Chemical composition Venus atmosphere

Jupiter and Uranus are outer planets composed mainly of gases. Jupiter s atmosphere contains reddish-brown clouds of ammonia. Uranus has an atmosphere made up mainly of hydrogen and helium with clouds of water vapor. This combination looks greenish to an outside observer. In addition, Mars has an atmosphere that is 95% carbon dioxide, and Venus has a permanent cloud cover of sulfur dioxide that appears pale yellow to an observer. Mercury has no permanent atmosphere. Saturn has 1 km thick dust and ice rings that orbit the planet. The eight planets in our solar system are diverse, each having different chemical compositions within and surrounding the planets. Out Earth is by far the friendliest planet for human existence. 

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... 

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). 

The most recent mission to Venus is the European Space Agency s Venus Express spacecraft, launched on November 5, 2005. The spacecraft reached the planet in April 2006 and settled into orbit on May 6. It has now transmitted some of the best images of and data about the planet s atmosphere ever obtained, including the first images ever of its south pole. Among the new data transmitted by Venus Express are the chemical composition of the lower atmosphere, temperature variations at different levels of the atmosphere, temperature measurements of the planet s surface, and reactions between oxygen and nitrogen oxides in the middle and upper atmosphere. 

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...

The chemical composition of the Martian atmosphere is given in Table VI, along with plausible sources and sinks. The abundances are taken primarily from (75), with new abundances for He 20), H2 and HD (27), H2O2 22, 23), and CH4 24). The Martian atmosphere is dominantly CO2, which is continually converted to O2 and CO by solar UV light. However, as on Venus, the observed abundances of CO2, O2, and CO cannot be explained simply by the direct recombination of CO and O atoms to CO2 because this reaction is too slow to maintain the high CO2 and low CO and O2 abundances. Instead, OH radicals produced from atmospheric water vapor by UV photolysis or by reaction with electronically excited O atoms enter into catalytic cycles such as that shown in Table VII, which recombine CO and O atoms to CO2. 

The necessary starting point for any study of the chemistry of a planetary atmosphere is the dissociation of molecules, which results from the absorption of solar ultraviolet radiation. This atmospheric chemistry must take into account not only the general characteristics of the atmosphere (constitution), but also its particular chemical constituents (composition). The absorption of solar radiation can be attributed to carbon dioxide (C02) for Mars and Venus, to molecular oxygen (02) for the Earth, and to methane (CH4) and ammonia (NH3) for Jupiter and the outer planets. 

At this point, it is impossible to assess the likelihood of this, or almost any other hypothesized reaction. The problem is that scientists still lack sufficient data to build models about the structure and composition of Venus s atmosphere and surface and of possible chemical interactions among the components of both. It is for this reason that Venus scholars look forward so eagerly to the results of the Venus Express mission currently under way. The results of that mission should provide much of the data needed about Venus s atmosphere... 

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