Near-lunar proton velocity distribution explained by electrostatic acceleration

Abstract

The observation of parallel ion velocity in the near-lunar wake approximately equal to external solar wind velocity \emph{can} be explained within uncertainties by an analytic electrostatic expansion model. The one-dimensional model frequently used is inadequate because it does not account for the moon's spherical shape. However, application of a more recent generalization to three-dimensions of the solution along characteristics predicts higher velocities, and is probably sufficient to account for the SARA observations on the Chandrayaan-1 space-craft.