Planetary Sciences American and Soviet Research/Proceedings from the U.S.-U.S.S.R. Workshop on Planetary Sciences (1991) / Chapter Skim
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16. Lithospheric and Atmospheric Interaction on the Planet Venus
16. Lithospheric and Atmospheric Interaction on the Planet Venus
Pages 218-233
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From page 218... ...
At the same time, critical issues such as the chemical constituents of the near-surface layer of Venus' atmosphere, cloud particle chemistry, and the mineralogy of iron and sulfur in surface rock obviously cannot be definitely resolved until further landing craft will have been sent to the surface of Venus. Several research projects have been conducted in the USSR and the United States, which used physical-chemical and thermodynamic methods 218
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From page 219... ...
Factual material from the studies of the atmosphere and surface of Venus, gathered with the "Venera" series spacecraft and during the "Pioneer Venus" mission, can be used to compare our view of the distribution, chemical composition, and physical properties of products of lithosphericatmospheric interaction on Venus. MANIFESTATION OF EXOGENIC PROCESSES USING PHOTOGEOLOGICAL DATA The following conclusions on the nature and scope of exogenic processes were made after the probes "Venera-15" and "Venera-16" finished mapping Venus: · The present surface relief of Venus was formed as a result of the combined processes of crater formation, volcanism, and tectonic activity; · The rate of renewal of Venus' relief is estimated to take a million years for the first several centimeters (in the last three billion years)
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From page 220... ...
and wind speed of up to 3 m/see-i, signs of rippling occur when saltation of particles of up to 75 Am in diameter takes place. Theoretical estimates of the threshold rates of the separation of particles of varying dimensions produced similar results.
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From page 221... ...
and chemical (condensation and vaporization of cloud particles, gas-phase reactions, and gas-mineral types of interaction) processes in the atmosphere which lead to the existence of vertical and horizontal gradients of microconstituent concentrations (H2O, SO2 and CO; see Figure 1~.
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From page 222... ...
hypothesis for quite some time. He proposed "Wollastonite" equilibrium as a mechanism for buffering PCO2 in the global, equilibrium atmosphere-crust system (Mueller 1963; Vinogradov and Volkov 1971; Lewis and Kreimendahl 1980~: CaC03 + SiO2 ~ CaSiO3 + CO2 calcite quartz Wollastonite The thermodynamic calculations performed in these studies demonstrated that the mineral association of calcite-quartz-Vollastonite on the surface of Venus can buffer Pcog (~ ~ bar)
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From page 223... ...
processes compete; · The portion of the troposphere below the cloud base, which is the zone where thermochemical equilibria are predominant. This model brought us to a closer understanding of the Venusian troposphere as a complex, predominantly nonequilibrious system, even though numerical estimates of microconstituent concentrations (primarily SO2)
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From page 224... ...
Gas 1 2 3 4 5 6 CO 2.104 5.l0-S l.7.l0-s l.5.l0-S 7.210~ l.7.l0-s H2O 5.104 3.2.104 2.l0-s 2~104 2.l0-s 2.10-5 so2 3.10-7 8.lo-6 1.3.104 1.3.104 1.3.104 1.3.104 H2S 5.lo-6 1.2~10-6 52.lo-8 3.10-7 8~10-9 8.l0-s COS s.lo-s 3.2-10-S 2.3-10-S 2.l0-s 3.lo-6 4elo-s s2 2~10-8 4 10-8 1.8~10-? 10-7 1 3-10-8 2~10-8-8~10-7 H2 7.10-7 10-7 2.410-9 2.lo-8 10-9 2.5.l0-S O2 8 10-26 10-24 10-23 10-23 1.8.10-S Notes: The underlined figures are initial data of measurements on space probes or groundbased facilities; 1: Mueller (1969)
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From page 225... ...
Unfortunately, we have yet to resolve the question of the oxidationreduction regime on Venus' surface, as well as the problem of the existence of free oxygen in the troposphere. THE MINERAL COMPOSITION OF SURFACE ROCK ON VENUS Many investigations have attempted to estimate the possible mineral associations on the surface of Venus using chemical thermodynamic methods.
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From page 226... ...
The computations were based on troposphere chemical analysis data from the Soviet "Venera" series of probes, "Pioneer Venus," thermodynamic constants of about 150 phases, the chemical components of terrestrial magmatic rock, and the results of x-ray-fluorescent analysis of rock at three probe landing sites ("Venera-13," "Venera-14," and "Vega2"~. Compilation of this material can be found in VoLkov et al.
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From page 227... ...
were in contact with the atmosphere longer than the bedrock at the landing sites of the Soviet "Venera-13" and "Venera-14" probes. In his 1985 study, Zolotov conducted thermodynamic assessments of carbonate stability depending on the concentration of SO2, since a reaction such as: CaC03 + 1.5SO2 ~ CaSO4 + CO2 + 0.25S2 takes place in Venus surface conditions free of kinetic constraints.
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From page 228... ...
THE CYCLES OF VOLATILE COMPONENTS Interpretation of data on Venus' atmospheric chemistry, and in particular, consideration of the photochemical processes in the stratosphere (Krasnopolskii 1982; Yung and De More 1982) demonstrated that nitrogen and carbon cycles are completed in the atmosphere.
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From page 229... ...
contemporary geological epoch, participates in the Cyclical mass exchange between the atmosphere and the crust. Sulfur's behavior as a constituent of the cloud layer essentially determines its structure and dynamics.
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From page 230... ...
An excess of SO2 compared with its equilibrium concentration in the atmosphere-crust system create an SO2 flux in the form of sulfates in surface rock. Two factors determine the scales and rates of flux:
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From page 231... ...
surface; The rate of heterogeneous mineral = gas reactions on the planet's The residence span in which mineral particle are in contact with the atmosphere, for example, the surface relief renewal rate. The completing of the "geological" cycle probably occurs as the altered surface rock (rich CaS04)
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From page 232... ...
We can make the following conclusions based on our interpretation of the entire set of observational data: (1) The processes of lithospheric-atmospheric interaction substantially alter primary basalts and subject them to chemical weathering.
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From page 233... ...
1984. Physical-Chemical modeling of the mineral composition of the surface rock of Venus.
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