The Oxidation State of the Lower Atmosphere and Surface of Venus

Bruce Fegley, Mikhail Yu Zolotov, Katharina Lodders

Research output: Contribution to journalArticlepeer-review

77 Scopus citations


We present a comprehensive study of the redox state of the lower atmosphere and surface of Venus. This study constrains the CO concentration and oxygen fugacity at the surface of Venus. It incorporates: (1) gas phase thermochemical equilibrium and kinetic calculations to model the chemistry of the near-surface atmosphere, (2) a reanalysis of the thermodynamics of the CONTRAST experiment on the Venera 13 and 14 landers, (3) carefully selected thermodynamic data to model the stability of magnetite and hematite on the surface of Venus, and (4) the Venera 9 and 10 lander spectral reflectance data presented by Pieters et al. (1986, Science 234, 1379-1383). The results of our work predict that: (1) the CO concentration at 0 km (735 K) is in the range of 3-20 parts per million by volume, (2) the oxygen fugacity (fO2) at 0 km is in the range of 10-217 to 10-20.0 bars, (3) the fO2 of the atmosphere at 0 km is indistinguishable, within the uncertainties of the thermodynamic data, from the magnetite-hematite phase boundary, (4) gas phase thermochemical equilibrium is reached only, if at all, in the lowest levels of the atmosphere below about 0.7 km (730 K), (5) a disequilibrium region which is more oxidizing than predicted by thermochemical equilibrium exists at higher elevations, and (6) hematite forms at higher elevations due to the more oxidizing conditions in the disequilibrium region. Finally, we suggest experimental, observational, and theoretical studies which can be used to test our predictions and to provide a foundation for the design of experiments on future spacecraft lander missions to Venus.

Original languageEnglish (US)
Pages (from-to)416-439
Number of pages24
Issue number2
StatePublished - Feb 1997
Externally publishedYes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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