Exotic Nanophase Iron as a New Agent for Space Weathering on the Moon

Abstract

Nanophase iron (np-Fe) particles in space-weathered lunar regolith are widely concerning as they can change the spectral, chemical, and physical properties of lunar soils. These np-Fe particles were previously believed to be produced from lunar surface materials by space weathering processes, while the source of np-Fe particles from exotic micrometeorite (flux = ∼5 × 108 t/Ma) has been overlooked. In this study, we report the discovery of np-Fe particles in the micrometeorite impactor residue on a plagioclase crystal from Chang’e-5 lunar soil. Our results show that the source of these np-Fe particles does not originate from lunar materials, but rather are sourced from micrometeorites (i.e., exotic origin). This work provides mineralogical evidence that exotic np-Fe particles can be delivered and preserved by micrometeorite impact melting and reduction on the Moon. The estimated production rate of exotic np-Fe particles is as high as ∼5 × 106 t/Ma on the Moon. We therefore suggest that these exotic np-Fe particles have a nonnegligible influence on the interpretation of the space weathering process in special environments (e.g., permanently shadowed regions) of the Moon and other airless planetary bodies in the solar system.