The interaction between the Moon and the solar wind

TL;DR

This study uses a 3D hybrid plasma model to analyze how the Moon interacts with the solar wind, revealing different wake structures and kinetic features, and comparing results with spacecraft observations.

Contribution

It introduces a hybrid plasma simulation of lunar wake interactions under various magnetic field orientations, highlighting kinetic effects and comparing with real spacecraft data.

Findings

Identified two distinct wake structures based on magnetic field orientation.

Observed kinetic features like magnetic field kinks and density variations.

Model results agree with WIND spacecraft measurements for magnetic fields and ion velocities.

Abstract

We study the interaction between the Moon and the solar wind using a three-dimensional hybrid plasma solver. The proton fluxes and electromagnetical fields are presented for typical solar wind conditions with different magnetic field directions. We find two different wake structures for an interplanetary magnetic field that is perpendicular to the solar wind flow, and for one that is parallell to the flow. The wake for intermediate magnetic field directions will be a mix of these two extreme conditions. Several features are consistent with a fluid interaction, e.g., the presence of a rarefaction cone, and an increased magnetic field in the wake. There are however several kinetic features of the interaction. We find kinks in the magnetic field at the wake boundary. There are also density and magnetic field variations in the far wake, maybe from an ion beam instability related to the wake refill. The results are compared to observations by the WIND spacecraft during a wake crossing. The model magnetic field and ion velocities are in agreement with the measurements. The density and the electron temperature in the central wake are not as well captured by the model, probably from the lack of electron physics in the hybrid model.