He, Ne, and Ar isotope systematics in Chang’e-5 plagioclase reveal diffusive loss and reirradiation processes

Abstract

Understanding the elemental and isotopic composition of the Sun is key to reconstructing planetary formation, atmospheric evolution and solar activity over time. Noble gases from solar wind implanted into lunar regolith provide a unique archive of solar history, but their interpretation is complicated by implantation uncertainties and secondary processes (e.g., diffusion, regolith gardening, solar and galactic cosmic ray exposure). Here we report the isotopic composition of the noble gases (helium, neon, and argon) in thirty six high-purity plagioclase grains from Chang’e-5 lunar soil to assess the preservation of implanted solar wind in lunar materials. Compared with plagioclase from several Apollo sites, the grains retain a more pristine solar wind record, revealing a dynamic equilibrium between solar wind and cosmic ray irradiation and intense diffusive loss driven by localized heating likely due to micro-impacts or temperature gradients at the lunar surface. These coupled mechanisms explain the observed inter-grain He/Ne/Ar variations. Our data further indicate that kinetic diffusion during solar wind implantation, rather than post-implantation alteration, is the primarily driver of elemental fractionation relative to original solar wind values in plagioclase. Collectively, these findings reveal pathways of solar wind-driven noble gas retention and loss in lunar materials and further accounts for the presence of solar wind-derived He and Ne in the lunar exosphere. They also underscore the need to correct for process-related modifications when reconstructing past solar wind compositions, thereby enabling improved inference of solar evolution, planetary volatiles origins, and the initial solar nebula composition.