A theoretical lunar ionosphere

Abstract

The consequences of a mechanism originally used by Herring and Licht for computing a possible lunar ionosphere are investigated in more detail than was done by these authors. The mechanism assumes that protons of the solar flux which strike the moon are re-emitted as hydrogen atoms, some of which are reconverted to protons by charge exchange. There results a single layer ionosphere. In this paper simplifying assumptions made by Herring and Licht of complete spherical symmetry and an everywhere constant mean radial velocity for the emitted atoms are removed. Quite different procedures are then necessary and the effects of an incident flux coming from only one direction are brought out. For typical quiet sun solar stream parameters the resulting ionesphere has a single layer with a maximum electron number density of roughly 350 cm-3 at 0.6 lunar radii above the lunar surface on the moon-sun connecting line. There is only slow variation with angle of the radial location and magnitude of the maximum of the layer until about 60[deg] off this direction; then rapid decreases in both location and magnitude begin. During times of enhanced solar activity the ionesphere according to this model would increase. However, the theory will likely not hold during storms associated with solar magnetic tongues.