Astronomy

Venusian polar surface temperatures

Venusian polar surface temperatures


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I've stumbled across several articles about how the Venusian polar high atmosphere is really cold. What these articles appear to fail to specify is what the surface temperatures of the poles are. I am interested in knowing the polar surface temperatures. I would think that convection would lower the polar surface temperature to lower amounts, but I don't know a lot about Venus's poles to say anything about this.


Venus's surface temperature is hot everywhere at about 460⁰C. There may some small differences due to latitude, but not nearly as pronounced as on Earth or Mars. The supercritial CO2 that forms the lower atmosphere is a good conductor of heat, keeping surface temperatures very stable.

The article you refer to notes that models of the Venusian atmosphere predict somewhat higher temperatures at high altitude and latitude than can be inferred from measurements made during aerobraking. This tells us that the models of the atmosphere need to be tweaked. It doesn't mean that there is a region of cool temperatures at the poles.


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. [1] [2] [3] Terraforming Venus was first proposed in a scholarly context by the astronomer Carl Sagan in 1961, [4] 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: [3]

  1. Reducing Venus's surface temperature of 737 K (464 °C 867 °F) [5]
  2. Eliminating most of the planet's dense 9.2 MPa (91 atm) carbon dioxide and sulfur dioxideatmosphere via removal or conversion to some other form
  3. The addition of breathable oxygen to the atmosphere.

These three changes are closely interrelated because Venus's extreme temperature is due to the high pressure of its dense atmosphere and the greenhouse effect.


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The surface of Venus is comparatively flat. When 93% of the topography was mapped by Pioneer Venus Orbiter, scientists found that the total distance from the lowest point to the highest point on the entire surface was about 13 kilometres (8.1 mi), about the same as the vertical distance between the Earth's ocean floor and the higher summits of the Himalayas. This similarity is to be expected as the maximum attainable elevation contrasts on a planet are largely dictated by the strength of the planet's gravity and the mechanical strength of its lithosphere, these are similar for Earth and Venus. [2] : 183

According to data from the Pioneer Venus Orbiter altimeters, nearly 51% of the surface is located within 500 meters (1640 feet) of the median radius of 6,052 km (3,761 mi) only 2% of the surface is located at elevations greater than 2 kilometres (1.2 mi) from the median radius.

The altimetry experiment of Magellan confirmed the general character of the landscape. According to the Magellan data, 80% of the topography is within 1 km (0.62 mi) of the median radius. The most important elevations are in the mountain chains that surround Lakshmi Planum: Maxwell Montes (11 km, 6.8 mi), Akna Montes (7 km, 4.3 mi) and Freya Montes (7 km, 4.3 mi). Despite the relatively flat landscape of Venus, the altimetry data also found large inclined plains. Such is the case on the southwest side of Maxwell Montes, which in some parts seems to be inclined some 45°. Inclinations of 30° were registered in Danu Montes and Themis Regio.

About 75% of the surface is composed of bare rock.

Based on altimeter data from the Pioneer Venus Orbiter probe, supported by Magellan data, the topography of the planet is divided into three provinces: lowlands, deposition plains, and highlands.

Highlands Edit

This unit covers about 10% of the planet's surface, with elevations greater than 2 km (1.2 mi). The largest provinces of the highlands are Aphrodite Terra, Ishtar Terra, and Lada Terra, as well as the regions Beta Regio, Phoebe Regio and Themis Regio. The regions Alpha Regio, Bell Regio, Eistla Regio and Tholus Regio are smaller regions of highlands.

Some of the terrain in these areas is particularly efficient at reflecting radar signals. [3] : p. 1 This is possibly analogous to snow lines on Earth and is likely related to temperatures and pressures there being lower than in the other provinces due to the higher elevation, which allows for distinct mineralogy to occur. [note 1] It is thought that high-elevation rock formations may contain or be coated by minerals that have high dielectric constants. [3] : 1 The high dielectric minerals would be stable at the ambient temperatures in the highlands, but not on the plains that comprise the rest of the planet's surface. Pyrite, an iron sulfide, matches these criteria and is widely suspected as a possible cause it would be produced by chemical weathering of the volcanic highlands after long-term exposure to the sulfur-bearing Venusian atmosphere. [5] The presence of pyrite on Venus has been contested, with atmospheric modeling showing that it might not be stable under Venusian atmospheric conditions. [6] Other hypotheses have been put forward to explain the higher radar reflectivity in the highlands, including the presence of a ferroelectric material whose dielectric constant changes with temperature (with Venus having a changing temperature gradient with elevation). [7] It has been observed that the character of the radar-bright highlands is not consistent across the surface of Venus. For example, Maxwell Montes shows the sharp, snow line-like change in reflectivity that is consistent with a change in mineralogy, whereas Ovda Regio shows a more gradual brightening upwards trend. The brightening upwards trend on Ovda Regio is consistent with a ferroelectric signature, and has been suggested to indicate the presence of chlorapatite. [8]

Deposition plains Edit

Deposition plains have elevations averaging 0 to 2 km and cover more than half of the planet's surface.

Lowlands Edit

The rest of the surface is lowlands and generally lies below zero elevation. Radar reflectivity data suggest that at a centimeter scale these areas are smooth, as a result of gradation (accumulation of fine material eroded from the highlands).

Ten spacecraft have successfully landed on Venus and returned data, all were flown by the Soviet Union. Venera 9, 10, 13, and 14 had cameras and returned images of soil and rock. Spectrophotometry results showed that these four missions kicked up dust clouds on landing, which means that some of the dust particles must be smaller than about 0.02 mm. The rocks at all four sites showed fine layers, some layers were more reflective than others. Experiments on rocks at the Venera 13 and 14 sites found that they were porous and easily crushed (bearing maximum loads of 0.3 to 1 MPa) [note 2] these rocks may be weakly lithified sediments or volcanic tuff. [4] : 1709 Spectrometry found that the surface materials at the Venera 9, 10, 14 and Vega 1 and 2 landing had chemical compositions similar to tholeiitic basalts, while the Venera 8 and 13 sites chemically resembled alkaline basalts. [4] : 1707–1709

Earth-based radar surveys made it possible to identify some topographic patterns related to craters, and the Venera 15 and Venera 16 probes identified almost 150 such features of probable impact origin. Global coverage from Magellan subsequently made it possible to identify nearly 900 impact craters.

Compared to Mercury, the Moon and other such bodies, Venus has very few craters. In part, this is because Venus's dense atmosphere burns up smaller meteorites before they hit the surface. [11] The Venera and Magellan data are in agreement: there are very few impact craters with a diameter less than 30 kilometres (19 mi), and data from Magellan show an absence of any craters less than 2 kilometres (1.2 mi) in diameter. The small craters are irregular and appear in groups, thus pointing to the deceleration and the breakup of impactors. [11] However, there are also fewer of the large craters, and those appear relatively young they are rarely filled with lava, showing that they were formed after volcanic activity in the area ceased, and radar data indicates that they are rough and have not had time to be eroded down.

Compared to the situation on bodies such as the Moon, it is more difficult to determine the ages of different areas of the surface on Venus, on the basis of crater counts, due to the small number of craters at hand. [12] However, the surface characteristics are consistent with a completely random distribution, [13] implying that the surface of the entire planet is roughly the same age, or at least that very large areas are not very different in age from the average.

Taken together, this evidence suggests that the surface of Venus is geologically young. The impact crater distribution appears to be most consistent with models that call for a near-complete resurfacing of the planet. Subsequent to this period of extreme activity, process rates declined and impact craters began to accumulate, with only minor modification and resurfacing since.

A young surface all created at the same time is a different situation compared with any of the other terrestrial planets.

Age estimates based on crater counts indicate a young surface, in contrast to the much older surfaces of Mars, Mercury, and the Moon. [note 3] For this to be the case on a planet without crustal recycling by plate tectonics requires explanation. One hypothesis is that Venus underwent some sort of global resurfacing about 300–500 million years ago that erased the evidence of older craters. [14]

One possible explanation for this event is that it is part of a cyclic process on Venus. On Earth, plate tectonics allows heat to escape from the mantle by advection, the transport of mantle material to the surface and the return of old crust to the mantle. But Venus has no evidence of plate tectonics, so this theory states that the interior of the planet heats up (due to the decay of radioactive elements) until material in the mantle is hot enough to force its way to the surface. [15] The subsequent resurfacing event covers most or all of the planet with lava, until the mantle is cool enough for the process to start over.

The surface of Venus is dominated by volcanism. Although Venus is superficially similar to Earth, it seems that the tectonic plates so active in Earth's geology do not exist on Venus. About 80% of the planet consists of a mosaic of volcanic lava plains, dotted with more than a hundred large isolated shield volcanoes, and many hundreds of smaller volcanoes and volcanic constructs such as coronae. These are geological features believed to be almost unique to Venus: huge, ring-shaped structures 100–300 kilometers (60–180 mi) across and rising hundreds of meters above the surface. The only other place they have been discovered is on Uranus's moon Miranda. It is believed that they are formed when plumes of rising hot material in the mantle push the crust upwards into a dome shape, which then collapses in the centre as the molten lava cools and leaks out at the sides, leaving a crown-like structure: the corona.

Differences can be seen in volcanic deposits. In many cases, volcanic activity is localized to a fixed source, and deposits are found in the vicinity of this source. This kind of volcanism is called "centralized volcanism," in that volcanoes and other geographic features form distinct regions. The second type of volcanic activity is not radial or centralized flood basalts cover wide expanses of the surface, similar to features such as the Deccan Traps on Earth. These eruptions result in "flow type" volcanoes.

Volcanoes less than 20 kilometres (12 mi) in diameter are very abundant on Venus and they may number hundreds of thousands or even millions. Many appear as flattened domes or 'pancakes', thought to be formed in a similar way to shield volcanoes on Earth. [ citation needed ] [note 4] These pancake dome volcanoes are fairly round features that are less than 1-kilometre (0.62 mi) in height and many times that in width. It is common to find groups of hundreds of these volcanoes in areas called shield fields. The domes of Venus are between 10 and 100 times larger than those formed on Earth. They are usually associated with "coronae" and tesserae. The pancakes are thought to be formed by highly viscous, silica-rich lava erupting under Venus's high atmospheric pressure. Domes called scalloped margin domes (commonly called ticks because they appear as domes with numerous legs), are thought to have undergone mass wasting events such as landslides on their margins. Sometimes deposits of debris can be seen scattered around them.

On Venus, volcanoes are mainly of the shield type. [ citation needed ] Nevertheless, the morphology of the shield volcanoes of Venus is different from shield volcanoes on Earth. On the Earth, shield volcanoes can be a few tens of kilometers wide and up to 10 kilometers high (6.2 mi) in the case of Mauna Kea, measured from the sea floor. On Venus, these volcanoes can cover hundreds of kilometers in area, but they are relatively flat, with an average height of 1.5 kilometres (0.93 mi).

Other unique features of Venus's surface are novae (radial networks of dikes or grabens) and arachnoids. A nova is formed when large quantities of magma are extruded onto the surface to form radiating ridges and trenches which are highly reflective to radar. These dikes form a symmetrical network around the central point where the lava emerged, where there may also be a depression caused by the collapse of the magma chamber.

Arachnoids are so named because they resemble a spider's web, featuring several concentric ovals surrounded by a complex network of radial fractures similar to those of a nova. It is not known whether the 250 or so features identified as arachnoids actually share a common origin, or are the result of different geological processes.

Despite the fact that Venus appears to have no global plate tectonic system as such, the planet's surface shows various features associated with local tectonic activity. Features such as faults, folds, and volcanoes are present there and may be driven largely by processes in the mantle.

The active volcanism of Venus has generated chains of folded mountains, rift valleys, and terrain known as tesserae, a word meaning "floor tiles" in Greek. Tesserae exhibit the effects of eons of compression and tensional deformation.

Unlike those on Earth, the deformations on Venus are directly related to regional dynamic forces within the planet's mantle. Gravitational studies suggest that Venus differs from Earth in lacking an asthenosphere—a layer of lower viscosity and mechanical weakness that allows Earth's crustal tectonic plates to move. The apparent absence of this layer on Venus suggests that the deformation of the Venusian surface must be explained by convective movements within the planet's mantle.

The tectonic deformations on Venus occur on a variety of scales, the smallest of which are related to linear fractures or faults. In many areas these faults appear as networks of parallel lines. Small, discontinuous mountain crests are found which resemble those on the Moon and Mars. The effects of extensive tectonism are shown by the presence of normal faults, where the crust has sunk in one area relative to the surrounding rock, and superficial fractures. Radar imaging shows that these types of deformation are concentrated in belts located in the equatorial zones and at high southern latitudes. These belts are hundreds of kilometers wide and appear to interconnect across the whole of the planet, forming a global network associated with the distribution of volcanoes.

The rifts of Venus, formed by the expansion of the lithosphere, are groups of depressions tens to hundreds of meters wide and extending up to 1,000 km (620 mi) in length. The rifts are mostly associated with large volcanic elevations in the form of domes, such as those at Beta Regio, Atla Regio and the western part of Eistla Regio. These highlands seem to be the result of enormous mantle plumes (rising currents of magma) which have caused elevation, fracturing, faulting, and volcanism.

The highest mountain chain on Venus, Maxwell Montes in Ishtar Terra, was formed by processes of compression, expansion, and lateral movement. Another type of geographical feature, found in the lowlands, consists of ridge belts elevated several meters above the surface, hundreds of kilometers wide and thousands of kilometers long. Two major concentrations of these belts exist: one in Lavinia Planitia near the southern pole, and the second adjacent to Atalanta Planitia near the northern pole.

Tesserae are found mainly in Aphrodite Terra, Alpha Regio, Tellus Regio and the eastern part of Ishtar Terra (Fortuna Tessera). These regions contain the superimposition and intersection of grabens of different geological units, indicating that these are the oldest parts of the planet. It was once thought that the tesserae were continents associated with tectonic plates like those of the Earth in reality they are probably the result of floods of basaltic lava forming large plains, which were then subjected to intense tectonic fracturing. [4]

Venus's crust appears to be 70 kilometres (43 mi) thick, and composed of silicate rocks. [4] : 1729 Venus's mantle is approximately 2,840 kilometres (1,760 mi) thick, its chemical composition is probably similar to that of chondrites. [4] : 1729 Since Venus is a terrestrial planet, it is presumed to have a core made of semisolid iron and nickel with a radius of approximately 3,000 kilometres (1,900 mi). [ citation needed ]

The unavailability of seismic data from Venus severely limits what can be definitely known about the structure of the planet's mantle, but models of Earth's mantle have been modified to make predictions. It's expected that the uppermost mantle, from about 70 kilometres (43 mi) to 480 kilometres (300 mi) deep is mostly made of the mineral olivine. Descending through the mantle, the chemical composition remains largely the same but at somewhere between about 480 kilometres (300 mi) and 760 kilometres (470 mi), the increasing pressure causes the crystal structure of olivine to change to the more densely packed structure of spinel. Another transition occurs between 760 kilometres (470 mi) and 1,000 kilometres (620 mi) deep, where the material takes on the progressively more compact crystal structures of ilmenite and perovskite, and gradually becomes more like perovskite until the core boundary is reached. [4] : 1729–1730

Venus is similar to Earth in size and density, and so probably also in bulk composition, but it does not have a significant magnetic field. [4] : 1729–1730 Earth's magnetic field is produced by what is known as the core dynamo, consisting of an electrically conducting liquid, the nickel-iron outer core that rotates and is convecting. Venus is expected to have an electrically conductive core of similar composition, and although its rotation period is very long (243.7 Earth days), simulations show that this is adequate to produce a dynamo. [16] This implies that Venus lacks convection in its outer core. Convection occurs when there is a large difference in temperature between the inner and outer part of the core, but since Venus has no plate tectonics to let off heat from the mantle, it is possible that outer core convection is being suppressed by a warm mantle. It's also possible that Venus may lack a solid inner core for the same reason, if the core is either too hot or is not under enough pressure to allow molten nickel-iron to freeze there. [4] : 1730 [note 5]

Lava flows on Venus are often much larger than Earth's, up to several hundred kilometers long and tens of kilometers wide. It is still unknown why these lava fields or lobate flows reach such sizes, but it is suggested that they are the result of very large eruptions of basaltic, low-viscosity lava spreading out to form wide, flat plains. [4]

On Earth, there are two known types of basaltic lava: ʻaʻa and pāhoehoe. ʻAʻa lava presents a rough texture in the shape of broken blocks (clinkers). Pāhoehoe lava is recognized by its pillowy or ropy appearance. Rough surfaces appear bright in radar images, which can be used to determine the differences between ʻaʻa and pāhoehoe lavas. These variations can also reflect differences in lava age and preservation. Channels and lava tubes (channels that have cooled down and over which a dome has formed) are very common on Venus. Two planetary astronomers from the University of Wollongong in Australia, Dr Graeme Melville and Prof. Bill Zealey, researched these lava tubes, using data supplied by NASA, over a number of years and concluded that they were widespread and up to ten times the size of those on the Earth. Melville and Zealey said that the gigantic size of the Venusian lava tubes (tens of meters wide and hundreds of kilometers long) may be explained by the very fluid lava flows together with the high temperatures on Venus, allowing the lava to cool slowly.

For the most part, lava flow fields are associated with volcanoes. The central volcanoes are surrounded by extensive flows that form the core of the volcano. They are also related to fissure craters, coronae, dense clusters of volcanic domes, cones, wells and channels.

Thanks to Magellan, more than 200 channels and valley complexes have been identified. The channels were classified as simple, complex, or compound. Simple channels are characterized by a single, long main channel. This category includes rills similar to those found on the Moon, and a new type, called canali, consisting of long, distinct channels which maintain their width throughout their entire course. The longest such channel identified (Baltis Vallis) has a length of more than 6,800 kilometres (4,200 mi), about one-sixth of the circumference of the planet.

Complex channels include anastomosed networks, in addition to distribution networks. This type of channel has been observed in association with several impact craters and important lava floods related to major lava flow fields. Compound channels are made of both simple and complex segments. The largest of these channels shows an anastomosed web and modified hills similar to those present on Mars.

Although the shape of these channels is highly suggestive of fluid erosion, there is no evidence that they were formed by water. In fact, there is no evidence of water anywhere on Venus in the last 600 million years. While the most popular theory for the channels' formation is that they are the result of thermal erosion by lava, there are other hypotheses, including that they were formed by heated fluids formed and ejected during impacts.

Wind Edit

Liquid water and ice are nonexistent on Venus, and thus the only agent of physical erosion to be found (apart from thermal erosion by lava flows) is wind. Wind tunnel experiments have shown that the density of the atmosphere allows the transport of sediments with even a small breeze. [17] Therefore, the seeming rarity of eolian land forms must have some other cause. [18] This implies that transportable sand-size particles are relatively scarce on the planet which would be a result of very slow rates of mechanical erosion. [19] : p. 112 The process that is most important for the production of sediment on Venus may be crater-forming impact events, which is bolstered by the seeming association between impact craters and downwind eolian land forms. [20] [21] [22]

This process is manifest in the ejecta of impact craters expelled onto the surface of Venus. The material ejected during a meteorite impact is lifted to the atmosphere, where winds transport the material toward the west. As the material is deposited on the surface, it forms parabola-shaped patterns. This type of deposit can be established on top of various geologic features or lava flows. Therefore, these deposits are the youngest structures on the planet. Images from Magellan reveal the existence of more than 60 of these parabola-shaped deposits that are associated with crater impacts.

The ejection material, transported by the wind, is responsible for the process of renovation of the surface at speeds, according to the measurements of the Venera soundings, of approximately one metre per second. Given the density of the lower Venusian atmosphere, the winds are more than sufficient to provoke the erosion of the surface and the transportation of fine-grained material. In the regions covered by ejection deposits one may find wind lines, dunes, and yardangs. The wind lines are formed when the wind blows ejection material and volcanic ash, depositing it on top of topographic obstacles such as domes. As a consequence, the leeward sides of domes are exposed to the impact of small grains that remove the surface cap. Such processes expose the material beneath, which has a different roughness, and thus different characteristics under radar, compared to formed sediment.

The dunes are formed by the depositing of particulates that are the size of grains of sand and have wavy shapes. Yardangs are formed when the wind-transported material carves the fragile deposits and produces deep furrows.

The line-shaped patterns of wind associated with impact craters follow a trajectory in the direction of the equator. This tendency suggests the presence of a system of circulation of Hadley cells between medium latitudes and the equator. Magellan radar data confirm the existence of strong winds that blow toward the east in the upper surface of Venus, and meridional winds on the surface.

Chemical erosion Edit

Chemical and mechanical erosion of the old lava flows is caused by reactions of the surface with the atmosphere in the presence of carbon dioxide and sulfur dioxide (see carbonate–silicate cycle for details). These two gases are the planet's first and third most abundant gases, respectively the second most abundant gas is inert nitrogen. The reactions probably include the deterioration of silicates by carbon dioxide to produce carbonates and quartz, as well as the deterioration of silicates by sulfur dioxide to produce anhydrate calcium sulfate and carbon dioxide.

NASA's Goddard Institute for Space Studies and others have postulated that Venus may have had a shallow ocean in the past for up to 2 billion years, [23] [24] [25] [26] [27] with as much water as Earth. [28] Depending on the parameters used in their theoretical model, the last liquid water could have evaporated as recently as 715 million years ago. [25] Currently, the only known water on Venus is in the form of a tiny amount of atmospheric vapor (20 ppm). [29] [30] Hydrogen, a component of water, is still being lost to space nowadays as detected by ESA's Venus Express spacecraft. [28]


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As one of the brightest objects in the sky, Venus has been known since prehistoric times, and as such, many ancient cultures recorded observations of the planet. 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 named the planet after the goddess Inanna, who was known as Ishtar by the later Akkadians and Babylonians. [1] She had a dual role as a goddess of both love and war, thereby representing a deity that presided over birth and death. [2] [3] One of the oldest surviving astronomical documents, from the Babylonian library of Ashurbanipal around 1600 BC, is a 21-year record of the appearances of Venus.

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 immediately recognize Venus as single entity instead, they assumed it to be two separate stars on each horizon: the morning star and the evening star. The Ancient Egyptians, for example, believed Venus to be two separate bodies and knew the morning star as Tioumoutiri and the evening star as Ouaiti. [4] The Ancient Greeks called the morning star Φωσφόρος , Phosphoros (Latinized Phosphorus), the "Bringer of Light" or Ἐωσφόρος , Eosphoros (Latinized Eosphorus), the "Bringer of Dawn". The evening star they called Hesperos (Latinized Hesperus) ( Ἓσπερος , the "star of the evening"). [5] By Hellenistic times, the ancient Greeks identified it as a single planet, [6] [7] which they named after their goddess of love, Aphrodite (Αφροδίτη) (Phoenician Astarte), [8] a planetary name that is retained in modern Greek. [9] Hesperos became a loanword in Latin as Vesper and Phosphoros was translated as Lucifer ("Light Bearer").

Venus was considered the most important celestial body observed by the Maya, who called it Chac ek, [10] or Noh Ek', "the Great Star". The Maya monitored the movements of Venus closely and observed it in daytime. The positions of Venus and other planets were thought to influence life on Earth, so the Maya and other ancient Mesoamerican cultures timed wars and other important events based on their observations. In the Dresden Codex, the Maya included an almanac showing Venus's full cycle, in five sets of 584 days each (approximately eight years), after which the patterns repeated (since Venus has a synodic period of 583.92 days). [11] The Maya civilization developed a religious calendar, based in part upon the motions of the planet, and held the motions of Venus to determine the propitious time for events such as war. They also named it Xux Ek', the Wasp Star. The Maya were aware of the planet's synodic period, and could compute it to within a hundredth part of a day. [12]

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

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

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

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

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

Before radio observations in the 1960s, many believed that Venus contained a lush, Earth-like environment. This was due to the planet's size and orbital radius, which suggested a fairly Earth-like situation as well as to the thick layer of clouds which prevented the surface from being seen. Among the speculations on Venus were that it had a jungle-like environment or that it had oceans of either petroleum or carbonated water. However, microwave observations by C. Mayer et al., [13] indicated a high-temperature source (600 K). Strangely, millimetre-band observations made by A. D. Kuzmin indicated much lower temperatures. [14] Two competing theories explained the unusual radio spectrum, one suggesting the high temperatures originated in the ionosphere, and another suggesting a hot planetary surface.

In September 2020 a team at Cardiff University announced that observations of Venus using the James Clerk Maxwell Telescope and Atacama Large Millimeter Array in 2017 and 2019 indicated that the Venusian atmosphere contained phosphine (PH3) in concentrations 10,000 times higher than those that could be ascribed to any known non-biological source on Venus. The phosphine was detected at heights of at least 30 miles above the surface of Venus, and was detected primarily at mid-latitudes with none detected at the poles of Venus. This indicates the potential presence of biological organisms on Venus. [15] [16]

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

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

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

Early flybys Edit

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

The first successful flyby Venus probe was the American Mariner 2 spacecraft, which flew past Venus in 1962, coming within 35,000 km. A modified Ranger Moon probe, it established that Venus has practically no intrinsic magnetic field and measured the temperature of the planet's atmosphere to be approximately 500 °C (773 K 932 °F). [17]

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

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

Early landings Edit

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

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

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

The first successful landing on Venus was by Venera 7 on December 15, 1970 — the first successful soft (non-crash) landing on another planet, as well as the first successful transmission of data from another planet’s surface to Earth. [18] [19] Venera 7 remained in contact with Earth for 23 minutes, relaying surface temperatures of 455 °C to 475 °C (855 °F to 885 °F). Venera 8 landed on July 22, 1972. In addition to pressure and temperature profiles, a photometer showed that the clouds of Venus formed a layer ending over 35 kilometres (22 mi) above the surface. A gamma ray spectrometer analyzed the chemical composition of the crust.

Lander/orbiter pairs Edit

Venera 9 and 10 Edit

The Soviet probe Venera 9 entered orbit on October 22, 1975, becoming the first artificial satellite of Venus. A battery of cameras and spectrometers returned information about the planet's clouds, ionosphere and magnetosphere, as well as performing bi-static radar measurements of the surface. The 660 kg (1,455 lb) descent vehicle [21] separated from Venera 9 and landed, taking the first pictures of the surface and analyzing the crust with a gamma ray spectrometer and a densitometer. During descent, pressure, temperature and photometric measurements were made, as well as backscattering and multi-angle scattering (nephelometer) measurements of cloud density. It was discovered that the clouds of Venus are formed in three distinct layers. On October 25, Venera 10 arrived and carried out a similar program of study.

Pioneer Venus Edit

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

Further Soviet missions Edit

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

In 1982, the Soviet Venera 13 sent the first colour image of Venus's surface and analysed the X-ray fluorescence of an excavated soil sample. The probe operated for a record 127 minutes on the planet's hostile surface. Also in 1982, the Venera 14 lander detected possible seismic activity in the planet's crust.

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

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

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

Orbiters Edit

Venera 15 and 16 Edit

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

Magellan Edit

On August 10, 1990, the American Magellan probe, named after the explorer Ferdinand Magellan, arrived at its orbit around the planet and started a mission of detailed radar mapping at a frequency of 2.38 GHz. [22] Whereas previous probes had created low-resolution radar maps of continent-sized formations, Magellan mapped 98% of the surface with a resolution of approximately 100 m. The resulting maps were comparable to visible-light photographs of other planets, and are still the most detailed in existence. Magellan greatly improved scientific understanding of the geology of Venus: the probe found no signs of plate tectonics, but the scarcity of impact craters suggested the surface was relatively young, and there were lava channels thousands of kilometers long. After a four-year mission, Magellan, as planned, plunged into the atmosphere on October 11, 1994, and partly vaporized some sections are thought to have hit the planet's surface.

Venus Express Edit

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

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

Akatsuki Edit

Akatsuki was launched on May 20, 2010, by JAXA, and was planned to enter Venusian orbit in December 2010. However, the orbital insertion maneuver failed and the spacecraft was left in heliocentric orbit. It was placed on an alternative elliptical Venerian orbit on 7 December 2015 by firing its attitude control thrusters for 1233-seconds. [23] The probe will image the surface in ultraviolet, infrared, microwaves, and radio, and look for evidence of lightning and volcanism on the planet. Astronomers working on the mission reported detecting a possible gravity wave that occurred on the planet Venus in December 2015. [24]

Recent flybys Edit

Several space probes en route to other destinations have used flybys of Venus to increase their speed via the gravitational slingshot method. These include the Galileo mission to Jupiter and the Cassini–Huygens mission to Saturn (two flybys). Rather curiously, during Cassini's examination of the radio frequency emissions of Venus with its radio and plasma wave science instrument during both the 1998 and 1999 flybys, it reported no high-frequency radio waves (0.125 to 16 MHz), which are commonly associated with lightning. This was in direct opposition to the findings of the Soviet Venera missions 20 years earlier. It was postulated that perhaps if Venus did have lightning, it might be some type of low-frequency electrical activity, because radio signals cannot penetrate the ionosphere at frequencies below about 1 megahertz. At the University of Iowa, Donald Gurnett's examination of Venus's radio emissions by the Galileo spacecraft during its flyby in 1990 were interpreted at the time to be indicative of lightning. However the Galileo probe was over 60 times further from Venus than Cassini was during its flyby, making its observations substantially less significant. The mystery as to whether or not Venus does in fact have lightning in its atmosphere was not solved until 2007, when the scientific journal Nature published a series of papers giving the initial findings of Venus Express. It confirmed the presence of lightning on Venus and that it is more common on Venus than it is on Earth. [25] [26]

MESSENGER passed by Venus twice on its way to Mercury. The first time, it flew by on October 24, 2006, passing 3000 km from Venus. As Earth was on the other side of the Sun, no data was recorded. [27] The second flyby was on July 6, 2007, where the spacecraft passed only 325 km from the cloudtops. [28]

BepiColombo flew by Venus on October 15th, 2020. It is set to pass near Venus a second time before arriving at Mercury. [29] During this approach, two monitoring cameras and seven science instruments were switched on.


Extended Data Fig. 1 Magellan SAR image of Mead Basin.

Radar-bright regions highlight faults surrounding the crater, with the main bright faults being the circumferential ring faults. Note the terrace zone comprised of extensive small-scale faults in between the main ring faults. Image courtesy of NASA JPL, Magellan Mission, Image PIA00148.

Extended Data Fig. 2 Thermal profile and strength profiles for combinations of crustal thicknesses and thermal gradients for models with 723 K surface temperature and 30 km crust.

a, Thermal profile. b, Strength profile. The different crustal thicknesses are highlighted by the dashed lines in b. The thermal profiles are the same regardless of the crustal thickness used, but the strength profiles show a discontinuity associated with the compositional difference.

Extended Data Fig. 3 Thermal profile and strength profiles for combinations of crustal thicknesses and thermal gradients for models with 350 K surface temperature and 30 km crust.

a, Thermal profile. b, Strength profile. The different crustal thicknesses are highlighted by the dashed lines in b. The thermal profiles are the same regardless of the crustal thickness used, but the strength profiles show a discontinuity associated with the compositional difference.

Extended Data Fig. 4 Influence of surface temperature and thermal gradient on ring fault spacing.

af, Inner and outer ring fault locations are shown for models with surface temperatures of 723 K (red) and 350 K (blue) for combinations of projectile sizes and crustal thicknesses. Ring locations are binned according to the thermal gradient tested (shown along the x-axis). Projectile size and crustal thickness are noted in the upper left corner of each panel. Data for each surface temperature are offset for clarity. Inner ring fault locations, defined as the innermost fault intersecting the basin floor or along the basin wall, are marked by circles outer ring fault locations, defined as the outermost fault that intersects the surface at or beyond the basin rim, are marked by squares. A line spans the range of fault diameters for simulations with both inner and outer rings. Distances shown have an uncertainty of approximately ±5 km.

Extended Data Fig. 5 Effect of thermal gradient on basin ring location and spacing for basins formed with a 24-km-diameter projectile, 723 K surface temperature and 30 km crust.

af, A series of 3× vertically exaggerated plots highlighting ring fault locations and the associated displacement. Vertical grey bars mark the current surface locations of Mead Basin’s ring faults 17 and are intended to guide the eye. All plots are taken 500 s after impact. Tracer lines are coloured according to composition, with black lines representing a basalt crust and blue lines representing a dunite mantle. Tracers lines are initially horizontal and spaced 1 km apart.

Extended Data Fig. 6 Effect of thermal gradient on basin ring location and spacing for basins formed with a 30-km-diameter projectile, 723 K surface temperature and 30 km crust.

af, A series of 3× vertically exaggerated plots highlighting ring fault locations and the associated displacement. Vertical grey bars mark the current surface locations of Mead Basin’s ring faults 17 and are intended to guide the eye. All plots are taken 500 s after impact. Tracer lines are coloured according to composition, with black lines representing a basalt crust and blue lines representing a dunite mantle. Tracers lines are initially horizontal and spaced 1 km apart.

Extended Data Fig. 7 Effect of crustal thickness on material strength.

Material strength is plotted for two thermal gradients (6 K km −1 and 14 K km −1 ), showing how the depth of transition from a basaltic crust to a dunite mantle affects the target strength. Surface temperature is 723 K for each case.

Extended Data Fig. 8 Effect of thermal gradient on basin ring location and spacing for basins formed with a 36-km-diameter projectile striking a 20-km-thick basaltic crust on a target with 723 K surface temperature.

af, A series of 3× vertically exaggerated plot highlighting ring fault locations and the associated displacement. Vertical grey bars mark the current surface locations of Mead Basin’s ring faults 17 and are intended to guide the eye. All plots are taken 500 s after impact. Tracer lines are coloured according to composition, with black lines representing a basalt crust and blue lines representing a dunite mantle. Tracers lines are initially horizontal and spaced 1 km apart.

Extended Data Fig. 9 Effect of thermal gradient on basin ring location and spacing for basins formed with a 36-km-diameter projectile, 350 K surface temperature and 30 km crust.

af, A series of 3× vertically exaggerated plot highlighting ring fault locations and the associated displacement. Vertical grey bars mark the current surface locations of Mead Basin’s ring faults 17 and are intended to guide the eye. All plots are taken 500 s after impact. Tracer lines are coloured according to composition, with black lines representing a basalt crust and blue lines representing a dunite mantle. Tracers lines are initially horizontal and spaced 1 km apart.


Venus

Background

With the exception of Earth, Venus is the largest of the terrestrial planets, with a diameter of 95% of Earth's. It is similar to Earth in a number ways, with a mass 80% of Earth's, and a slightly lower density. However, its orbit is significantly closer to the Sun, with a mean radius of 0.72 Au. Furthermore, Venus's rotation is very slow, with a period of 243 days, longer than the Venusian year of 225 days!. The slow rotation is probably the reason why Venus does not possess a significant global magnetic field.

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Environment

Unlike Mercury, Venus has a thick atmosphere, which accounts for the planet's high albedo of 0.57. The first close-up study of Venus was undertaken by the Mariner 2 spacecraft, which revealed high surface temperatures (in excess of 400C), and very little water in the planet's atmosphere.

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More recent studies of Venus have revealed that the atmosphere is primarily comprised of carbon dioxide, with smaller amounts of sulphur dioxide, sulphuric acid and hydrogen sulphide. As discussed in [link:diploma-3|Lecture 3], the presence of these gasses in Venus's atmosphere led to a runaway greenhouse effect, where incoming radiation from the Sun was trapped, causing the continual rise in the planet's temperature.

The source of Venus's atmosphere was outgassing from volcanic activity, which accounts for the high levels of sulphur. The Magellan spacecraft, which orbited Venus in 1990 and measured the plant's terrain, found evidence that this volcanic activity was still occurring in the planet's recent past (10 million years ago), and may be continuing today.

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Computer-generated image of Maat Mons, one of Venus's volcanoes

Prospects for Life

Like Mercury, the prospects for life on Venus appear to be poor. There is very little water on the planet, since most of it has been lost through photodissociation (see [link:diploma-3|Lecture 3]). What water does remain has no chance of being liquid on the surface, since the temperatures there are far too high.

However, recent evidence has caused some scientists to rethink their views of life on Venus. The presence of sulphur dioxide and hydrogen sulphide together in the atmosphere is puzzling, since these gasses quickly react with one another and are destroyed. Although volcanic activity can replenish the gasses, the fact that their concentrations are highest far above ground level (around 50km) suggests something else might be going on.

Temperatures within Venus's atmosphere

Pressures within Venus's atmosphere

Interestingly, at around 50km above the Venusian surface, the temperature ranges between 30C and 80C (see figure above), allowing water to condense into droplets. Furthermore, the pressure is similar to Earth's sea-level pressure. It is conceivable that acidophiles may exist in these droplets, accounting for the unusual concentrations of sulphur dioxide and hydrogen sulphide.

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Ultraviolet image of Venus

Support for the existence of such lifeforms comes from ultraviolet images of Venus, which show dark patches and bands. If living organisms in the Venusian clouds were synthesizing food using a form of anoxygenic photosynthesis, they would absorb UV radiation and lead to the dark patches observed.

To resolve whether there is indeed life on Venus, further missions to the planet are needed. As part of its trip to Mercury, a fly-by of Venus is scheduled for the MESSENGER mission (see above). More significantly, the European Space Agency (ESA) has now approved the Venus Express mission, after some uncertainty.

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The Venus Express spacecraft

Venus Express will leave for Venus in December 2005, arriving at the planet the following summer. It will spend 2 Venusian days (around 500 Earth days!) orbiting the planet, performing an analysis of the atmosphere and surface.


Venus

Introduction Venus is the second planet from the Sun and our closest planetary neighbor. Similar in structure and size to Earth, Venus spins slowly in the opposite direction from most planets. Its thick atmosphere traps heat in a runaway greenhouse effect, making it the hottest planet in our solar system with surface temperatures hot enough to melt lead. Glimpses below the clouds reveal volcanoes and deformed mountains.

Venus is named for the ancient Roman goddess of love and beauty, who was known as Aphrodite to the Ancient Greeks.

Size and Distance

With a radius of 3,760 miles (6,052 kilometers), Venus is roughly the same size as Earth — just slightly smaller.

From an average distance of 67 million miles (108 million kilometers), Venus is 0.7 astronomical units away from the sun. One astronomical unit (abbreviated as AU), is the distance from the sun to Earth. It takes sunlight 6 minutes to travel from the sun to Venus.

Orbit and Rotation

Venus' rotation and orbit are unusual in several ways. Venus is one of just two planets that rotate from east to west. Only Venus and Uranus have this "backwards" rotation. It completes one rotation in 243 Earth days — the longest day of any planet in our solar system, even longer than a whole year on Venus. But the sun doesn't rise and set each "day" on Venus like it does on most other planets. On Venus, one day-night cycle takes 117 Earth days because Venus rotates in the direction opposite of its orbital revolution around the sun.

Venus makes a complete orbit around the sun (a year in Venusian time) in 225 Earth days or slightly less than two Venusian day-night cycles. Its orbit around the sun is the most circular of any planet — nearly a perfect circle. Other planet's orbits are more elliptical, or oval-shaped.

With an axial tilt of just 3 degrees, Venus spins nearly upright, and so does not experience noticeable seasons.

When the solar system settled into its current layout about 4.5 billion years ago, Venus formed when gravity pulled swirling gas and dust together to form the second planet from the Sun. Like its fellow terrestrial planets, Venus has a central core, a rocky mantle and a solid crust.

When the solar system settled into its current layout about 4.5 billion years ago, Venus formed when gravity pulled swirling gas and dust in to become the second planet from the sun. Like its fellow terrestrial planets, Venus has a central core, a rocky mantle and a solid crust.

Structure

Venus is in many ways similar to Earth in its structure. It has an iron core that is approximately 2,000 miles (3,200 kilometers) in radius. Above that is a mantle made of hot rock slowly churning due to the planet's interior heat. The surface is a thin crust of rock that bulges and moves as Venus' mantle shifts and creates volcanoes.

Surface

From space, Venus is bright white because it is covered with clouds that reflect and scatter sunlight. At the surface, the rocks are different shades of grey, like rocks on Earth, but the thick atmosphere filters the sunlight so that everything would look orange if you were standing on Venus.

Venus has mountains, valleys, and tens of thousands of volcanoes. The highest mountain on Venus, Maxwell Montes, is 20,000 feet high (8.8 kilometers), similar to the highest mountain on Earth, Mount Everest. The landscape is dusty, and surface temperatures reach a scalding 880 degrees Fahrenheit (471 degrees Celsius).

It is thought that Venus was completely resurfaced by volcanic activity 300 to 500 million years ago. Venus has two large highland areas: Ishtar Terra, about the size of Australia, in the north polar region and Aphrodite Terra, about the size of South America, straddling the equator and extending for almost 6,000 miles (10,000 kilometers).

Venus is covered in craters, but none are smaller than 0.9 to 1.2 miles (1.5 to 2 kilometers) across. Small meteoroids burn up in the dense atmosphere, so only large meteoroids reach the surface and create impact craters.

Almost all the surface features of Venus are named for noteworthy Earth women — both mythological and real. A volcanic crater is named for Sacajawea, the Native American woman who guided Lewis and Clark's exploration. A deep canyon is named for Diana, Roman goddess of the hunt.

Atmosphere

Venus' atmosphere consists mainly of carbon dioxide, with clouds of sulfuric acid droplets. The thick atmosphere traps the Sun's heat, resulting in surface temperatures higher than 880 degrees Fahrenheit (470 degrees Celsius). The atmosphere has many layers with different temperatures. At the level where the clouds are, about 30 miles up from the surface, it's about the same temperature as on the surface of the Earth.

As Venus moves forward in its solar orbit while slowly rotating backwards on its axis, the top level of clouds zips around the planet every four Earth days, driven by hurricane-force winds traveling at about 224 miles (360 kilometers) per hour. Atmospheric lightning bursts light up these quick-moving clouds. Speeds within the clouds decrease with cloud height, and at the surface are estimated to be just a few miles per hour.

On the ground, it would look like a very hazy, overcast day on Earth. And the atmosphere is so heavy it would feel like you were 1 mile (1.6 kilometers) deep underwater.

Potential for Life

No human has visited Venus, but the spacecraft that have been sent to the surface of Venus do not last very long there. Venus' high surface temperatures overheat electronics in spacecraft in a short time, so it seems unlikely that a person could survive for long on the Venusian surface.

There is speculation about life existing in Venus' distant past, as well as questions about the possibility of life in the top cloud layers of Venus' atmosphere, where the temperatures are less extreme.

Moons

Rings

Magnetosphere

Even though Venus is similar in size to the Earth and has a similarly-sized iron core, Venus' magnetic field is much weaker than the Earth's due to Venus' slow rotation. ​


Death Plunge Of Venus Spacecraft Reveals Surprisingly Cold Temperatures On The Hottest Planet

In December 2014, the European Space Agency’s (ESA) Venus Express probe was purposefully sent to its death in the atmosphere of Venus at the end of its mission. Now, scientists have revealed some of the science returned from that fatal plunge – and the results are truly fascinating.

The dip into the Venusian atmosphere began in June 2014. The spacecraft, which launched in November 2005, was nearing the end of its mission. With limited fuel available, scientists decided to make the most of a unique opportunity to probe unexplored regions of Venus, namely its upper atmosphere and its poles. The findings from this finale have now been published in the journal Nature Physics.

"None of Venus Express&apos instruments were actually designed to make such in-situ atmosphere observations,” said lead author Ingo Müller-Wodarg of Imperial College London, UK, in a statement. “We only realized in 2006 – after launch! – that we could use the Venus Express spacecraft as a whole to do more science."

What these results reveal is that parts of Venus are much, much colder than expected. The average temperature on Venus makes it the hottest world in the Solar System, with its thick atmosphere trapping heat and giving rise to scorching temperatures of 460ଌ (860ଏ) on the surface.

But measurements taken by Venus Express at an altitude of 130 to 140 kilometers (81 to 87 miles) above the surface have revealed the atmosphere near the poles has temperatures far below that on Earth. In fact, the polar atmosphere on Venus drops to -157ଌ (-251ଏ), which is 70 degrees colder than expected. It is also 22 to 40 percent less dense than thought.

"These lower densities could be at least partly due to Venus&apos polar vortices, which are strong wind systems sitting near the planet&aposs poles,” said Müller-Wodarg. 𠇊tmospheric winds may be making the density structure both more complicated and more interesting!"

Venus Express used the atmosphere of Venus to slow its velocity, known as aerobraking.਎SA/C. Carreau

Another interesting finding was that the polar region is dominated by something known as atmospheric gravity waves. Don’t be fooled by the name, though these are nothing to do with the more widely-known gravitational waves. Instead, atmospheric gravity waves are ripples in the atmosphere that travel vertically, from low to high altitudes, as the density decreases. We actually have some of these on Earth.

Venus Express found that there were atmospheric waves originating from the upper cloud layer on Venus, about 90 kilometers (56 miles)ꂫove the surface. In addition, larger-scale waves caused by the planet’s spin, known as planetary waves, were also found to be present.

To make these findings, Venus Express was required to perform aerobraking maneuvers, using the Venusian atmosphere to slow the spacecraft’s velocity. And this maneuver਌ould have implications for the European Trace Gas Orbiter, currently on its way to Mars, which will use a similar technique to measure the composition of various gases in the Martian atmosphere.

Venus Express may have died a fiery death more than a year ago, but results from the mission are still turning up some surprises. And with Japan’s Akatsuki mission recently beginning its own science mission around Venus, it&aposs clear there is still much to learn about the second planet from the Sun. 


Low Water Abundances on Exoplanets?

Interesting paper in the Astrophysical Journal Letters from Welbanks et al. 2019. This is a fairly small sample so you have to suspend a bit of judgement on the results - but, its a start. Their key discussion point is as follows:

"The overall low H2O abundances across the sample contrasts with solar system predictions. Besides the carbon enhancements seen in the solar system, other elements such as nitrogen, sulfur, phosphorous, and noble-gases are also enhanced in Jupiter (Atreya et al.2018) the oxygen abundance is unknown as H2O condenses at the low temperatures of solar system giants. Considering that oxygen is the most cosmically abundant element after H and He, it is expected to be even more enhanced than carbon in giant planets, according to solar system predictions (Mousis et al.2012). Therefore, the consistent depletion of H2O abundances in our sample suggest different formation pathways for these close-in exoplanets compared to the long-period solar system giants."


Watch the video: Η αποπνικτική κόλαση της Αφροδίτης. Astronio #30 (May 2022).