Further studies of non-maxwellian effects associated with the thermal escape of a planetary atmosphere

A recent calculation by Lindenfeld and Shizgal (1979) for the non-Maxwellian effects associated with the thermal escape of a dilute gas from a planetary atmosphere is extended. The modifications include retention of a non-linear term in the integral equation for the velocity distribution function, neglected in the earlier work. The retention of the non-linear term yields for low values of the escape parameter correction factors for the escape flux somewhat in better agreement with the Monte-Carlo results. In addition, the escaping gas density in this paper is given by the barometric distribution, instead of the previous assumption of a constant dependence with altitude. A detailed discussion of the role of the altitude dependence of the number density on the escape flux is also presented.