On the loss of gases from a planetary atmosphere

Abstract

An analysis of the collisional transition between the lower atmosphere and the collisionless exosphere is carried out based upon an integral formulation of the Boltzmann equation. This investigation utilizes a collision model which is a combination of Lorentz-gas and relaxation collision models. The results of this analysis indicate that intermolecular collisions act in two ways to affect the atmosphere. First, there is a critical layer, similar to the apparent photospheric surface of the Sun, from which the material escaping from the planet originates. This layer is determined by collision suffered by particles moving on orbits which skim tangentially by the planet. Secondly, collisions reduce the vertical flux of material in a manner analogous to the diffusion processes which occur in the lower atmosphere.