Venus

Last updated

Venus Venus symbol.svg
Venus-real color.jpg
A real-colour image taken by Mariner 10 processed from two filters. The surface is obscured by thick sulfuric acid clouds
Designations
Pronunciation /ˈvnəs/ ( Loudspeaker.svg listen )
Adjectives Venusian or (rarely) Cytherean, Venerean
Orbital characteristics [2] [3]
Epoch J2000
Aphelion
  • 0.728213  AU
  • 108,939,000 km
Perihelion
  • 0.718440 AU
  • 107,477,000 km
  • 0.723332 AU
  • 108,208,000 km
Eccentricity 0.006772 [4]
  • 224.701 d [2]
  • 0.615198  yr
  • 1.92 Venus solar day
583.92 days [2]
Average orbital speed
35.02 km/s
50.115°
Inclination
76.680° [4]
54.884°
Satellites None
Physical characteristics
Mean radius
  • 6,051.8±1.0 km [6]
  • 0.9499 Earths
Flattening 0 [6]
  • 4.6023×108 km2
  • 0.902 Earths
Volume
  • 9.2843×1011 km3
  • 0.866 Earths
Mass
  • 4.8675×1024 kg [7]
  • 0.815 Earths
Mean density
5.243 g/cm3
  • 8.87 m/s2
  • 0.904 g
10.36 km/s (6.44 mi/s) [8]
Sidereal rotation period
−243.025 d(retrograde) [2]
Equatorial rotation velocity
6.52 km/h (1.81 m/s)
2.64° (for retrograde rotation)
177.36° (to orbit) [2] [note 1]
North pole right ascension
  •  18h 11m 2s
  • 272.76° [9]
North pole declination
67.16°
Albedo
Surface temp. minmeanmax
Kelvin 737 K [2]
Celsius462 °C
Fahrenheit 864 °F (462 °C)
−4.92 to −2.98 [12]
9.7″–66.0″ [2]
Atmosphere
Surface pressure
92  bar (9.2  MPa)
Composition by volume
  1. Defining the rotation as retrograde, as done by NASA space missions and the USGS, puts Ishtar Terra in the northern hemisphere and makes the axial tilt 2.64°. Following the right-hand rule for prograde rotation puts Ishtar Terra in the southern hemisphere and makes the axial tilt 177.36°.

Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. [13] It has the longest rotation period (243 days) of any planet in the Solar System and rotates in the opposite direction to most other planets (meaning the Sun rises in the west and sets in the east). [14] It does not have any natural satellites. It is named after the Roman goddess of love and beauty. It is the second-brightest natural object in the night sky after the Moon, reaching an apparent magnitude of −4.6 – bright enough to cast shadows at night and, rarely, visible to the naked eye in broad daylight. [15] [16] Orbiting within Earth's orbit, Venus is an inferior planet and never appears to venture far from the Sun; its maximum angular distance from the Sun (elongation) is 47.8°.

Planet Class of astronomical body directly orbiting a star or stellar remnant

A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.

Sun Star at the centre of the Solar System

The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 1.39 million kilometers, or 109 times that of Earth, and its mass is about 330,000 times that of Earth. It accounts for about 99.86% of the total mass of the Solar System. Roughly three quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron.

Earth Third planet from the Sun in the Solar System

Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.

Contents

Venus is a terrestrial planet and is sometimes called Earth's "sister planet" because of their similar size, mass, proximity to the Sun, and bulk composition. It is radically different from Earth in other respects. It has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the planet's surface is 92 times that of Earth, or roughly the pressure found 900 m (3,000 ft) underwater on Earth. Venus is by far the hottest planet in the Solar System, with a mean surface temperature of 735 K (462 °C; 863 °F), even though Mercury is closer to the Sun. Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in visible light. It may have had water oceans in the past, [17] [18] but these would have vaporized as the temperature rose due to a runaway greenhouse effect. [19] The water has probably photodissociated, and the free hydrogen has been swept into interplanetary space by the solar wind because of the lack of a planetary magnetic field. [20] Venus's surface is a dry desertscape interspersed with slab-like rocks and is periodically resurfaced by volcanism.

Terrestrial planet planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun, i.e. Mercury, Venus, Earth, and Mars

A terrestrial planet, telluric planet, or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun, i.e. Mercury, Venus, Earth, and Mars. The terms "terrestrial planet" and "telluric planet" are derived from Latin words for Earth, as these planets are, in terms of structure, "Earth-like". These planets are located between the Sun and the Asteroid Belt.

Atmosphere The layer of gases surrounding an astronomical body held by gravity

An atmosphere is a layer or a set of layers of gases surrounding a planet or other material body, that is held in place by the gravity of that body. An atmosphere is more likely to be retained if the gravity it is subject to is high and the temperature of the atmosphere is low.

Carbon dioxide chemical compound

Carbon dioxide (chemical formula CO2) is a colorless gas with a density about 60% higher than that of dry air. Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms. It occurs naturally in Earth's atmosphere as a trace gas. The current concentration is about 0.04% (410 ppm) by volume, having risen from pre-industrial levels of 280 ppm. Natural sources include volcanoes, hot springs and geysers, and it is freed from carbonate rocks by dissolution in water and acids. Because carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes, ice caps, glaciers and seawater. It is present in deposits of petroleum and natural gas. Carbon dioxide is odorless at normally encountered concentrations. However, at high concentrations, it has a sharp and acidic odor.

As one of the brightest objects in the sky, Venus has been a major fixture in human culture for as long as records have existed. It has been made sacred to gods of many cultures, and has been a prime inspiration for writers and poets as the morning star and evening star. Venus was the first planet to have its motions plotted across the sky, as early as the second millennium BC. [21]

As the planet with the closest approach to Earth, Venus has been a prime target for early interplanetary exploration. It was the first planet beyond Earth visited by a spacecraft ( Mariner 2 in 1962), and the first to be successfully landed on (by Venera 7 in 1970). Venus's thick clouds render observation of its surface impossible in visible light, and the first detailed maps did not emerge until the arrival of the Magellan orbiter in 1991. Plans have been proposed for rovers or more complex missions, but they are hindered by Venus's hostile surface conditions.

Mariner 2 space probe

Mariner 2, an American space probe to Venus, was the first robotic space probe to conduct a successful planetary encounter. The first successful spacecraft in the NASA Mariner program, it was a simplified version of the Block I spacecraft of the Ranger program and an exact copy of Mariner 1. The missions of Mariner 1 and 2 spacecraft are together sometimes known as the Mariner R missions. Original plans called for the probes to be launched on the Atlas-Centaur, but serious developmental problems with that vehicle forced a switch to the much smaller Agena B stage. As such, the design of the Mariner R vehicles was greatly simplified. Far less instrumentation was carried than on the Soviet Venera probes of this period, including no TV camera as the Atlas-Agena B had only half as much lift capacity as the Soviet 8K78 booster. The Mariner 2 spacecraft was launched from Cape Canaveral on August 27, 1962 and passed as close as 34,773 kilometers (21,607 mi) to Venus on December 14, 1962.

Venera 7

Venera 7 was a Soviet spacecraft, part of the Venera series of probes to Venus. When it landed on the Venusian surface, it became the first spacecraft to land on another planet and first to transmit data from there back to Earth.

<i>Magellan</i> (spacecraft) space probe

The Magellan spacecraft, also referred to as the Venus Radar Mapper, was a 1,035-kilogram (2,282 lb) robotic space probe launched by NASA of the United States, on May 4, 1989, to map the surface of Venus by using synthetic aperture radar and to measure the planetary gravitational field.

Physical characteristics

Size comparison with Earth Venus, Earth size comparison.jpg
Size comparison with Earth

Venus is one of the four terrestrial planets in the Solar System, meaning that it is a rocky body like Earth. It is similar to Earth in size and mass, and is often described as Earth's "sister" or "twin". [22] The diameter of Venus is 12,103.6 km (7,520.8 mi)—only 638.4 km (396.7 mi) less than Earth's—and its mass is 81.5% of Earth's. Conditions on the Venusian surface differ radically from those on Earth because its dense atmosphere is 96.5% carbon dioxide, with most of the remaining 3.5% being nitrogen. [23]

Nitrogen Chemical element with atomic number 7

Nitrogen is a chemical element with symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772. Although Carl Wilhelm Scheele and Henry Cavendish had independently done so at about the same time, Rutherford is generally accorded the credit because his work was published first. The name nitrogène was suggested by French chemist Jean-Antoine-Claude Chaptal in 1790, when it was found that nitrogen was present in nitric acid and nitrates. Antoine Lavoisier suggested instead the name azote, from the Greek ἀζωτικός "no life", as it is an asphyxiant gas; this name is instead used in many languages, such as French, Russian, and Turkish, and appears in the English names of some nitrogen compounds such as hydrazine, azides and azo compounds.

Geography

The Venusian surface was a subject of speculation until some of its secrets were revealed by planetary science in the 20th century. Venera landers in 1975 and 1982 returned images of a surface covered in sediment and relatively angular rocks. [24] The surface was mapped in detail by Magellan in 1990–91. The ground shows evidence of extensive volcanism, and the sulfur in the atmosphere may indicate that there have been recent eruptions. [25] [26]

Planetary science science of astronomical objects apparently in orbit around one or more stellar objects within a few light years

Planetary science or, more rarely, planetology, is the scientific study of planets, moons, and planetary systems and the processes that form them. It studies objects ranging in size from micrometeoroids to gas giants, aiming to determine their composition, dynamics, formation, interrelations and history. It is a strongly interdisciplinary field, originally growing from astronomy and earth science, but which now incorporates many disciplines, including planetary geology, cosmochemistry, atmospheric science, oceanography, hydrology, theoretical planetary science, glaciology, and exoplanetology. Allied disciplines include space physics, when concerned with the effects of the Sun on the bodies of the Solar System, and astrobiology.

Volcanology of Venus

The surface of Venus is dominated by volcanic features and has more volcanoes than any other planet in the Solar System. It has a surface that is 90% basalt, and about 65% of the planet consists of a mosaic of volcanic lava plains, indicating that volcanism played a major role in shaping its surface. There are more than 1,000 volcanic structures and possible periodic resurfacing of Venus by floods of lava. The planet may have had a major global resurfacing event about 500 million years ago, from what scientists can tell from the density of impact craters on the surface. Venus has an atmosphere rich in carbon dioxide, with a density that is 90 times greater than Earth's atmosphere.

Sulfur Chemical element with atomic number 16

Sulfur or sulphur is a chemical element with symbol S and atomic number 16. It is abundant, multivalent, and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula S8. Elemental sulfur is a bright yellow, crystalline solid at room temperature.

About 80% of the Venusian surface is covered by smooth, volcanic plains, consisting of 70% plains with wrinkle ridges and 10% smooth or lobate plains. [27] Two highland "continents" make up the rest of its surface area, one lying in the planet's northern hemisphere and the other just south of the equator. The northern continent is called Ishtar Terra after Ishtar, the Babylonian goddess of love, and is about the size of Australia. Maxwell Montes, the highest mountain on Venus, lies on Ishtar Terra. Its peak is 11 km (7 mi) above the Venusian average surface elevation. [28] The southern continent is called Aphrodite Terra, after the Greek goddess of love, and is the larger of the two highland regions at roughly the size of South America. A network of fractures and faults covers much of this area. [29]

The absence of evidence of lava flow accompanying any of the visible calderas remains an enigma. The planet has few impact craters, demonstrating that the surface is relatively young, approximately 300–600 million years old. [30] [31] Venus has some unique surface features in addition to the impact craters, mountains, and valleys commonly found on rocky planets. Among these are flat-topped volcanic features called "farra", which look somewhat like pancakes and range in size from 20 to 50 km (12 to 31 mi) across, and from 100 to 1,000 m (330 to 3,280 ft) high; radial, star-like fracture systems called "novae"; features with both radial and concentric fractures resembling spider webs, known as "arachnoids"; and "coronae", circular rings of fractures sometimes surrounded by a depression. These features are volcanic in origin. [32]

Most Venusian surface features are named after historical and mythological women. [33] Exceptions are Maxwell Montes, named after James Clerk Maxwell, and highland regions Alpha Regio, Beta Regio, and Ovda Regio. The latter three features were named before the current system was adopted by the International Astronomical Union, the body which oversees planetary nomenclature. [34]

The longitudes of physical features on Venus are expressed relative to its prime meridian. The original prime meridian passed through the radar-bright spot at the centre of the oval feature Eve, located south of Alpha Regio. [35] After the Venera missions were completed, the prime meridian was redefined to pass through the central peak in the crater Ariadne. [36] [37]

Surface geology

False-colour image of Maat Mons with a vertical exaggeration of 22.5 Maat Mons on Venus.jpg
False-colour image of Maat Mons with a vertical exaggeration of 22.5

Much of the Venusian surface appears to have been shaped by volcanic activity. Venus has several times as many volcanoes as Earth, and it has 167 large volcanoes that are over 100 km (62 mi) across. The only volcanic complex of this size on Earth is the Big Island of Hawaii. [32] :154 This is not because Venus is more volcanically active than Earth, but because its crust is older. 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, [38] whereas the Venusian surface is estimated to be 300–600 million years old. [30] [32]

Several lines of evidence point to ongoing volcanic activity on Venus. During the Soviet Venera program, the Venera 9 orbiter obtained spectroscopic evidence of lightning on Venus, [39] and the Venera 12 descent probe obtained additional evidence of lightning and thunder. [40] [41] The European Space Agency's Venus Express in 2007 detected whistler waves further confirming the occurrence of lightning on Venus. [42] [43] One possibility is that ash from a volcanic eruption was generating the lightning. Another piece of evidence comes from measurements of sulfur dioxide concentrations in the atmosphere, which dropped by a factor of 10 between 1978 and 1986, jumped in 2006, and again declined 10-fold. [44] This may mean that levels had been boosted several times by large volcanic eruptions. [45] [46]

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, [47] [n 1] near the shield volcano Maat Mons. Three of the spots were observed in more than one successive orbit. These spots are thought to represent lava freshly released by volcanic eruptions. [48] [49] The actual temperatures are not known, because the size of the hot spots could not be measured, but are likely to have been in the 800–1,100 K (527–827 °C; 980–1,520 °F) range, relative to a normal temperature of 740 K (467 °C; 872 °F). [50]

Impact craters on the surface of Venus (false-colour image reconstructed from radar data) PIA00103 Venus - 3-D Perspective View of Lavinia Planitia.jpg
Impact craters on the surface of Venus (false-colour image reconstructed from radar data)

Almost a thousand impact craters on Venus are evenly distributed across its surface. On other cratered bodies, such as Earth and the Moon, craters show a range of states of degradation. On the Moon, degradation is caused by subsequent impacts, whereas on Earth it is caused by wind and rain erosion. On Venus, about 85% of the craters are in pristine condition. The number of craters, together with their well-preserved condition, indicates the planet underwent a global resurfacing event about 300–600 million years ago, [30] [31] followed by a decay in volcanism. [51] Whereas Earth's crust is in continuous motion, Venus is thought to be unable to sustain such a process. Without plate tectonics to dissipate heat from its mantle, Venus instead undergoes a cyclical process in which mantle temperatures rise until they reach a critical level that weakens the crust. Then, over a period of about 100 million years, subduction occurs on an enormous scale, completely recycling the crust. [32]

Venusian craters range from 3 to 280 km (2 to 174 mi) in diameter. No craters are smaller than 3 km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy are slowed down so much by the atmosphere that they do not create an impact crater. [52] Incoming projectiles less than 50 m (160 ft) in diameter will fragment and burn up in the atmosphere before reaching the ground. [53]

Internal structure

The internal structure of Venus - the crust (outer layer), the mantle (middle layer) and the core (yellow inner layer) Venus structure.jpg
The internal structure of Venus – the crust (outer layer), the mantle (middle layer) and the core (yellow inner layer)

Without seismic data or knowledge of its moment of inertia, little direct information is available about the internal structure and geochemistry of Venus. [54] The similarity in size and density between Venus and Earth suggests they share a similar internal structure: a core, mantle, and crust. Like that of Earth, the Venusian core is at least partially liquid because the two planets have been cooling at about the same rate. [55] The slightly smaller size of Venus means pressures are 24% lower in its deep interior than Earth's. [56] 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. [57] Instead, Venus may lose its internal heat in periodic major resurfacing events. [30]

Atmosphere and climate

Venuspioneeruv.jpg
Cloud structure in the Venusian atmosphere in 1979, revealed by observations in the ultraviolet band by Pioneer Venus Orbiter
Venus globe.jpg
Global radar view of Venus (without the clouds) from Magellan between 1990 and 1994

Venus has an extremely dense atmosphere composed of 96.5% carbon dioxide, 3.5% nitrogen, and traces of other gases, most notably sulfur dioxide. [58] The mass of its atmosphere is 93 times that of Earth's, whereas the pressure at its surface is about 92 times that at Earth's—a pressure equivalent to that at a depth of nearly 1 kilometre (0.62 mi) under Earth's oceans. The density at the surface is 65 kg/m3, 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 CO
2
-rich atmosphere generates the strongest greenhouse effect in the Solar System, creating surface temperatures of at least 735 K (462 °C; 864 °F). [13] [59] This makes Venus's surface hotter than Mercury's, which has a minimum surface temperature of 53 K (−220 °C; −364 °F) and maximum surface temperature of 700 K (427 °C; 801 °F), [60] [61] even though Venus is nearly twice Mercury's distance from the Sun and thus receives only 25% of Mercury's solar irradiance. This temperature is higher than that used for sterilization.

Studies have suggested that billions of years ago Venus's atmosphere was much more like Earth's than it is now, and that there may have been substantial quantities of liquid water on the surface, but after a period of 600 million to several billion years, [62] a runaway greenhouse effect was caused by the evaporation of that original water, which generated a critical level of greenhouse gases in its atmosphere. [63] Although the surface conditions on Venus are no longer hospitable to any Earthlike life that may have formed before this event, there is speculation on the possibility that life exists in the upper cloud layers of Venus, 50 km (31 mi) up from the surface, where the temperature ranges between 303 and 353 K (30 and 80 °C; 86 and 176 °F) but the environment is acidic. [64] [65] [66]

Thermal inertia and the transfer of heat by winds in the lower atmosphere mean that the temperature of Venus's surface does not vary significantly between the night and day sides, despite Venus's extremely 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 if the heat, pressure, and lack of oxygen were not a problem. [67]

Above the dense CO
2
layer are thick clouds consisting mainly of sulfuric acid, which is formed by sulfur dioxide and water through a chemical reaction resulting in sulfuric acid hydrate. Additionally, the atmosphere consists of approximately 1% ferric chloride. [68] [69] 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. [68] These clouds reflect and scatter about 90% of the sunlight that falls on them back into space, and prevent visual observation of Venus's surface. The permanent cloud cover means that although Venus is closer than Earth to the Sun, it receives less sunlight on the ground. Strong 300 km/h (185 mph) winds at the cloud tops go around Venus about every four to five Earth days. [70] Winds on Venus move at up to 60 times the speed of its rotation, whereas Earth's fastest winds are only 10–20% rotation speed. [71]

The surface of Venus is effectively isothermal; it retains a constant temperature not only between day and night sides but between the equator and the poles. [2] [72] Venus's minute axial tilt—less than 3°, compared to 23° on Earth—also minimises seasonal temperature variation. [73] The only appreciable variation in temperature occurs with altitude. The highest point on Venus, Maxwell Montes, is therefore the coolest point on Venus, with a temperature of about 655 K (380 °C; 715 °F) and an atmospheric pressure of about 4.5 MPa (45 bar). [74] [75] In 1995, the Magellan spacecraft imaged a highly reflective substance at the tops of the highest mountain peaks that bore a strong resemblance to terrestrial snow. This substance likely formed from a similar process to snow, albeit at a far higher temperature. Too volatile to condense on the surface, it rose in gaseous form to higher elevations, where it is cooler and could precipitate. The identity of this substance is not known with certainty, but speculation has ranged from elemental tellurium to lead sulfide (galena). [76]

The clouds of Venus may be capable of producing lightning. [77] 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 of that on Earth. [42] In 2007, Venus Express discovered that a huge double atmospheric vortex exists at the south pole. [78] [79]

Venus Express also discovered, in 2011, that an ozone layer exists high in the atmosphere of Venus. [80] On 29 January 2013, ESA scientists reported that the ionosphere of Venus streams outwards in a manner similar to "the ion tail seen streaming from a comet under similar conditions." [81] [82]

In December 2015 and to a lesser extent in April and May 2016, researchers working on Japan's Akatsuki mission observed bow shapes in the atmosphere of Venus. This was considered direct evidence of the existence of perhaps the largest stationary gravity waves in the solar system. [83] [84] [85]

Atmospheric composition
Synthetic atmosphere absorption spectrum.gif
Absorption spectrum of a simple gas mixture corresponding to Earth's atmosphere
Synthetic Venus atmosphere absorption spectrum.gif
The composition of the atmosphere of Venus based on HITRAN data [86] created using HITRAN on the Web system. [87]
Green colour – water vapour, red – carbon dioxide, WN – wavenumber (other colours have different meanings, lower wavelengths on the right, higher on the left).

Magnetic field and core

In 1967, Venera 4 found Venus's magnetic field to be much weaker than that of Earth. This magnetic field is induced by an interaction between the ionosphere and the solar wind, [88] [89] rather than by an internal dynamo as in the Earth's core. Venus's small induced magnetosphere provides negligible protection to the atmosphere against cosmic radiation.

The lack of an intrinsic magnetic field at Venus was surprising, given that it is similar to Earth in size, and was expected also to contain a dynamo at its core. A dynamo requires three things: a conducting liquid, rotation, and convection. The core is thought to be electrically conductive and, although its rotation is often thought to be too slow, simulations show it is adequate to produce a dynamo. [90] [91] This implies that the dynamo is missing because of a lack of convection in Venus's core. On Earth, convection occurs in the liquid outer layer of the core because the bottom of the liquid layer is much hotter than the top. On Venus, a global resurfacing event may have shut down plate tectonics and led to a reduced heat flux through the crust. This caused the mantle temperature to increase, thereby reducing the heat flux out of the core. As a result, no internal geodynamo is available to drive a magnetic field. Instead, the heat from the core is being used to reheat the crust. [92]

One possibility is that Venus has no solid inner core, [93] or that its core is not cooling, so that the entire liquid part of the core is at approximately the same temperature. Another possibility is that its core has already completely solidified. The state of the core is highly dependent on the concentration of sulfur, which is unknown at present. [92]

The weak magnetosphere around Venus means that the solar wind is interacting directly with its outer atmosphere. Here, ions of hydrogen and oxygen are being created by the dissociation of neutral molecules from ultraviolet radiation. The solar wind then supplies energy that gives some of these ions sufficient velocity to escape Venus's gravity field. This erosion process results in a steady loss of low-mass hydrogen, helium, and oxygen ions, whereas higher-mass molecules, such as carbon dioxide, are more likely to be retained. Atmospheric erosion by the solar wind probably led to the loss of most of Venus's water during the first billion years after it formed. [94] The erosion has increased the ratio of higher-mass deuterium to lower-mass hydrogen in the atmosphere 100 times compared to the rest of the solar system. [95]

Orbit and rotation

Venus orbits the Sun at an average distance of about 108 million kilometres (about 0.7 AU) and completes an orbit every 224.7 days. Venus is the second planet from the Sun and orbits the Sun approximately 1.6 times (yellow trail) in Earth's 365 days (blue trail) Venusorbitsolarsystem.gif
Venus orbits the Sun at an average distance of about 108 million kilometres (about 0.7  AU) and completes an orbit every 224.7 days. Venus is the second planet from the Sun and orbits the Sun approximately 1.6 times (yellow trail) in Earth's 365 days (blue trail)

Venus orbits the Sun at an average distance of about 0.72  AU (108 million  km ; 67 million  mi ), and completes an orbit every 224.7 days. Although all planetary orbits are elliptical, Venus's orbit is the closest to circular, with an eccentricity of less than 0.01. [2] 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). [2] The planet reaches inferior conjunction every 584 days, on average. [2] 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; then there are none for about 60,158 years. [96]

All the planets in the Solar System orbit the Sun in a anticlockwise direction as viewed from above Earth's north pole. Most planets also rotate on their axes in an anti-clockwise direction, but Venus rotates clockwise in retrograde rotation once every 243 Earth days—the slowest rotation of any planet. Because its rotation is so slow, Venus is very close to spherical. [97] A Venusian sidereal day thus lasts longer than a Venusian year (243 versus 224.7 Earth days). Venus's equator rotates at 6.52 km/h (4.05 mph), whereas Earth's rotates at 1,669.8 km/h (1,037.6 mph). [98] Venus's rotation has slowed down in the 16 years between the Magellan spacecraft and Venus Express visits; each Venusian sidereal day has increased by 6.5 minutes in that time span. [99] Because of the retrograde rotation, the length of a solar day on Venus is significantly shorter than the sidereal day, at 116.75 Earth days (making the Venusian solar day shorter than Mercury's 176 Earth days). [100] One Venusian year is about 1.92 Venusian solar days. [101] To an observer on the surface of Venus, the Sun would rise in the west and set in the east, [101] although Venus's opaque clouds prevent observing the Sun from the planet's surface. [102]

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. [103] [104] The 584-day average interval between successive close approaches to Earth is almost exactly equal to 5 Venusian solar days, [105] but the hypothesis of a spin–orbit resonance with Earth has been discounted. [106]

Venus has no natural satellites. [107] It has several trojan asteroids: the quasi-satellite 2002 VE68 [108] [109] and two other temporary trojans, 2001 CK32 and 2012 XE133 . [110] 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. [111] About 10 million years later, according to the study, another impact reversed the planet's spin direction and caused the Venusian moon gradually to spiral inward until it collided with Venus. [112] 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. [107]

Observation

Venus is always brighter than all other planets or stars (except the Sun) as seen from Earth. The second brightest object on the image is Jupiter. Venus-pacific-levelled.jpg
Venus is always brighter than all other planets or stars (except the Sun) as seen from Earth. The second brightest object on the image is Jupiter.

To the naked eye, Venus appears as a white point of light brighter than any other planet or star (apart from the Sun). [113] The planet's mean apparent magnitude is -4.14 with a standard deviation of 0.31. [12] The brightest magnitude occurs during crescent phase about one month before or after inferior conjunction. Venus fades to about magnitude −3 when it is backlit by the Sun. [114] The planet is bright enough to be seen in a clear midday sky [115] and 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. [116]

Venus "overtakes" Earth every 584 days as it orbits the Sun. [2] 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".

Phases

The phases of Venus and evolution of its apparent diameter Phases Venus.jpg
The phases of Venus and evolution of its apparent diameter

As it orbits the Sun, Venus displays phases like those of the Moon in a telescopic view. The planet appears as a small and "full" disc when it is on the opposite side of the Sun (at superior conjunction). Venus shows a larger disc and "quarter phase" at its maximum elongations from the Sun, and appears its brightest in the night sky. The planet presents a much larger thin "crescent" in telescopic views as it passes along the near side between Earth and the Sun. Venus displays its largest size and "new phase" when it is between Earth and the Sun (at inferior conjunction). Its atmosphere is visible through telescopes by the halo of sunlight refracted around it. [116]

Transits

2004 transit of Venus Venustransit 2004-06-08 07-49.jpg
2004 transit of Venus

The Venusian orbit is slightly inclined relative to Earth's orbit; thus, when the planet passes between Earth and the Sun, it usually does not cross the face of the Sun. Transits of Venus occur when the planet's inferior conjunction coincides with its presence in the plane of Earth's orbit. Transits of Venus occur in cycles of 243 years with the current pattern of transits being pairs of transits separated by eight years, at intervals of about 105.5 years or 121.5 years—a pattern first discovered in 1639 by the English astronomer Jeremiah Horrocks. [117]

The latest pair was June 8, 2004 and June 5–6, 2012. The transit could be watched live from many online outlets or observed locally with the right equipment and conditions. [118]

The preceding pair of transits occurred in December 1874 and December 1882; the following pair will occur in December 2117 and December 2125. [119] The oldest film known is the 1874 Passage de Venus , showing the 1874 Venus transit of the sun. 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 Horrocks in 1639. [120] Captain Cook's exploration of the east coast of Australia came after he had sailed to Tahiti in 1768 to observe a transit of Venus. [121] [122]

Pentagram of Venus

The pentagram of Venus. Earth is positioned at the centre of the diagram, and the curve represents the direction and distance of Venus as a function of time. Venus geocentric orbit curve simplified Line (pentagram).svg
The pentagram of Venus. Earth is positioned at the centre of the diagram, and the curve represents the direction and distance of Venus as a function of time.

The pentagram of Venus is the path that Venus makes as observed from Earth. Successive inferior conjunctions of Venus repeat very near a 13:8 orbital resonance (Earth orbits 8 times for every 13 orbits of Venus), shifting 144° upon sequential inferior conjunctions. The resonance 13:8 ratio is approximate. 8/13 is approximately 0.615385 while Venus orbits the Sun in 0.615187 years. [123]

Daylight apparitions

Naked eye observations of Venus during daylight hours exist in several anecdotes and records. Astronomer Edmund Halley calculated its maximum naked eye brightness in 1716, when many Londoners were alarmed by its appearance in the daytime. French emperor Napoleon Bonaparte once witnessed a daytime apparition of the planet while at a reception in Luxembourg. [124] 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. [125] Although naked eye visibility of Venus's phases is disputed, records exist of observations of its crescent. [126]

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. [127] [40]

Studies

Early studies

The "black drop effect" as recorded during the 1769 transit Venus Drawing.jpg
The "black drop effect" as recorded during the 1769 transit

Though some ancient civilizations referred to Venus both as the "morning star" and as the "evening star", names that reflect the assumption that these were two separate objects, the earliest recorded observations of Venus by the ancient Sumerians show that they recognized Venus as a single object, [128] and associated it with the goddess Inanna. [128] [129] [130] Inanna's movements in several of her myths, including Inanna and Shukaletuda and Inanna's Descent into the Underworld appear to parallel the motion of the planet Venus. [128] The Venus tablet of Ammisaduqa, believed to have been compiled around the mid-seventeenth century BCE, [131] shows the Babylonians understood the two were a single object, referred to in the tablet as the "bright queen of the sky", and could support this view with detailed observations. [132]

The Chinese historically referred to the morning Venus as "the Great White" (Tài-bái太白) or "the Opener (Starter) of Brightness" (Qǐ-míng啟明), and the evening Venus as "the Excellent West One" (Cháng-gēng長庚). [133]

The ancient Greeks also 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 BCE, [134] while Diogenes Laërtius argued that Parmenides was probably responsible for this rediscovery. [135] 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 are located between the Sun and the Earth. The 11th century Persian astronomer Avicenna claimed to have observed the transit of Venus, [136] which later astronomers took as confirmation of Ptolemy's theory. [137] In the 12th century, the Andalusian astronomer Ibn Bajjah observed "two planets as black spots on the face of the Sun"; these were later identified as the transits of Venus and Mercury by the Maragha astronomer Qotb al-Din Shirazi in the 13th century, though this identification cannot be true as there were no Venus transits in Ibn Bajjah's lifetime. [138] [n 2]

Galileo's discovery that Venus showed phases (although remaining near the Sun in Earth's sky) proved that it orbits the Sun and not Earth Phases-of-Venus.svg
Galileo's discovery that Venus showed phases (although remaining near the Sun in Earth's sky) proved that it orbits the Sun and not Earth

When the Italian physicist Galileo Galilei first observed the planet in the early 17th century, he found it showed phases like the Moon, varying from crescent to gibbous to full and vice versa. When Venus is furthest from the Sun in the sky, it shows a half-lit phase, and when it is closest to the Sun in the sky, it shows as a crescent or full phase. This could be possible only if Venus orbited the Sun, and this was among the first observations to clearly contradict the Ptolemaic geocentric model that the Solar System was concentric and centred on Earth. [141] [142]

The 1639 transit of Venus was accurately predicted by Jeremiah Horrocks and observed by him and his friend, William Crabtree, at each of their respective homes, on 4 December 1639 (24 November under the Julian calendar in use at that time). [143]

The atmosphere of Venus was discovered in 1761 by Russian polymath Mikhail Lomonosov. [144] [145] 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. [146] 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. [147]

Ground-based research

Modern telescopic view of Venus from Earth's surface Venus telescope.jpg
Modern telescopic view of Venus from Earth's surface

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, radar 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. [148]

Spectroscopic observations in the 1900s gave the first clues about the Venusian rotation. Vesto Slipher tried to measure the Doppler shift of light from Venus, but found he could not detect any rotation. He surmised the planet must have a much longer rotation period than had previously been thought. [149] Later work in the 1950s showed the rotation was retrograde. 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 modern value. [150]

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 (980 ft) radio telescope at Arecibo Observatory, and the echoes revealed two highly reflective regions, designated the Alpha and Beta regions. The observations also revealed a bright region attributed to mountains, which was called Maxwell Montes. [151] These three features are now the only ones on Venus that do not have female names. [34]

Exploration

Artist's impression of Mariner 2, launched in 1962, a skeletal, bottle-shaped spacecraft with a large radio dish on top Mariner 2.jpg
Artist's impression of Mariner 2 , launched in 1962, a skeletal, bottle-shaped spacecraft with a large radio dish on top

The first robotic space probe mission to Venus, and the first to any planet, began with the Soviet Venera program in 1961. [152] The United States' exploration of Venus had its first success with the Mariner 2 mission on 14 December 1962, becoming the world's first successful interplanetary mission, passing 34,833 km (21,644 mi) above the surface of Venus, and gathering data on the planet's atmosphere. [153] [154]

On 18 October 1967, the Soviet Venera 4 successfully entered the atmosphere and deployed science experiments. Venera 4 showed the surface temperature was hotter than Mariner 2 had calculated, at almost 500 °C (932 °F), determined that the atmosphere is 95% carbon dioxide (CO
2
), and discovered that Venus's atmosphere was considerably denser than Venera 4's designers had anticipated. [155] The joint Venera 4 Mariner 5 data were analysed by a combined Soviet–American science team in a series of colloquia over the following year, [156] in an early example of space cooperation. [157]

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.

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

In 1975, the Soviet Venera 9 and 10 landers transmitted the first images from the surface of Venus, which were in black and white. In 1982 the first colour images of the surface were obtained with the Soviet Venera 13 and 14 landers.

NASA obtained additional data in 1978 with the Pioneer Venus project that consisted of two separate missions: [158] Pioneer Venus Orbiter and Pioneer Venus Multiprobe. [159] The successful Soviet Venera program came to a close in October 1983, when Venera 15 and 16 were placed in orbit to conduct detailed mapping of 25% of Venus's terrain (from the north pole to 30°N latitude) [160]

Several other Venus flybys took place in the 1980s and 1990s that increased the understanding of Venus, including Vega 1 (1985), Vega 2 (1985), Galileo (1990), Magellan (1994), Cassini–Huygens (1998), and MESSENGER (2006). Then, Venus Express by the European Space Agency (ESA) entered orbit around Venus in April 2006. Equipped with seven scientific instruments, Venus Express provided unprecedented long-term observation of Venus's atmosphere. ESA concluded that mission in December 2014.

As of 2016, Japan's Akatsuki is in a highly elliptical orbit around Venus since 7 December 2015, and there are several probing proposals under study by Roscosmos, NASA, and India's ISRO.

In 2016, NASA announced that it was planning a rover, the Automaton Rover for Extreme Environments, designed to survive for an extended time in Venus's environmental conditions. It would be controlled by a mechanical computer and driven by wind power. [161]

In culture

Venus is portrayed just to the right of the large cypress tree in Vincent van Gogh's 1889 painting The Starry Night. Van Gogh - Starry Night - Google Art Project.jpg
Venus is portrayed just to the right of the large cypress tree in Vincent van Gogh's 1889 painting The Starry Night .

Venus is a primary feature of the night sky, and so has been of remarkable importance in mythology, astrology and fiction throughout history and in different cultures. Classical poets such as Homer, Sappho, Ovid and Virgil spoke of the star and its light. [164] Romantic poets such as William Blake, Robert Frost, Alfred Lord Tennyson and William Wordsworth wrote odes to it. [165]

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 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 indicates that the ancient Sumerians already knew that the morning and evening stars were the same celestial object. The Sumerians associated the planet with the goddess Inanna (known as Ishtar by the later Akkadians and Babylonians), and their myths of Inanna are often allegories for the apparent motions and cycles of the planet. [128] In the Old Babylonian period, the planet Venus was known as Ninsi'anna, and later as Dilbat. [166] 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 color of the morning and evening sky. [167] Venus is described in Babylonian cuneiform texts such as the Venus tablet of Ammisaduqa, which relates observations that possibly date from 1600 BC. [168]

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 [169] 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. [170] The word Shukra is also associated with semen, or generation. Venus 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. [171] [172] [173]

The Ancient Egyptians and Greeks believed Venus to be two separate bodies, a morning star and an evening star. The Egyptians knew the morning star as Tioumoutiri and the evening star as Ouaiti. [174] The Greeks used the names Phosphoros (meaning "light-bringer"; alternately Heosphoros, meaning "dawn-bringer") for the morning star, and Hesperus (meaning "Western one") for the evening star. [175] 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 Hesperus. [175] [176]

Venus was considered the most important celestial body observed by the Maya, who called it Chac ek, [177] or Noh Ek', "the Great Star". [178]

Modern fiction

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

The impenetrable Venusian cloud cover gave science fiction writers free rein to speculate on conditions at its surface; all the more so when early observations showed that not only was it similar in size to Earth, it possessed a substantial atmosphere. Closer to the Sun than Earth, the planet was frequently depicted as warmer, but still habitable by humans. [179] 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. [180] As scientific knowledge of Venus advanced, so science fiction authors tried to keep pace, particularly by conjecturing human attempts to terraform Venus. [181]

Symbol

Venus symbol.svg

The astronomical symbol for Venus is the same as that used in biology for the female sex: a circle with a small cross beneath. [182] The Venus symbol also represents femininity, and in Western alchemy stood for the metal copper. [182] Polished copper has been used for mirrors from antiquity, and the symbol for Venus has sometimes been understood to stand for the mirror of the goddess. [182]

Habitability

The speculation of the existence of life on Venus decreased significantly since the early 1960s, when spacecraft began studying Venus and it became clear that the conditions on Venus are extreme compared to those on Earth.

The fact that Venus is located closer to the Sun than Earth, raising temperatures on the surface to nearly 735 K (462 °C; 863 °F), the atmospheric pressure is ninety times that of Earth, and the extreme impact of the greenhouse effect, make water-based life as currently known unlikely. A few scientists have speculated that thermoacidophilic extremophile microorganisms might exist in the lower-temperature, acidic upper layers of the Venusian atmosphere. [183] [184] [185] The atmospheric pressure and temperature fifty kilometres above the surface are similar to those at Earth's surface. This has led to proposals to use aerostats (lighter-than-air balloons) for initial exploration and ultimately for permanent "floating cities" in the Venusian atmosphere. [186] Among the many engineering challenges are the dangerous amounts of sulfuric acid at these heights. [186]

See also

Notes

  1. Misstated as "Ganiki Chasma" in the press release and scientific publication. [48]
  2. Several claims of transit observations made by medieval Islamic astronomers have been shown to be sunspots. [139] Avicenna did not record the date of his observation. There was a transit of Venus within his lifetime, on 24 May 1032, although it is questionable whether it would have been visible from his location. [140]

    Related Research Articles

    Mercury (planet) Smallest and closest planet to the Sun in the Solar System

    Mercury is the smallest and innermost planet in the Solar System. Its orbital period around the Sun of 87.97 days is the shortest of all the planets in the Solar System. It is named after the Roman deity Mercury, the messenger of the gods.

    Solar System planetary system of the Sun

    The Solar System is the gravitationally bound planetary system of the Sun and the objects that orbit it, either directly or indirectly. Of the objects that orbit the Sun directly, the largest are the eight planets, with the remainder being smaller objects, such as the five dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly—the moons—two are larger than the smallest planet, Mercury.

    Saturn Sixth planet from the Sun in the Solar System

    Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius about nine times that of Earth. It has only one-eighth the average density of Earth, but with its larger volume Saturn is over 95 times more massive. Saturn is named after the Roman god of agriculture; its astronomical symbol (♄) represents the god's sickle.

    Uranus Seventh planet from the Sun in the Solar System

    Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. Uranus is similar in composition to Neptune, and both have bulk chemical compositions which differ from that of the larger gas giants Jupiter and Saturn. For this reason, scientists often classify Uranus and Neptune as "ice giants" to distinguish them from the gas giants. Uranus' atmosphere is similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium, but it contains more "ices" such as water, ammonia, and methane, along with traces of other hydrocarbons. It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K, and has a complex, layered cloud structure with water thought to make up the lowest clouds and methane the uppermost layer of clouds. The interior of Uranus is mainly composed of ices and rock.

    <i>Venus Express</i> space probe

    Venus Express (VEX) was the first Venus exploration mission of the European Space Agency (ESA). Launched in November 2005, it arrived at Venus in April 2006 and began continuously sending back science data from its polar orbit around Venus. Equipped with seven scientific instruments, the main objective of the mission was the long term observation of the Venusian atmosphere. The observation over such long periods of time had never been done in previous missions to Venus, and was key to a better understanding of the atmospheric dynamics. It was hoped that such studies can contribute to an understanding of atmospheric dynamics in general, while also contributing to an understanding of climate change on Earth. ESA concluded the mission in December 2014.

    Circumstellar habitable zone Zone around a star with strong possibilities for stable liquid water on a suitable planet

    In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure. The bounds of the CHZ are based on Earth's position in the Solar System and the amount of radiant energy it receives from the Sun. Due to the importance of liquid water to Earth's biosphere, the nature of the CHZ and the objects within it may be instrumental in determining the scope and distribution of Earth-like extraterrestrial life and intelligence.

    Venera 4 space probe

    Venera 4, also designated 1V (V-67) s/n 310 was a probe in the Soviet Venera program for the exploration of Venus. The probe comprised an entry probe, designed to enter the Venus atmosphere and parachute to the surface, and a carrier/flyby spacecraft, which carried the entry probe to Venus and served as a communications relay for the entry probe.

    Geology of Venus Geological structure and composition of the second planet from the Sun

    Venus is a planet with striking geology. Of all the other planets in the Solar System, it is the one nearest to Earth and most like it in terms of mass, but has no magnetic field or recognizable plate tectonic system. Much of the ground surface is exposed volcanic bedrock, some with thin and patchy layers of soil covering, in marked contrast with Earth, the Moon, and Mars. Some impact craters are present, but Venus is similar to Earth in that there are much fewer craters than on the other rocky planets that are largely covered by them. This is due in part to the thickness of the Venusian atmosphere disrupting small impactors before they strike the ground, but the paucity of large craters may be due to volcanic re-surfacing, possibly of a catastrophic nature. Volcanism appears to be the dominant agent of geological change on Venus. Some of the volcanic landforms appear to be unique to the planet. There are shield and composite volcanoes similar to those found on Earth. Given that Venus has approximately the same size, density, and composition as Earth, it is plausible that volcanism may be continuing on the planet today, although convincing direct observations of a volcanic eruption have not yet occurred, leaving modern volcanism an open question.

    Atmospheric escape

    Atmospheric escape is the loss of planetary atmospheric gases to outer space. A number of different mechanisms can be responsible for atmospheric escape, operating at different time scales; the most prominent is Jeans Escape, named after British astronomer Sir James Jeans, who described the process of atmospheric loss to the molecular kinetic energy. The relative importance of each loss process is a function of the planet's mass, its atmosphere composition, and its distance from its sun.

    Observations and explorations of Venus

    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.

    Terraforming of Venus

    The terraforming of Venus is the hypothetical process of engineering the global environment of the planet Venus in such a way as to make it suitable for human habitation. Terraforming Venus was first scholarly proposed by the astronomer Carl Sagan in 1961, although fictional treatments, such as The Big Rain of The Psychotechnic League by novelist Poul Anderson, preceded it. Adjustments to the existing environment of Venus to support human life would require at least three major changes to the planet's atmosphere:

    1. Reducing Venus' surface temperature of 462 °C
    2. eliminating most of the planet's dense 9.2 MPa (91 atm) carbon dioxide and sulfur dioxide atmosphere via removal or conversion to some other form
    3. the addition of breathable oxygen to the atmosphere.
    Formation and evolution of the Solar System Formation of the Solar System by gravitational collapse of a molecular cloud and subsequent geological history

    The formation and evolution of the Solar System began 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed.

    Atmosphere of Venus atmosphere of the planet Venus

    The atmosphere of Venus is the layer of gases surrounding Venus. It is composed primarily of carbon dioxide and is much denser and hotter than that of Earth. The temperature at the surface is 740 K, and the pressure is 93 bar (9.3 MPa), roughly the pressure found 900 m (3,000 ft) underwater on Earth. The Venusian atmosphere supports opaque clouds made of sulfuric acid, making optical Earth-based and orbital observation of the surface impossible. Information about the topography has been obtained exclusively by radar imaging. Aside from carbon dioxide, the other main component is nitrogen. Other chemical compounds are present only in trace amounts.

    Habitability of natural satellites

    The habitability of natural satellites is a measure of the potential of natural satellites to have environments hospitable to life. Habitable environments do not necessarily harbor life. Planetary habitability is an emerging study which is considered important to astrobiology for several reasons, foremost being that natural satellites are predicted to greatly outnumber planets and that it is hypothesized that habitability factors are likely to be similar to those of planets. There are, however, key environmental differences which have a bearing on moons as potential sites for extraterrestrial life.

    Life on Venus life on the planet Venus

    The speculation of life currently existing on Venus decreased significantly since the early 1960s, when spacecraft began studying Venus and it became clear that the conditions on Venus are extreme compared to those on Earth.

    Earth analog Another planet with environmental conditions similar to those found on the planet Earth

    An Earth analog is a planet or moon with environmental conditions similar to those found on Earth.

    Venus snow Brightening of the radar reflection from the surface of Venus at high elevations

    Venus snow is a brightening of the radar reflection from the surface of Venus at high elevations. The "snow" appears to be a mineral condensate of lead sulfide and bismuth sulfide precipitated from the atmosphere at altitudes above 2,600 m (8,500 ft).

    In astronomy a phase curve describes the brightness of a reflecting body as a function of its phase angle. The brightness usually refers the object's absolute magnitude, which, in turn, is its apparent magnitude at a distance of one astronomical unit from the Earth and Sun. The phase angle equals the arc subtended by the observer and the sun as measured at the body.

    The following outline is provided as an overview of and topical guide to Venus:

    References

    1. Lakdawalla, Emily (21 September 2009). "Venus Looks More Boring Than You Think It Does". The Planetary Society. Retrieved 4 December 2011.
    2. 1 2 3 4 5 6 7 8 9 10 11 12 Williams, David R. (15 April 2005). "Venus Fact Sheet". NASA. Archived from the original on 10 March 2016. Retrieved 12 October 2007.
    3. Yeomans, Donald K. "HORIZONS Web-Interface for Venus (Major Body=2)". JPL Horizons On-Line Ephemeris System .—Select "Ephemeris Type: Orbital Elements", "Time Span: 2000-01-01 12:00 to 2000-01-02". ("Target Body: Venus" and "Center: Sun" should be defaulted to.) Results are instantaneous osculating values at the precise J2000 epoch.
    4. 1 2 Simon, J.L.; Bretagnon, P.; Chapront, J.; Chapront-Touzé, M.; Francou, G.; Laskar, J. (February 1994). "Numerical expressions for precession formulae and mean elements for the Moon and planets". Astronomy and Astrophysics . 282 (2): 663–683. Bibcode:1994A&A...282..663S.
    5. "The MeanPlane (Invariable plane) of the Solar System passing through the barycenter". 3 April 2009. Archived from the original on 17 April 2012. Retrieved 10 April 2009. (produced with Solex 10 (Archived 29 April 2009 at WebCite ) written by Aldo Vitagliano; see also Invariable plane)
    6. 1 2 Seidelmann, P. Kenneth; Archinal, Brent A.; A'Hearn, Michael F.; et al. (2007). "Report of the IAU/IAG Working Group on cartographic coordinates and rotational elements: 2006". Celestial Mechanics and Dynamical Astronomy . 98 (3): 155–180. Bibcode:2007CeMDA..98..155S. doi:10.1007/s10569-007-9072-y.
    7. Konopliv, A. S.; Banerdt, W. B.; Sjogren, W. L. (May 1999). "Venus Gravity: 180th Degree and Order Model" (PDF). Icarus . 139 (1): 3–18. Bibcode:1999Icar..139....3K. CiteSeerX   10.1.1.524.5176 . doi:10.1006/icar.1999.6086. Archived from the original (PDF) on 26 May 2010.
    8. "Planets and Pluto: Physical Characteristics". NASA. 5 November 2008. Retrieved 26 August 2015.
    9. "Report on the IAU/IAG Working Group on cartographic coordinates and rotational elements of the planets and satellites". International Astronomical Union. 2000. Retrieved 12 April 2007.
    10. Mallama, Anthony; Krobusek, Bruce; Pavlov, Hristo (2017). "Comprehensive wide-band magnitudes and albedos for the planets, with applications to exo-planets and Planet Nine". Icarus. 282: 19–33. arXiv: 1609.05048 . Bibcode:2017Icar..282...19M. doi:10.1016/j.icarus.2016.09.023.
    11. Haus, R.; et al. (July 2016). "Radiative energy balance of Venus based on improved models of the middle and lower atmosphere". Icarus. 272: 178–205. Bibcode:2016Icar..272..178H. doi:10.1016/j.icarus.2016.02.048.
    12. 1 2 Mallama, Anthony; Hilton, James L. (October 2018). "Computing apparent planetary magnitudes for The Astronomical Almanac". Astronomy and Computing. 25: 10–24. arXiv: 1808.01973 . Bibcode:2018A&C....25...10M. doi:10.1016/j.ascom.2018.08.002.
    13. 1 2 "Venus: Facts & Figures". NASA. Archived from the original on 29 September 2006. Retrieved 12 April 2007.
    14. Castro, Joseph (3 February 2015). "What Would It Be Like to Live on Venus?". Space.com. Retrieved 15 March 2018.
    15. Lawrence, Pete (2005). "In Search of the Venusian Shadow". Digitalsky.org.uk. Archived from the original on 11 June 2012. Retrieved 13 June 2012.
    16. Walker, John. "Viewing Venus in Broad Daylight". Fourmilab Switzerland. Retrieved 19 April 2017.
    17. Hashimoto, G. L.; Roos-Serote, M.; Sugita, S.; Gilmore, M. S.; Kamp, L. W.; Carlson, R. W.; Baines, K. H. (2008). "Felsic highland crust on Venus suggested by Galileo Near-Infrared Mapping Spectrometer data". Journal of Geophysical Research: Planets . 113 (E9): E00B24. Bibcode:2008JGRE..113.0B24H. doi:10.1029/2008JE003134.
    18. David Shiga (10 October 2007). "Did Venus's ancient oceans incubate life?". New Scientist.
    19. Jakosky, Bruce M. (1999). "Atmospheres of the Terrestrial Planets". In Beatty, J. Kelly; Petersen, Carolyn Collins; Chaikin, Andrew. The New Solar System (4th ed.). Boston: Sky Publishing. pp. 175–200. ISBN   978-0-933346-86-4. OCLC   39464951.
    20. "Caught in the wind from the Sun". European Space Agency. 28 November 2007. Retrieved 12 July 2008.
    21. Evans, James (1998). The History and Practice of Ancient Astronomy. Oxford University Press. pp. 296–7. ISBN   978-0-19-509539-5 . Retrieved 4 February 2008.
    22. Lopes, Rosaly M. C.; Gregg, Tracy K. P. (2004). Volcanic worlds: exploring the Solar System's volcanoes. Springer Publishing. p. 61. ISBN   978-3-540-00431-8.
    23. "Atmosphere of Venus". The Encyclopedia of Astrobiology, Astronomy, and Spaceflght. Retrieved 29 April 2007.
    24. Mueller, Nils (2014). "Venus Surface and Interior". In Tilman, Spohn; Breuer, Doris; Johnson, T. V. Encyclopedia of the Solar System (3rd ed.). Oxford: Elsevier Science & Technology. ISBN   978-0-12-415845-0.
    25. Esposito, Larry W. (9 March 1984). "Sulfur Dioxide: Episodic Injection Shows Evidence for Active Venus Volcanism". Science . 223 (4640): 1072–1074. Bibcode:1984Sci...223.1072E. doi:10.1126/science.223.4640.1072. PMID   17830154 . Retrieved 29 April 2009.
    26. Bullock, Mark A.; Grinspoon, David H. (March 2001). "The Recent Evolution of Climate on Venus" (PDF). Icarus . 150 (1): 19–37. Bibcode:2001Icar..150...19B. CiteSeerX   10.1.1.22.6440 . doi:10.1006/icar.2000.6570. Archived from the original (PDF) on 23 October 2003.
    27. Basilevsky, Alexander T.; Head, James W., III (1995). "Global stratigraphy of Venus: Analysis of a random sample of thirty-six test areas". Earth, Moon, and Planets . 66 (3): 285–336. Bibcode:1995EM&P...66..285B. doi:10.1007/BF00579467.CS1 maint: Multiple names: authors list (link)
    28. Jones, Tom; Stofan, Ellen (2008). Planetology: Unlocking the Secrets of the Solar System. National Geographic Society. p. 74. ISBN   978-1-4262-0121-9.
    29. Kaufmann, W. J. (1994). Universe. New York: W. H. Freeman. p. 204. ISBN   978-0-7167-2379-0.
    30. 1 2 3 4 Nimmo, F.; McKenzie, D. (1998). "Volcanism and Tectonics on Venus". Annual Review of Earth and Planetary Sciences . 26 (1): 23–53. Bibcode:1998AREPS..26...23N. doi:10.1146/annurev.earth.26.1.23.
    31. 1 2 Strom, Robert G.; Schaber, Gerald G.; Dawson, Douglas D. (25 May 1994). "The global resurfacing of Venus". Journal of Geophysical Research . 99 (E5): 10899–10926. Bibcode:1994JGR....9910899S. doi:10.1029/94JE00388.
    32. 1 2 3 4 Frankel, Charles (1996). Volcanoes of the Solar System. Cambridge University Press. ISBN   978-0-521-47770-3.
    33. Batson, R.M.; Russell J. F. (18–22 March 1991). "Naming the Newly Found Landforms on Venus" (PDF). Proceedings of the Lunar and Planetary Science Conference XXII. Houston, Texas. p. 65. Retrieved 12 July 2009.
    34. 1 2 Carolynn Young, ed. (1 August 1990). The Magellan Venus Explorer's Guide. California: Jet Propulsion Laboratory. p. 93. Retrieved 13 January 2016.
    35. Davies, M. E.; Abalakin, V. K.; Bursa, M.; Lieske, J. H.; Morando, B.; Morrison, D.; Seidelmann, P. K.; Sinclair, A. T.; Yallop, B.; Tjuflin, Y. S. (1994). "Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements of the Planets and Satellites". Celestial Mechanics and Dynamical Astronomy. 63 (2): 127–148. Bibcode:1996CeMDA..63..127D. doi:10.1007/BF00693410.
    36. "USGS Astrogeology: Rotation and pole position for the Sun and planets (IAU WGCCRE)". United States Geological Survey. JPL Publication 90-24. Archived from the original on 24 October 2011. Retrieved 22 October 2009.
    37. Carolynn Young, ed. (1 August 1990). The Magellan Venus Explorer's Guide. California: Jet Propulsion Laboratory. pp. 99–100. Retrieved 13 January 2016.
    38. Karttunen, Hannu; Kroger, P.; Oja, H.; Poutanen, M.; Donner, K. J. (2007). Fundamental Astronomy. Springer. p. 162. ISBN   978-3-540-34143-7.
    39. Kranopol'skii, V. A. (1980). "Lightning on Venus according to Information Obtained by the Satellites Venera 9 and 10". Cosmic Research. 18 (3): 325–330. Bibcode:1980CosRe..18..325K.
    40. 1 2 Russell, C. T.; Phillips, J. L. (1990). "The Ashen Light". Advances in Space Research . 10 (5): 137–141. Bibcode:1990AdSpR..10..137R. doi:10.1016/0273-1177(90)90174-X.
    41. "Venera 12 Descent Craft". National Space Science Data Center . NASA. Retrieved 10 September 2015.
    42. 1 2 Russell, C. T.; Zhang, T. L.; Delva, M.; Magnes, W.; Strangeway, R. J.; Wei, H. Y. (November 2007). "Lightning on Venus inferred from whistler-mode waves in the ionosphere" (PDF). Nature . 450 (7170): 661–662. Bibcode:2007Natur.450..661R. doi:10.1038/nature05930. PMID   18046401.
    43. "Venus also zapped by lightning". CNN.com. 29 November 2007. Archived from the original on 30 November 2007. Retrieved 29 November 2007.
    44. Bauer, Markus (3 December 2012). "Have Venusian volcanoes been caught in the act?". European Space Agency. Archived from the original on 3 November 2013. Retrieved 20 June 2015.
    45. Glaze, Lori S. (August 1999). "Transport of SO
      2
      by explosive volcanism on Venus". Journal of Geophysical Research . 104 (E8): 18899–18906. Bibcode:1999JGR...10418899G. doi:10.1029/1998JE000619.
    46. Marcq, Emmanuel; Bertaux, Jean-Loup; Montmessin, Franck; Belyaev, Denis (January 2013). "Variations of sulphur dioxide at the cloud top of Venus's dynamic atmosphere". Nature Geoscience. 6 (1): 25–28. Bibcode:2013NatGe...6...25M. doi:10.1038/ngeo1650.
    47. "Ganis Chasma". Gazetteer of Planetary Nomenclature. USGS Astrogeology Science Center. Archived from the original on 14 December 2016. Retrieved 19 June 2015.
    48. 1 2 Lakdawalla, Emily (18 June 2015). "Transient hot spots on Venus: Best evidence yet for active volcanism". The Planetary Society . Retrieved 20 June 2015.
    49. "Hot lava flows discovered on Venus". European Space Agency. 18 June 2015. Archived from the original on 19 June 2015. Retrieved 20 June 2015.
    50. Shalygin, E. V.; Markiewicz, W. J.; Basilevsky, A. T.; Titov, D. V.; Ignatiev, N. I.; Head, J. W. (17 June 2015). "Active volcanism on Venus in the Ganiki Chasma rift zone". Geophysical Research Letters . 42 (12): 4762–4769. Bibcode:2015GeoRL..42.4762S. doi:10.1002/2015GL064088.
    51. Romeo, I.; Turcotte, D. L. (2009). "The frequency-area distribution of volcanic units on Venus: Implications for planetary resurfacing" (PDF). Icarus. 203 (1): 13–19. Bibcode:2009Icar..203...13R. doi:10.1016/j.icarus.2009.03.036.
    52. Herrick, R. R.; Phillips, R. J. (1993). "Effects of the Venusian atmosphere on incoming meteoroids and the impact crater population". Icarus. 112 (1): 253–281. Bibcode:1994Icar..112..253H. doi:10.1006/icar.1994.1180.
    53. Morrison, David; Owens, Tobias C. (2003). The Planetary System (3rd ed.). San Francisco: Benjamin Cummings. ISBN   978-0-8053-8734-6.
    54. Goettel, K. A.; Shields, J. A.; Decker, D. A. (16–20 March 1981). "Density constraints on the composition of Venus". Proceedings of the Lunar and Planetary Science Conference. Houston, TX: Pergamon Press. pp. 1507–1516. Bibcode:1982LPSC...12.1507G.
    55. Faure, Gunter; Mensing, Teresa M. (2007). Introduction to planetary science: the geological perspective. Springer eBook collection. Springer. p. 201. ISBN   978-1-4020-5233-0.
    56. Aitta, A. (April 2012), "Venus' internal structure, temperature and core composition", Icarus, 218 (2): 967–974, Bibcode:2012Icar..218..967A, doi:10.1016/j.icarus.2012.01.007 , retrieved 17 January 2016.
    57. Nimmo, F. (2002). "Crustal analysis of Venus from Magellan satellite observations at Atalanta Planitia, Beta Regio, and Thetis Regio". Geology . 30 (11): 987–990. Bibcode:2002Geo....30..987N. doi:10.1130/0091-7613(2002)030<0987:WDVLAM>2.0.CO;2. ISSN   0091-7613.
    58. Taylor, Fredric W. (2014). "Venus: Atmosphere". In Tilman, Spohn; Breuer, Doris; Johnson, T. V. Encyclopedia of the Solar System. Oxford: Elsevier Science & Technology. ISBN   978-0-12-415845-0 . Retrieved 12 January 2016.
    59. "Venus". Case Western Reserve University. 13 September 2006. Archived from the original on 26 April 2012. Retrieved 21 December 2011.
    60. Lewis, John S. (2004). Physics and Chemistry of the Solar System (2nd ed.). Academic Press. p. 463. ISBN   978-0-12-446744-6.
    61. Prockter, Louise (2005). Ice in the Solar System (PDF). Volume 26. Johns Hopkins APL Technical Digest. Archived from the original on September 11, 2006. Retrieved July 27, 2009.CS1 maint: BOT: original-url status unknown (link)
    62. Grinspoon, David H.; Bullock, M. A. (October 2007). "Searching for Evidence of Past Oceans on Venus". Bulletin of the American Astronomical Society . 39: 540. Bibcode:2007DPS....39.6109G.
    63. Kasting, J. F. (1988). "Runaway and moist greenhouse atmospheres and the evolution of Earth and Venus". Icarus. 74 (3): 472–494. Bibcode:1988Icar...74..472K. doi:10.1016/0019-1035(88)90116-9. PMID   11538226.
    64. Mullen, Leslie (13 November 2002). "Venusian Cloud Colonies". Astrobiology Magazine. Archived from the original on 16 August 2014.
    65. Landis, Geoffrey A. (July 2003). "Astrobiology: The Case for Venus" (PDF). Journal of the British Interplanetary Society. 56 (7–8): 250–254. Bibcode:2003JBIS...56..250L. NASA/TM—2003-212310. Archived from the original (PDF) on 7 August 2011.
    66. Cockell, Charles S. (December 1999). "Life on Venus". Planetary and Space Science . 47 (12): 1487–1501. Bibcode:1999P&SS...47.1487C. doi:10.1016/S0032-0633(99)00036-7.
    67. Moshkin, B. E.; Ekonomov, A. P.; Golovin Iu. M. (1979). "Dust on the surface of Venus". Kosmicheskie Issledovaniia (Cosmic Research). 17 (2): 280–285. Bibcode:1979CosRe..17..232M.
    68. 1 2 Krasnopolsky, V. A.; Parshev, V. A. (1981). "Chemical composition of the atmosphere of Venus". Nature. 292 (5824): 610–613. Bibcode:1981Natur.292..610K. doi:10.1038/292610a0.
    69. Krasnopolsky, Vladimir A. (2006). "Chemical composition of Venus atmosphere and clouds: Some unsolved problems". Planetary and Space Science . 54 (13–14): 1352–1359. Bibcode:2006P&SS...54.1352K. doi:10.1016/j.pss.2006.04.019.
    70. W. B. Rossow; A. D. del Genio; T. Eichler (1990). "Cloud-tracked winds from Pioneer Venus OCPP images". Journal of the Atmospheric Sciences . 47 (17): 2053–2084. Bibcode:1990JAtS...47.2053R. doi:10.1175/1520-0469(1990)047<2053:CTWFVO>2.0.CO;2. ISSN   1520-0469.
    71. Normile, Dennis (7 May 2010). "Mission to probe Venus's curious winds and test solar sail for propulsion". Science. 328 (5979): 677. Bibcode:2010Sci...328..677N. doi:10.1126/science.328.5979.677-a. PMID   20448159.
    72. Lorenz, Ralph D.; Lunine, Jonathan I.; Withers, Paul G.; McKay, Christopher P. (2001). "Titan, Mars and Earth: Entropy Production by Latitudinal Heat Transport" (PDF). Ames Research Center, University of Arizona Lunar and Planetary Laboratory. Retrieved 21 August 2007.
    73. "Interplanetary Seasons". NASA. Archived from the original on 16 October 2007. Retrieved 21 August 2007.
    74. Basilevsky A. T.; Head J. W. (2003). "The surface of Venus". Reports on Progress in Physics . 66 (10): 1699–1734. Bibcode:2003RPPh...66.1699B. doi:10.1088/0034-4885/66/10/R04.
    75. McGill, G. E.; Stofan, E. R.; Smrekar, S. E. (2010). "Venus tectonics". In T. R. Watters; R. A. Schultz. Planetary Tectonics. Cambridge University Press. pp. 81–120. ISBN   978-0-521-76573-2.
    76. Otten, Carolyn Jones (2004). ""Heavy metal" snow on Venus is lead sulfide". Washington University in St Louis . Retrieved 21 August 2007.
    77. Upadhyay, H. O.; Singh, R. N. (April 1995). "Cosmic ray Ionization of Lower Venus Atmosphere". Advances in Space Research . 15 (4): 99–108. Bibcode:1995AdSpR..15...99U. doi:10.1016/0273-1177(94)00070-H.
    78. Hand, Eric (November 2007). "European mission reports from Venus". Nature (450): 633–660. doi:10.1038/news.2007.297.
    79. Staff (28 November 2007). "Venus offers Earth climate clues". BBC News . Retrieved 29 November 2007.
    80. "ESA finds that Venus has an ozone layer too". European Space Agency. 6 October 2011. Retrieved 25 December 2011.
    81. "When A Planet Behaves Like A Comet". European Space Agency. 29 January 2013. Retrieved 31 January 2013.
    82. Kramer, Miriam (30 January 2013). "Venus Can Have 'Comet-Like' Atmosphere". Space.com . Retrieved 31 January 2013.
    83. Fukuhara, Tetsuya; Futaguchi, Masahiko; Hashimoto, George L.; et al. (16 January 2017). "Large stationary gravity wave in the atmosphere of Venus". Nature Geoscience. 10 (2): 85–88. Bibcode:2017NatGe..10...85F. doi:10.1038/ngeo2873 . Retrieved 17 January 2017.
    84. Rincon, Paul (16 January 2017). "Venus wave may be Solar System's biggest". BBC News. Retrieved 17 January 2017.
    85. Chang, Kenneth (16 January 2017). "Venus Smiled, With a Mysterious Wave Across Its Atmosphere". The New York Times. Retrieved 17 January 2017.
    86. "The HITRAN Database". Atomic and Molecular Physics Division, Harvard-Smithsonian Center for Astrophysics . Retrieved 8 August 2012. HITRAN is a compilation of spectroscopic parameters that a variety of computer codes use to predict and simulate the transmission and emission of light in the atmosphere.
    87. "HITRAN on the Web Information System". V.E. Zuev Institute of Atmospheric Optics . Retrieved 11 August 2012.
    88. Dolginov, Sh.; Eroshenko, E. G.; Lewis, L. (September 1969). "Nature of the Magnetic Field in the Neighborhood of Venus". Cosmic Research . 7: 675. Bibcode:1969CosRe...7..675D.
    89. Kivelson G. M.; Russell, C. T. (1995). Introduction to Space Physics. Cambridge University Press. ISBN   978-0-521-45714-9.
    90. Luhmann, J. G.; Russell, C. T. (1997). "Venus: Magnetic Field and Magnetosphere". In Shirley, J. H.; Fainbridge, R. W. Encyclopedia of Planetary Sciences. New York: Chapman and Hall. pp. 905–907. ISBN   978-1-4020-4520-2.
    91. Stevenson, D. J. (15 March 2003). "Planetary magnetic fields" (PDF). Earth and Planetary Science Letters . 208 (1–2): 1–11. Bibcode:2003E&PSL.208....1S. doi:10.1016/S0012-821X(02)01126-3.
    92. 1 2 Nimmo, Francis (November 2002). "Why does Venus lack a magnetic field?" (PDF). Geology. 30 (11): 987–990. Bibcode:2002Geo....30..987N. doi:10.1130/0091-7613(2002)030<0987:WDVLAM>2.0.CO;2. ISSN   0091-7613 . Retrieved 28 June 2009.
    93. Konopliv, A. S.; Yoder, C. F. (1996). "Venusian k2 tidal Love number from Magellan and PVO tracking data". Geophysical Research Letters . 23 (14): 1857–1860. Bibcode:1996GeoRL..23.1857K. doi:10.1029/96GL01589. Archived from the original on 12 May 2011. Retrieved 12 July 2009.
    94. Svedhem, Håkan; Titov, Dmitry V.; Taylor, Fredric W.; Witasse, Olivier (November 2007). "Venus as a more Earth-like planet". Nature. 450 (7170): 629–632. Bibcode:2007Natur.450..629S. doi:10.1038/nature06432. PMID   18046393.
    95. Donahue, T. M.; Hoffman, J. H.; Hodges, R. R.; Watson, A. J. (1982). "Venus Was Wet: A Measurement of the Ratio of Deuterium to Hydrogen". Science. 216 (4546): 630–633. Bibcode:1982Sci...216..630D. doi:10.1126/science.216.4546.630. ISSN   0036-8075. PMID   17783310.
    96. "Venus Close Approaches to Earth as predicted by Solex 11". Archived from the original on 9 August 2012. Retrieved 19 March 2009. Numbers generated by Solex
    97. Squyres, Steven W. (2016). "Venus". Encyclopædia Britannica Online. Retrieved 7 January 2016.
    98. Bakich, Michael E. (2000). "Rotational velocity (equatorial)". The Cambridge Planetary Handbook. Cambridge University Press. p. 50. ISBN   978-0-521-63280-5.
    99. "Could Venus Be Shifting Gear?". Venus Express. European Space Agency. 10 February 2012. Retrieved 7 January 2016.
    100. "Planetary Facts". The Planetary Society. Archived from the original on 11 May 2012. Retrieved 20 January 2016.
    101. 1 2 "Space Topics: Compare the Planets". The Planetary Society. Archived from the original on 18 February 2006. Retrieved 12 January 2016.
    102. Serge Brunier (2002). Solar System Voyage. Translated by Dunlop, Storm. Cambridge University Press. p. 40. ISBN   978-0-521-80724-1.
    103. Correia, Alexandre C. M.; Laskar, Jacques; De Surgy, Olivier Néron (May 2003). "Long-Term Evolution of the Spin of Venus, Part I: Theory" (PDF). Icarus. 163 (1): 1–23. Bibcode:2003Icar..163....1C. doi:10.1016/S0019-1035(03)00042-3.
    104. Laskar, Jacques; De Surgy, Olivier Néron (2003). "Long-Term Evolution of the Spin of Venus, Part II: Numerical Simulations" (PDF). Icarus. 163 (1): 24–45. Bibcode:2003Icar..163...24C. doi:10.1016/S0019-1035(03)00043-5.
    105. Gold, T.; Soter, S. (1969). "Atmospheric Tides and the Resonant Rotation of Venus". Icarus. 11 (3): 356–66. Bibcode:1969Icar...11..356G. doi:10.1016/0019-1035(69)90068-2.
    106. Shapiro, I. I.; Campbell, D. B.; De Campli, W. M. (June 1979). "Nonresonance Rotation of Venus". Astrophysical Journal . 230: L123–L126. Bibcode:1979ApJ...230L.123S. doi:10.1086/182975.
    107. 1 2 Sheppard, Scott S.; Trujillo, Chadwick A. (July 2009). "A Survey for Satellites of Venus". Icarus. 202 (1): 12–16. arXiv: 0906.2781 . Bibcode:2009Icar..202...12S. doi:10.1016/j.icarus.2009.02.008.
    108. Mikkola, S.; Brasser, R.; Wiegert, P.; Innanen, K. (July 2004). "Asteroid 2002 VE68: A Quasi-Satellite of Venus". Monthly Notices of the Royal Astronomical Society . 351 (3): L63. Bibcode:2004MNRAS.351L..63M. doi:10.1111/j.1365-2966.2004.07994.x.
    109. De la Fuente Marcos, Carlos; De la Fuente Marcos, Raúl (November 2012). "On the Dynamical Evolution of 2002 VE68". Monthly Notices of the Royal Astronomical Society . 427 (1): 728–39. arXiv: 1208.4444 . Bibcode:2012MNRAS.427..728D. doi:10.1111/j.1365-2966.2012.21936.x.
    110. De la Fuente Marcos, Carlos; De la Fuente Marcos, Raúl (June 2013). "Asteroid 2012 XE133: A Transient Companion to Venus". Monthly Notices of the Royal Astronomical Society. 432 (2): 886–93. arXiv: 1303.3705 . Bibcode:2013MNRAS.432..886D. doi:10.1093/mnras/stt454.
    111. Musser, George (10 October 2006). "Double Impact May Explain Why Venus Has No Moon". Scientific American . Retrieved 7 January 2016.
    112. Tytell, David (10 October 2006). "Why Doesn't Venus Have a Moon?". Sky & Telescope . Retrieved 7 January 2016.
    113. Dickinson, Terrence (1998). NightWatch: A Practical Guide to Viewing the Universe. Buffalo, NY: Firefly Books. p. 134. ISBN   978-1-55209-302-3 . Retrieved 12 January 2016.
    114. Mallama, A. (2011). "Planetary magnitudes". Sky & Telescope. 121 (1): 51–56.
    115. Tony Flanders (25 February 2011). "See Venus in Broad Daylight!". Sky & Telescope . Retrieved 11 January 2016.
    116. 1 2 Espenak, Fred (1996). "Venus: Twelve year planetary ephemeris, 1995–2006". NASA Reference Publication 1349. NASA/Goddard Space Flight Center. Archived from the original on 17 August 2000. Retrieved 20 June 2006.
    117. Anon. "Transit of Venus". History. University of Central Lancashire. Archived from the original on 30 July 2012. Retrieved 14 May 2012.
    118. Boyle, Alan (5 June 2012). "Venus transit: A last-minute guide". NBC News. Archived from the original on 18 June 2013. Retrieved 11 January 2016.
    119. Espenak, Fred (2004). "Transits of Venus, Six Millennium Catalog: 2000 BCE to 4000 CE". Transits of the Sun. NASA. Retrieved 14 May 2009.
    120. Kollerstrom, Nicholas (1998). "Horrocks and the Dawn of British Astronomy". University College London . Retrieved 11 May 2012.
    121. Hornsby, T. (1771). "The quantity of the Sun's parallax, as deduced from the observations of the transit of Venus on June 3, 1769". Philosophical Transactions of the Royal Society. 61: 574–579. doi:10.1098/rstl.1771.0054.
    122. Woolley, Richard (1969). "Captain Cook and the Transit of Venus of 1769". Notes and Records of the Royal Society of London . 24 (1): 19–32. doi:10.1098/rsnr.1969.0004. ISSN   0035-9149. JSTOR   530738.
    123. Baez, John (4 January 2014). "The Pentagram of Venus". Azimuth. Archived from the original on 14 December 2015. Retrieved 7 January 2016.
    124. Chatfield, Chris (2010). "The Solar System with the naked eye". The Gallery of Natural Phenomena. Retrieved 19 April 2017.
    125. Gaherty, Geoff (26 March 2012). "Planet Venus Visible in Daytime Sky Today: How to See It". Space.com. Retrieved 19 April 2017.
    126. Goines, David Lance (18 October 1995). "Inferential Evidence for the Pre-telescopic Sighting of the Crescent Venus". Goines.net. Retrieved 19 April 2017.
    127. Baum, R. M. (2000). "The enigmatic ashen light of Venus: an overview". Journal of the British Astronomical Association . 110: 325. Bibcode:2000JBAA..110..325B.
    128. 1 2 3 4 Cooley, Jeffrey L. (2008). "Inana and Šukaletuda: A Sumerian Astral Myth". KASKAL. 5: 161–172. ISSN   1971-8608.
    129. Black, Jeremy; Green, Anthony (1992). Gods, Demons and Symbols of Ancient Mesopotamia: An Illustrated Dictionary. The British Museum Press. pp. 108–109. ISBN   978-0-7141-1705-8.
    130. Nemet-Nejat, Karen Rhea (1998), Daily Life in Ancient Mesopotamia, Daily Life, Greenwood, p. 203, ISBN   978-0313294976
    131. Hobson, Russell (2009). The Exact Transmission of Texts in the First Millennium B.C.E. (PDF) (Ph.D.). University of Sydney, Department of Hebrew, Biblical and Jewish Studies.
    132. Waerden, Bartel (1974). Science awakening II: the birth of astronomy. Springer. p. 56. ISBN   978-90-01-93103-2 . Retrieved 10 January 2011.
    133. Needham, Joseph (1959). Science and Civilisation in China, Volume 3: Mathematics and the Sciences of the Heavens and the Earth. Science and Civilisation in China: Volume 3. 3. Cambridge: Cambridge University Press. p. 398. Bibcode:1959scc3.book.....N. ISBN   978-0-521-05801-8.
    134. Pliny the Elder (1991). Natural History II:36–37. translated by John F. Healy. Harmondsworth, Middlesex, UK: Penguin. pp. 15–16.
    135. Burkert, Walter (1972). Lore and Science in Ancient Pythagoreanism. Harvard University Press. p. 307. ISBN   978-0-674-53918-1.
    136. Goldstein, Bernard R. (March 1972). "Theory and Observation in Medieval Astronomy". Isis . 63 (1): 39–47 [44]. doi:10.1086/350839.
    137. "AVICENNA viii. Mathematics and Physical Sciences". Encyclopedia Iranica.
    138. S. M. Razaullah Ansari (2002). History of Oriental Astronomy: Proceedings of the Joint Discussion-17 at the 23rd General Assembly of the International Astronomical Union, Organised by the Commission 41 (History of Astronomy), Held in Kyoto, August 25–26, 1997. Springer Science+Business Media. p. 137. ISBN   978-1-4020-0657-9.
    139. J.M. Vaquero; M. Vázquez (2009). The Sun Recorded Through History. Springer Science & Business Media. p. 75. ISBN   978-0-387-92790-9.
    140. Fredrick Kennard. Thought Experiments: Popular Thought Experiments in Philosophy, Physics, Ethics, Computer Science & Mathematics. p. 113. ISBN   978-1-329-00342-2.
    141. Palmieri, Paolo (2001). "Galileo and the discovery of the phases of Venus". Journal for the History of Astronomy . 21 (2): 109–129. Bibcode:2001JHA....32..109P.
    142. Fegley Jr, B (2003). Heinrich D. Holland; Karl K. Turekian, eds. Venus. Treatise on Geochemistry. Elsevier. pp. 487–507. ISBN   978-0-08-043751-4.
    143. Kollerstrom, Nicholas (2004). "William Crabtree's Venus transit observation" (PDF). Proceedings IAU Colloquium No. 196, 2004: 34. Bibcode:2005tvnv.conf...34K. doi:10.1017/S1743921305001249 . Retrieved 10 May 2012.
    144. Marov, Mikhail Ya. (2004). D.W. Kurtz, ed. Mikhail Lomonosov and the discovery of the atmosphere of Venus during the 1761 transit. Proceedings of IAU Colloquium No. 196. Preston, U.K.: Cambridge University Press. pp. 209–219. Bibcode:2005tvnv.conf..209M. doi:10.1017/S1743921305001390.
    145. "Mikhail Vasilyevich Lomonosov". Encyclopædia Britannica Online. Retrieved 12 July 2009.
    146. Russell, H. N. (1899). "The Atmosphere of Venus". Astrophysical Journal. 9: 284–299. Bibcode:1899ApJ.....9..284R. doi:10.1086/140593.
    147. Hussey, T. (1832). "On the Rotation of Venus". Monthly Notices of the Royal Astronomical Society. 2 (11): 78–126. Bibcode:1832MNRAS...2...78H. doi:10.1093/mnras/2.11.78d.
    148. Ross, F. E. (1928). "Photographs of Venus". Astrophysical Journal. 68–92: 57. Bibcode:1928ApJ....68...57R. doi:10.1086/143130.
    149. Slipher, V. M. (1903). "A Spectrographic Investigation of the Rotation Velocity of Venus". Astronomische Nachrichten . 163 (3–4): 35–52. Bibcode:1903AN....163...35S. doi:10.1002/asna.19031630303.
    150. Goldstein, R. M.; Carpenter, R. L. (1963). "Rotation of Venus: Period Estimated from Radar Measurements". Science. 139 (3558): 910–911. Bibcode:1963Sci...139..910G. doi:10.1126/science.139.3558.910. PMID   17743054.
    151. Campbell, D. B.; Dyce, R. B.; Pettengill G. H. (1976). "New radar image of Venus". Science. 193 (4258): 1123–1124. Bibcode:1976Sci...193.1123C. doi:10.1126/science.193.4258.1123. PMID   17792750.
    152. Mitchell, Don (2003). "Inventing The Interplanetary Probe". The Soviet Exploration of Venus. Retrieved 27 December 2007.
    153. Mayer; McCullough & Sloanaker (January 1958). "Observations of Venus at 3.15-cm Wave Length". The Astrophysical Journal. 127: 1. Bibcode:1958ApJ...127....1M. doi:10.1086/146433.
    154. Jet Propulsion Laboratory (1962). "Mariner-Venus 1962 Final Project Report" (PDF). SP-59. NASA.
    155. Mitchell, Don (2003). "Plumbing the Atmosphere of Venus". The Soviet Exploration of Venus. Retrieved 27 December 2007.
    156. "Report on the Activities of the COSPAR Working Group VII". Preliminary Report, COSPAR Twelfth Plenary Meeting and Tenth International Space Science Symposium. Prague, Czechoslovakia: National Academy of Sciences. 11–24 May 1969. p. 94.
    157. Sagdeev, Roald; Eisenhower, Susan (28 May 2008). "United States-Soviet Space Cooperation during the Cold War" . Retrieved 19 July 2009.
    158. Colin, L.; Hall, C. (1977). "The Pioneer Venus Program". Space Science Reviews . 20 (3): 283–306. Bibcode:1977SSRv...20..283C. doi:10.1007/BF02186467.
    159. Williams, David R. (6 January 2005). "Pioneer Venus Project Information". NASA/Goddard Space Flight Center. Retrieved 19 July 2009.
    160. Greeley, Ronald; Batson, Raymond M. (2007). Planetary Mapping. Cambridge University Press. p. 47. ISBN   978-0-521-03373-2 . Retrieved 19 July 2009.
    161. Hall, Loura (1 April 2016). "Automaton Rover for Extreme Environments (AREE)". NASA. Retrieved 29 August 2017.
    162. Whitney, Charles A. (September 1986). "The Skies of Vincent van Gogh". Art History. 9 (3): 356.
    163. Boime, Albert (December 1984). "Van Gogh's Starry Night: A History of Matter and a Matter of History" (PDF). Arts Magazine: 88.
    164. Aaron J. Atsma. "Eospheros & Hespheros". Theoi.com. Retrieved 15 January 2016.
    165. Dava Sobel (2005). The Planets. Harper Publishing. pp. 53–70. ISBN   978-0-14-200116-5.
    166. Enn Kasak, Raul Veede. Understanding Planets in Ancient Mesopotamia. Folklore Vol. 16. Mare Kõiva & Andres Kuperjanov, Eds. ISSN 1406-0957
    167. Heimpel, W. 1982. "A catalog of Near Eastern Venus deities." Syro-Mesopotamian Studies 4/3: 9-22.
    168. 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.
    169. Bhalla, Prem P. (2006). Hindu Rites, Rituals, Customs and Traditions: A to Z on the Hindu Way of Life. Pustak Mahal. p. 29. ISBN   978-81-223-0902-7.
    170. Behari, Bepin; Frawley, David (2003). Myths & Symbols of Vedic Astrology (2nd ed.). Lotus Press. pp. 65–74. ISBN   978-0-940985-51-3.
    171. 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.
    172. 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   978-0415056090.
    173. Hulbert, Homer Bezaleel (1909). The passing of Korea. Doubleday, Page & company. p. 426. Retrieved 2010-01-08.
    174. Cattermole, Peter John; Moore, Patrick (1997). Atlas of Venus. Cambridge University Press. p. 9. ISBN   978-0-521-49652-0.
    175. 1 2 "Lucifer" in Encyclopaedia Britannica]
    176. Cicero, De Natura Deorum.
    177. The Book of Chumayel: The Counsel Book of the Yucatec Maya, 1539-1638. Richard Luxton. 1899. pp. 6, 194. ISBN   9780894122446.
    178. 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.
    179. Miller, Ron (2003). Venus. Twenty-First Century Books. p. 12. ISBN   978-0-7613-2359-4.
    180. Dick, Steven (2001). Life on Other Worlds: The 20th-Century Extraterrestrial Life Debate. Cambridge University Press. p. 43. ISBN   978-0-521-79912-6.
    181. Seed, David (2005). A Companion to Science Fiction. Blackwell Publishing. pp. 134–135. ISBN   978-1-4051-1218-5.
    182. 1 2 3 Stearn, William (May 1968). "The Origin of the Male and Female Symbols of Biology". Taxon . 11 (4): 109–113. doi:10.2307/1217734. JSTOR   1217734.
    183. Clark, Stuart (26 September 2003). "Acidic clouds of Venus could harbour life". New Scientist. Retrieved 30 December 2015.
    184. Redfern, Martin (25 May 2004). "Venus clouds 'might harbour life'". BBC News. Retrieved 30 December 2015.
    185. Dartnell, Lewis R.; Nordheim, Tom Andre; Patel, Manish R.; Mason, Jonathon P.; et al. (September 2015). "Constraints on a potential aerial biosphere on Venus: I. Cosmic rays". Icarus. 257: 396–405. Bibcode:2015Icar..257..396D. doi:10.1016/j.icarus.2015.05.006 . Retrieved 20 August 2015.
    186. 1 2 Landis, Geoffrey A. (2003). "Colonization of Venus". AIP Conference Proceedings. 654. pp. 1193–1198. doi:10.1063/1.1541418. Archived from the original on 11 July 2012.

    Cartographic resources