Venus, atmospheric composition

Hoffman JH, Hodges RR, McElroy MB, Donahue TM, Kolpin M (1979) Composition and structure of the Venus atmosphere results from Pioneer Venus. Science 205 49-52 Hoffman PE, Kaufman AJ, Halverson GP, Schrag DP (1998) Neoproterozoic snowball earth. Science 281 1342-1346... 

The atmospheric composition of Venus is similar to that of Mars (see Table VIII—3). Carbon dioxide is the main constituent. The CO mixing ratio is about 5 x 10"5, but the Oz mixing ratio is less than 10 6. Minor constituents that are present in the Venus atmosphere but not in the Martian atmosphere are HC1 and HF in mixing ratios of 6 x 10 7 and 1.5 x 10 9, respectively. 

The atmospheric composition of Jupiter is much different from tlx --< of Mars and Venus. It is similar to the primitive stellar atmospheres. I In... 

One important point should be emphasized here. This is the paucity of spacecraft data on the chemical composition and thermal structure of Venus lower atmosphere below —22 km altitude (von Zahn et al., 1983). About 80% of Venus atmospheric mass is below this altitude. Furthermore, altitudes of 0-12 km span the region where the atmosphere is interacting with the surface. However, with three exceptions we have no data on the chemical composition of Venus nearsurface atmosphere. First is the older measurements of CO2 and N2 from crude chemical experiments on the Venera 4-6 landers. Second, the water-vapor profile measured by the Pioneer Venus large probe neutral mass spectrometer. Third, the measurements of water-vapor and gaseous sulfur by spectrophotometer experiments on the Venera II-I4 landers. The gas chromatograph and mass spectrometer experiments on... 

Aug. 17, 1970 Venera 7, lander Dec. 15, 1970, first soft landing on Venus, measured atmospheric composition, pressure, and temperature, survived 23 min (Marov, 1972)... 

Other books of interest include Lewis and Prinn (1984), which emphasizes the use of observational data for understanding the origin, evolution, and present-day chemistry of planetary atmospheres. Krasnopolsky (1986) focuses on chemistry of the atmospheres of Mars and Venus. He also reviews the atmospheric composition, thermal structure, and cloud measurements by the Soviet Venera and Vega missions. Chamberlain and Hunten (1987) is the classic... 

The chemical composition of Venus atmosphere is described below. This discussion is based on sources listed in Table 3, Fegley and Treiman (1992), and Warneck (1988). 

Table 4 summarizes the data on the isotopic composition of Venus atmosphere. Aside from the noble gases, the most important difference between Venus and Earth is the high D/H ratio, which is —150 times greater than the D/H ratio of 1.558 X 10 in standard mean ocean water (SMOW). The high D/H ratio strongly suggests. 

Venus. Venus is characterized only by the immensely valuable but still incomplete and relatively imprecise reconnaissance data from the Pioneer Venus and Venera spacecraft missions of the late 1970s. Additional in situ measurements, at precisions within the capabilities of current spacecraft instrumentation, are now necessary to refine atmospheric evolution models. Unfortunately, the possibilities of documenting the volatile inventories of the interior of the planet are more remote. A significant question that must be addressed is whether nonradiogenic xenon on Venus is compositionally closer to SW-Xe (as seen on Mars) or to the U-Xe that is seen on the Earth and so is expected to have been present within the inner solar system. Also, the extent of xenon fractionation will be an important parameter for hydrodynamic escape models if intense solar EUV radiation drove hydrodynamic escape on the Earth, it would also impact Venus, while losses from the Earth driven by a giant impact would not be recorded there. 

It can clearly be seen from Table 1 that the Earth s atmosphere consists mainly of nitrogen and oxygen. However, this composition, which makes the present life on our planet possible, cannot be considered normal in the solar system. Thus, even the nearest planets like Mars and Venus have a very different atmospheric composition. 

Oyama, V. I., G. C. Carle, F. Woeller, and J. B. Pollack (1979). Venus lower atmospheric composition. Analysis by gas chromatography. Science 203, 802-805. 

Table II gives the chemical composition of Venus atmosphere, which is dominantly CO2 with 3.5% of N2 and smaller amounts of SO2, H2O, CO, and many reactive trace gases. The probable major sources and sinks for each gas are given in Table II. The gas abundances are taken primarily from (II), with new values for H2SO4 (12) and NO (13). Chemistry in Venus lower atmosphere is driven by high temperatures (740 K) and pressures (95 bars) generated by the...

Hoffman JH, Oyama VI, von Zahn U (1980a) Measurements of the Venus lower atmosphere composition a comparison of results. J Geophys Res 85 7871-7881... 

There are limited probe data available for the isotopic composition of the Venus atmosphere, and of course none available for noble gases in the Venus interior. Wieler (2002, this volume, p. 41 his Table 8 and references therein) provides the most recent compilation and assessment of the available data. 

Application to Venus. Data from in situ compositional measurements of the Venus atmosphere by mass spectrometers and gas chromatographs on the Pioneer Venus and Venera spacecraft are reviewed and assessed by von Zahn et al. (1983) an updated summary is set out in Table 8 of Wider (2002). One might suspect that planets as alike as Earth and Venus in size and heliocentric distance would have acquired compositionally similar primary atmospheres from similar sources. It is not obvious, however, from comparison of volatile mass distributions on Earth and Venus, that these two atmospheres are end products of similar evolutionary processes acting on similar primordial volatile sources. Absolute abundances on Venus exceed those on Earth by a factor >70 for Ar, but only by factors of 3-6 for Kr and Xe. Consequently, as noted above, there is a pronounced solar-like signature in relative Ar Kr Xe abundances. This similarity does not extend to Ne the Ne/ Ar ratio is low, close to terrestrial. Venusian Ne/ Ne, however, is significantly higher (i.e., more solar-like) than on Earth, and the nominal value of the Ar/ Ar ratio is somewhat above the terrestrial value. There are no measurements of Kr and Xe isotopic compositions. 

If this is the case, atmospheric compositions on Venus are enormously important in the context of models for the origin and evolution of terrestrial planet volatiles, particular in the case of Xe. The general similarity of nonradiogenic Xe isotope ratios on Earth and Mars is the strongest argument in favor of the fractionation of Xe on common pre-planetary carriers rather than on the planets themselves, although the correspondence does not appear to be exact. The ability of Venusian Xe to rule between the predictions of... 

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