Mathematics
Scientific paper
Sep 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992lpico.789...36g&link_type=abstract
In Lunar and Planetary Inst., Papers Presented to the International Colloquium on Venus p 36-37 (SEE N93-14288 04-91)
Mathematics
Atmospheric Models, Hydrology, Mathematical Models, Planetary Composition, Steady State, Venus (Planet), Volcanoes, Water, Water Loss, Water Resources, Estimates, Hydrogen, Isotopes, Monte Carlo Method, Near Infrared Radiation, Outgassing, Pioneer Venus Spacecraft, Planetary Radiation, Recombination Reactions
Scientific paper
In 1987, Grinspoon proposed that the data on hydrogen abundance, isotopic composition, and escape rate were consistent with the hypothesis that water on Venus might be in steady state rather than monotonic decline since the dawn of time. This conclusion was partially based on a derived water lifetime against nonthermal escape of approximately 108 yr. De Bergh et al., preferring the earlier Pioneer Venus value of 200 ppm water to the significantly lower value detected by Bezard et al., found H2O lifetimes of greater than 109 yr. Donahue and Hodges derived H2O lifetimes of 0.4-5 x 10 9 yr. Both these analyses used estimates of H escape flux between 0.4 x 107 and 1 x 107 cm-2s-1 from Rodriguez et al. Yet in more recent Monte Carlo modeling, Hodges and Tinsley found an escape flux due to charge exchange with hot H(+) of 2.8 x 107 cm-2s-1. McElroy et al. estimated an escape flux of 8 x 106 cm-2s-1 from collisions with hot O produced by dissociative recombination of O2(+). Brace et al. estimated an escape flux of 5 x 106 cm-2s-1 from ion escape from the ionotail of Venus. The combined estimated escape flux from all these processes is approximately 4 x 107 cm-2s-1. The most sophisticated analysis to date of near-IR radiation from Venus' nightside reveals a water mixing ratio of approximately 30 ppm, suggesting a lifetime against escape for water of less than 108 yr. Large uncertainties remain in these quantities, yet the data point toward a steady state. Further evaluation of these uncertainties, and new evolutionary modeling incorporating estimates of the outgassing rate from post-Magellan estimates of the volcanic resurfacing rate are presented.
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