Electrostatic Waves and Electron Heating Observed over Lunar Magnetic Anomalies

Abstract:

In the absence of a global magnetic field and a thick atmosphere, the surface of the Moon directly interacts with the incident solar wind plasma. This lunar interaction becomes more complicated over the small-scale magnetic anomalies, as large fractions of solar wind electrons and ions can be reflected above these regions and stream back towards the solar wind flow, leading to a number of interesting effects, such as electrostatic instabilities and waves. These electrostatic signatures can also interact with the background plasma, resulting in electron heating and scattering. We present a study of the electrostatic waves and electron heating observed over the lunar magnetic anomalies by analyzing data from the ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun) spacecraft. Based on the measurements made during two lunar flyby events 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. Additionally, we find that ECDI, along with the modified two‐stream instability (MTSI), may provide a mechanism responsible for strong electron isotropic heating observed over the magnetic anomalies.