Near-lunar proton velocity distribution explained by electrostatic acceleration

TL;DR

This paper explains near-lunar proton velocities using an advanced electrostatic model that accounts for the moon's shape, providing a better match to observations than previous simpler models.

Contribution

It introduces a three-dimensional electrostatic expansion model that improves upon previous one-dimensional models for explaining lunar wake ion velocities.

Findings

The model matches Chandrayaan-1 observations of proton velocities.

Three-dimensional modeling predicts higher velocities than 1D models.

Electrostatic acceleration explains the observed near-lunar proton velocities.

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.