VENUS

Data from Wikipedia and NASA (C)

Venus is the second planet of Solar Sistema in order of distance from the sun. It hasn’t of satellites or rings.

Historical signals

Venus is one of the planets more easy individuable in the morning or evening sky and for this is famous since the antiquity, when was called Lucifero like star of mattino or the Vespero like star of the evening.

Observation from Earth

Since the planet is found near the Sun, can be seen of usual only for little hours and in the vicinities of the same Sun: during the day the solar brightness renders it difficultly visible, is instead a lot shining after the sunset, on the horizon to the west, or little before the dawn towards east, compatibly with its position. It has the aspect of a bright star, yellow-whitish color. The orbits of the planet are inner regarding those of the Earth, therefore we will see it to move alternatively to East and the West of the Sun. Periodically it passes in front or behind the Sun, entering therefore in "conjunction"; when the passage happens behind, a superior conjunction is had, when happens in front is had an inferior conjunction. Because of its orbit comprised between the Earth and the Sun, from the Earth Venus shows its phases, analogous to the Moon. Galileo Galilei was the first person to observe the phases of Venus in the December of 1610, noticing also changes in the visible diameter of the planet in the various phases and assuming that it was more distant from the earth when he was in the full phase and more neighbor when it was in the increasing phase. These observations supported the eliocentrica description of Copernico of Solar Sistema. Venus, like Mercury, is not visible from the Earth when it is in the full phase, because in that period is found in the superior conjunction, rising and setting together to the Sun therefore invisibile. Venus is more shining when 25% approximately of its disc are illuminated, typically 37 days before (in the evening sky) or after (in the early sky) its inferior conjunction. The greater elongation happens approximately 70 days before and after its inferior conjunction, when it is illuminated to half, and appears illuminated a few minus the illuminated to the half because of the Schröter effect, noticed in 1793 and explained in 1996 like an effect of its atmosphere. Between these two intervals the planet is visible during the day, if it is known exactly where to watch. The period of retrograde motion is of 20 days on both sides of the inferior conjunction.

Orbital parameters

The orbit of Venus is nearly circular and the variations of the its maximum elongazione are due more to the variation of the distance between Earth and Sun that to the shape of the orbit of Venus. These measure always an included angle between 45° and 47°, giving to the planet a extended visibility more before rising of the Sun or after the sunset. The ecliptic on the horizon is the more important factor for the visibility of Venus. In the boreal hemisphere the inclination is maximum after the sunset in the period of the spring equinox, or before the dawn in the period of the equinox of autumn. The angle formed from its orbit and the ecliptic is important also, in fact Venus can be approached the Earth until 40 million km and catching up an inclination of approximately 8° on the ecliptic, having a strong effect on its visibility. Venus is the planet of the solar system more similar to the Earth for various aspects: its mass and the medium density are like those earthlings, being respective equal to 4,869 × 1024 kg (81.5% of earth mass) and 5,25 × 103 kg/m³ (the earth medium density are equal to 5,51 × 103 kg/m³). Its diameter is equal to 12104 km (inferior to that earth of 5%) and the volume is 85.7% of the correspondent earth value. The medium distance of the planet from the Sun is 108 million km (0,723 astronomical units), therefore Venus is the planet with the orbit nearer that earthling, inner regarding the Sun. The orbit is covered in 225 earth days while the period of rotation is amazingly along: measure 243 earth days (more of the period than revolution) and happens in retrograde sense (from east towards the west, that is in hour sense, for an observer place to the North Pole of the planet). Perhaps for via of a gravitational resonance, or for a simple coincidence the periods of rotation and revolution of Venus are sincronizated n such way that the planet shows always the same face towards the Earth when the two planets catch up the minimal mutual distance.

Venus atmosphere

Venus has a dense atmosphere thick 65 kilometers; the pressure to level of the surface is equal to approximately 90 times that one of the Earth. The atmosphere is composed mainly from carbon dioxide (97%), and in smaller amounts from sulfuric acid, noble nitrogen and gases. Oxygen is absent. The highest temperature (around 480°C) created from the effect greenhouse present on the planet does not allow the presence of water to the liquid state, and therefore of life. The dense clouds and the values of pressure and temperature have always rendered much difficult for the probes the survey on the surface and some of they have gone destroyed. The higher clouds travel to a speed of approximately 400 km/h, while lowest they travel to 2 km/h. Since such clouds are composed from sulfuric acid drops, the venusian rains are highly corrosiv and have destroyed some probes. The venusiana atmosphere is crossed from occasional discharge electrical workers of remarkable power. The citerea atmosphere shows moreover small sulphur dioxide and sulfur amounts, probably emitted from volcanos of the planet; these gases, reacting with the insufficient present watery vapor, give origin to sulfuric acid. Although they are sulfuric acid rains in the intermediate layers of the atmosphere, they never do not catch up the surface, because they come vaporizate from the elevated temperatures. The probes landed on the planet have identified the presence of three distinguished cloud layers: a advanced layer, composed from small drips of it sulfuric acid circulars, to a quota of 60-70 km; a intermediate layer, constituted from greater and less numerous drops, placed to 52-59 km of altitude; and finally an inferior layer denser and constituted from the larger particles, that it comes down until 48 km of quota. Under such level the temperature so is elevated vaporizate the drops, generating a haze that extends until 31 km. The lower part of the atmosphere is finally relatively limpid. The Soviet probes Venera, than for first they landed on the venusian surface, were structured like bathyscaphs but survived only a pair of hours to the hostile atmospheric conditions of the planet. To difference of earth clouds, than they are originated from the ascending air cooling and from the consequent condensation of the watery vapor, those venusiane are the product of reactions chemistries that happen between sulphur dioxide and the water, primed from the solar light (in the high atmosphere) or from the heat (more low). Because of the highest atmospheric pressure, to the ground the winds are practically absent; their speed increases with the quota, until catching up a maximum of approximately 360 km/h medium to the top of clouds, above the superior layer of the atmosphere. The entire citereo cloudy layer completes therefore a complete rotation around the planet in only 4 days (for comparison, the period of rotation of Venus is equal to 243 days).

Surface

The citerea surface has a structure much complex, and shows for 60% waved plains cut from goes long hundred of kilometers. It is composed mainly of basaltic cliffs. The planet has two goes plateaus similar to continents. That northerner is called Ishtar Earth, where are present the hightest mountains of Venus: the mounts Maxwell (high 11000 m). That meridional is called Aphrodite Earth. Of the surface of Venus we possess currently least images, envoys to Earth from the Soviet probes Venera between 1975 and 1980. The landscape shown in the photographies is desert, rich of effusive magmatic cliffs (basalts) deriving from the solidification of volcanic washes; it esteem that approximately 85% of the surface of the planet is constituted from solid lavic taps. This is not however sufficient to guarantee that the volcanic activity is still in course in the present, if not in some points of the surface. The last great period of diffused volcanic activity laughed to 800 million years ago (the most ancient lava would be datable around that age). The venusian surface has turned out to be particularly uniform, without excessiv unevennesses (max 2 km), probably because of the highest atmospheric pressure. Approximately 65% of the surface is covered from waved plains; there are moreover some continental plateaus that emerge above the medium level (6051 km from the center of the planet). The main continents are Ishtar Earth, in the northern hemisphere, and Aphrodite Earth, near the Equator. Some characteristic formations found from the probe Magellano are called volcanos plates, perhaps eruptions of wash particularly dense, and the collassate crowns, tettonic cupolas on great magmatic rooms.

Nomenclature

The dominant structures on the venusian surface are the wide waved plains, irregularly interrupted from reliefs. The most extended mountly regions are already cited Aphrodite Terra and Ishtar Earth; this last one is dominated from a great plateau, the Lakshmi Planum, encircled from the hightest mountains of Venus. Between two plateaus are present immense depressions that take the generic name of planitiae. Inner structure thinks commonly that the inner structure of Venus coincides with that one of the Earth; the crust would have to be sturdier and therefore to resist better to the sollicitations caused from the convettiv currents of the cape. The inner nucleus of Venus it believed is ferrous, since the planet is much similar one to the Earth in structure and dimensions, and is in fused state because of a magnetic field, except that one of the solar wind. It thinks that the nucleus has a thickness of approximately 3000 km and the cape of approximately 2900 km, while the crust would have to be little inferior to that earthling, that is approximately 60 km. The analyses completed from the Soviet probes indicate that the structure of the crust and of the surface is similar to the granito and to the basalt. Because of the convection of the cape on the surface are produced some anomalies, (corrugamenti, rigonfiamenti, splits etc.) that but they are concentrated in small zones and not to the limit of tettoniche sods. The radioactive decay to the inside of the planet generates heat that arrives to the outside through shapes of vulcanism and zones where the crust is thin generating characteristic said formations domes.

Exploration

Has been completed many missions without crew on Venus: ten Russian probes have carried out a soft landing on the surface, with more than 110 minuts of communications from the surface. The launch windows ollow every 19 months, and from 1962 to 1985 they were numerous launch of probes. On 12 February 1961 the Soviet probe Venera 1 was the first to being sended on an other planet. The overheating of the guideline sensor provoked an breakdown that it made to lose the contacts seven days after the beginning of the mission, when the probe was 2 million Km from the Earth, but it comprised all the members of a interplanetary probe: solar paddles, parabolic antenna for the telemetry, stabilization on the 3 axes, motor of correction of route and the launch from a parking orbit. While the American probe Mariner 1 came lost during the launch, Mariner 2 was the first probe to catch up Venus on 14 December 1962. It measured an extremely high temperature, approximately 425° (placing term to every hypothesis of life on the planet), but it was not in a position to finding the presence of a magnetic field or bands of radiations analogous to the land Bands of van Allen. The Soviet probe Zond 1, launch towards Venus on 2 april 1964 went in damage after the session of telemetry of 16 May. In 1967 the probe Venera 4 was the first to send data from the inside of the venusian atmosphere and in the same period the probe Mariner 5 measured the magnetic field of the planet. In 1974 the probe Mariner 10 passed near Venus along its travel towards Mercury and make images to ultraviolet of clouds, demonstrating one speed of the twenty extremely elevated. 1 March 1966 the probe Venera 3 was before to land on an other planet, even if it was not a soft landing. The probe Venera 4 entered in the venusiana atmosphere on 18 October 1967, and for before the time it sended measures from an other planet, between which temperature, pressure, density and 11 chemical experiments for the analysis of the atmosphere. The first data showed that the atmosphere was composed for 95% from carbon dioxide and that the pressure in surface was the much largest one of the forecasts (from 75 to 100 atmospheres). The successive day, 19 October, was the time of the probe Mariner 5. It had been planned like probe of reservoir for Mariner 4; when this last one had happened, Mariner 5 came red-adapt for a mission on Venus, and equipped with instruments more sensitive than those of Mariner 2. The data collected from the probes Mariner 5 and Venera 4 were analyze from a scientific team Soviet-American during the successive year, in a first example of cooperation in the missions space. These data came verified and improve from the twin probes Venera 5 and Venera 6 on 17 May 1969, but no mission still had succeeded to transmit data until to the landing on the surface: the batteries of Venera 4 were unloaded while it was still in the atmosphere (probably because of the high atmospheric density that very slowed down the landing with the parachute) and the probes Venera 5 and 6 were destroyed from the pressure to a height of approximately 18 km. They were planned in order to resist to a pressure of 25 atmospheres, against 75-100 the present ones on the planet. The first succeeding landing was carried out from Venera 7 on 15 Decembers 1970 (planned in order to resist until 180 bars), transmitting data on the temperature for 23 minuteren (from 455 °C to 475 °C) while Venera 8 landed on 22 July 1972, showing that the clouds of the planet formed a layer that finished 22 miles over the surface and analyzing the chemical composition of the crust through a gamma rays spectrometer. The probe Venera 9 entered in orbit on 22 October 1975 becoming the first artificial satellite of Venus. A series of cameras and spectrometers sended to Earth information on clouds, on the ionosphere, magnetosfera and carried out measures radar of the surface. The vehicle of landing (heavy 660 Kg) was separated from the probe and landed on the planet, releasing the first photos of the surface and analyzing the land with aspectrometer to gamma rays and a densimeter. During the reduction they came measured the pressure and the temperature, beyond to photometric surveys and of the density of clouds. It discovered that they were formed from three distinguished layers. A similar scientific program was carried out also from the probe Venera 10, that arrived on the planet on 25 October. NASA sended on Venus two probes Pioneer, composed from two separately launch members: orbiter and a multiprobe. This last one transported three small atmospheric probes and a larger probe, that it came launch 16 November 1978 . They entered in the venusian atmosphere on 9 December. Even if it was not previewed that they survived to the landing, they continued to operate for 45 minutes after to have caught up the ground. The orbiter it came inserted in a elliptic orbit around the planet on 4 December 1978 and executed 17 experiments, operating until the exhaustion of the fuel used in order maintaining the orbit. The probe came destroyed from re-enters in the atmosphere in August 1992. Always in the 1978 the probes Venera 11 and Venera 12 flew towards Venus, throwing modules of landing on 21 December and 25 December. These lander transported colors cameras and an analyzer for the land, than ill-fatedly it did not work. Every lander it carried out measures with a nefelometro, a spectrometer of mass, a gas chromatograph and a chemical analyzer based on fluorescence X that unexpectedly revealed a great chlorine amount in clouds, beyond to sulfur. Also found a strongly activity of lightnings. In 1981 the probe Venera 13 sended the first color image of the surface and analyzed a land champion with fluorescence X, operating for a duration record of 127 minutes on the hostile surface of the planet. In the same Venera 14 found also a possible activity. On 10 and 11 October 1983 Venera 15 and Venera 16 entered in polar orbit. The first mapped the superior atmosphere with a spectrometer to transformed of Fourier in the infrared. From 11 November to the 10 July both mapped the part north of the planet with a radar to synthetic opening, and supplied the first acquaintances detailed of geology, included the discovery of enormous volcano like shield. Venus does not shows tettonica to plates, less than a third party of the planet it is not an only plate. The data of altimetry have a advanced resolution four times to those of the Pioneer missions. In 1985 the Soviet Union, taking advantage of the opportunity to arrange a mission on Venus with the passage of the comet of Halley, launch two probes Vega calls Vega 1 and Vega 2 that reached on the planet on 11 june and on 15 june 1985 and launch a football of helium to a height of 50 Km from the surface (where the temperature and the pressure were like to those of the land surface) in order to study dynamics of the more active part of the venusian atmosphere. The lander transported experiments in order to study the composition and the structure of the aerosol of clouds, through a spectrometer to ultraviolet absorption, an aerosol particle analyzer, and dispositives in order to collect and to analyze to the material of the aerosol through a mass spectrometer, a gas chromatograph, a spectrometer to fluorescence X. It discovered the two superior layers of clouds were composed from sulfuric acid, while the inferior layer probably was composed from a solution of phosphoric acid. The ground came analyzed from a spectrometer to gamma rays, but did not come images because cameras were not previewed. The aerostatic footballs fluctuated to a height of 53 Km approximately for 46 and 60 hours respective, travelling for approximately a third party of the planet and measuring the speed of the winds, the temperature, the pressure and the density of clouds. It came discovered a greater turbulence and convettive activity regarding that one previewed. On 10 August 1990 the Magellano Probe became in orbit around Venus and began a detailed mapping radar. It came mapped 98% of the surface with a resolution of approximately 100m and 95% of the gravitational field. After four years of activity, like planned, the probe sank in the atmosphere on 11 October 1994 and partially vaporized. It is believed that some fragment can have caught up the land. Many probes space directed on other destinations have completed flyby of Venus in order to increase the own speed through the effect of gravitational sling. Between they are included the Galileo mission for Giove and the Cassini-Huygens mission for Saturn, that make two flyby. Curious, during both overflights of 1998 and 1999 of Venus, the Cassini probe examined the emissions radio of the planet without to find no radio wave to vhf (from 0.125 to 16 MHz) generally associated with the lightnings (to the contrary of the surveys of the probes Venera carries out 20 years before). It is believed that, if exists lightnings on Venus, they could derive from activity electrical worker to vlf: the radio signals with frequency inferior to 1 MHz cannot in fact penetrate the ionosphere. Donald Gurnett of the university of the Iowa has examined the radio emissions found from the Galileo probe during the flyby of 1990 concluding that they had been interpreted like a pointer of the presence of lightnings, but the probe Galileo found less to 60 times from Venus of the Cassini probe. Currently the presence of lightnings in the venusiana atmosphere is still controversial. The probe Venus Express of the ESA is studying in detail the planet from its polar orbit, from 11 april 2006. The mapping mission has a duration previewed of two venusiani years (approximately 500 days). The first data of the mission comprise the discovery of an enormous polar vortex to the South Pole of Venus. Futures flyby of missions destined elsewhere comprise the missions Messenger and BepiColombo (directed on Mercury).