Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115011]
1Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, USA
2Solar System Exploration Research Virtual Institute, NASA Ames Research Center, Moffett Field, CA, USA
3Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
The standard view of space weathering on the Moon is that the solar wind and micrometeoroid impacts alter the optical properties of lunar soil. A third process—dielectric breakdown driven by solar energetic particles (SEPs)—has also been suggested to contribute to space weathering. It has been difficult to determine the relative roles of these processes. The Earth’s magnetotail, however, provides a way to distinguish between them, because it affects only charged particles. Earth’s magnetotail blocks the solar wind, and here we show that it also likely reduces the flux of SEPs traveling across the tail and impacting the tail-facing hemisphere of the Moon when it is entering or leaving. Consequently, we make two predictions that distinguish how the tail affects dielectric breakdown weathering patterns from how it affects solar wind weathering patterns. First, the magnetotail should create two minima in the total amount of breakdown weathering that has occurred: one near and a deeper one near longitude. Second, the tail should create east–west asymmetries in the breakdown weathering of crater walls, with the greatest asymmetries occuring at longitude. Although the first prediction has proven difficult to test, we find that the second prediction is supported by observations. Therefore, we conclude that investigations of space weathering must consider, not only micrometeoroid and solar wind bombardment, but also dielectric breakdown.