ICARUS 130, 475±494 (1997) ARTICLE NO. IS975838 Hydrous Silicates and Water on Venus Mikhail Yu. Zolotov Planetary Chemistry Laboratory, Department of Earth and Planetary Sciences, Washington University, Campus Box 1169, One Brookings Drive, St. Louis, Missouri 63130-4899; Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygin Str. 19, Moscow 117975, Russia and Bruce Fegley, Jr., and Katharina Lodders Planetary Chemistry Laboratory, Department of Earth and Planetary Sciences, Washington University, Campus Box 1169, One Brookings Drive, St. Louis, Missouri 63130-4899 E-mail:
[email protected] Received May 21, 1997; revised September 8, 1997 INTRODUCTION We used thermochemical equilibrium calculations to predict stabilities of pure rock-forming hydrous silicates on Venus' Water vapor, present at 30±45 parts per million by vol- surface as a function of elevation, atmospheric H2O and SO2 ume (ppmv) in Venus' subcloud atmosphere (Drossart concentrations, and oxygen fugacity (f ). About 50 different O2 et al. 1993; Pollack et al. 1993; DeBergh et al. 1995; Mead- hydrous silicates were included in our calculations. We ®nd ows and Crisp 1996; Ignatiev et al. 1997), is one of the three that many of these are unstable on Venus's surface because of most important greenhouse gases (CO ,HO, SO )inthe the low atmospheric H O content of 30±45 parts per million 2 2 2 2 present-day atmosphere of Venus. Water vapor is also the by volume (ppmv) and the high surface temperatures (660 K on Maxwell Montes to 740 K in the plains). Hydrous Fe21- major reservoir of hydrogen in the lower atmosphere, and bearing silicates are unstable due to oxidation to magnetite is an important reactant in chemical weathering reactions and/or hematite at the f of the near-surface atmosphere.