Solar energetic particles pose significant hazards to space exploration and habitation. In the context of the Moon, understanding the access of these high-energy particles to the lunar environment is critical when studying the composition of the surface, quantifying energy deposition at depth, and when considering the planned exploration during crewed and robotic missions. During its orbit around Earth, the Moon is exposed to the solar wind during approximately two-thirds of the time, where the incident solar energetic particle population has nearly unrestricted access to the lunar surface. However, for the other one-third of its orbit, the Moon is embedded deep within the tail of Earth’s magnetosphere. We show that although the strong terrestrial magnetic field prevents high-energy particles from reaching Earth’s surface, the Moon does not receive the same protection while located within the terrestrial magnetotail. Instead, the high-energy ions and electrons readily penetrate the tail along field lines that are open to the solar wind far downstream of the Moon. By applying a combination of data analysis and modeling techniques, we highlight the overall lack of shielding from these particles at any phase of the lunar orbit during extreme solar energetic particle events, but we also identify localized regions on the surface that may still be protected from precipitation by high-energy electrons by the solid body of the Moon. Our findings provide context for understanding access of high-energy solar particles to the lunar surface and are relevant for the safety of astronauts during the upcoming missions to explore the lunar environment.

Dr. Lucas Liuzzo is an Assistant Research Scientist at UC Berkeley’s Space Sciences Laboratory, where he joined in 2019. He received his PhD from the Georgia Institute of Technology in 2018 and graduated with a bachelor’s degree from the University of Michigan in 2014. Currently, Dr. Liuzzo combines data analysis and modeling techniques to study the plasma interactions of various moons throughout the solar system, with particular interest in characterizing their low- and high-energy plasma environments. He is a science team member of NASA’s THEMIS-ARTEMIS mission, a consultant for ESA’s Juice mission, and is part of the selected DUSTER team from the recently Artemis-IV deployed instrument program that will place a rover and dust detector onto the lunar surface.