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Water loss from Venus: Implications for the Earth's early atmosphereThe atmosphere of Venus outgassed rapidly as a result of planetary heating during accretion, resulting in massive water loss. The processes affecting atmospheric chemistry following accretion have consisted largely of hydrogen escape and internal re-equilibrium. The initial bulk composition of Venus and Earth are assumed to have been roughly similar. Chemical speciation on Venus was controlled by the temperature and oxygen buffering capacity of the surface magma. It is also assumed that the surfaces of planetary bodies of the inner solar system were partly or wholly molten during accretion with a temperature estimated at 1273 to 1573 K. To investigate the range of reasonable initial atmospheric compositions on Venus, limits have to be set for the proportion of total hydrogen and the buffered fugacity of oxygen. Using the C/H ratio of 0.033 set for Earth, virtually all of the water generated during outgassing must later have been lost in order to bring the current CO2/H2O ratio for Venus up to its observed value of 10 sup 4 to 10 sup 5. The proportion of H2O decreases in model atmospheres with successfully higher C/H values, ultimately approaching the depleted values currently observed on Venus. Increasing C/H also results in a rapid increase in CO/H2O and provides an efficient mechanism for water loss by the reaction CO+H2O = CO2 + H2. This reaction, plus water loss mechanisms involving crustal iron, could have removed a very large volume of water from the Venusian atmosphere, even at a low C/H value.
Document ID
19850024774
Document Type
Conference Paper
Authors
Richardson, S. M. (Iowa State Univ. of Science and Technology Ames, United States)
Pollack, J. B. (NASA Ames Research Center Moffett Field, CA, United States)
Reynolds, R. T. (NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
August 12, 2013
Publication Date
January 1, 1985
Publication Information
Publication: Lunar and Planetary Inst. Workshop on the Early Earth: The Interval from Accretion to the Older Archean
Subject Category
LUNAR AND PLANETARY EXPLORATION
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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IDRelationTitle19850024749Analytic PrimaryWorkshop on the Early Earth: The Interval from Accretion to the Older Archean