Comment on “Oxygen ionization rates at Mars and Venus: Relative contributions of impact ionization and charge exchange” by M. H. Zhang, J. G. Luhmann, A. F. Nagy, J. R. Spreiter, and S. S. Stahara

The accuracy of estimates of electron impact ionization which are based on the gasdynamic model of the solar wind interaction with Venus is discussed. Employing the hybrid simulations and in situ data on electron temperature or electron fluxes the electron impact ionization is reevaluated. The electron impact ionization rate estimated in this paper is typically 4–8 times less than the value derived from the gasdynamic model Zhang et al. [1993]. During solar maximum the photoionization rate is typically greater than the electron impact ionization rate.