Depletion of satellite atoms in a collisionless exosphere by radiation pressure

Abstract

Hydrogen atoms in Keplerian orbits about a planet are dynamically perturbed by solar Ly α radiation. These perturbations are examined here by analyzing the rates of change of the classical orbital elements, with rather different conclusions from those drawn by Bertaux and Blamont (1973) from numerical integration of sample orbits. There are three main effects: high inclination orbits with eccentricities e ⪆ 0.4 are forced toward the ecliptic plane within a few weeks; the perigees of direct [or retrograde] orbits drift rapidly (i.e., in a few days) toward stable positions roughly westward [or eastward] of the planet; satellite orbits in or near such a stable point rapidly lower their perigees and the satellite's life is ended by a collision in the atmosphere. Thus there are effects tending to diminish the number of highly eccentric orbits with distant apogees in all six principal directions (N, S; Sun, anti-Sun; E, W). The various lifetimes are compared for a sample of initial elements.