Unrestricted Solar Energetic Particle Access to the Moon While Within the Terrestrial Magnetotail

Abstract

AbstractThis study presents observations of Solar Energetic Particle (SEP) protons that have penetrated Earth's magnetotail to reach the lunar environment. We apply data from Wind as an upstream monitor and compare to observations from THEMIS‐ARTEMIS within the tail to show clear signatures of SEPs at the Moon during two events. Combining modeling and data analysis, we show that SEPs above energies of ∼25 keV gain access to the Moon's position deep within the magnetotail through field lines that are open on one end to the solar wind. These results contradict previous studies that have suggested that the magnetotail is effective in shielding the Moon from SEPs with energies up to 1 GeV. Instead, we highlight that Earth's magnetosphere provides poor protection to the Moon from SEPs, which irradiate the lunar surface even within the tail. Our results have important implications regarding the safety of astronauts during upcoming lunar missions.