¹Satoru Yamamoto,¹Moe Matsuoka,²Hiroshi Nagaoka,³Makiko Ohtake,¹Ayame Ikeda
Journal of Geophysical Research (Planets) (in Press) Link to Artice [https://doi.org/10.1029/2024JE008663]
¹Geological Survey of Japan (GSJ), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
²Earth and Space Exploration Center, Ritsumeikan University, Kusatsu Shiga, Japan
³School of Computer Science and Engineering, The University of Aizu, Aizuwakamatsu, Japan
Published by arrangement with John Wiley & Sons

We studied the global distribution and geological features of lunar surface sites whose spectra indicate an ilmenite-rich composition. Hyperspectral data obtained by the Kaguya Spectral Profiler were used for data mining to identify diagnostic features of a 1- and 2-μ
m spectral reflectance of ilmenite, revealing the global distribution of sites showing ilmenite-rich spectra. The results show that regions with ilmenite-rich spectra are concentrated at the margins of impact basins on the lunar nearside, whereas no such regions are identified in the Feldspathic Highland Terrain or the South Pole-Aitken basin. Using multiband images and a digital terrain model obtained by the Kaguya Multiband Imager and Terrain Camera, we examined the geological features of each site showing ilmenite-rich spectra and found that most of the sites are distributed on pyroclastic deposits overlying highland materials. Spectra interpreted as glass-rich material are prevalent in and around areas having ilmenite-rich spectra. However, sites showing ilmenite-rich spectra do not correspond to mare regions with
-rich basalts. These results may indicate that the concentration of ilmenite in pyroclastic deposits is high enough to exhibit diagnostic features of 1- and 2-μ
m spectral reflectance of ilmenite, whereas the concentration in mare regions with
-rich basalt is not. Since pyroclastic deposits are expected to be extensive, deep unconsolidated deposits of relatively block-free debris, resulting in high processing efficiency in the hydrogen reduction processes, our data may be useful for developing an efficient exploration strategy for ilmenite as a lunar resource.

^1,2Huanyu Wu,^1,2Yuan Zou,³Chi Zhang,³Wei Yang,^2,4Bo Wu,^2,5Kai-Leung Yung,^1,2Qi Zhao
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008787]
¹Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China
²Research Centre for Deep Space Explorations, The Hong Kong Polytechnic University, Hong Kong, China
³Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
⁴Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University, Hong Kong, China
⁵Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hong Kong, China
Published by arrangement with John Wiley & Sons

Chang’e-5 (CE-5) lunar regolith samples were scanned using X-ray micro-computed tomography (micro-CT), and over 0.7 million particles were extracted from the images through machine learning-based segmentation. This is the largest three-dimensional (3D) image data set on lunar regolith particles to date, offering a unique opportunity to study the key characteristics of the lunar regolith. The image intensity was correlated with mineral density, allowing for the assessment of the bulk density (1.58 g/cm3), true density (3.17 g/cm3), and mineralogy of the lunar regolith. Glass and plagioclase contributed 45.6 wt.% of the samples, while pyroxene and olivine made up 49.7 wt.%, and ilmenite accounted for 4.7 wt.%. The median grain size of CE-5 was 57.5 μm, smaller than the Apollo 11, 16 and Luna 16, 20 and 24 samples. Spherical harmonic (SH) analysis and aspect ratio (AR) measurement revealed that the CE-5 lunar regolith particles have more complex shapes than two common terrestrial soils and exhibit less spherical shapes than Apollo 11, 16 and Luna 16, 20 and 24 samples. We recommend using size and shape characteristics cautiously when inferring the lunar regolith maturity because the intrinsic crystal size of the protolith and complex lunar surface weathering can cause significant size and shape variations. Additionally, characterizing particle shapes requires a large sample size (>1,000) to prevent skewed results from outliers. Our non-destructive examination method offers a novel and appealing approach for analyzing critical physical, mineralogical, and morphological properties of million-scale extraterrestrial soil particles, paving the way for future deep space explorations.