Observations and explorations of Venus

Venus in attempted depiction as it might appear to the naked eye

Venus is always brighter than the brightest stars outside the Solar System, as can be seen here over the Pacific Ocean

Phases of Venus and evolution of its apparent diameter

Observations of the planet Venus include those in antiquity, telescopic observations, and from visiting spacecraft. Spacecraft have performed various flybys, orbits, and landings on Venus, including balloon probes that floated in the atmosphere of Venus. Study of the planet is aided by its relatively close proximity to the Earth, compared to other planets, but the surface of Venus is obscured by an atmosphere opaque to visible light.

Historical observations and impact

Venus as a brilliant "Evening Star" next to crescent moon

Mesopotamia

As one of the brightest objects in the sky, Venus has been known since prehistoric times and as such has gained an entrenched position in human culture. It is described in Babylonian cuneiformic texts such as the Venus tablet of Ammisaduqa, which relates observations that possibly date from 1600 BCE.^[1] The Babylonians named the planet Ishtar (Sumerian Inanna), the personification of womanhood, and goddess of love.^[2] She had a dual role as a goddess of war, thereby representing a deity that presided over birth and death.^[3] One of the oldest surviving astronomical documents, from the Babylonian library of Ashurbanipal around 1600 BC, is a 21-year record of the appearances of Venus (which the early Babylonians called Nindaranna).

The ancient Sumerians and Babylonians called Venus Dil-bat or Dil-i-pat; in Akkadia it was the special star of the mother-god Ishtar.

Asia

In Chinese the planet is called Jīn-xīng (金星), the golden planet of the metal element. In India Shukra Graha ("the planet Shukra") which is named after a powerful saint Shukra. Shukra which is used in Indian Vedic astrology^[4] 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.^[5] The word Shukra is also associated with semen, or generation.

It is known as "Kejora" in Indonesian and Malay. Modern Chinese, Japanese and Korean cultures refer to the planet literally as the "metal star" (金星), based on the Five elements.^[6][7][8]

Egypt

The Ancient Egyptians believed Venus to be two separate bodies and knew the morning star as Tioumoutiri and the evening star as Ouaiti.^[9]

Greeks and Romans

The Ancient Greeks called the morning star Φωσφόρος, Phosphoros (Latinized Phosphorus), the "Bringer of Light" or Ἐωσφόρος, Eosphoros (Latinized Eosphorus), the "Bringer of Dawn". The evening star they called Hesperos (Latinized Hesperus) (Ἓσπερος, the "star of the evening").^[10] By Hellenistic times, the ancient Greeks identified it as a single planet,^[11][12] which they named after their goddess of love, Aphrodite (Αφροδίτη) (Phoenician Astarte),^[13] a planetary name that is retained in modern Greek.^[14] Hesperos would be translated into Latin as Vesper and Phosphoros as Lucifer ("Light Bearer"), a poetic term later used to refer to the fallen angel cast out of heaven.^{[lower-alpha 1]}

The Romans, who derived much of their religious pantheon from the Greek tradition, named the planet Venus after their goddess of love.^[15] Pliny the Elder (Natural History, ii,37) identified the planet Venus with Isis.^[16]

Shukra is the Sanskrit name for Venus

The Pre-Columbian Mayan Dresden Codex, which calculates Venus appearances

Persia

In Iranian mythology, especially in Persian mythology, the planet usually corresponds to the goddess Anahita. In some parts of Pahlavi literature the deities Aredvi Sura and Anahita are regarded as separate entities, the first one as a personification of the mythical river and the latter as a goddess of fertility, which is associated with the planet Venus. As the goddess Aredvi Sura Anahita—and simply called Anahita as well—both deities are unified in other descriptions, e. g. in the Greater Bundahishn, and are represented by the planet. In the Avestan text Mehr Yasht (Yasht 10) there is a possible early link to Mithra. The Persian name of the planet today is "Nahid", which derives from Anahita and later in history from the Pahlavi language Anahid.^{[17][18][19][20]}

Maya

Venus was considered the most important celestial body observed by the Maya, who called it Chac ek,^[21] or Noh Ek', "the Great Star". The Maya monitored the movements of Venus closely and observed it in daytime. The positions of Venus and other planets were thought to influence life on Earth, so the Maya and other ancient Mesoamerican cultures timed wars and other important events based on their observations. In the Dresden Codex, the Maya included an almanac showing Venus's full cycle, in five sets of 584 days each (approximately eight years), after which the patterns repeated (since Venus has a synodic period of 583.92 days).^[22]

The Maya civilization developed a religious calendar, based in part upon the motions of the planet, and held the motions of Venus to determine the propitious time for events such as war. They also named it Xux Ek', the Wasp Star. The Maya were aware of the planet's synodic period, and could compute it to within a hundredth part of a day.^[23]

Other cultures

The Maasai people named the planet Kileken, and have an oral tradition about it called The Orphan Boy.^[24]

Venus is important in many Australian aboriginal cultures, such as that of the Yolngu people in Northern Australia. The Yolngu gather after sunset to await the rising of Venus, which they call Barnumbirr. As she approaches, in the early hours before dawn, she draws behind her a rope of light attached to the Earth, and along this rope, with the aid of a richly decorated "Morning Star Pole", the people are able to communicate with their dead loved ones, showing that they still love and remember them. Barnumbirr is also an important creator-spirit in the Dreaming, and "sang" much of the country into life.^[25]

Venus plays a prominent role in Pawnee mythology. The Pawnee, a North American native tribe, until as late as 1838, practiced a morning star ritual in which a girl was sacrificed to the morning star.^[26]

In western astrology, derived from its historical connotation with goddesses of femininity and love, Venus is held to influence desire and sexual fertility.^[27]

In the metaphysical system of Theosophy, it is believed that on the etheric plane of Venus there is a civilization that existed hundreds of millions of years before Earth's^[28] and it is also believed that the governing deity of Earth, Sanat Kumara, is from Venus.^[29]

Impact on literature

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.^[30] 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.^[31] As scientific knowledge of Venus advanced, so science fiction authors tried to keep pace, particularly by conjecturing human attempts to terraform Venus.^[32]

Another appearance of Venus in popular culture is as the harbinger of destruction in Immanuel Velikovsky's Worlds in Collision (1950). In this controversial book, Velikovsky argued that many seemingly unbelievable stories in the Old Testament are true recollections of times when Venus, which Velikovsky claimed had somehow been ejected from Jupiter as a comet, nearly collided with the Earth. He contended that Venus caused most of the strange events of the Exodus story. He cites legends in many other cultures (including the Greek, Mexican, Chinese and Indian) indicating that the effects of the near-collision were global. The scientific community rejected his unorthodox book, but it became a bestseller.^[33]

Phases

Phases of Venus

Because its orbit takes it between the Earth and the Sun, Venus as seen from Earth exhibits visible phases in much the same manner as the Earth's Moon. Galileo Galilei was the first person to observe the phases of Venus in December 1610, an observation which supported Copernicus's then contentious heliocentric description of the Solar System. He also noted changes in the size of Venus's visible diameter when it was in different phases, suggesting that it was farther from Earth when it was full and nearer when it was a crescent. This observation strongly supported the heliocentric model. Venus (and also Mercury) is not visible from Earth when it is full, since at that time it is at superior conjunction, rising and setting concomitantly with the Sun and hence lost in the Sun's glare.

Venus is brightest when approximately 25% of its disk is illuminated; this typically occurs 37 days both before (in the evening sky) and after (in the morning sky) its inferior conjunction. Its greatest elongations occur approximately 70 days before and after inferior conjunction, at which time it is half full; between these two intervals Venus is actually visible in broad daylight, if the observer knows specifically where to look for it. The planet's period of retrograde motion is 20 days on either side of the inferior conjunction. In fact, through a telescope Venus at greatest elongation appears less than half full due to Schröter's effect first noticed in 1793 and shown in 1996 as due to its thick atmosphere.

Venus in daylight at 5 p.m. in the southern hemisphere - December 2005

On rare occasions, Venus can actually be seen in both the morning (before sunrise) and evening (after sunset) on the same day. This scenario arises when Venus is at its maximum separation from the ecliptic and concomitantly at inferior conjunction; then one hemisphere (Northern or Southern) will be able to see it at both times. This opportunity presented itself most recently for Northern Hemisphere observers within a few days on either side of March 29, 2001, and for those in the Southern Hemisphere, on and around August 19, 1999. These respective events repeat themselves every eight years pursuant to the planet's synodic cycle.

Transit and early terrestrial observations

2004 transit of Venus across the Sun

Transits of Venus directly between the Earth and the Sun's visible disc are rare astronomical events. The first such transit to be predicted and observed was the Transit of Venus, 1639, seen and recorded by English astronomers Jeremiah Horrocks and William Crabtree. The observation by Mikhail Lomonosov of the transit of 1761 provided the first evidence that Venus had an atmosphere, and the 19th-century observations of parallax during Venus transits allowed the distance between the Earth and Sun to be accurately calculated for the first time. Transits can only occur either in early June or early December, these being the points at which Venus crosses the ecliptic (the orbital plane of the Earth), and occur in pairs at eight-year intervals, with each such pair more than a century apart. The previous pair of transits of Venus occurred in 1874 and 1882, and the current pair is in 2004 and 2012.

In the 19th century, many observers stated that Venus had a period of rotation of roughly 24 hours. Italian astronomer Giovanni Schiaparelli was the first to predict a significantly slower rotation, proposing that Venus was tidally locked with the Sun (as he had also proposed for Mercury). While not actually true for either body, this was still a reasonably accurate estimate. The near-resonance between its rotation and its closest approach to Earth helped to create this impression, as Venus always seemed to be facing the same direction when it was in the best location for observations to be made. The rotation rate of Venus was first measured during the 1961 conjunction, observed by radar from a 26 m antenna at Goldstone, California, the Jodrell Bank Radio Observatory in the UK, and the Soviet deep space facility in Eupatoria, Crimea. Accuracy was refined at each subsequent conjunction, primarily from measurements made from Goldstone and Eupatoria. The fact that rotation was retrograde was not confirmed until 1964.

Before radio observations in the 1960s, many believed that Venus contained a lush, Earth-like environment. This was due to the planet's size and orbital radius, which suggested a fairly Earth-like situation as well as to the thick layer of clouds which prevented the surface from being seen. Among the speculations on Venus were that it had a jungle-like environment or that it had oceans of either petroleum or carbonated water. However, microwave observations by C. Mayer et al.,^[34] indicated a high-temperature source (600 K). Strangely, millimetre-band observations made by A. D. Kuzmin indicated much lower temperatures. Two competing theories explained the unusual radio spectrum, one suggesting the high temperatures originated in the ionosphere, and another suggesting a hot planetary surface.

Terrestrial radar mapping

After the Moon, Venus was the second object in the Solar System to be explored by radar from the Earth. The first studies were carried out in 1961 at NASA's Goldstone Observatory, part of the Deep Space Network. At successive inferior conjunctions, Venus was observed both by Goldstone and the National Astronomy and Ionosphere Center in Arecibo. The studies carried out were similar to the earlier measurement of transits of the meridian, which had revealed in 1963 that the rotation of Venus was retrograde (it rotates in the opposite direction to that in which it orbits the Sun). The radar observations also allowed astronomers to determine that the rotation period of Venus was 243.1 days, and that its axis of rotation was almost perpendicular to its orbital plane. It was also established that the radius of the planet was 6,052 kilometres (3,761 mi), some 70 kilometres (43 mi) less than the best previous figure obtained with terrestrial telescopes.

Interest in the geological characteristics of Venus was stimulated by the refinement of imaging techniques between 1970 and 1985. Early radar observations suggested merely that the surface of Venus was more compacted than the dusty surface of the Moon. The first radar images taken from the Earth showed very bright (radar-reflective) highlands christened Alpha Regio, Beta Regio, and Maxwell Montes; improvements in radar techniques later achieved an image resolution of 1–2 kilometres.

Observation by spacecraft

There have been numerous unmanned missions to Venus. Ten Soviet probes have achieved a soft landing on the surface, with up to 110 minutes of communication from the surface, all without return. Launch windows occur every 19 months.

Early flybys

On February 12, 1961, the Soviet spacecraft Venera 1 was the first probe launched to another planet. An overheated orientation sensor caused it to malfunction, losing contact with Earth before its closest approach to Venus of 100,000 km. However, the probe was first to combine all the necessary features of an interplanetary spacecraft: solar panels, parabolic telemetry antenna, 3-axis stabilization, course-correction engine, and the first launch from parking orbit.

Global view of Venus in ultraviolet light done by Mariner 10.

The first successful Venus probe was the American Mariner 2 spacecraft, which flew past Venus in 1962, coming within 35,000 km. A modified Ranger Moon probe, it established that Venus has practically no intrinsic magnetic field and measured the planet's temperature range as 490 to 590 K.

The Soviet Union launched the Zond 1 probe to Venus in 1964, but it malfunctioned sometime after its May 16 telemetry session.

During another American flyby in 1967, Mariner 5 measured the strength of Venus's magnetic field. In 1974, Mariner 10 swung by Venus on its way to Mercury and took ultraviolet photographs of the clouds, revealing the extraordinarily high wind speeds in the Venusian atmosphere.

Early landings

Location of Soviet Venus landers

On March 1, 1966 the Venera 3 Soviet space probe crash-landed on Venus, becoming the first spacecraft to reach the surface of another planet. Its sister craft Venera 2 had failed due to overheating shortly before completing its flyby mission.

The descent capsule of Venera 4 entered the atmosphere of Venus on October 18, 1967, making it the first probe to return direct measurements from another planet's atmosphere. The capsule measured temperature, pressure, density and performed 11 automatic chemical experiments to analyze the atmosphere. It discovered that the atmosphere of Venus was 95% carbon dioxide (CO
2), and in combination with radio occultation data from the Mariner 5 probe, showed that surface pressures were far greater than expected (75 to 100 atmospheres).

These results were verified and refined by the Venera 5 and Venera 6 in May 1969. But thus far, none of these missions had reached the surface while still transmitting. Venera 4's battery ran out while still slowly floating through the massive atmosphere, and Venera 5 and 6 were crushed by high pressure 18 km (60,000 ft) above the surface.

The first successful landing on Venus was by Venera 7 on December 15, 1970. It remained in contact with Earth for 23 minutes, relaying surface temperatures of 455 °C to 475 °C (855 °F to 885 °F). Venera 8 landed on July 22, 1972. In addition to pressure and temperature profiles, a photometer showed that the clouds of Venus formed a layer, ending over 35 kilometres (22 mi) above the surface. A gamma ray spectrometer analyzed the chemical composition of the crust.

Lander/orbiter pairs

Venera 9 and 10

The Soviet probe Venera 9 entered orbit on October 22, 1975, becoming the first artificial satellite of Venus. A battery of cameras and spectrometers returned information about the planet's clouds, ionosphere and magnetosphere, as well as performing bi-static radar measurements of the surface. The 660 kg (1,455 lb) descent vehicle^[35] separated from Venera 9 and landed, taking the first pictures of the surface and analyzing the crust with a gamma ray spectrometer and a densitometer. During descent, pressure, temperature and photometric measurements were made, as well as backscattering and multi-angle scattering (nephelometer) measurements of cloud density. It was discovered that the clouds of Venus are formed in three distinct layers. On October 25, Venera 10 arrived and carried out a similar program of study.

Pioneer Venus

In 1978, NASA sent two Pioneer spacecraft to Venus. The Pioneer mission consisted of two components, launched separately: an orbiter and a multiprobe. The Pioneer Venus Multiprobe carried one large and three small atmospheric probes. The large probe was released on November 16, 1978 and the three small probes on November 20. All four probes entered the Venusian atmosphere on December 9, followed by the delivery vehicle. Although not expected to survive the descent through the atmosphere, one probe continued to operate for 45 minutes after reaching the surface. The Pioneer Venus Orbiter was inserted into an elliptical orbit around Venus on December 4, 1978. It carried 17 experiments and operated until the fuel used to maintain its orbit was exhausted and atmospheric entry destroyed the spacecraft in August 1992.

Further Soviet missions

Also in 1978, Venera 11 and Venera 12 flew past Venus, dropping descent vehicles on December 21 and December 25 respectively. The landers carried colour cameras and a soil drill and analyzer, which unfortunately malfunctioned. Each lander made measurements with a nephelometer, mass spectrometer, gas chromatograph, and a cloud-droplet chemical analyzer using X-ray fluorescence that unexpectedly discovered a large proportion of chlorine in the clouds, in addition to sulfur. Strong lightning activity was also detected.

In 1981, the Soviet Venera 13 sent the first colour image of Venus's surface and analysed the X-ray fluorescence of an excavated soil sample. The probe operated for a record 127 minutes on the planet's hostile surface. Also in 1981, the Venera 14 lander detected possible seismic activity in the planet's crust.

In December 1984, during the apparition of Halley's Comet, the Soviet Union launched the two Vega probes to Venus. Vega 1 and Vega 2 encountered Venus in June 1985, each deploying a lander and an instrumented helium balloon. The balloon-borne aerostat probes floated at about 53 km altitude for 46 and 60 hours respectively, traveling about 1/3 of the way around the planet and allowing scientists to study the dynamics of the most active part of Venus's atmosphere. These measured wind speed, temperature, pressure and cloud density. More turbulence and convection activity than expected was discovered, including occasional plunges of 1 to 3 km in downdrafts.

The landing vehicles carried experiments focusing on cloud aerosol composition and structure. Each carried an ultraviolet absorption spectrometer, aerosol particle-size analyzers, and devices for collecting aerosol material and analyzing it with a mass spectrometer, a gas chromatograph, and an X-ray fluorescence spectrometer. The upper two layers of the clouds were found to be sulfuric acid droplets, but the lower layer is probably composed of phosphoric acid solution. The crust of Venus was analyzed with the soil drill experiment and a gamma ray spectrometer. As the landers carried no cameras on board, no images were returned from the surface. They would be the last probes to land on Venus for decades. The Vega spacecraft continued to rendezvous with Halley's Comet nine months later, bringing an additional 14 instruments and cameras for that mission.

The multiaimed Soviet Vesta mission, developed in cooperation with European countries for realisation in 1991–1994 but canceled due to the Soviet Union disbanding, included the delivering the balloons and small lander to Venus according to first plan.

Orbiters

Venera 15 and 16

In October 1983, Venera 15 and Venera 16 entered polar orbits around Venus. The images had a 1–2 kilometre (0.6–1.2 mile) resolution, comparable to those obtained by the best Earth radars. Venera 15 analyzed and mapped the upper atmosphere with an infrared Fourier spectrometer. From November 11, 1983 to July 10, 1984, both satellites mapped the northern third of the planet with synthetic aperture radar. These results provided the first detailed understanding of the surface geology of Venus, including the discovery of unusual massive shield volcanoes such as coronae and arachnoids. Venus had no evidence of plate tectonics, unless the northern third of the planet happened to be a single plate. The altimetry data obtained by the Venera missions had a resolution four times better than Pioneer's.

A portion of western Eistla Regio displayed in a three-dimensional perspective view acquired by the Magellan probe.

Magellan

On August 10, 1990, the US Magellan probe, named after the explorer Ferdinand Magellan, arrived at its orbit around the planet and started a mission of detailed radar mapping at a frequency of 2.38 GHz.^[36] Whereas previous probes had created low-resolution radar maps of continent-sized formations, Magellan mapped 98% of the surface with a resolution of approximately 100 m. The resulting maps were comparable to visible-light photographs of other planets, and are still the most detailed in existence. Magellan greatly improved scientific understanding of the geology of Venus: the probe found no signs of plate tectonics, but the scarcity of impact craters suggested the surface was relatively young, and there were lava channels thousands of kilometers long. After a four-year mission, Magellan, as planned, plunged into the atmosphere on October 11, 1994, and partly vaporized; some sections are thought to have hit the planet's surface.

Venus Express

Venus Express was a mission by the European Space Agency to study the atmosphere and surface characteristics of Venus from orbit. The design was based on ESA's Mars Express and Rosetta missions. The probe's main objective was the long-term observation of the Venusian atmosphere, which it is hoped will also contribute to an understanding of Earth's atmosphere and climate. It also made global maps of Venerean surface temperatures, and attempted to observe signs of life on Earth from a distance.

Venus Express successfully assumed a polar orbit on April 11, 2006. The mission was originally planned to last for two Venusian years (about 500 Earth days), but was extended to the end of 2014 until its propellant was exhausted. Some of the first results emerging from Venus Express include evidence of past oceans, the discovery of a huge double atmospheric vortex at the south pole, and the detection of hydroxyl in the atmosphere.

Akatsuki

Akatsuki was launched on May 20, 2010, by JAXA, and was planned to enter Venusian orbit in December 2010. However, the orbital insertion maneuver failed and the spacecraft was left in heliocentric orbit. It was placed on an alternative elliptical Venerian orbit on 7 December 2015 by firing its attitude control thrusters for 1233-seconds.^[37] The probe will image the surface in ultraviolet, infrared, microwaves, and radio, and look for evidence of lightning and volcanism on the planet.

Recent flybys

Venus in 2007 by MESSENGER

Several space probes en route to other destinations have used flybys of Venus to increase their speed via the gravitational slingshot method. These include the Galileo mission to Jupiter and the Cassini–Huygens mission to Saturn (two flybys). Rather curiously, during Cassini's examination of the radio frequency emissions of Venus with its radio and plasma wave science instrument during both the 1998 and 1999 flybys, it reported no high-frequency radio waves (0.125 to 16 MHz), which are commonly associated with lightning. This was in direct opposition to the findings of the Soviet Venera missions 20 years earlier. It was postulated that perhaps if Venus did have lightning, it might be some type of low-frequency electrical activity, because radio signals cannot penetrate the ionosphere at frequencies below about 1 megahertz. At the University of Iowa, Donald Gurnett's examination of Venus's radio emissions by the Galileo spacecraft during its flyby in 1990 were interpreted at the time to be indicative of lightning. However the Galileo probe was over 60 times further from Venus than Cassini was during its flyby, making its observations substantially less significant. The mystery as to whether or not Venus does in fact have lightning in its atmosphere was not solved until 2007, when the scientific journal Nature published a series of papers giving the initial findings of Venus Express. It confirmed the presence of lightning on Venus and that it is more common on Venus than it is on Earth.^[38][39]

MESSENGER passed by Venus twice on its way to Mercury. The first time, it flew by on October 24, 2006, passing 3000 km from Venus. As Earth was on the other side of the Sun, no data was recorded.^[40] The second flyby was on July 6, 2007, where the spacecraft passed only 325 km from the cloudtops.^[41]

Future missions

Artist's impression of a Stirling cooled Venus Rover

Future flybys en route to other destinations include the BepiColombo mission to Mercury, and the Solar Probe+ mission to the solar corona.

An older concept for a Venus aircraft

In 2003, NASA proposed the Venus In-Situ Explorer (VISE), originally proposed for a 2013 launch, currently a candidate to launch by 2022 as part of NASA's New Frontiers program. If selected, it would land and perform experiments on the surface of Venus, including taking a core sample and measuring its composition. ESA has proposed the Venus Entry Probe to be launched around the same time.

Also, the Venera-D spacecraft has been proposed by Roscosmos. It would be launched around 2024,^[42] and its prime purpose is to map Venus's surface using more powerful radar than Magellan. The mission would also include a lander capable to function for a long duration on the surface.

Proposals

The Venus Multiprobe Mission proposed sending 16 atmospheric probes into Venus.^[43]

To overcome the severely inhospitable surface conditions, a team led by Geoffrey Landis of NASA's Glenn Research Center in Ohio has proposed the first surface rover in communication with a solar-powered aircraft. The aircraft would carry the mission's sensitive electronics in the relatively mild temperatures of Venus' upper atmosphere.^[44] Another more recent rover design proposal by Landis uses a Stirling cooler powered by a nuclear power source to keep an electronics package at a relatively comfortable 200 °C (392 °F)^[45] Some examples of proposed mission include VESAT, VESPER, Morning Star, VAMP, and VMPM.^[46]

Zephyr is a proposed sail driven surface rover that NASA is working on.^[47]

NASA Langley have proposed the High Altitude Venus Operational Concept (HAVOC) mission.^[48]

Landis also makes a case for Venus as a target for human colonization. At 50 km above the surface, the temperature range is 0-50 °C, the air pressure drops to 1 atmosphere, the gravity is 0.9 that of Earth, and the resources for life are plentiful.^[49]

Timeline of Venus exploration

Objectives are listed in order of increasing difficulty: fly-by, impactor, orbiter, lander (soft), rover, sample return sources. Development unofficial names are listed in italics.

Past missions

Mission (1960–1969)	Launch	Arrival	Termination	Objective	Result
Tyazhely Sputnik	4 February 1961		26 February 1961	Flyby	Launch failure
Venera 1	12 February 1961		26 February 1961	Flyby	Failure (contact lost before the 19 May 1962 100,000 km flyby)
Mariner 1	22 July 1962		22 July 1962	Flyby	Launch failure
Venera 2MV-1 No.1	25 August 1962		28 August 1962	Lander	Launch failure
Mariner 2	27 August 1962	14 December 1962	3 January 1963	Flyby	Success (measurements suggested cool clouds and extremely hot surface)
Venera 2MV-1 No.2	1 September 1962		6 September 1962	Lander	Launch failure
Venera 2MV-2 No.1	12 September 1962		14 September 1962	Flyby	Launch failure
Kosmos 21	11 November 1962		14 November 1962	Flyby?	Launch failure (unknown mission: technology test or fly-by)
Venera 3MV-1 No.2	19 February 1964			Flyby	Launch failure
Kosmos 27	27 March 1964			Landing	Launch failure
Zond 1	2 April 1964	14 July 1964	14 May 1964	Lander	Failure (contact lost before a 100,000 km flyby)
Venera 2	12 November 1965	27 February 1966		Lander	Failure (contact lost before a 24,000 km flyby)
Venera 3	16 November 1965	1 March 1966		Lander	Failure (contact lost before the landing)
Kosmos 96	23 November 1965			Flyby	Failure (did not leave Earth orbit)
Venera 4	12 June 1967	18 October 1967	18 October 1967	Lander	Success (first chemical analysis of the Venusian atmosphere, measurements proved that Venus is extremely hot and its atmosphere far denser than expected)
Mariner 5	14 June 1967	19 October 1967	November 1967	Flyby	Success (radio occultation atmospheric study, 3,990 km flyby)
Kosmos 167	17 June 1967			Lander	Failure (failed in Earth orbit)
Venera 5	5 January 1969	16 May 1969	16 May 1969	Atmospheric probe	Success (with knowledge about atmosphere gathered by Venera 4 its descent was optimised to analyze the atmosphere further deeper)
Venera 6	10 January 1969	17 May 1969	17 May 1969	Atmospheric probe	Success
Mission (1970–1979)	Launch	Arrival	Termination	Objective	Result
Venera 7	17 August 1970	15 December 1970	15 December 1970	Lander	Success (first man-made spacecraft to successfully land on another planet and to transmit surface conditions to Earth, temperature 475±20 C and pressure 90±15 atm.)
Kosmos 359	22 August 1970			Lander	Failure
Venera 8	27 March 1972	22 July 1972	22 July 1972	Lander	Success
Kosmos 482	31 March 1972			Lander	Failure
Mariner 10	3 November 1973	5 February 1974	24 March 1975	Flyby	Success (near-ultraviolet images of atmosphere shown unprecedented detail, 5,768 km flyby then continued towards Mercury)
Venera 9	8 June 1975	20 October 1975	~December 25, 1975?	Orbiter	Success (explored cloud layers and atmospheric parameters)
		22 October 1975	22 October 1975	Lander	Success (first images from the surface of another planet)
Venera 10	14 June 1975	23 October 1975		Orbiter	Success
		25 October 1975	25 October 1975	Lander	Success
Pioneer Venus Orbiter	20 March 1978	4 December 1978	August 1992	Orbiter	Success (over thirteen years studying the atmosphere and mapping the surface with S-band radar, conducted joint mapping with the 1990 Magellan probe)
Pioneer Venus Multiprobe	8 August 1978	9 December 1978	9 December 1978	Bus	Success
				Large probe	Success
				North probe	Success
				Night probe	Success
				Day probe	Success (continued to send radio signals back after impact, for over an hour)
Venera 11	9 September 1978	25 December 1978	February 1980	Flyby	Success (as did Venera 12 found evidence of lightnings)
		25 December 1978	25 December 1978	Lander	Partial success (failed to deploy some instruments)
Venera 12	14 September 1978	19 December 1978	April 1980	Flyby	Success
		21 December 1978	21 December 1978	Lander	Partial success (failed to deploy some instruments)
Mission (1980–1989)	Launch	Arrival	Termination	Objective	Result
Venera 13	30 October 1981	1 March 1982		Flyby	Success
		1 March 1982	1 March 1982	Lander	Success (first colour images from surface and X-ray fluorescence spectrometry soil characterisation)
Venera 14	4 November 1981			Flyby	Success
		5 March 1982	5 March 1982	Lander	Success
Venera 15	2 June 1983	10 October 1983	~July 1984	Orbiter	Success (synthetic aperture radar on 15 and 16 probes allowed to map 25% of surface)
Venera 16	7 June 1983	11 October 1983	~July 1984	Orbiter	Success
Vega 1	15 December 1984	11 June 1985	30 January 1987	Flyby	Success (intercepted the Halley comet next year)
			11 June 1985	Lander	Failed (surface experiments were inadvertently activated at 20 km from the surface)
			13 June 1985	Balloon	Success (first balloon in another planet, flew al least 11,600 km)
Vega 2	20 December 1984	15 June 1985	24 March 1987	Flyby	Success (intercepted the Halley comet next year)
			15 June 1985	Lander	Success
			17 June 1985	Balloon	Success (flew al least 11,100 km)
Magellan	4 May 1989	10 August 1990	12 October 1994	Orbiter	Success (provided high-resolution gravimetric data for 94% of the planet, Synthetic Aperture Radar generated a high resolution map of 98% of the surface)
Galileo	18 October 1989	10 February 1990	21 September 2003	Flyby	Success (took some data on its route to Jupiter, 16,106 km maximum approach)
Mission (1990–1999)	Launch	Arrival	Termination	Objective	Result
Cassini Huygens	15 October 1997	26 April 1998 and 24 June 1999	ongoing	2 Flybys	Success (radio-frequency observations on its way to Saturn shown no signs of lightnings in Venus)
Mission (2000–2009)	Launch	Arrival	Termination	Objective	Result
MESSENGER	3 August 2004	24 October 2006 and 5 June 2007	30 April 2015	2 Flybys	Success (very close second flyby at 338 km in which visible, near-infrared, ultraviolet and X-ray spectrometry of the upper atmosphere was made simultaneously with the Venus Express probe, no observations in first flyby)
Venus Express	9 November 2005	11 April 2006	16 December 2014	Orbiter	Success (detailed long-term observation of the Venusian atmosphere)
Mission (2000–2009)	Launch	Arrival	Termination	Objective	Result

Current missions

Mission (2010–present)	Launch	Arrival	Termination	Objective	Result
Akatsuki	20 May 2010	7 December 2015	ongoing	orbiter	Orbital insertion maneuver failed in 2010; Akatsuki's second attempt at orbital insertion succeeded on 7 December 2015 using four attitude control thrusters.[50]

Future missions

Name	Estimated launch	Elements	Notes
BepiColombo	January 2017	Flyby	2 orbiters to be launched together: Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO)

Under study

Name	Estimated launch	Elements	Notes
ISRO Venusian orbiter mission[51]	2017–2018	Orbiter	Idea for an Indian atmosphere probe.
VERITAS[52]	2021	Orbiter	Discovery Program mission concept for produce high resolution topography and imaging of Venus surface.
DAVINCI[52]	2021	Atmospheric probe	Discovery Program mission concept to study the chemical composition of Venus atmosphere during a 63-minute descent.
Venera-D[53]	NET 2025	Orbiter	To sense composition of the planet's atmosphere and its circulation patterns
		Balloons	Two balloons to sense acoustic and electrical activities of atmosphere
		Microprobes	Up to four atmospheric sensing probes launched from the balloons
		Lander	Designed for one-hour lifespan after touchdown in Tessera

See also

• Aspects of Venus
• Manned Venus Flyby

Notes

1. Jerome translated Septuagint heosphoros and Hebrew helel as lucifer, in Isaiah 14:12.

References

1. Sachs, A. (1974). "Babylonian Observational Astronomy". Philosophical Transactions of the Royal Society of London. 276 (1257): 43–50. Bibcode:1974RSPTA.276...43S. doi:10.1098/rsta.1974.0008.
2. Meador, Betty De Shong (2000). Inanna, Lady of Largest Heart: Poems of the Sumerian High Priestess Enheduanna. University of Texas Press. p. 15. ISBN 0-292-75242-3.
3. Littleton, C. Scott (2005). Gods, Goddesses, and Mythology. 6. Marshall Cavendish. p. 760. ISBN 0761475656.
4. Bhalla, Prem P. (2006). Hindu Rites, Rituals, Customs and Traditions: A to Z on the Hindu Way of Life. Pustak Mahal. p. 29. ISBN 81-223-0902-X.
5. Behari, Bepin; Frawley, David (2003). Myths & Symbols of Vedic Astrology (2nd ed.). Lotus Press. pp. 65–74. ISBN 0-940985-51-9.
6. De Groot, Jan Jakob Maria (1912). Religion in China: universism. a key to the study of Taoism and Confucianism. American lectures on the history of religions. 10. G. P. Putnam's Sons. p. 300. Retrieved 2010-01-08.
7. Crump, Thomas (1992). The Japanese numbers game: the use and understanding of numbers in modern Japan. Nissan Institute/Routledge Japanese studies series. Routledge. pp. 39–40. ISBN 0415056098.
8. Hulbert, Homer Bezaleel (1909). The passing of Korea. Doubleday, Page & company. p. 426. Retrieved 2010-01-08.
9. Cattermole, Peter John; Moore, Patrick (1997). Atlas of Venus. Cambridge University Press. p. 9. ISBN 0-521-49652-7.
10. "Definition of Hesperus". www.thefreedictionary.com. Retrieved 12 May 2013.
11. Fox, William Sherwood (1916). The Mythology of All Races: Greek and Roman. Marshall Jones Company. p. 247. ISBN 0-8154-0073-X. Retrieved 2009-05-16.
12. Greene, Ellen (1996). Reading Sappho: contemporary approaches. University of California Press. p. 54. ISBN 0-520-20601-0.
13. Greene, Ellen (1999). Reading Sappho: contemporary approaches. University of California Press. p. 54. ISBN 0-520-20601-0.
14. "Greek Names of the Planets". Retrieved 2012-07-14. Aphrodite is the Greek name of the planet Venus, which is named after Aphrodite, the goddess of Love. See also the Greek article about the planet.
15. Guillemin, Amédée; Lockyer, Norman; Proctor, Richard Anthony (1878). The heavens: an illustrated handbook of popular astronomy. London: Richard Bentley & Son. p. 67. Retrieved 2009-05-16.
16. Rees, Roger (2002). Layers of loyalty in Latin panegyric, AD 289–307. Oxford University Press. p. 112. ISBN 0-19-924918-0.
17. Boyce, Mary. "ANĀHĪD". Encyclopaedia Iranica. Center for Iranian Studies, Columbia University. Archived from the original on 1 May 2008. Retrieved 2010-02-20.
18. Schmidt, Hanns-Peter. "MITHRA". Encyclopaedia Iranica. Center for Iranian Studies, Columbia University. Archived from the original on 12 July 2008. Retrieved 2010-02-20.
19. MacKenzie, D. N. (2005). A concise Pahlavi Dictionary. London & New York: Routledge Curzon. ISBN 0-19-713559-5.
20. Mo'in, M. (1992). A Persian Dictionary. Six Volumes. 5–6. Tehran: Amir Kabir Publications. ISBN 1-56859-031-8.
21. The Book of Chumayel: The Counsel Book of the Yucatec Maya, 1539-1638. Richard Luxton. 1899. pp. 6,194. ISBN 9780894122446.
22. Milbrath, Susan (1999). Star Gods of The Mayans : Astronomy in Art, Folklore, and Calendars. Austin, TX: University of Texas Press. pp. 200–204, 383. ISBN 978-0-292-79793-2.
23. Sharer, Robert J.; Traxler, Loa P. (2005). The Ancient Maya. Stanford University Press. ISBN 0-8047-4817-9.
24. Verhaag, G. (2000). "Letters to the Editor: Cross-cultural astronomy". Journal of the British Astronomical Association. 110 (1): 49. Bibcode:2000JBAA..110...49V.
25. Norris, Ray P. (2004). "Searching for the Astronomy of Aboriginal Australians" (PDF). Conference Proceedings. Australia Telescope National Facility. pp. 1–4. Retrieved 2009-05-16.
26. Weltfish, Gene (1977) [First published 1965]. "Chapter 10: The Captive Girl Sacrifice". The Lost Universe: Pawnee Life and Culture. University of Nebraska Press. p. 117. ISBN 978-0-8032-5871-6.
27. Bailey, Michael David (2007). Magic and Superstition in Europe: a Concise History from Antiquity to the Present. Rowman & Littlefield. pp. 93–94. ISBN 0-7425-3387-5.
28. Powell, Arthor E. (1930). The Solar System. London: The Theosophical Publishing House. p. 33. ISBN 0-7873-1153-7.
29. Leadbeater, C.W. The Masters and the Path Adyar, Madras, India: 1925—Theosophical Publishing House (in this book, Sanat Kumara is referred to as Lord of the World.) See in index under "Lord of the World".
30. Miller, Ron (2003). Venus. Twenty-First Century Books. p. 12. ISBN 0-7613-2359-7.
31. Dick, Steven (2001). Life on Other Worlds: The 20th-Century Extraterrestrial Life Debate. Cambridge University Press. p. 43. ISBN 0-521-79912-0.
32. Seed, David (2005). A Companion to Science Fiction. Blackwell Publishing. pp. 134–135. ISBN 1-4051-1218-2.
33. Ellenberger, C. Leroy (Winter 1984). "Worlds in Collision in Macmillan's Catalogues". Kronos. 9 (2). Retrieved 2009-05-16. The 20 weeks at the top stated by Juergens in The Velikovsky Affair is incorrect.
34. Mayer, C. H.; McCollough, T. P.; Sloanaker, R. M. (1958). "Observations of Venus at 3.15-CM Wave Length". Astrophysical Journal. 127: 1–9. Bibcode:1958ApJ...127....1M. doi:10.1086/146433.
35. Braeunig, Robert A. (2008). "Planetary Spacecraft". Retrieved 2009-02-15.
36. W. T. K. Johnson, "Magellan Imaging Radar Mission To Venus," PROCEEDINGS OF THE IEEE, Vol 19, No 6, June 1991, available from IEEE
37. http://www.planetary.org/blogs/guest-blogs/2015/12060740-live-from-sagamihara.html
38. Hand, Eric (2007-11-27). "European mission reports from Venus". Nature (450): 633–660. doi:10.1038/news.2007.297.
39. "Venus offers Earth climate clues". BBC News. November 28, 2007. Retrieved 2007-11-29.
40. "MESSENGER performs first flyby of Venus". NASA's Solar System Exploration: News & Events: News Archive. Retrieved 2007-08-20.
41. "MESSENGER performs second flyby of Venus". NASA's Solar System Exploration: News & Events: News Archive. Retrieved 2007-08-20.
42. "РАН: запуск "Венеры-Д" состоится не ранее 2024 года". Gazieta.ru. 9 April 2012. Retrieved September 26, 2013.
43. Discovery Missions Under Consideration
44. "To conquer Venus, try a plane with a brain". NewScience. Retrieved 2007-09-03.
45. Landis, Geoffrey A.; Kenneth C. Mellott (December 2007). "Venus surface power and cooling systems". Acta Astronautica. 61 (11–12): 995–1001. Bibcode:2007AcAau..61..995L. doi:10.1016/j.actaastro.2006.12.031.
46. Missions to Venus
47. Report: "NASA Will Launch a Venus Rover in 2023" 2016
48. Exploring Venus By Airship: Cool Concept, But Certainly Not New. Dec 2014
49. "Venus Related Papers". Geoffrey A. Landis. Retrieved 2007-09-03.
50. Clark, Stephan. "Japanese probe fires rockets to steer into orbit at Venus". Retrieved 7 December 2015.
51. Srikanth, B.R. "After Mars, Isro aims for Venus probe in 2-3 years". Archived from the original on May 30, 2015. Retrieved May 30, 2015.
52. http://www.jpl.nasa.gov/news/news.php?feature=4727
53. Zak, Anatoly. "Venera-D mission". RussianSpaecWeb. Retrieved 11 January 2011.

External links

• Double vortex at Venus South Pole unveiled!
• Planetary Missions at National Space Science Data Center (NASA)
• Soviet Venus-rover ХМ-ВД2
• Exploring Venus by Solar Airplane - G. Landis