Venus surface

Fegley Jr, B., Treiman, A. H. Sharpton, V. 1. (1992) Venus surface mineralogy Observational and theoretical constraints. Proc. 22nd Lunar Planet. Sci. Conf. (Lunar Planet. Inst., Houston), pp. 3-19. 

The Pioneer Venus mission provided the first radar imaging and altimetry of Venus surface from synthetic aperture radar on an orbiting spacecraft. Subsequently, the Venera 15 and 16 orbiters also carried out radar imaging and altimetry of part of Venus northern hemisphere. Orbital spacecraft radar observations of Venus culminated with the very successful Magellan mission in the early 1990s. 

The high atmospheric abundances of CO2, SO2, OCS, HCl, and HF on Venus are due to the high temperatures at Venus surface (Fegley and Treiman, 1992). All these gases are present at much lower abundances in the Earth s atmosphere. For example, average mixing ratios in the terrestrial troposphere of CO2, SO2, OCS, HCl, and HF are 360 ppmv, 20-90 pptv, 500 pptv, —1 ppbv, and —25 pptv, respectively (cf. Table 3). Also the major sources and sinks for these gases on Earth are different from their probable sources and sinks on Venus. 

Our knowledge of the geochemistry and mineralogy of Venus surface primarily comes from six types of information (i) elemental analyses of several major elements by X-ray fluorescence (XRF) spectroscopy (ii) analyses of potassium, uranium, and thorium by y-ray spectroscopy ... 

The high temperatures and pressures drive chemical reactions of CO2, SO2, OCS, H2S, HCl, and HF with rocks and minerals on Venus surface. A possible exception is sulfur vapor chemistry initiated by absorption of blue sunlight. After the Mariner 2 flyby Mueller (1963) wrote that Venus surface temperature corresponds with those [temperatures] attained during moderately high degrees of metamorphism on Earth. It is... 

Arguments in favor of carbonates include the following. Some of the flow features on Venus surface look like they were made by magmas, such as carbonatites, with water-Uke rheologies. If correct, these geomorphological interpretations... 

There are two major arguments against carbonates. Most terrestrial carbonates are sedimentary, while Venus is dry without liquid water. However, the high D/H ratio suggests that Venus was wet in the past and carbonates may have formed at that time. Second, calculations and experiments predict that carbonates on Venus will react with atmospheric SO2 to form anhydrite (CaS04). However, the Venera XRF analyses show CaO/SOs ratios less than unity, so Venus surface is not anhydrite saturated. Also, wind-driven erosion may abrade anhydrite layers and expose the underlying carbonate. But at present the questions of whether or not carbonates are present on Venus and are bulfering atmospheric CO2 remain unresolved. Sample return or in situ analyses that are sensitive to calcite and other carbonates are needed to answer these questions. 

The oxidation of Fe " "-bearing minerals in basalt (and other volcanic rocks on Venus surface) is potentially very important for water loss via oxidation of the surface and hydrogen escape to space. The overall process is schematically represented by... 

Another important question is which, if any, gases in Venus atmosphere are buffered by mineral assemblages on Venus surface. Interpretations of data from Pioneer Venus and the Venera and Vega probes about the chemistry of Venus lower atmosphere and surface are based upon this assumption, which has not been verified experimentally. Instead, research shows kinetic control of reactions of SO2 and water vapor with minerals at Venus surface temperatures (Fegley and Prinn, 1989 Johnson and Fegley, 2000). 

Pettengill G. H., Ford P. G., and Simpson R. A. (1996) Electrical properties of the Venus surface from bistatic radar observations. Science 272, 1628-1631. 

Space probes into Venus have shown that its atmosphere consists mostly of carbon dioxide. At the surface of Venus the temperature is 460°C and the pressure is 75 atm. Compare the density of CO2 on Venus surface to that on earth s surface at 25°C and one atmosphere. 

For example stabilities of pure rock-forming hydrous silicates on Venus surface as a function of elevation were investigated by Zolotov, Fegley and Fodders, 1997 [376]. 

Venus surface temperature range from 660 K (on the high Maxwell mountains) to 740 K (in the plains), the water content in the subcloud atmosphere is about 30 ppmv (Bailey, 2009 [15]). 

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