Global Effects of Magnetic Anomalies on the Near‐Surface Lunar Plasma Environment

Abstract The interaction between lunar magnetic anomalies and the solar wind plasma creates unique structures known as “lunar mini‐magnetospheres,” which reflect and partially shield the lunar surface from impinging solar wind protons. Using data from the Sub‐KeV Atom Reflecting Analyzer onboard Chandrayaan‐1, we produce new surface maps of energetic neutral atom (ENA) and reflected proton emissions. We show that solar wind proton precipitation can be reduced by up to 80% inside magnetic anomalies and increased by up to 50% on scales larger than 1,000 km around magnetic anomalies. The morphology of these proton precipitation enhancement and depletion regions varies differently as a function of upstream solar wind dynamic pressure for small, isolated anomalies compared to the large South Pole‐Aitken (SPA) magnetic cluster. In contrast to small magnetic anomalies, which are compressed and less effective at shielding the surface from the solar wind at high dynamic pressures, the SPA magnetic cluster creates a large “mini‐magnetosphere” that alters proton precipitation patterns on global‐scales (>1,000 km) inside and around the cluster. We show that this behavior may result from the interaction between protons reflected by the SPA magnetic anomaly cluster and the solar wind.