|Venus in natural colors, captured by Mariner 10|
|Properties of the orbit|
|Major semi-axis||0.723 AU
(108.16 million km)
|Perihelion - aphelion||0.718-0.728 AU|
|Inclination of the orbit plane||3.3947 °|
|Sidereal period||224,701 days|
|Synodic period||583.92 days|
|Mean orbital velocity||35.02 km / s|
|Smallest - largest distance to earth||0.255-1.745 AU|
|Equatorial diameter *||12,103.6 km|
|Pole diameter *||12,103.6 km|
|Dimensions||≈0.815 earth masses
4.875 · 10 24 kg
|Medium density||5.243 g / cm 3|
|Gravitational acceleration *||8.87 m / s 2|
|Escape speed||10.36 km / s|
|Rotation period||243 days 36 min|
|Inclination of the axis of rotation||177.36 °|
|Max. Apparent brightness||−4.8 m|
|Properties of the atmosphere|
|Pressure *||92 bar|
min. - average - max.
|710 K (437 ° C)
737 K (464 ° C)
770 K (497 ° C)
|* based on the zero level of the planet|
|Size comparison between Venus (left as radar map) and Earth|
The Venus is at an average distance from the sun of 108 million kilometers, the second innermost and with a diameter of 12,100 kilometers, the third smallest planet of the solar system . It is one of the four earth-like planets , which are also called terrestrial or rocky planets .
Venus is the planet that on its orbit of the earth's orbit is at a minimum distance of 38 million kilometers closest. It is similar in size to the earth , but differs in terms of geology and especially in terms of its atmosphere. This consists of 96% carbon dioxide and its surface pressure is 90 times higher than on earth.
After the moon , Venus is the brightest star in the night sky . Because it is one of the lower planets only visible in the morning or evening sky and never around midnight, it is also called the morning star and evening star . Even with a small telescope it can be observed in the daytime sky , sometimes even with bare eyes . But even when it is close to the earth (approx. Every 1½ years), only the cloud strips of the extremely dense atmosphere can be seen. Exploring the surface requires radar.
The major orbit half-axis of Venus measures 108,208,930 km; that is the distance between its center of gravity and the common center of gravity with the sun , which is only 264 km away from the center of the sun because of the comparatively small mass of Venus. The major semi-axis is about 72.3% of the mean radius of the earth's orbit, that is 0.723 astronomical units (AU). The point of the orbit closest to the Sun, the perihelion , is 0.718 AU and its point furthest from the Sun , the aphelion , is 0.728 AU. Venus is closer to Earth than any other planet (minimum 0.256 AU), but on average Mercury is closer to Venus (0.779 AU) and Earth (1.039). The mean distance to the earth is 1.136 AU. Venus is just outside the habitable zone because it is too close to the sun for liquid water to exist. The orbital plane of Venus is 3.39471 ° inclined to the ecliptic plane of the Earth. The sidereal period of rotation - the duration of a Venus year - is 224.701 (Earth) days.
The orbit of Venus has the least eccentricity of all planetary orbits. The numerical eccentricity is only around 0.0068; this means that the deviation of the planetary orbit from an ideal circular path is very small. So Venus has the most circular orbit of all planets. Only the orbits of a few moons and some asteroids have even smaller deviations from the circular shape in the solar system . On the other hand, the inclination of Venus' orbit against the orbit plane of the earth is about 3.4 ° after the inclination of Mercury (7.0 °) with the greatest, albeit significantly more moderate.
The rotation of Venus is in contrast to the otherwise almost exclusively predominant direction of rotation of the planets and the orbital motion of the planets and most of the moons in the solar system , retrograde. This means that Venus rotates clockwise as seen from its north pole . According to the definition of the International Astronomical Union (IAU), the north pole of a planet is the one that lies on the same side of the ecliptic as the north pole of the earth. Thus on Venus the sun rises in the west and sets in the east. The inclination of the axis of rotation is therefore usually not given as 2.64 °, but as 177.36 °, as if the axis had been tilted upside down in the original prograde direction of rotation. Among the planets in the solar system, apart from Venus, only Uranus has a retrograde sense of rotation; among the known dwarf planets , this is only the case with Pluto . Due to the slight inclination of the equator of Venus against the plane of the orbit, there are no seasons on the planet .
The retrograde self-rotation of Venus is also extraordinarily slow: A sidereal period of rotation (that is, relative to the fixed stars ) lasts 243.025 earth days, and thus even 8 percent longer than the orbital period (224.701 earth days). Due to the retrograde direction of rotation, the period of rotation related to the sun - ie a Venus day - lasts “only” 116.75 earth days; in the right case, the ratio between the rotational speed and the orbital speed would mean almost a bound rotation , as in the completed example of the earth's moon, which thereby constantly turns the same side of the earth. Venus would thus have a similar fate compared to the sun. The cause of the retrograde direction of rotation and the particularly low speed of Venus rotation is not known. According to one hypothesis, it could be the result of a collision with a large asteroid.
The synodic period of rotation of Venus (that is, relative to Earth) averages 145.928 days. This is the rotation with which a Venus meridian lies parallel to the heliocentric longitude of the earth. Since the five-fold period corresponds exactly to two earth years within a few hours, there is an approximately pentagram-like distribution of these positions. According to measurements by the Venus Express space probe , the period of rotation of Venus has become approximately 6.5 minutes longer than measured by the Magellan space probe .
Railway disturbances and resonances
Together with the Earth's orbit period of 365.256 days, the period between two successive closest approximations results in a period of 583.924 days or 1.599 years, which can also be understood as a mutual orbital disruption period . Seen from the earth, this is the synodic period of Venus. The orbital times of Venus and Earth are in the commensurability 8:13 (exactly 8: 13.004); that is, they are in a relationship that is based on a common measure and can accordingly be expressed almost exactly using small whole numbers. Within 8 orbits of the earth 13 orbits of Venus are covered, both planets are afterwards almost at the same place. From the difference between the two numbers ( ), in the case of the same direction of rotation, it can be seen that the closest approximations, ideally, would be distributed exactly evenly from exactly circular paths to five different points on the path. The spatial order of the orbit points after a whole and three fifths of a solar revolution results in the Venus pentagram with imaginary connecting lines. This peculiarity is possibly one of the reasons for the very low eccentricity of the Venus orbit. Due to the resonance effect, commensurabilities lead to severe orbit disturbances, which are more pronounced the more precisely the ratio of the numbers is achieved and the smaller the difference between them. The best-known example is the influence of Jupiter on the distribution of the asteroids , which leads to commensurability gaps ( Kirkwood gaps ) and clusters through such resonance effects within the asteroid belt. The orbital movements among the moons of Saturn have similar effects on the structure of its ring system . All neighboring planets and regular moons move in commensurable orbital conditions and thus underline the certain regularity of the orbital distances in the solar system (see also: Titius-Bode series ).
The mean orbital distance to Mercury , the smallest planet and inner orbit neighbor of Venus, is around 50.3 million km (0.336 astronomical units). That is only slightly less than its large orbit half-axis (0.387 astronomical units). The mean orbital disturbance period between Venus and Mercury is 144.565 days. Their periods of rotation have the commensurable ratio of 5: 2 (exactly 5: 1.957). Ideally, the closest approximations would be evenly distributed over three orbital points, but Mercury's orbit is almost as eccentric as that of the dwarf planet Pluto.
The total two-year period of the interaction of Venus' rotation with the earth's movement is 729.64 days in a ratio of 4: 5 (4: 4.998) to the synodic period of Venus. The synodic year of Venus comprises four mean synodic rotations (1: 4.001) with 583.924 days. An observer on Venus would - with unimpaired visibility - find the earth every 146 earth days or every 1.25 days in Venus at the same position. Venus, for example, turns towards the earth with every upper and every lower conjunction, as well as, seen from the sun, in every 90 ° position (to the east or to the west) practically always one and the same side - the side of the prime meridian. From this location the earth would peak every 146 days alternately at noon, around sunset, at midnight and around sunrise. The striking example of the earth alignment of the hemisphere of the prime meridian relates to the same spatial earth positions as the sole sequence of the lower conjunctions, only with the faster period and in the reverse order of the pentagram pattern. The small deviation of the Venus rotation means only a systematic shift of a good half a degree of longitude towards the east.
During eight orbital periods of the earth or thirteen orbital periods of Venus with five conjunctions to each other, Venus rotates, also almost to the day, twelve times relative to the stars, 20 times relative to the earth and 25 times relative to the sun. It is reasonable to assume that it is all about a resonance phenomenon.
|Comparison of the distances from Earth, Venus and Mercury to the Sun:|
Planet without a moon
Venus does not have a natural satellite . In 1672 the Italian astronomer Giovanni Domenico Cassini claimed to have discovered one and named it Neith, after the Egyptian goddess Neith ("the terrible"). Belief in a moon of Venus was widespread until 1892, before it emerged that stars had apparently been mistaken for a moon.
Since the mid-1960s, various scientists have hypothesized that Mercury, which looks very much like an Earth's moon, is an escaped satellite of Venus. Through its tidal interaction, it is said to have reversed the rotation of Venus, among other things. This assumption can also explain why the two planets are the only ones in the solar system without a companion.
In 2006, Alex Alemi and David Stevenson of the California Institute of Technology published their hypothesis that a former moon of Venus would have crashed due to its retrograde rotation. The satellite was said to have been created, analogous to the formation of the Earth's moon, by a large, almost only grazing collision, the debris products of which had largely united in Venus' orbit to form a satellite. According to the general opinion among astronomers, there were very large impacts on the planet in the early days of the solar system, one of which, according to this theory, is said to have reversed the sense of rotation of Venus. Alemi and Stevenson also assume that the latter collision of Venus was the second after the formation of the former Venusian moon and that the satellite no longer slowly moved away from its planet like the Earth's moon due to the reversal of the tidal action, but instead approached again and with it who reunited Venus. However, it is difficult to prove this, because the volcanic deformation of Venus should have long since erased all conceivable traces.
The size and general structure of Venus are very similar to Earth . At 12,103.6 kilometers, Venus has almost the same diameter as Earth and almost the same mean density. The two “planetary sisters” are often referred to as “twins”. But as much as they are similar in mass and chemical composition, the surfaces and atmospheres of the two planets are very different.
The atmosphere of Venus consists mainly of carbon dioxide . Nitrogen makes up 3.5%, traces of sulfur dioxide (150 ppm ), argon (70 ppm) and water (20 ppm) are found. Because of the large total mass of the atmosphere, there is about five times as much nitrogen in it as in the earth's atmosphere . The Venusian atmosphere has around 90 times as much mass as the Earth's air envelope and causes a pressure of 92 bar at the mean ground level. This is equivalent to the pressure at a depth of around 910 m. The density of the atmosphere on the surface is on average around 50 times that on Earth.
Below a height of 28 kilometers one finds around 90 percent of the mass of the atmosphere, which corresponds to around a third of the mass of the terrestrial ocean . The electromagnetic impulses recorded by various probes, which speak for very frequent lightning discharges, were ascribed to this thick layer of haze far below the cloud cover . Within the cloud would of thunderstorms flashing lightning have been obvious at night, but on the night side of Venus could no corresponding luminous phenomena are observed. Above the clouds, outer layers of haze reach up to a height of about 90 kilometers. The troposphere ends around 10 km higher . In the 40 km thick mesosphere above , the temperature reaches lows of around −100 ° C. On the next floor, the thermosphere , the temperature rises as a result of the absorption of solar radiation . Sub-zero temperatures only prevail at the bottom of the thermal atmosphere down to the upper cloud layers. The exosphere as the outermost layer of the atmosphere extends at a height of around 220 to 250 kilometers.
The fact that the atmosphere of Venus is completely opaque from the outside is not due to the great mass and density of the gas envelope, but mainly due to an always closed cloud cover. This is with its underside at a height of about 50 km and is around 20 km thick. Its main component is about 75 percent by mass of droplets of sulfuric acid . There are also aerosols containing chlorine and phosphorus . In the lower of a total of three cloud layers there may also be admixtures of elemental sulfur . Larger droplets of sulfuric acid rain down, but only not far from the bottom of the cloud cover, where they evaporate due to the high temperatures and then decompose into sulfur dioxide, water vapor and oxygen . These gases rise to the uppermost cloud areas and react and condense there again to form sulfuric acid. The sulfur was originally emitted by volcanoes in the form of sulfur dioxide.
The spherical albedo of the creamy yellow and mostly structureless cloud surface is 0.77; that is, it scatters 77% of the light arriving from the sun practically parallel. The earth , on the other hand, reflects only 30.6% on average. Around two thirds of the radiation not reflected by Venus is absorbed by the cloud cover. This energy drives the uppermost equatorial cloud layers to a speed of about 100 m / s, with which they always move around the planet once in just four days in the direction of rotation of Venus. The high atmosphere thus rotates around 60 times faster than Venus itself. This phenomenon is called " super rotation ". The reason why the effects happen this way and not differently has not yet been satisfactorily clarified - at least in the case of Venus. The phenomena of the Venus atmosphere were investigated in detail using the space probe Venus Express . The only other examples of such a fast atmospheric circulation in the solar system are the strong wind bands in the higher atmosphere of the earth and the cloud ceiling of the Saturn moon Titan , whose nitrogen atmosphere on the ground has at least one and a half times the pressure of the earth's air envelope. So there is a super rotation only in the three solid world bodies of the solar system, which have a dense atmosphere.
Images from Venus Express showed that within ten years of Venus, the speed at which the clouds move around the planet increased from 300 to 400 km / h.
In 2011, Venus Express discovered a relatively thin ozone layer at an altitude of around 100 kilometers.
After arriving at Venus, Venus Express was able to detect a sharp rise in sulfur dioxide levels above the clouds, which decreased over time due to the splitting of the SO 2 by the sunlight. Since Pioneer Venus 1 already encountered similarly high values after its arrival and was able to follow their decline, the cause, in addition to volcanic eruptions, is a regular ascent of the gas from deeper atmospheric layers into the upper atmosphere due to the Venusian climate.
Almost the entire gas envelope of Venus forms large Hadley cells by convection . The gas masses that have risen in the most intensely irradiated equatorial zone flow into the polar regions and sink there into lower layers, where they flow back to the equator . The structures of the cloud cover visible in ultraviolet light therefore have the shape of a Y lying in the direction of rotation . The first photos delivered by Venus Express showed - particularly clearly in the infrared spectral range - a cloud vortex spreading over most of the observed southern hemisphere with its center above the pole. More detailed observations of the south vortex made its center visible as a double vortex. Images from the probe from September 2010 showed a single peculiar vortex instead of the enigmatic double vortex.
In December 2015, the Venus orbiter Akatsuki registered a 10,000-kilometer-long formation in the cloud cover over several days, which arched north and south across both hemispheres. The structure had a higher temperature than the atmospheric environment and did not move westward with the fast winds, like the cloud cover as a whole, but rather stood with its center largely stationary over the western edge of the equatorial highlands Aphrodite Terra. The arch structure was probably based on the phenomenon of a gravity wave , which in principle also occurs in the earth's atmosphere, but which on Venus even reaches the upper areas of the cloud cover.
Up to now, only low wind speeds of 0.5 to 2 m / s have been measured near the ground . Due to the high gas density, this corresponds to wind force 4 on earth , which means that it is like a moderate breeze that can move dust . Only two percent of the sunlight falling on Venus reaches the surface and results in an illuminance of around 5000 lux . The visibility there is around three kilometers, like on a cloudy afternoon.
The radiation not reflected or absorbed by the clouds is mainly absorbed by the lower, very dense atmosphere and converted into thermal radiation in the infrared range. In this wavelength range , the absorption capacity of carbon dioxide is very high and the thermal radiation is almost completely absorbed by the lower layer of the atmosphere. The strong greenhouse effect (also called Venus Syndrome ) is mainly due to the mass of carbon dioxide, but the small traces of water vapor and sulfur dioxide also play a major role in this. It ensures an average temperature of 464 ° C (737 K) on the ground. This is well above the equilibrium temperature of −41 ° C (232 K) calculated without the greenhouse effect , also well above the melting temperatures of tin (232 ° C) and lead (327 ° C) and even exceeds the maximum temperature on Mercury (427 ° C) C).
Despite the very slow rotation of Venus, the temperature differences between the day and night sides as well as between the equatorial region and the polar regions are very small. A minimum of around 440 ° C is never fallen below near the ground. The only exceptions are higher mountain regions, for example 380 ° C and a pressure of 45,000 hPa prevail at the highest peak. The maxima at the lowest points are 493 ° C and 119,000 hPa. Without the cloud cover with its high reflectivity, it would still be considerable on Venus hotter.
Since an observation by Giovanni Riccioli in 1643, lights have been reported on the night side of Venus again and again . Such a glow that is not very bright, but is conspicuous in the telescope, is claimed by both professional and amateur astronomers to this day. So far, however, there is no photographic evidence of this. Particularly strong lightning is usually assumed to be the cause of the lights. In 2001, an extremely faint Venus glow was observed at the Keck Observatory . This greenish light is created when the sun's ultraviolet radiation has broken down carbon dioxide and the released oxygen atoms combine to form an oxygen molecule. However, it is far too faint to be seen with much simpler telescopes.
Speculation about life in the atmosphere
There is evidence that there could be very resistant microorganisms in the clouds of Venus . According to Dirk Schulze-Makuch and Louis Irwin from the University of Texas in El Paso , this could explain the absence and presence of certain gases, among other things. In addition, Pioneer-Venus 2's large immersion probe found bacteria- sized particles in the clouds. Dark, rapidly changing spots in the clouds of Venus, whose spectroscopic features match those of terrestrial biomolecules and microbes, are also interpreted as an indication of life in the atmosphere. With radioteleskopischen measurements, which were published in 2020, was in higher layers of the atmosphere, about 50 kilometers above the surface, the gas monophosphane , also known as phosphine, proven. An abiotic, i.e. H. An explanation for the presence of this gas that can be traced back to non-biological processes is not yet apparent.
The 180 ° (left) and the 0 ° hemisphere. Radar map captured by the Magellan spacecraft .
|The generic names of the IAU - nomenclature for the topography of Venus|
|Singular plural)||Brief description||Rule for the individual names|
|Chasma (Chasmata)||steep-walled valley||Hunt goddesses|
|Collis (Colles)||hill||Sea goddesses|
|Corona (Coronae)||Slump crater||Goddesses of fertility|
|Dorsum (dorsa)||Ridge||Heaven and light goddesses|
|Farrum (Farra)||volcanic head of spring||Water goddesses and nymphs|
|Fluctus (Fluctus)||Lava flow field||Earth goddesses|
|Fossa (fossae)||long, narrow and flat valley||Goddesses of War and Valkyries|
|crater||Impact crater||significant women (crater> 20 km)
female first names (crater <20 km)
|Linea (Lineae)||linear surface shape||Goddesses of War and Amazons|
|Mons (Montes)||Mountain ( mountain )||Goddesses|
|Patera (paterae)||irregular, flat volcanic crater||Famous women in history|
|Planitia (Planitiae)||Plain with mares||Mythological heroines|
|Planum (plana)||Plateau||Goddess of love and war|
|Regio (regions)||High altitude with a continental character||Titans|
|Rupes (rupes)||Embankment , steep wall||Home and hearth goddesses|
|Terra (Terrae)||large highland mass||Venus in other languages|
|Tessera (Tesserae)||High position with parquet structure||Goddesses of fate|
|Tholus (tholi)||volcanic dome||Goddesses|
|Unda (Undae)||wavy surface shape||Desert goddesses|
|Vallis (Valles)||valley||River goddesses|
The floor of Venus is constantly glowing gray , but this would only be perceptible to the human eye during the night and only faintly. Due to the very high temperatures there are no bodies of water . The relief is mainly dominated by gently undulating levels. With relatively small differences in level of less than a thousand meters, they correspond to the global average level and, relatively similar to the earth's sea level , form a practical reference level for all altitude data. This zero level of Venus corresponds to a spherical radius of 6051.84 kilometers. The levels take up over 60% of the surface. A little less than 20% are lowlands up to 2 km deep. The remaining 20% are surveys, but only about 8% are pronounced highlands that rise more than 1.5 km above zero level. The hypsographic curve of the height distribution on Venus does not show a second main level as in the case of the Earth, whose extensive upper crust in the form of the continents forms around a third of the surface of the earth's crust in addition to the ocean floors . The height difference between the lowest and the highest point on Venus' surface is about 12,200 meters; that is around two thirds of the maximum height difference in the earth's crust with around 19,880 meters. The individual heights are often very different for Venus.
According to a convention of the International Astronomical Union (IAU), all formations on Venus have female names, with the exception of Alpha Regio and Beta Regio - the structures first discovered from Earth in 1963 - and the Maxwell Montes. As the highest point on the planet, the latter was named in honor of James Clerk Maxwell , who, among other things, created a basis for radar exploration of the surface of Venus with his electromagnetic wave equations .
Recent representations of the reliefs are mainly based on the radar measurements of the Venus orbiter Magellan of NASA , the 98% of the surface is mapped, with a horizontal resolution of 120 to 300 meters and a vertical resolution of 30 meters. Occasionally, however, the lower-resolution global map of Pioneer Venus 1 is also in use.
The high altitudes are mainly divided into two more extensive formations. The larger of the two, Aphrodite Terra , is about the size of South America and in the shape of a scorpion extends lengthways over about a third of the equator. The Ovda Regio plateau stands out in its western part, Thetis Regio in the northern center and Atla Regio in the east. The land of Aphrodite consists of domed terrain, which in its eastern half - the tail of the scorpion shape - are subdivided by large trenches and occupied by large volcanoes. The highland formation is part of the equatorial highland belt, which extends with individual larger islands to about 45 ° north and south latitude.
A long way north-west of Aphrodite, between the 45th and 80th parallel, is Ishtar Terra . The Ishtarland is most reminiscent of an earthly continent . It is only about the size of Australia , but on top of it are the Maxwell Mountains, with a peak height of up to around 10,800 meters. The Mount Everest on Earth, however, is with its height of 8848 meters above sea level not behind the Maxwell mountains back, because, considering the size of the Himalayas measures in a manner analogous to the middle crust level of the earth, the highest elevation of the earth has a height from around 11,280 meters.
In the Maxwell Mountains lies the Cleopatra impact crater, with a diameter of 104 km the eighth largest impact structure on Venus. Its nature as an impact crater could only be clarified through high-resolution radar measurements, as original assumptions made the object more of a volcanic crater due to its location.
The western part of Ishtar is formed by the relatively flat plateau Lakshmi Planum, unique on Venus, with the two large volcanic depressions Colette Patera and Sacajawea Patera. The plateau is about four kilometers above average level and is bordered by the highest chain mountains on the planet. In the south by the Danu Montes, in the west by the higher Akna Montes, in the northwest by the Freyja Montes, which is 6.5 km higher, and far to the east by the Maxwell Montes. These mountains resemble earthly, fringing fold mountains such as the Andes or the Himalayas. The formation of the Venus Mountains is still a mystery, because plate tectonics like that on Earth cannot be proven for the Venus crust. A tectonic compression of the crust and, as an alternative, a particularly large volcanic bulge directly below Ishtar Terra are discussed. There are no such mountain ranges on any other body of the solar system.
Radar-bright “snow caps” were found on many mountain ranges, which, given the prevailing conditions, very likely consist of a thin layer of precipitation of the heavy metal salts lead sulphide and bismuth sulphide .
The high elevations of the Tesserae (from Greek tessera: "tile" or "mosaic") belong to the special forms of the Venus relief. They consist of blocks broken like parquet patterns, each up to 20 km wide, which seem to have been deformed by tectonic stresses. They are characterized by parallel, linear faults that intersect at least in two basic directions approximately at right angles and are thus reminiscent of a tile pattern. These high altitudes, sometimes also known as “dice lands”, occupy large parts of the west and north of Aphrodite and the north and especially the east of Ishtar. The eastern part of Ishtar called Fortuna Tessera is a hilly plateau with an altitude of up to about 2.5 km above zero level.
Several Tesserae rise from the lowlands as islands, such as the three larger units Alpha Regio, with a diameter of about 1300 km, as well as Phoebe Regio and Tellus Tessera, which all belong to the equatorial highland belt.
Eve Corona is located close to the southern southern edge of the Alpha region (see picture). The structure, about 330 km in diameter, was originally thought to be an impact crater. Its bright central spot served as a reference point for determining the prime meridian.
|The nine largest craters on Venus|
|Mead||270 km||12.5 ° N; 057.2 ° E|
|Isabella||175 km||29.8 ° S; 204.2 ° E|
|Meitner||149 km||55.6 ° S; 321.6 ° E|
|Klenova||141 km||78.1 ° N; 104.5 ° E|
|Baker||109 km||62.5 ° N; 040.3 ° E|
|Stanton||107 km||23.3 ° S; 199.3 ° E|
|Cleopatra||105 km||65.8 ° N; 007.1 ° E|
|Rosa Bonheur||104 km||09.7 ° N; 288.8 ° E|
|Cochran||100 km||51.9 ° N; 143.4 ° E|
To date, 963 impact craters have been discovered on Venus . That is at least twice as many as has been proven so far on the earth's land surface ( see also: List of impact craters on earth ). The diameters of the Venus craters are in the size range between 1 and 300 kilometers. In this size, however, there are around a hundred times as many lunar craters on the front of the moon alone , the size of which is a 24th of Venus, despite the large mare basins largely smoothed by lava . Since the moon has no atmosphere and its surface is therefore not exposed to any corresponding erosion, its highlands, which are practically completely occupied even with much smaller impact structures and are still completely preserved, are based on the chemical age determination of the lunar rocks as the classic benchmark for the age estimation of other planets. and lunar surfaces. If the frequency of craters on the moon corresponded to that of Venus, it would only have around 80 craters in total.
The Venus craters are surprisingly evenly distributed over the surface for their small number. Since only larger meteoroids can penetrate the very dense atmosphere and create such impact structures, there are no crater diameters less than about 2 km, but instead only something like " smoke traces ". Smaller craters are often surrounded by radar-dark, i.e. smooth, terrain, which is probably due to the shock wave of the impact; In some of these circular areas, however, no central crater can be seen.
By far the largest Venusian crater, Mead, has a diameter of around 270 km. It is followed by seven more specimens in the size range of over 100 km. There are no craters with larger dimensions, such as those on the moon, Mars and also on Mercury , where in the most striking cases they even reach diameters well over 1000 or 2000 km. This can also be partly attributed to the abrasive effect of the particularly high density of the atmosphere, which it has for small impacting bodies ; on the other hand, there is the view that today's crust of Venus is relatively young, so that it cannot bear any traces of the so-called “ last great bombardment ” that is said to have plagued the planetary system in the early days . The relief of all the impact craters on Venus is very flat.
About 85 percent of the surface of Venus consists of clear traces of extensive magma extraction. Most of the craters were not affected by it, so they were formed later. With regard to its sparse and very even distribution in comparison with the lunar surface, this has led to the conclusion that the current surface of Venus is only about 500 to 800 million years old and emerged from extensive and relatively rapid lava floods, which the old relief with a covered up to three kilometers of magma layer. This view culminates in the declaration by the American scientists Gerald G. Schaber and Robert G. Strom that the volcanic heat release of Venus does not take place continuously as it does on Earth, but takes place in large periodic bursts. That would mean that the lithosphere of Venus is much thicker than that of Earth and therefore does not allow a relatively unhindered flow of heat. According to the explanatory approach, it accumulates over a longer period of time until the heat build-up is discharged with all its might in the form of strong tectonic activities and violent volcanism.
A second, competing, more uniform approach to a solution in addition to the catastrophe theory assumes that the volcanic activities constantly renewed the surface up to 750 million years ago and only since then have significantly decreased, so that the impact craters have only been able to accumulate since then. A team of American and Spanish scientists led by Vicki Hansen examined the mountain ranges protruding from the plains flooded with lava like islands and reconstructed the original course of the valleys on the basis of their flanks. The valleys were flooded at different times according to their different levels, and the lava layer could not be thicker than a kilometer. For the mountain heights that remained intact, Hansen calculated an age of at least one billion years. It is therefore clear that there was no global volcanic disaster. The data suggest that volcanic activity will fade slowly over a period of around two billion years.
The unique coronae (Latin for "crowns") are seen as a special sign of this change . They are the most characteristic structures on Venus. Hundreds of them are found in the plains, accumulate in the equatorial zone and shape large parts of the land of Aphrodite there. Because of their appearance, which is most likely to give the impression of sunken and deformed volcanoes, they are sometimes referred to as collapse craters. The circular and oval formations contain a flat, undulating basin lying below the surrounding level with a low, wide and slightly arched edge, which is surrounded by a wide ditch with concentric breaks and mountain ridges.
By far the largest such structure is Artemis Corona with a diameter of about 2600 km and the ring-shaped rift system Artemis Chasma . The giant formation is located in the south of the land of Aphrodite. Her size is followed by Heng-o Corona and Zisa Corona with diameters of 1060 and 850 kilometers. In most cases the span is between 100 and 400 km. The smallest diameters are around 40 kilometers.
Volcanoes are at least as numerous on Venus as they are on Earth. There are whole fields of shield volcanoes and fields with hundreds of small volcanic peaks and cones. The number of small volcanic elevations goes well over 50,000. There are at least 167 specimens of volcanoes with a base at least 100 km in diameter.
The largest lava mountains include the shield volcanoes Sif Mons and Gula Mons in Eistla Regio with heights of two and three kilometers and base diameters of 300 and 250 km respectively. Likewise in Beta Regio the Rhea Mons with a summit height of 4.5 km and the same high Theia Mons with a particularly large base diameter of 700 km. That is around 100 km more than the base of Olympus Mons on Mars, the highest mountain in the known solar system with a base height of around 27 km. The highest volcanoes of Venus are in Atla Regio, the easternmost section of Aphrodite Terra. In addition to the two-peaked Sapas Mons (4.5 and 400 km), there is also the Ozza Mons (six and 300 kilometers) and finally the Maat Mons , the highest volcano on Venus with more than eight kilometers and its second largest peak after the Maxwell Mountains. with a base diameter of just 200 km. The giant volcanoes of Venus are all part of the equatorial highland belt. As a rule, the closer they are to the equator, the larger they are. The mate Mons is almost exactly on it. Most volcanoes have a rather flat relief on Venus. The slopes are mostly only 1 to 2 degrees.
A special volcanic shape has been nicknamed "Tick" because of a certain similarity. There are similar volcanoes on the ocean floor of the earth.
The unique volcanic surface structures of Venus include very regularly built, circular spring domes , which are called pancake domes because of their appearance . They have a typical diameter of mostly around 25 km and a height of around 700 m, but this can also be up to over a kilometer. They also occur in groups and then often overlap. Its surface is characterized by a central opening and concentric and radial cracks. Apparently the structures were created by a very tough lava . It is puzzled how the lava could flow so evenly over the plains. Viscous lava also piles up in domes on the earth, but they are much smaller and not that symmetrical.
In the question of young volcanism is on summaries of measurements of the infrared spectrometer VIRTIS, which on the ESA -Planetensonde Venus Express has been installed, an international research group led by Suzanne E. Smrekar from JPL of NASA in a publication of 8 April 2010 on the Concluded that at least three regions apparently raised by mantle plumes were still volcanically active 2.5 million to 250,000 years ago or more recently. The three regions - Imdr Regio, Themis Regio and Dione Regio - show up to twelve percent higher emissivity in the vicinity of their centers compared to their surroundings; According to the researchers, this indicates a lower degree of weathering and therefore a correspondingly low rock age under these conditions.
Volcanic plains with large floods of lava are the most common type of terrain on Venus. In addition to the solidified lava flows, the Fluctus, which like Mylitta Fluctus reach a width of several hundred kilometers and over 1000 kilometers in length, other volcanic structures point to flows of very thin lava. So there are very remarkable valleys of erosion. Some assume that large impact craters are a broad outflow formation. They reach a length of up to 150 kilometers, have island-like structures on their bottom and lose themselves in the plains without further traces. Its walls, which are over 100 meters high, are curved in shape, which is why these formations were given the generic name Unda (Latin for "wave").
Probably the most extraordinary are the very long and clearly winding gullies. They are mostly only about 1.5 kilometers wide and also not very deep. The most impressive channel has a length of about 6,800 kilometers and thus even exceeds the Nile , the longest river on earth, by over 100 kilometers . The structure with the name Hildr Fossa meanders from Atla Regio to the great northern lowland Atalanta Planitia, in which the deepest point on Venus was measured at a depth of up to 1400 meters below zero level. The circular depression is roughly the size of the Gulf of Mexico . Due to the extremely high surface temperature, liquid water is out of the question as the cause of the "channels". On earth, however, the longest lava channels only extend a few dozen kilometers. Possibly it was extremely thin, salty lava masses with a correspondingly lower melting point that shaped the landscape at a time when the surface temperature was even higher across the planet. Pyroclastic flows of hot gas and dust are also contemplated.
It is one of the great mysteries of Venus that, despite the multitude and diversity of volcanic structures, it appears geologically dead today. However, one would not necessarily be a witness of a volcanic eruption in every case during just one single closer global exploration of the volcanically constantly active earth. Observed variations in the proportion of sulfur dioxide in the Venusian atmosphere and the density distribution in the upper haze layer actually indicate possible activities. The signs of lightning could also testify to this. The two large shield volcanoes in Beta Regio and Maat Mons are under particular suspicion. Parts of the volcanic flanks are radar dark, which means that they only reflect the scanning radar beams very little and are therefore fairly smooth. In this case, these evenness can be seen as a sign of fresh lava flows.
Clear signs of active volcanism were published in mid-2015. With the help of data from the space probe Venus Express from 2008, four regions were identified in which the temperature rose sharply in a few days. The smallest of the “hotspots” has an area of one km² and a temperature of 830 ° C.
Relatively steep-walled valleys, similar to a canyon , are called Chasma . The most impressive trench of its kind on Venus is Diana Chasma. It is located on Aphrodite Terra, strikingly in the vicinity of Artemis Corona, by far the largest corona, and partly forms the southern section of the edge trench of the large elliptical Ceres Corona. Diana Chasma is about 280 km wide and falls at the foot of the highest mountain ridge that surrounds it, about four kilometers deep to a level of more than one kilometer below zero. The structure has no comparable example on Earth and is often compared to the even more formidable Mariner Valley system on Mars . Presumably, like this one, it was created by tectonic activities. Both trenches extend almost parallel to the equator.
In the Beta Regio, the Rhea Mons and Theia Mons volcanoes are connected by the apparently tectonic rift Devana Chasma.
Systems of radially symmetrical fractions starting from a center are called Astrum or Nova.
Despite the low wind speeds that were measured on the ground, some regions show radar-bright, strip-shaped and fan-shaped structures in the manner of “wind flags” that emanate from individual craters and volcanic cones. Their course shows the prevailing wind direction during their formation. Most wind strips prefer a westerly and equatorial direction corresponding to the global atmospheric currents near the ground. However, it is not always clear whether the light-colored stripes consist directly of the blown material or whether loose material was removed all around and only remained in the slipstream.
Below the lithosphere , the interior of Venus likely resembles that of Earth . Since it has almost the same mass and a similar average density (5.24 g / cm³ compared to 5.52 g / cm³ in the case of the earth) and, according to cosmogony , originated in the same area of the solar system, it should also have an analogue Have shell structure. The fact that the earth has a slightly higher average density is not only due to its chemical composition, but also partly to a purely physical effect of its greater mass, which causes greater self-compression due to the correspondingly greater force of gravity. In contrast to the much smaller Mercury , Venus has a larger proportion of lighter elements than Earth, so it would have a lower mass even if it was the same size as Earth. This is not quite understandable for a planet within the earth's orbit, because according to the conventional theory of the formation of the solar system, the ratio between the light and the heavy elements of Venus should be between the ratios of the earth and Mercury, since the lighter elements in particular are through the particularly stormy particle stream of the young, emerging sun was driven into the outer areas. An explanation for the relatively large and heavy metallic core of the earth is offered by the theory , according to which the young earth collided with a Mars-sized planet called Theia; the core of this planet merged with the earth's core, its rock evaporated and after condensing formed the moon , which therefore has only a small core.
Given the classic shell structure of the earth, one can therefore conclude that instead of a relatively larger one, only a relatively smaller iron-nickel core and, instead, a somewhat larger jacket. The upper coat in particular is expected to be relatively thicker. As suggested by gravitational field measurements by the Venus probe Magellan, the lithosphere could also be considerably thicker than that of Earth. The explanation for the fact that there are no plate tectonics on Venus as on Earth is based on this consideration , as well as the hypothesis that the Venus surface is instead renewed in a long-period rhythm due to massive global volcanic activities.
Although a nickel-iron core of the same size as that of Earth is assumed for Venus, it only has an extremely weak magnetic field . This is due to the lack of a moon, which, through its tidal action, would reduce the rotation of Venus and thus enable induction currents to develop . The extremely slow rotation should also contribute, as it does not favor the dynamo effect . The magnetic field measured on the surface of Venus is extremely weak. It is induced by electrical currents in the ionosphere , which are caused there by the interaction with the electrically charged particles of the solar wind. In this magnetosphere there are no belts of trapped solar particles like those of the Van Allen belt of the earth and the radiation belts of Jupiter , Saturn and Uranus . On the ground, the Venus magnetic field only reaches a ten-thousandth of the strength of the earth's magnetic field on the earth's surface. The surface of Venus is not protected from the approaching particles of the solar wind by the magnetic field like the earth's surface, but by the ionosphere, which is co-induced by the particle flow itself, and by the very dense atmosphere.
Due to the dense, always closed cloud cover, an exploration of the surface of the planet was only possible with radio astronomical methods and with Venus probes. Early observations with the naked eye and telescopes could only study the geometry of the orbit and the cloud surface.
The oldest known written document of a planetary observation are the Venus tablets of Ammi-saduqa . The cuneiform tablets bear until about 800 BC. Copied texts of the Babylonian king Ammi-şaduqa about observations of the 584-day interval of Venus from 1645 BC. Chr.
During the first observations of Venus with telescopes by Galileo Galilei and his contemporaries in 1610, it was immediately apparent that Venus, like the moon, shows phases . This observation, which comes from the perspective of the earth, according to which Venus is a lower planet, was one of the great proofs at the time that Venus orbited the sun and not the earth. The phases of Venus were predicted by Nicolaus Copernicus as possible evidence of his heliocentric teaching. In Ptolemy's geocentric view of the world , Mercury and Venus can never appear as full discs.
However, there was also the so-called “Egyptian model” by Athanasius Kircher , which Herakleides Pontikos , a pupil of Plato , is said to have suggested, in which Mercury and Venus orbit the sun. The impressive discovery of the phases of Venus could not contribute to the decision between the geo-heliocentric model of Tycho Brahe and the heliocentric model of Copernicus.
Ever since Johannes Kepler predicted the transit of Venus in 1631, these rare events, when Venus can be seen as a dark disc in front of the sun, have been a particularly popular research area. With the help of these observations, the distance scale of the solar system in particular could be considerably improved (see also section: Venus transit ). On the occasion of the passage of Venus in 1761, Georg Christoph Silberschlag was the first to discover the atmosphere of Venus as a bright aura around the planet.
At the end of the 18th century, the Lilienthal astronomer Johann Hieronymus Schroeter carried out more detailed investigations into the phases of Venus. He notes that there are systematic differences between the geometrically calculated phase of Venus and the phase actually observed. First of all, Schroeter said that these irregularities, like those of the Earth's moon, are due to surface details such as mountain ranges. In a paper published in 1803 on the Venus phase at the time of the dichotomy ("Half Venus"), he correctly concluded that it was twilight effects in the atmosphere. This is why this phenomenon is now generally called the Schroeter effect after the name introduced by Patrick Moore . Through it, the dichotomy of Venus to its eastern elongation as an evening star appears one or two days earlier, and correspondingly later to its western elongation as a morning star. Even amateurs with a small telescope can easily observe the effect as "Venus horns" (see also section: Observation / Basics ).
1927 succeeded Frank Elmore Ross , by ultraviolet shots to become the first structures in the clouds of Venus visible. In 1932, using spectral analysis , it was possible for the first time to detect carbon dioxide as the main component of the Venusian atmosphere.
With the invention of radar and radio astronomy , further new observation possibilities were added in the middle of the 20th century. Microwave observations carried out by a team of astronomers led by Cornell H. Mayer (1921–2005) in 1956 indicated for the first time a very high surface temperature of Venus of at least 600 Kelvin (327 ° C).
In 1957, the French amateur astronomer Charles Boyer (1911-1989), member of the magistrate and president of the Brazzaville Court of Appeal, noticed a dark horizontal Y-structure on his ultraviolet photographs taken of Venus and concluded from their return that there was a four-day, retrograde atmospheric circulation. Outside France, astronomers were initially skeptical of this observation.
The period of rotation of Venus itself could first be measured during the lower conjunction in 1961. This was achieved with the help of a radar beam from the 26-meter antenna in Goldstone , California, the Jodrell Bank Radio Observatory in Great Britain and the Soviet radio telescope in Evpatoria in the Crimea. The retrograde sense of rotation could not be proven until 1964.
The measurement of the transit time of the radar beams also provided exact values for the distance between Venus and the earth in these investigations. In the course of these transit time measurements, the physicist Irwin I. Shapiro succeeded in 1968 in experimentally confirming the Shapiro delay that he predicted in 1964 and named after him . According to the general theory of relativity , the transit time of a radar signal when passing through the sun's gravitational field should be slightly longer than in the classical theory. The effect should be around 200 microseconds for the upper conjunction of Venus. This value has been confirmed with ever greater accuracy since the first measurements.
The surface exploration by means of the earth-based radar survey always only covers the hemisphere of Alpha Regio, with Beta Regio in the west and Ishtar Terra in the north, due to the resonance-like rotation of Venus, which is indirectly linked to the earth's movement. The central zero meridian of this “front” accordingly runs through Alpha Regio. In the north it runs over the Maxwell Montes. The coordinate system of Venus was determined in such a way that the longitudes are counted according to the retrograde rotation from west to east, from 0 ° to 360 ° east longitude. Due to the insignificance of the systematic deviation from a real resonance with only half a degree of longitude in the east, 347 such synodic Venus years have to pass, i.e. 554.7 earth years, until the "back" of Venus is also recorded in this way.
Exploration with space probes
Since the 1960s, a large number of space probes have been launched to the neighboring inner planet, such as the Soviet Venera probes 1 to 8. Some managed a soft landing, with communication times of up to 110 minutes from the surface. A return with samples was not planned.
The way to Venus
A flight to Venus requires less take-off speed than to any other planet. So you only need a speed change of 2.5 km / s to change from a circular orbit with 1 AU around the sun (corresponds to the earth's orbit) to a Hohmann transfer orbit whose perihelion is at Venus. A comparable maneuver for a flight to Mars requires a change in speed of 2.95 km / s. However, this only leads to a flyby of the respective planet.
|Escape from LEO||4.95 km / s||4.95 km / s|
|Hohmann 1||2.50 km / s||2.95 km / s|
|Hohmann 2||2.70 km / s||2.65 km / s|
|Orbit bullet||9.95 km / s||4.70 km / s|
|total||15.85 km / s||11.20 km / s|
In order to reach an orbit around the target planet, one must also switch from the elliptical transfer orbit to a circular orbit around the sun and then slow down into a Venus or Mars orbit. The former costs about the same for Venus and Mars at 2.7 km / s. Braking into an orbit around the target planet (e.g. 500 km above the surface) is, due to the greater mass of Venus, significantly more energy-intensive than that of Mars and, at 9.95 km / s, requires a change in speed that is more than twice as large as that 4.70 km / s on Mars.
The table opposite provides an overview of the required speed changes. The first and last two speed changes only have to be added quadratically for the overall balance due to the Oberth effect . As a result, a Venus flyby is energetically easier to achieve than a Mars flyby, but entering a Venus orbit costs significantly more energy.
Since Venus orbits the sun closer than the earth - its distance from the sun is only 72 percent of the solar distance of the earth - a Venus probe has to fly over 41 million km into the sun's gravitational potential , which leads to a considerable increase in its kinetic energy . Together with the high gravity of Venus, this leads to an increase in the speed of the probe, so that its speed and direction of movement must be changed more than with Mars in order to enter orbit from a flyby orbit.
On February 12, 1961, the Soviet Union launched Venera 1 on its way to Venus. The probe was the first spacecraft to fly to another planet. An overheated orientation sensor caused a malfunction, but for the first time Venera 1 combined all the features required for interplanetary flight: solar panels, parabolic communication antenna, three-axis stabilization, engine for flight path correction and a take-off from a parking orbit around the earth. The probe missed its target and passed Venus 100,000 km away on May 20 without being able to carry out its observations or communicate with Earth.
The first successful Venus probe was the American Mariner 2 , a modified Ranger lunar probe . On December 14, 1962, it was successfully used for a planned flyby over a distance of 34,773 km. She discovered that the planet has no magnetic field and measured its thermal microwave radiation.
Zond 1 started in the Soviet Union on April 2, 1964 , but after a last communication on May 16, radio contact was broken off. The lost probe passed Venus on July 19 at a distance of 110,000 km with no results.
The US's second successful Venus probe, Mariner 5 , passed the planet on October 19, 1967 at a distance of 3990 km. With its radio waves, the main properties of Venus and its atmosphere could be determined more precisely.
On February 5, 1974, Mariner 10 used Venus for a swing-by maneuver on its way to Mercury and transmitted numerous images of it. The probe was the first spacecraft to perform such a maneuver on a planet.
Early landings and orbiters
On March 1, 1966, the descent of the disengaged lander of the Soviet Venera 3 mission ended with an impact. The vehicle was the first probe to reach the surface of another planet, but it did not survive the hard landing . The sister probe Venera 2 failed shortly before the flyby due to overheating.
The landing capsule of the Venera 4 was immersed in the Venusian atmosphere on October 18, 1967. She measured temperature, pressure and density, and also carried out eleven automatic chemical experiments to analyze the atmosphere. It became the first space probe to provide direct measurement data from another planet. The data showed a carbon dioxide content of 95% and, in combination with the data from the Mariner 5 probe, a much higher than expected atmospheric pressure of 75 to 100 bar.
These data were confirmed and refined by the Venera 5 and Venera 6 missions on May 16 and 17, 1969. But none of these space probes reached the surface of Venus intact. The battery in Venera 4 drained while the probe was floating through the unexpectedly extremely dense atmosphere. Venera 5 and 6 were crushed by the high external pressure at a height of about 18 km above the ground.
The first successful landing was with the probe Venera 7 on December 15, 1970. It measured surface temperatures from 457 to 474 ° C and an external pressure of 90 bar. Venera 8 landed on July 22, 1972. In addition to the pressure and temperature profiles obtained, showed a light meter that the clouds form a layer that ends 35 km above the surface. A gamma ray spectrometer analyzed the chemical composition of the soil rock.
The Soviet space probe Venera 9 , the first of the new generation of heavy space probes to be launched with new proton rockets , entered Venus orbit on October 22, 1975. It thus became the first artificial satellite of Venus. A large number of cameras and spectrometers provided data on clouds, ionosphere and magnetosphere and also carried out the first bistatic radar measurements of the surface of Venus.
The 660 kg landing capsule from Venera 9 landed around an hour after separating from the orbiter . She provided the first images of the surface and also examined the soil with a gamma ray spectrometer and a densitometer. During the descent, pressure, temperature and light conditions were measured; In addition, measurements of cloud density were carried out with backscattering and multi-angle scattering (fog measuring device). The measurement data made it clear that the clouds are arranged in three separate layers. The sister probe Venera 10 arrived on October 25 and carried out a similar measurement program.
In 1978 NASA dispatched two Pioneer space probes to Venus: the orbiter Pioneer-Venus 1 and the multiprobe probe Pioneer-Venus 2, which were launched separately.
The Multiprobe probe had one large and three smaller atmospheric probes on board. The large probe was released on November 16, 1978, the three smaller ones on November 20. All four entered the atmosphere on December 9, followed by the launch vehicle itself. Although the probes were not designed to survive a landing, one of them radioed back data for 45 minutes after reaching the surface.
The Pioneer Venus orbiter reached an elliptical Venus orbit on December 4, 1978. He had 17 experiments on board, mapped Venus with radar (with a resolution of around 20 kilometers per pixel) and analyzed the highest layers of the atmosphere while flying through them in order to research their composition and the interactions between the high atmosphere and the solar wind. The orbiter was operated until the propellant used for position correction ran out. It was destroyed by burning up in the atmosphere in August 1992.
Further Soviet successes
Also in 1978, Venera 11 and Venera 12 passed Venus and released their landing capsules, which entered the atmosphere on December 21st and 25th. The landers carried color cameras, a ground drill, and an analyzer, none of which were working. Each lander carried out measurements with a fog meter, a mass spectrometer and a gas chromatograph. In addition, with the help of X-rays, an unexpectedly high proportion of chlorine in the clouds was discovered, in addition to the already known sulfur . Strong lightning activity was also measured.
Venera 13 and Venera 14 performed practically the same mission. They reached Venus on March 1st and 5th, 1982. This time the drilling and analysis experiments were successful, the color cameras also worked perfectly. An X-ray irradiation of the soil samples showed results that at Venera 13 were similar to basalt rich in potassium and 900 km further southeast, at the landing site of Venera 14, resembled the basalts of the terrestrial ocean floor.
On October 10 and 11, Venera 15 and Venera 16 entered polar orbits around Venus. Venera 15 observed and mapped the upper atmosphere with an infrared Fourier spectrometer. From November 10 to July 10, both satellites mapped the northern third of the planet's surface with a synthetic aperture radar . A total of about 30 percent of the surface could be recorded with a resolution of one to two kilometers, the created maps were about 10 times more detailed than those of Pioneer Venus 1. The results allowed the first more concrete ideas of the geological development of Venus.
The Soviet space probes Vega 1 and Vega 2 reached Venus on June 11th and 15th, 1985. The experiments of their landing units were focused on the study of the cloud composition and structure. Each lander carried an ultraviolet absorption spectrometer and a device to measure the size of the aerosol particles, as well as devices for collecting atmospheric samples, which were examined using a mass spectrometer, a gas chromatograph and an X-ray spectrometer. The two upper layers of the cloud were found to be composed of sulfuric acid, the lower layer probably composed of phosphoric acid. A drill rig and a gamma ray spectrometer were used on the surface of Venus. There were no pictures of the surface - the landers had no cameras on board. These were also the last landings on the surface of Venus so far.
The Vegas probes also each released a balloon in the atmosphere of Venus, which floated at an altitude of about 53 km for 46 and 60 hours respectively. During this time, the balloons covered a distance of about a third of the circumference of Venus and measured wind speed, temperature, pressure and cloud density. More storm and current activity was discovered than expected, as well as sudden changes in flight altitude by one to three kilometers. The Vega mother probes continued to fly to Halley's Comet , which they reached nine months later.
On August 10, 1990, Magellan, after Pioneer-Venus, reached the next US space probe into an orbit around Venus. The only instrument on the probe was a synthetic aperture radar , which was intended to map the surface of Venus. In the years that followed, 98% of the surface was mapped from 89 ° north to 89 ° south, with a resolution of around 100 meters per pixel. The maps were 200 times more detailed than Pioneer-Venus 1 and at least 15 times more detailed than Venera 15 and Venera 16. In addition, in the final phase of the mission, the orbit of the probe was chosen so that it flew through the uppermost layers of the atmosphere, allowing conclusions to be drawn about the density and composition of the atmosphere. As a result of these maneuvers, the already barely functioning probe was constantly slowed down and finally entered the deeper layers of Venus' atmosphere on October 12, 1994 and burned up; however, it cannot be ruled out that some residual parts of the probe reached the surface. We owe the Magellan probe the best of the maps of Venus available today.
Flyby in the 1990s
Some space probes on their way to targets far outside the Earth's orbit used Venus to increase their speed by swing-by maneuvers. In the 1990s, these were once the Galileo mission to Jupiter and twice the Cassini-Huygens mission to Saturn .
In 1990, the Galileo space probe made it possible for the first time to acquire spectral images of the surface of Venus in the “window” of the near infrared range . However, the resolution of these thermal images was very low, and because of the high speed of the probe during one flyby, only a small part of the planet was covered.
The onboard instruments of Cassini-Huygens were able to provide a lot of scientific data at the meetings in 1998 and 1999. The radar constructed for Saturn's moons resulted in the most accurate mapping of some Venus regions to date. Contrary to the data from the Soviet venereal probes, magnetometer tests showed no lightning from the 48-kilometer-high Venusian clouds.
Missions from 2000
From April 2006 until the end of the mission and the glowing up in the Venusian atmosphere at the end of 2014, Venus Express , the first Venus probe of the European Space Agency (ESA), examined the atmosphere and the surface of the planet. Above all, the mission gave researchers far more accurate data on the atmosphere and cloud cover. With her magnetometer, the unequivocal detection of lightning on Venus could be provided.
With MESSENGER , a US space probe orbited Mercury , which, among other things, used two flybys of Venus such as Mariner 10 to reduce orbital angular momentum in order to get to its destination far within Earth's orbit. The first of these swing-bys took place on October 24, 2006. However, Venus and the probe were in upper conjunction , i.e. behind the sun when viewed from Earth, so that no images or measurement data were transmitted due to the severely restricted radio traffic could become. The second passage was completed on June 6, 2007; For this time, all measuring instruments could be used at a distance of only 337 km. Due to the current mission of the orbiter Venus Express, Venus was examined by two space probes simultaneously for the first time during this flyby. This second MESSENGER swing-by took place on the face of the planet just facing Earth, while Venus Express was on the opposite side; As a result, a synchronous investigation of the same area was not possible, but the different investigation methods of the two probes complement each other somewhat offset in time.
The Japanese space agency JAXA launched the small Venus orbiter Akatsuki on May 20, 2010 . It was planned for a mission period of 4.5 years in total and after its arrival on December 8, 2010, it was supposed to observe Venus with cooled cameras in infrared light and study the superrotation of the atmosphere. Swinging the probe into Venus orbit initially failed. A second attempt on December 6, 2015 was then successful.
The NASA solar probe Parker Solar Probe was launched on August 12, 2018 and will complete a total of seven swing-by maneuvers on Venus: on October 3, 2018, on December 22, 2019, on July 6, 2020 [obsolete] , on September 16 , 2018 February and October 11, 2021, August 16, 2023 and November 2, 2024 .
- For the JUICE probe planned by ESA, one of several swing-by maneuvers is planned for Venus. It is scheduled to start in June 2022.
- Russia wants to build on the earlier Venera successes of the Soviet era with a new landing mission called Venera-D . But this time, unlike its predecessors, the lander should be able to remain in operation for several hours on the surface of Venus. The start is scheduled for 2025 at the earliest.
- The USA are also thinking about new missions to Venus , among other things as part of the New Frontiers program : The Venus lander SAGE (Surface and Atmosphere Geochemical Explorer) was supposed to start in the period 2015-2018, but could not stand up to the asteroid probe OSIRIS-REx push through. A large flagship mission is also being investigated that would, among other things, operate one or two balloons in the atmosphere.
- USA: Venus missions are also possible as part of the Discovery program : DAVINCI (Deep Atmosphere Venus Investigation of Noble Gases, Chemistry, and Imaging) is to investigate the Venus atmosphere. VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) is supposed to map Venus in an even higher resolution than Magellan's. However, the realization of these projects is still uncertain as there are other mission proposals for other celestial bodies to choose from.
Among the luminous points in the sky, Venus is the most striking. The oldest known pictorial representation of the walking star is on a Babylonian boundary stone, a kudurru of King Meli-Sipak from the 12th century BC. In addition to the symbols of the sun disk and the crescent moon, the stone relief shows Venus as a star with eight rays. The eight-pointed star symbol in Babylon also stood for the goddess Ištar . For the approximately 4000 year old Nebra sky disc, there is an interpretation that some of the gold dots distributed on it represent the movement pattern of Venus.
Because Venus is one of the lower planets, i.e. its orbit around the sun is within the earth's orbit, in contrast to the upper planets , it can never face the sun in the celestial sphere, i.e. come into opposition . Instead, instead of the conjunction of the outer planets, a distinction is made between the upper conjunction (Venus behind the sun) and the lower conjunction , in which Venus is in front of the sun. The greatest elongation - that is, the greatest possible east and west angular distance to the sun - is 48 °.
The inclination of Venus' orbit against the plane of the earth's orbit is about 3.4 °. Despite this relatively small inclination, it is very rare (also in comparison to Mercury) that there is a so-called passage in front of the sun disk in the lower conjunction . Since Venus is only about 41 million km away from Earth in the lower conjunction, an angular distance of up to almost 9 ° to the solar disk can result in perspective. So it can be seen for a few days (when passing north of the sun in the northern hemisphere and when passing south of the sun in the southern hemisphere) both in the evening and in the morning sky. There was not a single Venus transit in the 20th century.
On the other hand, because of its relatively large orbital inclination , the planet can sometimes become double-sighted , in that it can be observed with the naked eye both in bright dawn and bright dusk . This is possible in the days around the lower conjunction , when it does not just pass the sun, but up to 8 ° north or south of it.
If Venus is east of the sun, it can be observed as an evening star in the western sky ; if it is west, it can be seen as a morning star in the eastern sky . Visibility times of up to 4.5 hours (from the rise of Venus to sunrise or from sunset to sunset) are possible if Venus occupies a higher position than the sun in the ecliptic . This effect is strongest in late winter or spring when it is visible as an evening star, and when it appears as a morning star in autumn. Because of its great brightness and its greater angular distance, Venus is much easier to observe than Mercury. If the sky is very clear and the elongation is sufficiently large, it can also be observed with the naked eye during the day.
Due to its orbital movement, Venus shows different phases in the telescope depending on its position, like the phases of the moon . Before and after an upper conjunction (when it is on the other side of the sun) it appears as a small, almost round disc with a diameter of about 10 "( arc seconds ). As the angular distance from the sun increases, it comes closer to the earth, appears larger and takes the form of a decreasing "half-venus" towards maximum easterly elongation. Since the orbit is not circular, but elliptical, the geometrically calculable dichotomy does not fall exactly on the point of time of greatest elongation, but deviates from it by a few days. While Venus continues to strive for the lower conjunction, its angular distance from the sun becomes smaller again, it appears as a narrowing sickle and in the lower conjunction reaches its largest apparent diameter of around 60 ". The apparent brightness of Venus depends on its apparent diameter and phase. It reaches its greatest brightness (greatest shine) of around −4.3 m around 35 days before and after the lower conjunction, when around 30 percent of the surface illuminated by the sun can be seen from the earth. At a smaller angular distance to the sun, the refraction and scattering of the sunlight in the denser layers of its atmosphere, a strong elongation of the tips of the shining sickle can be observed, the so-called "reaching over the horns". The Venus sickle includes an arc of well over 180 ° near the lower conjunction, although an illuminated sphere should only show a sickle arc of exactly 180 °. The constantly closed cloud cover of Venus denies the eye any insight, but always intensifies its glow. Shortly before the lower conjunction, the crescent arc even completely closes into a circle. However, this effect is difficult to observe because of the close proximity to the sun.
The synodic visibility cycle of Venus is repeated five times in succession in front of a different star background according to the pentagram-like distribution of the conjuncture points on its path . Depending on the position in the ecliptic , two out of every five morning and evening visibilities are significantly more noticeable. This entire star cycle is repeated every eight years, almost to the day.
Venus is the third brightest object in the sky after the sun and the moon. After them it is the third celestial body that can cast a shadow on earth - even if only very weakly at the time of its greatest shine in the moonless nights in very dark areas. It is the only one of the five planets visible to the naked eye that can be found high above the horizon under favorable conditions in a bright daytime sky . Its eastern elongation provides evening visibility, and western elongation offers morning visibility. In these positions it is seen as the first or last clear star during twilight .
Of all the orbits among the planets in the solar system, the distance between those of Venus and Earth is the smallest. On average over time, however, Mercury is the closest to both Venus and Earth. The two planets come closest to each other when Venus for the lower conjunction is in aphelion and the earth is in perihelion if possible. The closest to earth since 1800 was reached on December 16, 1850 with 0.26413854 AU or 39,514,827 kilometers. Only on December 16, 2101, Venus will come almost as close to Earth as it was then at a distance of 0.26431736 AU or 39,541,578 kilometers (see also: Apsid rotation ).
If the lower conjunction meets the junction of Venus' orbit (an intersection with the ecliptic ), Venus is exactly in front of the solar disk and there is a transit . The last passage of Venus occurred on June 6th, 2012 and was seen in its final phase in Central Europe, the penultimate one on June 8th, 2004 was seen in full length in Europe. Further passages of Venus (according to the Gregorian calendar ):
- June 5, 1518
- June 2, 1526
- December 7, 1631 ( calculated in advance by Johannes Kepler , not visible in Europe)
- December 4, 1639 ( calculated and observed by Jeremiah Horrocks )
- June 6, 1761 (worldwide coordinated observation expeditions)
- June 3, 1769
- December 9, 1874
- December 6, 1882
- June 8, 2004
- June 6, 2012
- December 11, 2117
- December 8, 2125
- June 11, 2247
- June 9, 2255
Passages of Venus always take place alternately in June or December, because at these times the earth passes the nodes of Venus' orbit. The cycle of the transits is 243 years, with four rounds at intervals of 8 years, 121.5 years, again 8 and then after 105.5 years. By observing a Venus transit from different positions on earth, one can determine the distance earth-sun (the astronomical unit ) by measuring the horizontal parallax .
Coverings by Venus
Mutual occultations between planets are very rare. On May 28, 1737, Venus completely covered Mercury for about 10 minutes. This will happen next time on December 3rd, 2133 for about 13 minutes. The next occultation of Mars by Venus will not take place until June 4, 2327 for around 20 minutes.
On January 3, 1818, Venus covered Jupiter in a ring for a few minutes. On November 22, 2065, it will partially cover it and again on September 14, 2123.
On August 29, 1771, Saturn was briefly partially covered. This will not be repeated until August 12, 2243.
On March 4, 2251, it briefly completely covered Uranus, as well as Neptune on August 21, 2104.
The Sumerians associated the brightest walking star with the goddess Inanna , the Babylonians with Ištar , the goddess of love and war, and Ninsianna referred to the morning star . Even after the knowledge that they were the same celestial body, a distinction was still made in Babylonia and Assyria between morning and evening stars . In ancient Arabia Al-ʿUzzā was the goddess of the morning star, in Syria the brothers Šaḥar and Šalim .
Already at the beginning of the third millennium BC The Egyptians worshiped Venus under the name Netjer-duai as the morning star. In ancient Egypt , the walking star was associated with the goddess Isis .
In ancient China , according to the five-element theory, the planet Venus was assigned to the metal phase. That is why Venus is called “metal star” in Chinese and Japanese (金星Chin. Jīnxīng, Japanese. Kinsei ).
Persia - Iranian mythology
In Iranian mythology , the planet - apart from a possible reference in Yasht 10 to Mithra - is assigned to the deity Anahita , which is reflected in the Middle Persian language in the designation of the heavenly body as "Anāhid" and in Persian as "Nāhid". Here Anahita appears as a deity of water as well as a representation of the mythical cosmic primordial river and fertility.
In early ancient Greece , Venus was known as the morning star Phosphoros (something like "light bringer") - in Latin Lucifer -, sometimes also Eosphoros , and the evening star Hesperos . Only the later Hellenes related this planet to the goddess Aphrodite . Since ancient times, the pentagram has been used as a symbol for both the planet and the goddess Venus . The origin of this symbolism apparently lies in the special periodic movement of the planet, whose most conspicuous positions in the starry sky over a period of eight years describe a very precise pentagram. There are speculations that the Greeks organized the ancient Olympic Games on this cycle. The Venus symbol ♀ known today also stands for the goddess as well as for the planet in astronomy and astrology.
In Germanic mythology , Venus was associated with the goddess Freya . The German term Friday for the day of the week dies veneris, the day of Venus, possibly goes back to the latter . With the Renaissance , the name Venus (Latin for “ grace ”, “ charm ”), the Roman goddess of love, established itself for the planet .
Ancient American mythology
Venus was considered aggressive by the Maya . The success of military campaigns was calculated according to the Venus calendar. In Mesoamerica the god Tlahuizcalpantecuhtli was considered the personification of the morning star, his brother Xolotl is interpreted as the evening star.
In astrology, Venus is, among other things, the symbol of the ability to bond. In addition, this Venus symbol has also stood for the planetary metal copper since ancient times, which was assigned to the planet as the mirror metal of the goddess of love and beauty. Due to the general assignment of a female character in Western and Eastern cultures, the symbol of Venus also stands for femininity in today's society and in biology for the female sex .
In Christian tradition, the morning star is a symbol for the approaching Son of God and his light-filled appearance in the night of the world ( epiphany ). Astronomical theories for dating the star of Bethlehem include various conjunctions of Venus and Jupiter.
Reception in literature, film and music
"Oh thou my fair evening star."
Gottlob Frege illustrated in his essay On Sense and Meaning with the planet Venus the difference between the meaning and meaning of a name in his 1892 essay . His sentence “The morning star is the evening star” is still a standard example in analytic philosophy today .
In the first scientifically substantiated notions of Venus as a world body, this earth-like planet was considered to be a more life-friendly, young and very warm prehistoric world, which is characterized by jungles and deserts under the impenetrable cloud cover, due to its greater proximity to the sun in contrast to Mars . This was then also reflected in the later scientific fantasy of literature and film art, especially in the form of a wide variety of Venusians . With the exploration of the real conditions, especially since the second half of the 1960s, it has become quiet in this regard around Venus.
In the literature
In his future novel Das Erbe der Uraniden , published in 1926, Hans Dominik described Venus as a planet with flora and fauna similar to Earth, but without intelligent or humanoid inhabitants. Space travelers from Earth will find the remains of humanoid space travelers (uranids) from another planetary system who had to land on Venus because of an accident and who died from eating poisonous fruits.
Edgar Rice Burroughs , the creator of Tarzan , wrote a total of nine novels set on Venus from 1932 to 1970, including Pirates of Venus, Lost on Venus and War on Venus. His five-volume Amtor cycle is also called the Venus cycle .
Clive Staples Lewis wrote the novel Perelandra in 1943 - after his name for Venus. This second novel in the trilogy of the same name allegorically describes the travel destination Venus by the linguist Ransom as a planet on which paradise still exists.
In 1948 Robert A. Heinlein published the youth book Space Cadet (space cadets). An American officer student is an applicant for the interplanetary peace patrol in 2075, on duty for the peaceful coexistence of the different planetary peoples, his first trial by fire during a mission on Venus, where he interacts with its (peace-loving) amphibious inhabitants.
In 1950, Immanuel Velikovsky published the speculative book Worlds in Collision, in which Venus plays a central role in a catastrophic worldview . It uses stories and myths to draw conclusions about events over the past 5000 years. The young Venus, which is said to have formed as a comet from matter detached from Jupiter, devastated the earth several times on an irregular path with its comet's tail and through its gravitational and electromagnetic effect.
1951 followed after others with Between Planets (Between Planets), another book by Heinlein for young people, some of which is about Venus. Mars and Venus are colonized by Earth colonists who live in peaceful coexistence with native intelligent species. Here the colonists of the “foggy planet” Venus rebel against the government on earth.
In 1951 Stanisław Lem also published the novel Astronauci, which was published under the German titles Die Astronauten or Planet of Death . The science fiction film The Silent Star was created nine years later based on this novel . see also below.
Other science fiction novels followed, which depict Venus as a primeval jungle world:
- Gustav Harder: The nuclear ship. 1954, via a magnetic field thruster .
- Alexander Robé: SOS from Venus. 1956, about the Cretaceous and dinosaurs .
- Konstantin Volkov: Emergency landing on Venus. 1960, about boranes and silanes as fuel .
- Erich Dolezal : Planet in the Fog. 1962, about terraforming .
- Perry Rhodan booklet novels number 8, 9, 20, 22, 23, 24, all in the years 1961 and 1962. See also Venus in the Perrypedia .
In 1959 the novel Golkonda nuclear volcano by the Strugatzki brothers was published in the Soviet Union, describing the preparation, flight and landing of cosmonauts on Venus around the end of the 20th century. The interest of the geologists from the communist Soviet Union is in a kind of natural reactor on the surface of Venus, the Golkonda crater, in which radioactive ores are formed after a meteorite impact. The cosmonauts' dangerous search for it leads to the death of several participants in the expedition.
In 1964, the novel is The legacy of Phaetonen of Georgi Martynov published in German. Venus and its human-like inhabitants play a secondary role in the very varied story as a stopover in the search for traces of the ancient civilization of the fifth planet Arsenia ( Phaeton ), which was lost as an asteroid belt .
The 31-volume series of books for young people Weltraumpartisanen by Mark Brandis , which appeared in German between 1970 and 1987, chose Venus as the seat of the “Venus-Earth Society for Astronautics” after a terraforming that was not described in detail .
Ben Bova dedicated a volume of his "Grand Tour" through the solar system to Venus. The 2000 novel Venus is about an expensive expedition to find the remains of the son of one of the richest men on earth. An unexpected discovery in the atmosphere, however, almost ends the dangerous undertaking.
In the movie
Based on Stanisław Lem's novel Astronauci , the science fiction film The Silent Star was created between 1959 and 1960 as a joint production of the GDR and Poland (distribution title in Germany: space ship Venus does not answer ). The work relates to the danger of a nuclear world war. After a mysterious find was identified, an international expedition set out to investigate Venus in 1970 and on the way deciphered the evidence of a failed attack on Earth in 1908. When they arrived at their destination, the crew found a lifeless, radioactively contaminated world on which only the automatic systems of an annihilation machine were running, to which the inhabitants of Venus apparently themselves fell victim.
In 1956, It Conquered the World was one of Roger Corman's early films . After radio contact with a missing satellite in the USA, this space monster, which was carrying an invasive plan, is one of the last of its kind to return from Venus. Under the pretext of preventing the self-destruction of mankind, the monster from a cave hiding place with the help of small flying rays brings individual residents of a small American town under its control. In 1966 there was a remake under the title Zontar the Thing from Venus by Larry Buchanan.
In 1958, director Edward Bernds Queen of Outer Space was released . In 1961 the German dubbed version In den Krallen der Venus followed . The satirical plot of beautiful women and real guys takes place in 1985. A spaceship on Earth and its astronauts are thrown off course by an unknown force and abducted to Venus. After a war, all men with a few exceptions were banished to a neighboring planet.
In 1962, director Pavel Kluschanzew released the Soviet feature film Planet of Storms , based on a story of the same name by Alexander Kazantsev . It is about a first and costly expedition to Venus, the surviving participants including a humanoid robot land there separately in two groups according to their own plan and then have to look for each other. You come across primeval forms of life and traces of human-like inhabitants.
In 1961 sang Manfred Krug with the song Venus target's of the Soviet space program.
In 1962 Paul Kuhn brought the love hit We fly out to Venus .
The atmospheric appearance of the counter-twilight arc is called the Belt of Venus because of the morning or evening star that stands out in the twilight .
In 1955, the Venus Glacier on the Antarctic Alexander I Island was named after the planet.
Some traffic routes are named after the planet:
There is a Venusstrasse in the towns of Bayreuth , Berlin-Altglienicke , Berlin-Reinickendorf , Binningen , Bövinghausen (Dortmund) , Brinkum (Stuhr) , Büchenbach , Castrop- Rauxel , Flüren (Wesel) , and Gaimersheim , Germering , Gilching , Hahlen (Minden) , Haimbach (Fulda) , Hamm , Jöllenbeck (Bielefeld) , Krummhörn , Montabaur , Moosburg an der Isar , Nesselwang , Neuwied , Niederbühl (Rastatt) , Niederndorf (Herzogenaurach) , Ringheim (Großostheim) , Solingen , Stotzheim (Euskirchen) , Trotha (Halle) , Velbert , Wagenfeld , Weil (Upper Bavaria) , Wiesbaden-Bierstadt , and Willich .
There is a Venus Trail in Dronten , Essen-Überruhr , Feucht , Frankfurt (Oder) , Fürth , Hütteldorf (Vienna) , Leeuwarden , Magdeburg , Marl , Rieste and Speldorf (Mülheim an der Ruhr) .
There has been a Venus Square in Berlin-Neukölln since 1920 , and a Venus ring in Roringen (Göttingen) since 1984 . Bernau near Berlin and Flensburg have an arc of Venus. The old town of Duisburg-Mitte has a Venusgasse.
- Manned Venus Mission
- Colonization of Venus
- List of the planets of the solar system
- List of discoveries of planets and their moons
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