Loss of water from Venus. I. Hydrodynamic escape of hydrogen |
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Authors: | James F. Kasting James B. Pollack |
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Affiliation: | Space Science Division, NASA Ames Research Center, Moffett Field, California 94035, USA |
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Abstract: | A one-dimensional photochemical-dynamic model is used to study hydrodynamic loss of hydrogen from a primitive, water-rich atmosphere on Venus. The escape flux is calculated as a function of the H2O mixing ratio at the atmospheric cold trap. The cold-trap mixing ratio is then related in an approximate fashion to the H2O concentration in the lower atmosphere. Hydrodynamic escape should have been the dominant loss process for hydrogen when the H2O mass mixing ratio in the lower atmosphere exceeded ~0.1. The escape rate would have depended upon the magnitude of the solar ultraviolet flux and the atmospheric euv heating efficiency and, to a lesser extent, on the O2 content of the atmosphere. The time required for Venus to have lost the bulk of a terrestrial ocean of water is on the order of a billion years. Deutrium would have been swept away along with hydrogen if the escape rate was high enough, but some D/H enrichment should have occurred as the escape rate slowed down. |
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