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Science 3 February 1967:
Vol. 155. no. 3762, pp. 556 - 558
DOI: 10.1126/science.155.3762.556
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Articles

Venus: Atmospheric Evolution

Margaret O. Dayhoff 1, Richard V. Eck 1, Ellis R. Lippincott 2, and Carl Sagan 3

1 National Biomedical Research Foundation, Silver Spring, Maryland
2 Department of Chemistry, University of Maryland, College Park
3 Harvard University and Smithsonian Astrophysical Observatory, Cambridge, Massachusetts

Because of the high temperatures prevailing in the lower atmosphere of Venus, its chemistry is dominated by the tendency toward thermodynamic equilibrium. From the atomic composition deduced spectroscopically, the thermodynamic equilibrium composition of the atmosphere of Venus is computed, and the following conclusions drawn. (i) There can be no free carbon, hydrocarbons, formaldehyde, or any other organic molecule present in more than trace amounts. (ii) The original atomic composition of the atmosphere must have included much larger quantities of hydrogen and a carbon/oxygen ratio le 0.5. (This ratio is now almost precisely 0.5.) (iii) The present atomic proportions of the atmosphere of Venus are so unique that an evolutionary mechanism involving two independent processes seems necessary, as follows. Water, originally present in large quantities, has been photodissociated in the upper atmosphere, and the resulting atomic hydrogen has been lost in space. The resulting excess oxygen has been very effectively bound to the surface materials. (iv) There must be some weathering process, for example, violent wind erosion, to disturb and expose a sufficient quantity of reduced surface material to react with the oxygen produced by photodissociation.


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Planetary Probe: Origin of Atmosphere of Venus.
R. F. Mueller and R. F. Mueller (1969)
Science 163, 1322-1324
   Abstract »    PDF »
Dust in the Lower Atmosphere of Venus.
A. D. Anderson and A. D. Anderson (1969)
Science 163, 275-276
   Abstract »    PDF »
Ice Caps on Venus?.
W. F. Libby (1968)
Science 159, 1097-1098
   Abstract »    PDF »


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