Abstract
We developed a numerical model to study the hydrodynamic escape of neutral gas from planetary atmospheres by solving the time-dependent multi-component hydrodynamic equations. Hydrodynamic escape of hydrogen from a planetary atmosphere can remove heavier gases, which can be dragged along with the escaping hydrogen. Application of the developed numerical code to hypothetical episodes of hydrodynamic escape from Venus could solve the following problems: (1) substantial quantities of water may have been lost without the need to oxidize large amounts of the crust, (2) Ar and Ne isotope ratios indicate that Venus lost little or no Ar and 50% or less of its original complement of Ne. We focus the loss mechanism of Venusian water by the photo-dissociation of water vapor in the upper atmosphere, followed by the escape of hydrogen and dragged oxygen to space. And we discuss the effect of infrared cooling by CO, which may radiate away EUV energy that slow the speed of hydrodynamic flow. It would therefore be expected that some loss of Ne occurred, but that no loss of the heavier Ar took place.
