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Venus

Page history last edited by PBworks 13 years, 1 month ago

Venus

 


 

Planetary Data

 

Equatorial diameter12,103.7 km0.949 Earths
Surface area4.60×108 km20.902 Earths
Volume9.28×1011 km30.857 Earths
Mass4.8685×1024 kg0.815 Earths
Mean density5.204 g/cm3
Equatorial gravity8.87 m/s20.904 g
Escape velocity10.36 km/s
Rotation period−243.0185 d
Rotation velocity6.52 km/h(at the equator)
Axial tilt2.64°
Right ascension of North pole272.76°18 h 11 min 2 s
Declination67.16°
Albedo0.65
Surface* temp.min*228 K
mean737 K
max 773 K

 

(*min temperature refers to cloud tops only)

 

 

 

Atmospheric Data

Avg Atmospheric pressure9.3 MPa
Height250km
Constituents
Carbon dioxide~96.5%
Nitrogen~3.5%
Sulfur dioxide.015% (150ppm)
Argon.007% (70ppm)
Oxygen0.0001-0.0020%
Water vapor0.0001-0.0050%
Carbon monoxide.0017%(17ppm)
Helium.0012%(12ppm)
Neon.0007%(7ppm)
Carbonyl sulfidetrace
Hydrogen chloridetrace
Hydrogen fluoridetrace

 

Unsorted Refs

'Heavy metal' snow on blazing Venus is lead sulfide (galena). "When we looked at the chemistry, we found that the best candidates were actually lead and bismuth sulfides."

(link)

 

Magellan also revealed that the Venusian highlands are unusually bright, reflecting radar beams much better than lower elevations. Several explanations have been put forward, ranging from the presence of loose soil to a covering of metal "snow".

At Venus's hot lower layers, many metals would be vaporised and exist as a metallic mist. But at higher elevations, where it is a little cooler, they could condense to form a thin, highly reflective layer on the ground.

As for what the snow is made from, the rare metal tellurium and iron pyrites, or "Fool's Gold", have both been proposed as candidates.

Recent work by a team at the Washington University at St Louis suggests the metallic frost is more likely to be sulphides of lead or bismuth.

(link)

 

Detailed composition. - other components that CO2 (CO, HCl, HF) were highlighted with the development of the instrumental techniques after the second world war, also by infra-red spectroscopy, but it is only in 1967, with the module of descent of the Soviet probe Venera-4, that the concentrations of the components could for the first time measured in-situ. The analysis by gas chromatography, starting from the automatic mission Venera-11 (1978), revealed new minor molecular components such as H2, O2, Kr, H2O, H2S and COS. The presence of sulphur dioxide (SO2) is established in 1979 by the observation with average spectral resolution in the ultraviolet close relation since the Earth. Although in small quantities, this very reactive gas is an essential element of the chemistry of the atmosphere of Venus. Steam was detected in extremely small quantities (approximately 30 parts per million or ppm, 1 ppm = 0,001 %), which makes of Venus the driest planet of the solar system. The reports/ratios of mixture of CO, H2O and SO2 vary in an important way with altitude and represent the reactions of chemical balance between the various components.

 

Variation in the temperature of the atmosphere of Venus according to altitude, obtained in-situ at the time of the descent in the atmosphere of four automatic probes during the mission Pioneer-Venus in 1979 (milked continuous). On right-hand side, the relative average density of particles of the fogs and clouds according to altitude is represented, revealing several distinct layers. The clouds, located at an altitude included/understood into 45 and 70 km, consist of fine droplets of sulphuric acid in aqueous solution, made up to 75% of sulphuric acid (H2SO4) and to 25 % of water (H2O). Their diameter ranging between some dizièmes of mm and ten mm (1 mm = 10-3 mm). The lower atmosphere of Venus does not receive sunlight with the wavelengths lower than 400 Nm. In visible light, it is hardly 5% of the sunlight which reaches surface.

 

Constitution and formation of the clouds. - The clouds, located at an altitude included/understood into 45 and 70 km, consist of fine droplets of sulphuric acid in aqueous solution, constituted to 75% of sulphuric acid (H2SO4) and to 25 % of water (H2O). Their diameter ranging between some dizièmes of mm and ten mm (1 mm = 10-3 mm), the majority of these particles has a diameter of 0.2 mm or approximately 1 mm. An experiment on board large probe of descent of Pioneer Venus showed that five areas of clouds or fogs consist of particles of composition and optical and physical properties different. Higher fog (upper haze area, 70 km? Z? 90 km) have an average optical thickness from 0,05 to 1,0. At the top of the roadbase of the clouds (upper cloud area, 56.5? Z? 70 km) appear the droplets of H2SO4. The transition course (middle cloud area, 50.5? Z? 56.5 km) and the sub-base (lower cloud area, 47.5? Z? 50.5 km) are characterized by the presence of larger particles being able to reach several microns in diameter. All these particles in liquid phase are formed at very high altitude, on the level of summon roadbase of the clouds, where the ultraviolet radiation of the sun acts by photolysis on the atmospheric components. In particular, gas SO2 forms SO3 while reacting with O, product of the photolysis of CO2, then finally H2SO4 starting from H2O, which passes in the liquid state because of the pressure partial of the sulphur gas species in surrounding gas. Conversely, in the lower atmosphere, one attends the decomposition of the fine droplets of sulphuric acid H2SO4: migrating through the laminated structure of the clouds at the low speed from approximately 1 mm s-1, they are vaporized when they reach the hotter layers of the atmosphere at the base of the sub-base of the clouds, around 40 km of altitude.

(Link)

 

One of the most important confirmations from the first set of data being analysed by the scientists is the detection of the so called 'UV absorbers'- ultraviolet markings on the cloud top, also visible as darker features in the VMC mosaic image. They are so called because they absorb almost half of the solar energy received by the planet. The mysterious substance that causes this absorption still represents a true puzzle for the scientists.

 

"Understanding what is the origin of these ultraviolet markings and what makes their absorbing power so high is one of the major objectives of Venus Express," said Wojciech J. Markiewicz, VMC Principal Investigator, from the Max Planck Institute for Solar System Research in Lindau, Germany. "We now have confirmation that we can actually see them, so we can start working to understand what their source is. Because of their amazing absorbing power, they are very important to understand the overall radiative and thermal balance of the planet, and also the atmospheric dynamics".

 

...

 

"We were truly amazed to see how unexpectedly higher the haze at Venus can get. Actually, on Earth as well as on Venus, at around 20 kilometres it is sometimes possible to see droplets of sulphuric acid. On Earth they come from volcanic eruptions. It makes us wonder if on Venus, where differently from Earth the droplets form very thick clouds, their origin is volcanic too."

 

The haze phenomenon may be due to water condensation in ice crystals on the night side, but it is too early to rule out other explanations. "Now we need to gather and study more data to understand this phenomenon in the high atmosphere - an area that, before SpicaV, was still virtually unexplored," he concluded.

(Link)

 

For two decades, the peroxychloroformyl radical, ClC(O)OO, has played a central role in models of the chemical stability of the Venus atmosphere. No confirmation, however, has been possible in the absence of laboratory measurements for ClC(O)OO. We report the isolation of ClC(O)OO in a cryogenic matrix and its infrared and ultraviolet spectral signatures. These experiments show that ClC(O)OO is thermally and photolytically stable in the Venus atmosphere. These experimental discoveries validate the existence of ClC(O)OO, confirm several longstanding model assumptions, and provide a basis for the astronomical search for this important radical species.

(Link)

 

The Venus atmosphere presents a contrasting situation of a highly oxidized atmosphere with little free oxygen. In current models (Yung and DeMore, 1982; Krasnopolsky and Parshev, 1983), the CO2 atmosphere is stable and the O2 level is a balance between CO2 photolysis and catalytic cycles involving HOx and ClOx species, with the relative importance of the different processes still to be confirmed. However, the O2 abundance in these models is ten times the observational upper limit for this species. Further progress in understanding the level of free oxygen in Venus will require more observations and more laboratory measurements of rate coefficients for potentially important reactions.

(Link)

 

 

Conjecture

Sulphur, Chlorine, Phosphorus and Iron have all been identified as important elements in the cloud material.

 

Geological Data

Despite the fact that Venus appears to have no tectonic plates as such, the planet's surface shows various features usually associated with tectonic activity. Features such as faults, folds, volcanoes, large mountains and rift valleys are caused on Earth by plates moving over the planet's molten interior.

 

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

 

Terrain:

 

~85% rolling planes

~15% highland plateaus & mountain belts

Highlands are concentrated into two regions:

  • Ishtar Terra
  • Aphrodite Terra

These are not ancient highlands like the Moon.

 

Volcanoes:

Common terrain feature

None in chains, suggesting no plate tectonics

Pancake domes & coronae 100-200 km across

Are some volcanoes active today??

Tectonics, but not plate tectonics:

 

High temperatures makes the crustal rock soft.

Upwelling material from the mantle.

Downwelling causing compression.

(Link)

 

Orbital Data

Semi-major axis108,208,926 km0.723 331 99 AU
Orbital circumference680,000,000 km4.545 AU
Eccentricity0.006 773 23
Perihelion107,476,002 km0.718 432 70 AU
Aphelion108,941,849 km0.728 231 28 AU
Orbital period224.700 69 d0.615 197 0 a
Synodic period583.92 d
Avg. orbital speed35.020 km/s
Max. orbital speed35.259 km/s
Min. orbital speed34.784 km/s
Inclination3.394 71°3.86° to Sun's equator
Longitude of the ascending node76.680 69°
Argument of the perihelion54.852 29°
Number of satellites0

 

 

Cytherea

 

 

Links and Refs

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