Regolith mineral detection and abundance estimation based on the LMS spectral data of Chang’E-5 lander

Abstract

<p indent="0mm">Determining the mineral components of the lunar regolith is key to understanding the Moon’s genesis and evolution, and it is one of the important scientific objectives of the Chang’E-5 Mission. The <italic>in-situ</italic> spectra collected by the lunar mineralogical spectrometer (LMS) of Chang’E-5 provide valuable data for interpreting the mineral composition of the landing site. However, little work has been performed to analyze the LMS data, and the traditional lunar mineral detection method based on the radiation transfer model cannot simultaneously obtain information on the mineral end-member, abundance, and particle size. To achieve the multiple goals, we propose a sparse unmixing method based on the spectral library of various particle-size minerals. The mineral detection problem is transformed into a sparse optimization problem and solved by the alternating direction algorithm. We have analyzed eight sets of LMS reflectance spectra and found that the lunar soil in the sampling area is composed of agglutinates and glass (49.36%), pyroxene (14.08%), plagioclase (18.58%), ilmenite (16.11%), and olivine (1.86%). The detected mineral composition is consistent with the composition of young lunar mare basalts. In addition, 79.83% of the detected minerals have a small particle size of less than 75 μm, of which the average particle size of olivine, plagioclase, pyroxene, ilmenite, agglutinates, and glass is 48, 205, 59, 37.4, and 9.7 μm, respectively. Differences in mineral particle size suggest that the effects of space weathering on the lunar surface vary by the component minerals. Moreover, the LMS data provide <italic>in-situ</italic> spectral evidence of water existence on the lunar surface, i.e., the spectral absorption at <sc>2850 nm.</sc> We estimate the water content of the sampling area using the effective single-particle absorption-thickness (ESPAT) value and the temperature derived from an improved lunar thermal model that has been cross-validated with the temperature records of several thermal sensors on the Chang’E-5 lander. The result shows that rocks are more hydrous than the regolith at the Cheng’E-5 landing site. The water content of the rock is as high as <sc>201 ppm,</sc> while the average water content of the sampling area is <sc>67 ppm.</sc>