The Dominant Role of Energetic Ions in Solar Wind Interaction With the Moon

Abstract

AbstractWe use the results of 3‐D electromagnetic hybrid (kinetic ions and fluid electrons) simulations and observations by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) /Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) spacecraft to investigate the nature of the solar wind interaction with the moon and the resulting wake and tail structure. In the absence of a global magnetic field and an atmosphere at the moon, this interaction is due to the absorption of the solar wind plasma on the dayside and the means by which the resulting cavity in the tail is refilled. To explore this process, we conducted simulations of specific case studies well‐monitored by the ARTEMIS spacecraft. Preliminary runs revealed that when the solar wind core plasma is driving the interaction, the results deviate significantly from observations. When the small population of solar wind energetic ions is incorporated in the model, the observations are reproduced much better. Simulations with different density or energy of energetic ions show considerable changes in the results indicating their dominance in establishing the electromagnetic properties of the tail. In contrast, the results show less sensitivity to the solar wind flow speed. Here we conclude that the structure of the interaction region consists of compressional and rarefaction wakes and a central tail region with areas of enhanced and possibly reduced magnetic field level. The compressional wake diverts the flow away from the tail, and its presence is found to be highly time dependent while the rarefaction wake diverts the flow toward the tail and is found to be a semipermanent feature of the lunar interaction region.