Electrostatic Waves and Electron Heating Observed Over Lunar Crustal Magnetic Anomalies

Above lunar crustal magnetic anomalies, large fractions of solar wind electrons and ions can be scattered and stream back toward the solar wind flow, leading to a number of interesting effects such as electrostatic instabilities and waves. These electrostatic structures can also interact with the background plasma, resulting in electron heating and scattering. We study the electrostatic waves and electron heating observed over the lunar magnetic anomalies by analyzing data from the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft. Based on the analysis of two lunar flybys in 2011 and 2013, we find that the electron two‐stream instability (ETSI) and electron cyclotron drift instability (ECDI) may play an important role in driving the electrostatic waves. We also find that ECDI, along with the modified two‐stream instability (MTSI), may provide the mechanisms responsible for substantial isotropic electron heating over the lunar magnetic anomalies. Plain Language Summary Without a global magnetic field or a thick atmosphere, the solar wind directly impacts the surface of the Moon. However, over regions where the lunar crust is strongly magnetized, the charged particles in the solar wind can be reflected and travel back toward the incoming solar wind, generating interesting features like electrostatic waves. These waves can also in turn affect the solar wind by increasing the temperature of its charged particles. To understand the mechanisms causing the waves and heating, we analyze data from the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun spacecraft. Our results indicate that the lunar environment becomes unstable because of the reflected charged particles, thereby creating free energies that lead to the waves and heating. Key Points Two types of electrostatic instabilities are observed over the lunar crustal magnetic anomalies during ARTEMIS flyby Electron two‐stream instability and electron cyclotron drift instability may play an important role in driving the electrostatic waves Electron cyclotron drift instability, along with modified two‐stream instability, may cause isotropic electron heating