Dynamics of solar wind protons reflected by the Moon

TL;DR

This paper investigates how solar wind protons are reflected by the Moon's surface, affecting the lunar plasma environment, based on new observations and modeling, with implications for other similar celestial bodies.

Contribution

It provides the first detailed analysis of solar wind proton reflection at the Moon using new velocity spectrum data and modeling, highlighting its impact on the lunar plasma environment.

Findings

Reflected protons influence the Moon's plasma environment

Reflection depends on surface microscopic properties

Process likely occurs at all atmosphereless non-magnetized objects

Abstract

Solar system bodies that lack a significant atmosphere and significant internal magnetic fields, such as the Moon and asteroids, have been considered as passive absorbers of the solar wind. However, ion observations near the Moon by the SELENE spacecraft show that a fraction of the impacting solar wind protons are reflected by the surface of the Moon. Using new observations of the velocity spectrum of these reflected protons by the SARA experiment on-board the Chandrayaan-1 spacecraft at the Moon, we show by modeling that the reflection of solar wind protons will affect the global plasma environment. These global perturbations of the ion fluxes and the magnetic fields will depend on microscopic properties of the object's reflecting surface. This solar wind reflection process could explain past ion observations at the Moon, and the process should occur universally at all atmosphereless non-magnetized objects.