and the average surface temperature is 737 K 464 C 867 F above the critical points of both major constituents and making the surface atmosphere a supercritical fluid out of mainly supercritical carbon dioxide and some supercritical nitrogen Atmosphere and climate Main article Atmosphere of Venus Cloud structure of the Venusian atmosphere made visible through ultraviolet imaging Venus has a dense atmosphere composed of 96 5 carbon dioxide 3 5 nitrogen both exist as supercritical fluids at the planet s surface and traces of other gases including sulfur dioxide 33 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 oceans The density at the surface is 65 kg m3 4 1 lb cu ft 6 5 that of water or 50 times as dense as Earth s atmosphere at 293 K 20 C 68 F at sea level The CO2 rich atmosphere generates the strongest greenhouse effect in the Solar System creating surface temperatures of at least 735 K 462 C 864 F 25 34 This makes the Venusian surface hotter than Mercury 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 35 36 even though Venus is nearly twice Mercury s distance from the Sun and thus receives only 25 of Mercury s solar irradiance 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 28 29 Venus Temperature 37 Type SurfaceTemperatureMaximum 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 38 This enrichment indicates an early divergence from Earth in evolution An unusually large comet impact 39 or accretion of a more massive primary atmosphere from solar nebula 40 have been proposed to explain the enrichment However the atmosphere is depleted of radiogenic argon a proxy to mantle degassing suggesting an early shutdown of major magmatism 41 42 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 43 44 45 After a period of 600 million to several billion years 46 solar forcing from rising luminosity of the Sun and possibly large volcanic resurfacing caused the evaporation of the original water and the current atmosphere 47 A runaway greenhouse effect was created once a critical level of greenhouse gases including water was added to its atmosphere 48 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 49 witht 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 carbondioxide air 50 51 52 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 53 54 Later research attributed the spectroscopic signal that was interpreted as phosphine to sulfur dioxide 55 or found that in fact there was no absorption line 56 57 Temperature and pressure change by altitude in the atmosphere 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 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 58 Above the dense 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 clouds consist of approximately 1 ferric chloride 59 60 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 59 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 300 km h 185 mph winds at the cloud tops go around Venus about every four to five Earth days 61 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 62 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 5 63 Venus s minute axial tilt less than 3 compared to 23 on Earth also minimises seasonal temperature variation 64 Altitude is one of the few factors that affect Venusian temperature 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 65 66 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 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 67 Although Venus has no seasons as such 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 68 The existence of lightning in the atmosphere of Venus has been controversial 69 since the first suspected bursts were detected by the Soviet Venera probes 70 71 72 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 of that on Earth 73 however other instruments have not detected lightning at all 69 The origin of any lightning remains unclear but could originate from the clouds or Venusian volcanoes In 2007 Venus Express discovered that a huge double atmospheric polar vortex exists at the south pole 74 75 Venus Express discovered in 2011 that an ozone layer exists high in the atmosphere of Venus 76 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 77 78 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 waves in the solar system 79 80 81 Geography Main articles Mapping of Venus Geology of Venus and Surface features of Venus Color coded elevation map showing the elevated terrae continents in yellow and minor features of Venus The Venusian surface was a subject of speculation until some of its secrets were revealed by planetary science in the 20th century Venera landers in 1975 and 1982 returned images of a surface covered in sediment and relatively angular rocks 82 The surface was mapped in detail by Magellan in 1990 91 The ground shows evidence of extensive volcanism and the sulfur in the atmosphere may indicate that there have been recent eruptions 83 84 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 85 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 Maxwell Montes the highest mountain on Venus lies on Ishtar Terra Its peak is 11 km 7 mi above the Venusian average surface elevation 86 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 87 The absence of evidence of lava flow accompanying any of the visible calderas remains an enigma The planet has few impact craters demonstrating that the surface is relatively young at 300 600 million years old 88 89 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 20 to 50 km 12 to 31 mi across and from 100 to 1 000 m 330 to 3 280 ft 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 90 Most Venusian surface features are named after historical and mythological women 91 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 92 The longitude of physical features on Venus are 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 93 After the Venera missions were completed the prime meridian was redefined to pass through the central peak in the crater Ariadne on Sedna Planitia 94 95 Rectified and colourized surface image Venera 10 1975 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 22 96 The mechanism to generate a large amount of felsic crust usually requires the presence of water ocean and plate tectonics implying that habitable condition had existed on early Venus with large bodies of water at some point 97 However the nature of tessera terrains is far from certain 98 Volcanism Main article Volcanism on Venus Radar mosaic of two 65 km 40 mi wide and less than 1 km 0 62 mi high pancake domes in Venus s Eistla region 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 100 km 60 mi across The only volcanic complex of this size on Earth is the Big Island of Hawaii 90 154 More than 85 000 volcanoes on Venus were identified and mapped 99 100 This is not because Venus is more volcanically active than Earth but because its crust is older and is not subject to the same erosion process 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 101 whereas the Venusian surface is estimated to be 300 600 million years old 88 90 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 102 This may mean that levels had been boosted several times by large volcanic eruptions 103 104 It has been suggested that Venusian lightning discussed below could originate from volcanic activity i e volcanic lightning In January 2020 astronomers reported evidence that suggests that Venus is currently volcanically active specifically the detection of olivine a volcanic product that would weather quickly on the planet s surface 105 106 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 107 note 1 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 108 109 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 800 1 100 K 527 827 C 980 1 520 F range relative to a normal temperature of 740 K 467 C 872 F 110 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 have concluded that active volcanism was the cause 111 Craters Impact craters 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 300 600 million years ago 88 89 followed by a decay in volcanism 112 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 90 Venusian craters range from 3 to 280 km 2 to 174 mi 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 so much by the atmosphere that they do not create an impact crater 113 Incoming projectiles less than 50 m 160 ft in diameter will fragment and burn up in the atmosphere before reaching the ground 114 Internal structure The differentiated structure of Venus Without data from reflection seismology or knowledge of its moment of inertia little direct information is available about the internal structure and geochemistry of Venus 115 The similarity in size and density between Venus and Earth suggests 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 116 although a completely solid core cannot be ruled out 117 The slightly smaller size of Venus means pressures are 24 lower in its deep interior than Earth s 118 The predicted values for the moment of inertia based on planetary models suggest a core radius of 2 900 3 450 km 117 This is in line with the first observation based estimate of 3 500 km 119 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 120 Instead Venus may lose its internal heat in periodic major resurfacing events 88 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 121 122 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 reaching at elevations of 54 to 48 km Earth like levels 123 124 The lack of an intrinsic magnetic field at 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 125 126 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 127 One possibility is that Venus has no solid inner core 128 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 127 Another possibility 129 is that the absence of a late 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 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 water 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 could have led to the loss of most of Venus s water during the first billion years after it formed 130 However the planet may have retained a dynamo for its first 2 3 billion years so the water loss may have occurred more recently 131 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 132 Orbit and rotationMain article Orbit of Venus Venus is the second planet from the Sun making a full orbit in about 224 days Venus orbits the Sun at an average distance of about 0 72 AU 108 million km 67 million mi and completes an orbit every 224 7 days Although all planetary orbits are elliptical Venus s orbit is currently the closest to circular with an eccentricity of less than 0 01 5 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 the early climate evolution 133 The current near circular orbit of Venus means that 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 41 million km 25 million mi 5 note 2 134 The planet has a near orbital resonance of 8 Earth orbits to 13 Venus orbits 135 with inferior conjunctions occurring with a synodic period of 584 days on average 5 Because of the decreasing eccentricity of Earth s orbit the minimum distances will become greater over tens of thousands of years From the year 1 to 5383 there are 526 approaches less than 40 million km 25 million mi then there are none for about 60 158 years 136 While Venus approaches Earth the closest Mercury is more frequently the closest to Earth of all planets 137 Venus has the lowest gravitational potential difference to Earth than any other planet needing the lowest delta v to transfer between them 138 139 All planets in the Solar System orbit the Sun in an anticlockwise direction as viewed from above Earth s north pole Most planets rotate on their axes in an anticlockwise direction but Venus rotates clockwise in retrograde rotation once every 243 Earth days the slowest rotation of any planet This Venusian sidereal day lasts therefore longer than a Venusian year 243 versus 224 7 Earth days Slowed by its strong atmospheric current the length of the day also fluctuates by up to 20 minutes 140 Venus s equator rotates at 6 52 km h 4 05 mph whereas Earth s rotates at 1 674 4 km h 1 040 4 mph note 3 144 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 5 minutes 145 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 making the Venusian solar day shorter than Mercury s 176 Earth days the 116 day figure is close to the average number of days it takes Mercury to slip underneath the Earth in its orbit 11 One Venusian year is about 1 92 Venusian solar days 146 To an observer on the surface of Venus the Sun would rise in the west and set in the east 146 although Venus s opaque clouds prevent observing the Sun from the planet s surface 147 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 148 149 The 584 day average interval between successive close approaches to Earth is almost exactly equal to 5 Venusian solar days 5 001444 to be precise 150 but the hypothesis of a spin orbit resonance with Earth has been discounted 151 Venus has no natural satellites 152 It has several trojan asteroids the quasi satellite 2002 VE68 153 154 and two other temporary trojans 2001 CK32 and 2012 XE133 155 In the 17th century Giovanni Cassini reported a moon orbiting Venus which was named Neith and numerous sightings were reported over the following 200 years 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 156 About 10 million years 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 157 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 152 The orbital space of Venus has a dust ring cloud 158 with a suspected origin either from Venus trailing asteroids 159 interplanetary dust migrating in waves or the remains of the Solar System s original circumstellar disc that formed the planetary system 160 Observability Venus pictured center right is always brighter than all other planets or stars at their maximal brightness as seen from Earth Jupiter is visible at the top of the image To the naked eye Venus appears as a white point of light brighter than any other planet or star apart from the Sun 161 The planet s mean apparent magnitude is 4 14 with a standard deviation of 0 31 17 The brightest magnitude occurs during crescent phase about one month before or after inferior conjunction Venus fades to about magnitude 3 when it is backlit by the Sun 162 The planet is bright enough to be seen in broad daylight 163 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 164 Venus overtakes Earth every 584 days as it orbits the Sun 5 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 165 Phases Main article Phases of Venus The phases of Venus and evolution of its apparent diameter 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 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 164 The phases are clearly visible in a 4 telescope citation needed Daylight apparitions Naked eye observations of Venus during daylight hours exist in several anecdotes and records 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 166 Another historical daytime observation of the planet took place during the inauguration of the American president Abraham Lincoln in Washington D C on 4 March 1865 167 Although naked eye visibility of Venus s phases is disputed records exist of observations of its crescent 168 Transits Main article Transit of Venus 2012 transit of Venus projected to a white card by a telescope A transit of Venus is the appearance of Venus infront 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 above Earth Consequently Venus transits above Earth only occur when an inferior conjunction takes place during some days of June or December the time where the orbits of Venus and Earth cross a straight line with the Sun 169 This results in Venus transiting above Earth in a sequence of currently 8 years 105 5 years 8 years and 121 5 years forming cycles of 243 years 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 170 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 171 172 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 173 The preceding pair of transits occurred in December 1874 and December 1882 The next transit will occur in December 2117 and December 2125 174 Pentagram of Venus The pentagram of Venus Earth is positioned at the centre of the diagram and the curve represents the direction and distance of Venus as a function of time The pentagram of Venus is the path that Venus makes as observed from Earth Successive inferior conjunctions of Venus repeat with a orbital resonance of 13 8 Earth orbits eight times for every 13 orbits of Venus shifting 144 upon sequential inferior conjunctions The 13 8 ratio is approximate 8 13 is approximately 0 61538 while Venus orbits the Sun in 0 61519 years citation needed The pentagram of Venus is sometimes referred to as the petals of Venus due to the path s visual similarity to a flower 175 Ashen light 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 176 71 The ashen light has often been sighted when Venus is in the evening sky when the evening terminator of the planet is towards to Earth Observation and exploration historyMain article Observations and explorations of Venus Early observation 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 177 instead they assumed it to be two separate stars on each horizon the morning and evening star 177 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 178 177 179 In the Old Babylonian period the planet Venus was known as Ninsi anna and later as Dilbat 180 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 181 The Chinese historically referred to the morning Venus as the Great White Taibai 太白 or the Opener Starter of Brightness Qǐming 啟明 and the evening Venus as the Excellent West One Changgeng 長庚 182 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 183 while Diogenes Laertius argued that Parmenides was probably responsible for this discovery 184 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 185 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 are located between the Sun and the Earth The 11th century Persian astronomer Avicenna claimed to have observed the transit of Venus 186 which later astronomers took as confirmation of Ptolemy s theory 187 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 188 note 4 Venus and early modern astronomy In 1610 Galileo Galilei observed with his telescope that Venus showed phases despite remaining near the Sun in Earth s sky first image This proved that it orbits the Sun and not Earth as predicted by Copernicus s heliocentric model and disproved the then conventional geocentric model second image 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 191 192 The 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 4 December 1639 24 November under the Julian calendar in use at that time 193 The black drop effect as recorded during the 1769 transit The atmosphere of Venus was discovered in 1761 by Russian polymath Mikhail Lomonosov 194 195 Venus s atmosphere was observed in 1790 by German astronomer Johann Schroter Schroter 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 196 The atmosphere complicated efforts to determine a rotation period for the planet and observers such as Italian born astronomer Giovanni Cassini and Schroter incorrectly estimated periods of about 24 h from the motions of markings on the planet s apparent surface 197 Early 20th century advances 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 198 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 199 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 wasn t suspected at the time confusing the issue 200 Later work in the 1950s showed the rotation was retrograde Space age Further information List of missions to Venus Humanity s first interplanetary spaceflight was achieved in 1961 with the robotic space probe Venera 1 of the Soviet Venera program flying to Venus though it lost contact en route 201 Therefore the first successful interplanetary mission was the Mariner 2 mission to Venus of the United States Mariner program passing on 14 December 1962 at 34 833 km 21 644 mi above the surface of Venus and gathering data on the planet s atmosphere 202 203 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 204 After Venera 3 in 1966 humanity s first probe and lander to reach and impact another celestial body other than the Moon couldn t return data Venera 4 in 1967 successfully for the first time at location deployed science experiments before impacting Venera 4 showed the surface temperature was hotter than Mariner 2 had calculated at almost 500 C 932 F determined that the atmosphere was 95 carbon dioxide CO2 and discovered that Venus s atmosphere was considerably denser than Venera 4 s designers had anticipated 205 In an early example of space cooperation the data of Venera 4 was joint with the 1967 Mariner 5 data analysed by a combined Soviet American science team in a series of colloquia over the following year 206 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 207 In 1974 Mariner 10 swung by Venus to bend its path toward 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 300 m 1 000 ft 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 208 These three features are now the only ones on Venus that do not have female names 92 First view and first clear 180 degree panorama of Venus s surface as well as any other planet than Earth 1975 Soviet Venera 9 lander Black and white image of barren black slate like rocks against a flat sky The ground and the probe are the focus 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 that consisted of two separate missions 209 the Pioneer Venus Multiprobe and Pioneer Venus Orbiter orbiting Venus between 1978 and 1992 210 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 successful Soviet Venera program came to a close 211 Global topographic map of Venus with all probe landings marked In 1985 the Vega program with its Vega 1 and Vega 2 missions carried the last entry probes and carried the first ever extraterrestrial aerobots for the first time achiving atmospheric flight outside Earth by employing inflatable baloons Between 1990 and 1994 Magellan operated in orbit until deorbiting mapping the surface of Venus Furthermore probes like Galileo 1990 212 Cassini Huygens 1998 1999 and MESSENGER 2006 2007 visited Venus with flybys flying 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 213 2010 the first successful interplanetary solar sail spacecraft IKAROS traveled to Venus for a flyby Active and future missions Further information List of missions to Venus Future missions WISPR visible light footage 2021 of the nightside showing the hot faintly glowing surface and its Aphrodite Terra as large dark patch through the clouds which prohibit such observations on the dayside when they are illuminated 214 215 As of 2020 Japan s Akatsuki is since its orbital insertion on 7 December 2015 the only probe in orbit around Venus Additionally flybys by other probes have been performed studying Venus on their way as with the Parker Solar Probe and the Solar Orbiter There are several probing proposals under study by Roscosmos NASA ISRO ESA and the private sector e g by Rocketlab Search for lifeMain article Life on Venus Speculation on the possibility of life on Venus s surface decreased significantly after the early 1960s when it became clear that the conditions are extreme compared to those on Earth Venus s extreme temperature 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 216 217 218 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 219 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 68 Their light absorbance is almost identical to that of micro organisms in Earth s clouds Similar conclusions have been reached by other studies 220 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 221 54 53 222 223 One proposed source for this phosphine is living organisms 224 The phosphine was detected at heights of at least 30 miles 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 225 226 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 227 By late October 2020 re analysis of data with a proper subtraction of background did not show a statistically significant detection of phosphine 228 229 230 Planetary protection 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 231 This indicates that there is only a remote chance that spacecraft borne contamination could compromise investigations Human presenceMain article List of missions to Venus Venus is the place of the first interplanetary human presence mediated through robotic missions with the first successful landings on another planet and extraterrestrial body other than the Moon Currently in orbit is Akatsuki and other probes routinely use Venus for gravity assist maneuvers capturing some data about Venus on the way 232 The only nation that has sent lander probes to the surface of Venus has been the Soviet Union note 5 which has been used by Russian officials to call Venus a Russian planet 233 234 Crewed flight Studies of routes for crewed missions to Mars have since the 1960s proposed 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 235 236 Early in the space age the Soviet Union and the United States proposed the TMK MAVR and Manned Venus flyby crewed flyby missions to Venus though they were never realized Habitation See also Colonization of Venus and Floating cities and islands in fiction Venus Artist s rendering of a NASA High Altitude Venus Operational Concept HAVOC crewed floating outpost on Venus While the surface conditions of Venus are inhospitable the atmospheric pressure temperature or solar and cosmic radiation 50 km above the surface are similar to those at Earth s surface 124 123 With this in mind Soviet engineer Sergey Zhitomirskiy Sergej Zhitomirskij 1929 2004 in 1971 237 238 and NASA aerospace engineer Geoffrey A Landis in 2003 239 suggested the use of aerostats for crewed exploration and possibly for permanent floating cities in the Venusian atmosphere an alternative to the popular idea of living on planetary surfaces such as Mars 240 241 Among the many engineering challenges for any human presence in the atmosphere of Venus are the corrosive amounts of sulfuric acid in the atmosphere 239 NASA s High Altitude Venus Operational Concept is a mission concept that proposed a crewed aerostat design In cultureMain article Venus in culture Venus is a primary feature of the night sky and so has been of remarkable importance in mythology astrology and fiction throughout history and in different cultures The English name of Venus was originally the ancient Roman name for it Romans named Venus after their goddess of love who in turn was based on the ancient Greek goddess of love Aphrodite 242 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 243 244 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 The eight pointed star a symbol used in some cultures for Venus and sometimes combined into a star and crescent arrangement Here the eight pointed star is the Star of Ishtar the Babylonian Venus goddess alongside the solar disk of her brother Shamash and the crescent moon of their father Sin on a boundary stone of Meli Shipak II dating to the twelfth century BC Several hymns praise Inanna in her role as the goddess of the planet Venus 177 244 243 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 177 The discontinuous movements of Venus relate to both mythology as well as Inanna s dual nature 177 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 177 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 177 In Inanna and Shukaletuda and Inanna s Descent into the Underworld appear to parallel the motion of the planet Venus 177 In Inanna and Shukaletuda Shukaletuda is described as scanning the heavens in search of Inanna possibly searching the eastern and western horizons 245 In the same myth while searching for her attacker Inanna herself makes several movements that correspond with the movements of Venus in the sky 177 The Ancient Egyptians and ancient Greeks at first believed Venus to be two separate bodies a morning star and an evening star The Egyptians knew the morning star as Tioumoutiri and the evening star as Ouaiti 246 The Greeks used the names Phōsphoros Fwsϕoros meaning light bringer whence the element phosphorus alternately Eōsphoros Ἠwsϕoros meaning dawn bringer for the morning star and Hesperos Ἕsperos meaning Western one for the evening star 247 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 Lucifer and Vesper 247 248 Classical poets such as Homer Sappho Ovid and Virgil spoke of the star and its light 249 Poets such as William Blake Robert Frost Letitia Elizabeth Landon Alfred Lord Tennyson and William Wordsworth wrote odes to it 250 In India Shukra Graha the planet Shukra is named after the powerful saint Shukra Shukra which is used in Indian Vedic astrology 251 means clear pure or brightness clearness in Sanskrit 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 252 The word Shukra is also associated with semen or generation Venus is known as Kejora in Indonesian and Malaysian Malay In Chinese the planet is called Jin xing 金星 the golden planet of the metal element Modern Chinese Japanese Korean and Vietnamese cultures refer to the planet literally as the metal star 金星 based on the Five elements 253 254 255 256 The Maya considered Venus to be the most important celestial body after the Sun and Moon They called it Chac ek 257 or Noh Ek the Great Star 258 The cycles of Venus were important to their calendar and were described in some of their books such as Maya Codex of Mexico and Dresden Codex Modern culture See also Venus in fiction The Hidden Planet an anthology of short stories from 1959 depicting in its cover the tropical and exotic vision of Venus at the time caused by still being a hidden planet with the means not available yet to study what lies below its planetwide cloud cover With the invention of the telescope the idea that Venus was a physical world and possible destination began to take form 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 frequently depicted as warmer but still habitable by humans 259 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 the reality to be quite different and brought this particular genre to an end 260 As scientific knowledge of Venus advanced science fiction authors tried to keep pace particularly by conjecturing human attempts to terraform Venus 261 Symbols Main article Venus symbol 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 262 263 264 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 265 266 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 263 264 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 263 264 Beside 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 See also Solar System portal Outer space portal Astronomy portalGeodynamics of Venus Outline of Venus Venus zone Stats of planets in the Solar SystemNotes Misstated as Ganiki Chasma in the press release and scientific publication 108 It is important to be clear about the meaning of closeness In the astronomical literature the term closest planets often refers to the two planets that approach each other the most closely In other words the orbits of the two planets approach each other most closely However this does not mean 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