Article,
The oxidation state of the lower atmosphere and surface of Venus
Icarus, 125 (2): 416--439 (1997)
Abstract
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 (fO(2)) at 0 km is in the range of 10(-21.7) to 10(-20.0)
bars, (3) the fO(2) 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. (C) 1997 Academic
Press.
Tags
- abundance;
- atmosphere;
- deep
- equilibria;
- magnetite
- martian
- nightside;
- oxygen;
- properties;
- spectroscopy;
- thermodynamic
- topography;
