An Empirical Model to Estimate Abundance of Nanophase Metallic Iron (npFe⁰) in Lunar Soils

Lunar soils gradually become mature when they are exposed to a space environment, and nanophase metallic iron (npFe⁰) generates within them. npFe⁰ significantly changes the optical properties of lunar soils and affects the interpretation of the remotely sensed data of the lunar surface. In this study, a correlation analysis was conducted between npFe⁰ abundance and reflectance spectra at short wavelengths for lunar soil samples in four size groups based on their spectral and compositional data, collected by the Lunar Soil Characterization Consortium (LSCC). Results show that 540 nm single scattering albedo (SSA) of lunar soils correlates well with their corresponding npFe⁰ abundance for each size group of lunar soil samples. However, it is poorly correlated with npFe⁰ abundance when all size groups were considered because of the strong interference from grain size variation of lunar soils. To minimize the effect of grain size, the correlation of npFe⁰ abundance with the spectral ratio of 540 nm/810 nm SSA of all size groups for LSCC samples was calculated and results show that a higher correlation existed between them (R² = 0.91). This ratio can serve as a simple empirical model for estimating npFe⁰ abundance in lunar soils. However, bias could be introduced to the estimation result when lunar soils possess a high content of agglutinitic glass and ilmenite. Our future work will focus on improving the model’s performance for these lunar soils.