Venus

Atmosphere and climate

Venus has a dense atmosphere composed of 96.5% carbon dioxide, 3.5% nitrogen—both exist as supercritical fluids at the planet's surface with a density 6.5% that of water—and traces of other gases including sulphur dioxide. The mass of its atmosphere is 92 times that of Earth's, whereas the pressure at its surface is about 93 times that at Earth's—a pressure equivalent to that at a depth of nearly 1 km (5⁄8 mi) under Earth's ocean surfaces. The density at the surface is 65 kg/m³ (4.1 lb/cu ft), 6.5% that of water 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). This makes the Venusian surface hotter than Mercury's, even though Venus is nearly twice Mercury's distance from the Sun and thus receives only around a quarter of Mercury's solar irradiance, of 2,600 W/m² (double that of Earth). 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. Venus has thus been called a greenhouse planet.

Venus's atmosphere is rich in primordial noble gases compared to that of Earth. This enrichment indicates an early divergence from Earth in evolution. An unusually large comet impact or accretion of a more massive primary atmosphere from the solar nebula have been proposed to explain the enrichment. However, the atmosphere is poor in radiogenic argon-40, a proxy for mantle degassing, suggesting an early shutdown of major magmatism.

Studies have suggested that billions of years ago, the atmosphere of Venus may have been much more like the one surrounding the early Earth, and there may have been substantial quantities of liquid water on the surface. After a period of 600 million to several billion years, the rising luminosity of the Sun and possibly large volcanic resurfacing caused the evaporation of the original water. A runaway greenhouse effect was created once a critical level of greenhouse gases (including water) was reached in the atmosphere.

Thermal inertia and the transfer of heat by winds in the lower atmosphere mean that the surface temperature does not vary significantly between the hemispheres facing and not facing the Sun, despite Venus's slow rotation. Winds at the surface are slow, moving at a few kilometres per hour, but because of the high density of the atmosphere at the surface, they exert a significant amount of force against obstructions, and transport dust and small stones across the surface. This alone would make it difficult for a human to walk through, even without the heat, pressure, and lack of oxygen.

Above the dense CO₂ layer are thick clouds 45 to 70 km above the surface, consisting mainly of sulphuric acid, which is formed by a reaction catalyzed by UV radiation from sulphur dioxide molecules and then water, resulting in sulphuric acid hydrate. Additionally, the clouds contain approximately 1% ferric chloride. 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. These clouds cover the whole planet and prevent visual observation of the surface. The dense atmosphere and highly reflective clouds gives it a high albedo of 0.68, meaning it reflects nearly 70% of the incident sunlight. The permanent cloud cover means that although Venus is closer than Earth to the Sun, it receives less sunlight on the ground, with only 10% of the received sunlight reaching the surface, resulting in average daytime levels of illumination at the surface of 14,000 lux, comparable to that on Earth "in the daytime with overcast clouds".

Venus's atmosphere rotates much faster than its solid body, a phenomenon known as atmospheric super-rotation. This results in strong 300 km/h (185 mph) winds at the cloud tops, which complete a full rotation around the planet in about 4 days, corresponding to 60 times the speed of the planet's rotation, whereas Earth's strongest winds reach only 10–20% of its rotational speed.

Although Venus looks featureless in visible light, there are bands or streaks in the UV, whose origin has not been pinned down. The absorption of UV may be due to a compound of oxygen and sulfur, OSSO, which has a double bond between the sulfur atoms and exists in "cis" and "trans" forms, or due to polysulfur compounds from S₂ to S₈.

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. Venus's minute axial tilt—less than 3°, compared to 23° on Earth—also minimizes seasonal temperature variation. Altitude is one of the few factors that affect Venusian temperatures; in particular, the coolest points occur at the highest-altitude points, such as the mountain peaks of the Maxwell Montes range. In 1995, the Magellan spacecraft imaged a highly reflective substance at the tops of the highest mountain peaks, a "Venus snow" that bore a strong resemblance to terrestrial snow. This substance likely formed by a similar process to snow, albeit at a far higher temperature. Too volatile to condense on the surface, it rose in gaseous form to higher elevations, where it is cooler and could precipitate. The identity of this substance is not known with certainty, but speculation has ranged from elemental tellurium to lead sulfide (galena).

Although Venus has no seasons, in 2019 astronomers identified a cyclical variation in sunlight absorption by the atmosphere, possibly caused by opaque, absorbing particles suspended in the upper clouds. The variation causes observed changes in the speed of Venus's zonal winds and appears to rise and fall in time with the Sun's 11-year sunspot cycle.

The existence of lightning in the atmosphere of Venus has been controversial since the first suspected bursts were detected by the Soviet Venera probes. In 2006–07, Venus Express clearly detected whistler mode waves, the signatures of lightning. Their intermittent appearance indicates a pattern associated with weather activity. According to these measurements, the lightning rate is at least half that on Earth, however other instruments have not detected lightning at all. The origin of any lightning remains unclear, but could originate from clouds or Venusian volcanoes.

In 2007, Venus Express discovered that a huge double atmospheric polar vortex exists at the south pole. Venus Express discovered, in 2011, that an ozone layer exists high in the atmosphere of Venus. In 2013 ESA scientists reported that the ionosphere of Venus streams outwards in a manner similar to "the ion tail seen streaming from a comet under similar conditions."

In December 2015, and to a lesser extent in April and May 2016, researchers working on Japan's Akatsuki mission observed bow-shaped objects in the atmosphere of Venus. This was considered direct evidence of the existence of perhaps the largest stationary gravity waves in the solar system.

The colour and sound of the atmosphere at the surface have been recorded, with the sky having an orange-yellow colour, fading to white at higher altitudes.

Orbit and rotation

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. It completes 13 orbits in 7.998 years, so its position in our sky almost repeats every eight years. Although all planetary orbits are elliptical, Venus's orbit is currently the closest to circular, with an eccentricity of less than 0.01. Simulations of the early solar system orbital dynamics have shown that the eccentricity of the Venus orbit may have been substantially larger in the past, reaching values as high as 0.31 and possibly impacting early climate evolution.

Venus has retrograde rotation, meaning that unlike most planets, including Earth, it rotates clockwise around its own axis, opposite to its anticlockwise rotation around the Sun. Therefore, Venusian sidereal day, 243 Earth days, lasts longer than a Venusian year, 224.7 Earth days. If Venus were tidally locked to the Sun, it would always have the same face pointed to the Sun and its sidereal day would be 224.7 days. However, Venus's atmosphere is massive and it is close to the Sun, so differential heating of the atmosphere gives Venus a small retrograde rotation. The day length also fluctuates by up to 20 minutes for the same reason. 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. 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. One Venusian year is about 1.92 Venusian solar days. To an observer on the surface of Venus, the Sun would rise in the west and set in the east, although Venus's opaque clouds prevent observing the Sun from the planet's surface.

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. 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), but the hypothesis of a spin-orbit resonance with Earth has been discounted.

Venus has no natural satellites. It has several trojan asteroids: the quasi-satellite 524522 Zoozve and two other temporary trojans, 2001 CK₃₂ and 2012 XE133. 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. 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. 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.

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

Orbit in respect to Earth

Earth and Venus have a near orbital resonance of 13:8 (Earth orbits eight times for every 13 orbits of Venus). Therefore, they approach each other and reach inferior conjunction in synodic periods of 584 days, on average. The path that Venus makes in relation to Earth viewed geocentrically draws a pentagram over five synodic periods, shifting every period by 144°. This pentagram of Venus is sometimes referred to as the petals of Venus due to the path's visual similarity to a flower.

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). 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.

While Venus approaches Earth the closest, Mercury is more often the closest to Earth of all planets and to any other planet. Venus has been used as a waypoint for gravity assist manoeuvres, which has been identified as a more economic way to travel to Mercury, the Sun, asteroids, Mars, Jupiter and beyond.

Tidally Venus exerts the third strongest tidal force on Earth, after the Moon and the Sun, though significantly less.

Observability

To the naked eye, Venus appears as a white point of light with a maximum apparent magnitude of −4.92, brighter than any other planet or star apart from the Sun, even when faintest during its transit with an apparent magnitude of −2.98. The planet's mean apparent magnitude is −4.14 with a standard deviation of 0.31. The brightest magnitude occurs during the crescent phase about one month before or after an inferior conjunction. Venus fades to about magnitude −3 when it is backlit by the Sun, although the exact value depends on the phase angle. The planet is bright enough to be seen in broad daylight, 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.

Venus "overtakes" Earth every 584 days as it orbits the Sun. 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".

Because Venus comes close to the earth at inferior conjunction and has an orbit inclined to the plane of the earth's orbit, it can appear more than 8° north or south of the ecliptic, more than any other planet or the moon. Every eight years around March it appears this far north of the ecliptic, in Pisces (such as in mid-March 2025), and every eight years it appears this far south of the ecliptic in August or September in Virgo (as in late August 2023). Venus can thus be north of the sun and appear as a morning star and an evening star on the same day, in the northern hemisphere. The timing of these north or south excursions becomes slowly earlier in the year, and over thirty cycles (240 years) the cycle is gradually replaced by another cycle offset by three years, so the situation returns close to the original situation after 243 orbits of Earth, 395 of Venus.

Lunar occultations of Venus, in which the moon blocks the view of Venus for observers in certain parts of the earth, occur on average about twice a year, sometimes several times in a year (though rarely).

Phases

As it orbits the Sun, Venus displays phases like those of the Moon in a telescopic view. The planet appears as a small and "full" disc when it is on the opposite side of the Sun (at superior conjunction). Venus shows a larger disc and "quarter phase" at its maximum elongations from the Sun, and appears at its brightest in the night sky. The planet presents a much larger thin "crescent" in telescopic views as it passes along the near side between Earth and the Sun. Venus displays its largest size and "new phase" when it is between Earth and the Sun (at inferior conjunction). Its atmosphere is visible through telescopes by the halo of sunlight refracted around it. The phases are clearly visible in a 4" telescope. Although naked eye visibility of Venus's phases is disputed, records exist of observations of its crescent.

Daylight apparitions

When Venus is sufficiently bright with enough angular distance from the sun, it is easily observed in a clear daytime sky with the naked eye, though most people do not know to look for it. 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. 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.

Transits

A transit of Venus is the appearance of Venus in front of the Sun, during inferior conjunction. Since the orbit of Venus is slightly inclined relative to Earth's orbit, most inferior conjunctions with Earth, which occur every synodic period of 1.6 years, do not produce a transit of Venus. Consequently, Venus transits only occur when an inferior conjunction takes place during some days of June or December, when the orbits of Venus and Earth cross a straight line with the Sun. This results in Venus transiting above Earth in a sequence currently of 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).

Only seven Venus transits have been observed so far, since their occurrences were calculated in 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.

The latest pair was 8 June 2004 and 5–6 June 2012. The transit could be watched live from many online outlets or observed locally with the right equipment and conditions. The preceding pair of transits occurred in December 1874 and December 1882.

The next transits will occur in December 2117 and December 2125.

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

Observation and exploration history

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; instead, they assumed it to be two separate stars on each horizon: the morning and evening star. 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.

In the Old Babylonian period, the planet Venus was known as Ninsi'anna, and later as Dilbat. 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.

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).

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, while Diogenes Laërtius argued that Parmenides (early fifth century) was probably responsible for this discovery. 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, both of which are literal translations of their traditional Greek names.

In the second century, in his astronomical treatise Almagest, Ptolemy theorized that both Mercury and Venus were located between the Sun and the Earth. The 11th-century Persian astronomer Avicenna claimed to have observed a transit of Venus (although there is some doubt about it), which later astronomers took as confirmation of Ptolemy's theory. 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. Several claims of transit observations made by mediaeval Islamic astronomers have been shown to be sunspots.

Venus and early modern astronomy

When the planet was first observed with a telescope in December 1610, by the Italian physicist Galileo Galilei, 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, reported by Galileo in his 1613 Letters on Sunspots, becoming one of the first observations to clearly contradict the Ptolemaic geocentric model that the Solar System was concentric and centred on Earth.

The 1631 transit of Venus, while not recorded, was the first one successfully predicted, by Johannes Kepler and his calculations, which he published in 1629. The following 1639 transit of Venus was accurately predicted by Jeremiah Horrocks and observed by him and his friend, William Crabtree, at each of their respective homes, on 4 December 1639 (24 November under the Julian calendar in use at that time).

The atmosphere of Venus was discovered in 1761 by Russian polymath Mikhail Lomonosov. 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. 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.

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.

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.

It had been noted that Venus had no discernible oblateness in its disk, suggesting a slow rotation, and some astronomers concluded based on this that it was tidally locked like Mercury was believed to be at the time; but other researchers had detected a significant quantity of heat coming from the planet's nightside, suggesting a quick rotation (a high surface temperature was not suspected at the time), confusing the issue. Later work in the 1950s showed the rotation was retrograde.

First missions to Venus

The first interplanetary spaceflight attempt was in 1961 when the robotic space probe Venera 1 of the Soviet Venera programme flew to Venus. It lost contact en route.

The first successful interplanetary mission, also to Venus, was Mariner 2 of the United States' Mariner programme, 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.

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.

Venera 3, launched in 1966, became humanity's first probe and lander to reach and impact another celestial body other than the Moon, but could not return data as it crashed into the surface of Venus. In 1967, Venera 4 was launched and successfully deployed science experiments in the Venusian atmosphere before impacting. Venera 4 showed the surface temperature was hotter than Mariner 2 had calculated, at almost 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.

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

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.

In 1974, Mariner 10 swung by Venus to bend its path towards Mercury and took ultraviolet photographs of the clouds, revealing the extraordinarily high wind speeds in the Venusian atmosphere. This was the first interplanetary gravity assist ever used, a technique which would be used by later probes.

Radar observations in the 1970s revealed details of the Venusian surface for the first time. Pulses of radio waves were beamed at the planet using the 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. These three features are now the only ones on Venus that do not have female names.

In 1975, the Soviet Venera 9 and 10 landers transmitted the first images from the surface of Venus, which were in black and white. NASA obtained additional data with the Pioneer Venus project, consisting of two separate missions: the Pioneer Venus Multiprobe and Pioneer Venus Orbiter, orbiting Venus between 1978 and 1992. In 1982 the first monochrome colour filters images of the surface were obtained with the Soviet Venera 13 and 14 landers. After Venera 15 and 16 operated between 1983 and 1984 in orbit, conducting detailed mapping of 25% of Venus's terrain (from the north pole to 30°N latitude), the Soviet Venera programme came to a close.

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

Between 1990 and 1994, Magellan operated in orbit until deorbiting, mapping the surface of Venus. Furthermore, probes like Galileo (1990), and Cassini–Huygens (1998/1999) visited Venus with flybys en route to other destinations.

Renewed exploration

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. The same and following year MESSENGER visited Venus with flybys en route to other destinations.

In 2010, the first successful interplanetary solar sail spacecraft IKAROS travelled to Venus for a flyby.

Between 2015 and 2024 Japan's Akatsuki probe was active in orbit around Venus and BepiColombo performed flybys in 2020/2021.

Active and planned missions

As of 2025 there are no active probes at Venus, with Parker Solar Probe scheduled to return repeatedly to Venus until 2030.

Several probes are under development as well as multiple proposed missions still in their early conceptual stages. The next Venus mission scheduled is the Venus Life Finder, expected to launch not earlier than summer 2026.

Indian ISRO is working on Venus Orbiter Mission, aiming to launch it in 2028. UAE mission to asteroids, MBR Explorer, will perform a flyby of the planet. NASA approved two missions to the planet, VERITAS and DAVINCI, planned to be launched not earlier than 2031. ESA plans to launch EnVision also in 2031.

A project by the MIT with the rocket company Rocket Lab aims to be the first private interplanetary space craft with a proposal to look for organics by entering the atmosphere of Venus with a probe named Venus Life Finder.

Objectives

Venus has been identified for future research as an important case for understanding:

• the origins of the solar system and Earth, and if systems and planets like ours are common or rare in the universe.
• how planetary bodies evolve from their primordial states to today's diverse objects.
• the development of conditions leading to habitable environments and life.

Crewed mission concepts

Venus has been considered since the 1960s as a waypoint for crewed missions to Mars through opposition missions instead of direct conjunction missions with Venus gravity assist flybys, demonstrating that they should be quicker and safer missions to Mars, with better return or abort flight windows, and less or the same amount of radiation exposure from the flight as direct Mars flights.

Possible atmospheric habitation

While the surface conditions of Venus are extremely hostile, the atmospheric pressure, temperature, and solar and cosmic radiation 50 km above the surface are similar to those at Earth's surface ("clement conditions"). Among the many engineering challenges for any human presence in the atmosphere of Venus are the corrosive amounts of sulfuric acid in the atmosphere. Aerostats for crewed exploration and possibly for permanent "floating cities" in the Venusian atmosphere have been proposed as an alternative to the popular idea of living on planetary surfaces such as Mars. NASA's High Altitude Venus Operational Concept was a training concept to study a crewed aerostat design.

Possibility of life

Although the surface conditions on Venus are no longer hospitable to any terrestrial-like life that might have formed before this event, there is speculation that life may exist in the upper cloud layers of Venus, 50 km (30 mi) above the surface, where atmospheric conditions are the most Earth-like in the Solar System, with temperatures ranging between 303 and 353 K (30 and 80 °C; 86 and 176 °F), and the pressure and radiation being about the same as at Earth's surface, but with acidic clouds and the carbon dioxide air. More specifically, between heights of 48 and 59 km temperature and radiation conditions are suitable for life. At lower elevations water would evaporate and at higher elevation UV radiation would be too strong.

Speculation on the possibility of life on Venus's surface decreased significantly after the early 1960s when it became clear that conditions were extreme compared to those on Earth. Venus's extreme temperatures and atmospheric pressure make water-based life, as currently known, unlikely.

Some scientists have speculated that thermoacidophilic extremophile microorganisms might exist in the cooler, acidic upper layers of the Venusian atmosphere. 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.

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

The putative detection of an absorption line of phosphine in Venus's atmosphere, a gas not known to be produced by any known chemical processes on the Venusian surface or atmosphere, led to speculation in September 2020 that there could be extant life currently present in the atmosphere. Later research attributed the spectroscopic signal that was interpreted as phosphine to sulphur dioxide, or found that in fact there was no absorption line.

Planetary protection

Due to the harsh surface environment of Venus, Venus has been under the planetary protection category two, the second lowest. This gives it only a remote chance that spacecraft-borne interplanetary contamination could compromise investigations.

However, with findings of potential biosignatures this categorization for at least some atmospheric layers has been called into question, but since these layers have not been identified as sufficiently conducive to life, adjusting the categorization has not been recommended.

In culture

Venus is among the most prominent features in the night sky, and has been treated as particularly important in mythology, astrology and fiction across many different cultures.

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

Via Mesopotamian influence, it is possible that the Ancient Egyptians and Greeks knew that the morning star and the evening star were one and the same as early as the second millennium BC—or the Late Period at the latest. The Egyptians knew the morning star as Tioumoutiri and the evening star as Ouaiti. They depicted Venus at first as a phoenix or heron (see Bennu), calling it 'the crosser' or 'star with crosses', associating it with Osiris, and later depicting it as two-headed (with human or falcon heads), and associated it with Horus, son of Isis (which during the even later Hellenistic period was together with Hathor identified with Aphrodite). The Greeks used the names Phōsphoros, meaning 'light-bringer' (whence the element phosphorus; alternately Ēōsphoros, meaning 'dawn-bringer'), for the morning star, and Hesperos, meaning 'Western one', for the evening star, both children of dawn Eos and therefore grandchildren of Aphrodite. Though by the Roman era they were recognized as one celestial object, known as "the star of Venus", the traditional two Greek names continued to be used, though usually translated to Latin as Lucifer and Vesper.

Classical poets such as Homer, Sappho, Ovid and Virgil spoke of the star and its light. Poets such as William Blake, Robert Frost, Letitia Elizabeth Landon, Alfred Lord Tennyson and William Wordsworth wrote odes to it. The composer Holst included it as the second movement of his The Planets suite.

In India, the name for Venus in Sanskrit was Shukra Graha, meaning 'the planet Shukra'—in reference to Shukra, a powerful saint. As appears in Vedic astrology, the Sanskrit name Shukra means 'clear, pure' or 'brightness, clearness'. One of the nine Navagraha, it is held to affect wealth, pleasure and reproduction; it was the son of Bhrgu, preceptor of the Daityas, and guru of the Asuras.

The English name Venus stems originally from the ancient Romans. Romans named Venus after their goddess of love, who in turn was based on the ancient Greek love goddess Aphrodite, 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. The weekday of the planet and these goddesses is Friday, named after the Germanic goddess Frigg, who has been associated with the Roman goddess Venus.

In Chinese, the planet is called metal star or gold star (金星; Jīnxīng); of the five elements of traditional Chinese philosophy, Venus was historically associated with metal. These traditions are shared among modern Chinese, Japanese, Korean and Vietnamese cultures, including a name for the planet literally meaning 'metal star' (金星) in each language.

The Maya considered Venus to be the most important celestial body after the Sun and Moon. They called it Chac ek, or Noh Ek', 'the Great Star'. The cycles of Venus were important to their calendar and were described in some of their books, such as the Maya Codex of Mexico and Dresden Codex. The flag of Chile (Estrella Solitaria, 'Lone Star') depicts Venus.

Modern culture

The impenetrable Venusian cloud cover gave science fiction writers free rein to speculate on conditions at its surface; all the more so when early observations showed that not only was it similar in size to Earth, it possessed a substantial atmosphere. Closer to the Sun than Earth, the planet was often depicted as warmer, but still habitable by humans. The genre reached its peak between the 1930s and 1950s, at a time when science had revealed some aspects of Venus, but not yet the harsh reality of its surface conditions. Findings from the first missions to Venus showed reality to be quite different and brought this particular genre to an end. As scientific knowledge of Venus advanced, science fiction authors tried to keep pace, particularly by conjecturing human attempts to terraform Venus.

Carl Sagan remarked in the "Heaven and Hell" episode of the 1980 television series Cosmos: A Personal Voyage, "Far from the balmy paradise imagined by some early scientists, Venus is the one place in the solar system most like Hell."

Symbols

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, 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.

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), 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.

Besides the Venus symbol, many other symbols have been associated with Venus, other common ones are the crescent or particularly the star, as with the Star of Ishtar.