Venus

| density =

| surface_grav =

| escape_velocity =

| declination = 67.16°

| angular_size = or Venerean / Venerian

| atmosphere = yes

| atmosphere_ref = resulting in resurfacing, instead of plate tectonics. Venus may have had liquid surface water early in its history with a habitable environment, The surface pressure is , and the average surface temperature is , above the critical points of both major constituents and making the surface atmosphere a supercritical fluid of mainly supercritical carbon dioxide and some supercritical nitrogen.

Natural history

Formation

The rocky terrestrial planets including Venus are thought to have formed in 5 stages: dust settling, planetesimal formation, planetary embryos, giant impacts, and finally formation of atmospheres. Limited measurements from Venus have prevented a more detailed analysis of the formation timeline.

Future

Venus is expected to be destroyed, along with Mercury, and possibly the Earth and the Moon, when the Sun becomes a red giant in approximately seven or eight billion years.

Geography

The Venusian surface was a subject of speculation until some of its secrets were revealed by probes in the 20th century. Venera landers in 1975 and 1982 returned images of a surface covered in sediment and relatively angular rocks. such as flows on Sif Mons, a shield volcano, and on Niobe Planitia, a flat plain. However, the nature of tessera terrains is far from certain. Venus has gained interest as a case for research into the development of Earth-like planets and their habitability.

Volcanism

thumb|left|upright=1.1|Radar mosaic of two [[pancake domes in Venus's Eistla region—both wide and less than high]]

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 across. The only volcanic complex of this size on Earth is the Big Island of Hawaii. This is not because Venus is more volcanically active than Earth, but because its crust is older and is not subject to the erosion processes active on Earth. Earth's oceanic crust is continually recycled by subduction at the boundaries of tectonic plates, and has an average age of about 100 million years,

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,

Craters

thumb|upright=0.9|alt=The plains of Venus|[[Impact craters on the surface of Venus (false-colour, 3D projection image reconstructed from radar data)]]

There are almost a thousand impact craters on Venus, evenly distributed across its surface. On other cratered bodies, such as Earth and the Moon, craters show a range of states of degradation. On the Moon, degradation is caused by subsequent impacts, whereas on Earth it is caused by wind and rain erosion. On Venus, about 85% of the craters are in pristine condition. The number of craters, together with their well-preserved condition, indicates the planet underwent a global resurfacing event 300–600million years ago,

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.

The weak magnetosphere around Venus means that the solar wind interacts directly with its outer atmosphere. Here, ions of hydrogen and oxygen are being created by the dissociation of water molecules due to ultraviolet radiation. The solar wind then supplies energy that gives some of these ions sufficient speed to escape Venus's gravity field. This erosion process results in a steady loss of low-mass hydrogen, helium, and oxygen ions, whereas higher-mass molecules, such as carbon dioxide, are more likely to be retained. Atmospheric erosion by the solar wind could have led to the loss of most of Venus's water during the first billion years after it formed. a planet under a greenhouse inferno.

Venus's atmosphere is rich in primordial noble gases compared to that of Earth. 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. The dense atmosphere and highly reflective clouds gives it a high albedo of 0.68, meaning it reflects nearly 70% of the incident sunlight. This results in strong 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,

{|class="wikitable floatleft" style="font-size: 100%; margin-right: 1em;"

|+ Venus temperature of the atmosphere at the surface have been recorded, with the sky having an orange-yellow colour, while at higher altitudes being white.

Orbit and rotation

alt=Mars circling the Sun further and slower than Earth|thumb|upright=1.1|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 , 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. 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 6.5minutes.

Therefore, they approach each other and reach inferior conjunction in synodic periods of 584 days, on average. Venus has been used as a waypoint for gravity assist manoeuvres, which has been identified as a faster and economic way to travel to Mercury, the Sun, asteroids, Mars, Jupiter and beyond.

Observability

thumb|alt=A photograph of the night sky taken from the seashore. A glimmer of sunlight is on the horizon. There are many stars visible. Venus is at the centre, much brighter than any of the stars, and its light can be seen reflected in the ocean.|Venus, pictured centre-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 with a maximum apparent magnitude of −4.92 brighter than any other planet or star apart from the Sun, The planet is bright enough to be seen in broad daylight,

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

thumb|The phases of Venus and evolution of its apparent diameter|alt=Diagram illustrating the phases of Venus

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. Although naked eye visibility of Venus's phases is disputed, records exist of observations of its crescent. 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. This results in Venus transiting above Earth in a sequence currently of , , and , forming cycles of .

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). The surface and its features, like the visible dark patch in this image, the Ovda Regio plateau of Aphrodite Terra, is much less discernable by the human eye, though reportedly seen by some people, possibly due to higher sensitivity in the spectrum that the surface glows.]]

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 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.

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. 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.]]

Active and planned missions

thumb|upright=1.5|Global topographic map of Venus, with all probe landing sites marked (red: images returned; black dot: samples taken and on-site analysed)

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

thumb|In the 1970s the [[United States and the Soviet Union both designed crewed Venus missions, like the Apollo program derived Manned Venus Flyby design, or the depicted, the proposed Soviet TMK-MAVR craft on a Venus flyby]]

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

thumb|Artist's rendering of a NASA [[HAVOC|High Altitude Venus Operational Concept (HAVOC) crewed floating outpost on Venus]]

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").

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.

thumb|upright=1.2|The [[Octagram|eight-pointed star is a symbol used in some cultures to represent Venus, 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 12th century BC.]]

Several hymns praise Inanna in her role as the goddess of the planet Venus.

Notes

References

External links

Venus profile at NASA's Solar System Exploration site
Missions to Venus and Image catalogue at the National Space Science Data Center
Soviet Exploration of Venus and Image catalogue at Mentallandscape.com
Image catalogue from the Venera missions
Venus page at The Nine Planets
Transits of Venus at NASA.gov
Geody Venus, a search engine for surface features
Interactive 3D gravity simulation of the pentagram that the orbit of Venus traces when Earth is held fixed at the centre of the coordinate system

Cartographic resources

Map-a-Planet: Venus by the U.S. Geological Survey
Gazetteer of Planetary Nomenclature: Venus by the International Astronomical Union
Venus crater database by the Lunar and Planetary Institute
Map of Venus by Eötvös Loránd University
Google Venus 3D, interactive map of the planet