Mineralogy and regolith maturity at the Chang'E-5 landing site inferred from the Lunar Mineralogical Spectrometer

Abstract

Chang'E-5 (CE-5) landed in the northeast of the Oceanus Procellarum and successfully returned ∼1.73 kg lunar samples from a distinctively young mare basalt unit. The reflectance spectra between 0.45 μm to 3.20 μm at the landing site were acquired by the onboard Lunar Mineralogical Spectrometer before and after the sampling. The results from the spectral parameter analysis show the regolith is dominated by clinopyroxene, consistent with both orbital observations and laboratory analyses of the returned CE-5 samples. Optical maturity (OMAT) of regolith in the landing region of CE-5, Chang'E-4 (CE-4), and Chang'E-3 (CE-3) was analyzed, and the results show that the regoliths at CE-5 and CE-3 sites sitting on the ejecta blanket of the relatively young impact craters are both less mature than that at the CE-4 landing site. The OMAT and estimated content of submicroscopic metallic iron (SMFe) in the regolith show no obvious variations between the rock-shielded and unshielded regolith during the CE-5 descent, indicating the disturbance from rocket exhaust did not affect regolith maturity. Similar results on the effects of rocket exhaust were obtained from analyzing the regolith maturity along the CE-4 rover's traverse. Additionally, the surficial regolith and the scooped underlying layer in the centimeter-depth at CE-5 landing area exhibit similar maturities, suggestive of rapid gardening despite the geologically young age of the region. The results presented in this work shed light on the regolith evolution on the Moon and provide vital geological context for the analysis of the returned CE-5 samples.