Venus " the evening star "
| || Automatic translation|| ||Category: Planets and dwarf planets|
Updated June 01, 2013
Venus is a planet called interior and telluric, the second from the Sun. It is comparable in size to that of the Earth (6 378,14 km radius for the Earth, 6 051,8 km for Venus). According to the observations, Venus has no magnetic field. Instead, it drags in its wake a plasma tail, long of 45 million km, observed for the first time by the SOHO spacecraft in 1997.
Venus is the third object, the brighter the sky after the Sun and the Moon, it is very easy to identify among the stars.
One can observe phases like the Moon. These observations allowed to say that Galileo's heliocentric theory of Copernicus was true. Venus, because of the high percentage of variation of its distance from Earth, show a strong variation of its apparent size.
For Venus, the diameter varies between 10''and 64''.
Definition of a planet: "A planet is a celestial body that is in orbit around the Sun, which has sufficient mass for its gravity to overcome the cohesive forces of the solid body and maintain hydrostatic equilibrium (spherical), which eliminated any body moving in an orbit close." This definition was approved August 24, 2006, during the 26th General Assembly of the IAU (International Astronomical Union) by a show of hands about 400 scientists and astronomers after ten days of discussions.
nota: A planet is brighter than a star, it shines with a constant brightness among the stars.
The planets twinkle less than stars. To identify the planets must be familiar with the stars of the zodiac as they follow the ecliptic.
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Image: Comparative sizes of the terrestrial planets, Mercury left, Venus, Earth and Mars. The planet Venus represents 0.182% of the total mass of the planets of the solar system.
Atmosphere of Venus
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The size and density of the planet Venus are similar to those of Earth. It is covered with a very thick atmosphere whose mass is 90 times the mass of the Earth's atmosphere, atmospheric pressure is equivalent to that prevailing in 1 000 meters of water in our oceans. This atmosphere is so dense that it traps the sun's rays and create a greenhouse effect, the ground temperature is 470 ° C, the surface temperature is hot enough to melt lead. Weather conditions are extremely severe, it is rather short of hell for the man and then forbid us to go. This is the Mariner 10, which gave us the first picture of Venus. The visible part of Venus is above all, atmosphere. This atmosphere consists of carbon and nitrogen, runs much faster than the planet itself, clouds show abundant active circulation.
Several missions have put gear on the surface of Venus, which allowed to cross its atmosphere of high density, containing water and corrosive gases, such as hydrochloric acid and sulfuric acid. On Venus, meteorology acid does not prevent him from sending devices. They have withstood several hours time to analyze the rocks thick placed on a dusty floor. Venus' surface is relatively flat, it has gradients less than 1000 meters. However, there are mountains whose altitude exceeds 2000 meters, Mount Maxwell rises to 11,000 feet. Venus has no magnetic field. The sun rises in the west of Venus. The axis of the planet was reversed certainly due to the tidal force exerted by the Sun on the dense atmosphere of Venus. Gradually the rotation of the planet has slowed to turn the other way.
|Venus|| || |
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|Semi-major axis|| ||108 208 930 km|
|radius|| ||6 051,8 km|
|surface|| ||4,6x108 km2|
|volume|| ||9,28 x 1011 km3|
|Mass|| ||4,8685x1024 kg |
|rotation speed|| ||6,52 km/h|
|temperature of surface|| ||464 °C|
|mean period of rotation || ||≈243 days|
Venus Express Mission
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Venus Express mission of ESA was launched from Baikonur, Wednesday, November 9, 2005.
Venus Express, derived from the Mars Express takes a lot of aircraft systems and instruments of it.
It is in orbit around Venus since 2006.
Venus had to possess a quantity of water comparable to that of the Earth, but Greenhouse has vaporized the oceans that are easy initial dissipated into space after the runaway greenhouse effect.
Although this planet is closest to the Earth, exploration is difficult. History of missions: Russian probes Vega 1 et 2 (1984), Venera 4 first probe to plunge into the atmosphere of Venus (October 1967), Venera 9 which arose in June 1975 and transmits the first image of its surface, Mariner 2 the first American probe to 'fly' Venus at a distance of 41 000 kilometers (December 1962), Mariner 10, which passes before joining Venus Mercury (1974), Pioneer Venus 1 & 2 (1978) and Magellan (1989-1994) who have mapping is more than 98% of the planet.
The observations revealed that volcanoes on Venus appear to have been active, there are fewer than 2.5 million years.
This suggests that the planet may still be geologically active, which makes Venus one of the few worlds in our solar system have had volcanic activity over the last 3 million years. The small group of objects in our solar system known to have volcanic activity includes the Earth and Io, moon of Jupiter.
Image: Venus Express is a spacecraft of the European Space Agency (ESA) to study the planet Venus. The probe was placed in orbit around Venus in April 11, 2006 for a mission of 486 Earth days. The mission control is ensured, as all European space programs by the European Space Operations Centre (ESOC) of ESA in Darmstadt, Germany.
Artist Image of the probe Venus Express © Mylène Simoès, Art Director.
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Surface of Venus
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The surface of Venus is covered with lava cooled.
This reconstruction of computerized surface of Venus was created from data from the Magellan probe with its radar altimeters set to radio wavelengths, which the Venusian clouds are transparent.
Magellan turned around Venus for 4 years and has used its radar to map the planet from 1990 to 1994.
Magellan found many interesting structures on the surface of Venus, with large circular domes, typically 25 km in diameter (image opposite).
Volcanism appears to be the cause of these domes, although the mechanism remains unknown.
The surface of Venus is so hot and hostile that no surface probe has survived no more than a few minutes.
Image: Magellan probe mapped specifically the surface of Venus using radar altimeters operating at wavelengths at which the Venusian clouds are transparent.
This allowed the computer to reconstruct terrain in the world in computer graphics.
Credit: E. De Jong et al. (JPL), MIPL, Magellan Team, NASA.
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The enigma of Venus
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The sister planet Earth, periodically close to 40 million km, although made of the same mixture of rock, not like at all to the Earth. Venus is the hottest in the solar system. She suffers from an extreme greenhouse effect, the sky is covered at all times. Venus appears to have been fully covered by lava at some point in his life. Everywhere on Venus there is lava, volcanic everything. The atmosphere of Venus is extremely busy in CO2, infrared and heat are trapped at the surface is so intense (470 ° C), no form of life as we know, can not develop there. For a long time, Venus remained opaque, even with the largest telescopes can not see anything of its surface covered with a thick layer of cloud. It was not until 1962 that it is discovered that Venus rotates on its axis very slowly. Its sidereal rotation period of about 243 Earth days, the more it is done in the opposite direction, with only planet Uranus have retrograde rotation. Atmosphere rotates much faster in 4 days. Venus being closer to the Sun than the Earth, solar radiation accelerated the runaway greenhouse effect. Venus has gradually developed a thick, hazy atmosphere.
Volcanoes have generated a large amount of carbon was mixed with oxygen until there is more than just CO2. The Magellan spacecraft between 1989 and 1994, will provide us with real images of Venus by placing in orbit around Venus.
Its radar is sweeping the entire surface of Venus converting radar data in pictures. The planet will become visible to humans. Magellan discovered a thousand large meteorite craters. There are very few small craters, below a few km in diameter.
The dense atmosphere of Venus filter small meteorites that below a certain size, are consumed.
In addition, the number of craters tell us about the age of the craters, some cratered surface is generally younger. The density of meteorite impacts is the same over the entire surface of the planet. This means that the craters are less than a billion years and the traces of old craters have been erased. This proves that there was a significant volcanic activity, there are about 500 million years. No smoking cone was observed, it seems that there is no volcanic activity today. All reliefs, except for the relief of Mount Maxwell, have women's names (Eve, Helen, Cleopatra, Ishtar, Leda, Aphrodite, Diana, Inanna (Babylonian goddess of fertility)...).
Astronomers believe that there are from time to time, major disasters, long periods of intense volcanic activity, which erase the traces of ancient impacts.
For lack of water, plate tectonics on Venus is seized, but Venus in the bowels of the heat will eventually be expelled to the surface.
If no volcanic flow has been detected so far, the next could indicate the onset of a giant cataclysm.
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Image: The Magellan space probe, we found an orange, pretty realistic, the surface of the planet Venus.