Cometary Water on Venus: Implications of Stochastic Impacts 1

The short lifetime of water on Venus suggests t ha t the water abundance is in a near steady-state balance between loss by escape and replenishment by infall. In addition, the observed deuterium-to-hydrogen ratio on Venus is consistent with a steady state and does not necessarily imply a past water excess. We present results of a model incorporating a stochastic cometary source and nonthermal escape of hydrogen that produces the observed water abundance and D / H rat io. The stochastic variability of each of these quantities is shown to be large. We conclude that water on Venus is in a quasi-steady state mediated by large comet impacts and tha t the early history of water on the planet has been obscured by a history of random impacts. © 1988 Academic Press, Inc.