¹Hyunseob Baik, ²Eun-Jin Cho, ¹Kwang-Eun Kim
Icarus (in Press)
Open Access Link to Article [DOI: 10.1016/j.icarus.2026.117341]
¹Resources Exploration & Development Research Division, Korea Institute of Geosciences and Mineral Resources (KIGAM), Daejeon, Republic of Korea
²Division of Space Exploration, Korea Astronomy and Space Science Institute (KASI), Daejeon, Republic of Korea

Copyright Elsevier

The Moon Mineralogy Mapper (M³) acquired 85-band hyperspectral data (430–3000 nm) at 140 m/pixel resolution between 2008 and 2009 for spectral imaging of the lunar surface. Conventional per-pixel methods, such as the Modified Gaussian Model (MGM) and Integrated Band Depth (IBD), have been widely used for lunar mineral detection but address complementary problems and do not provide sub-pixel abundance estimates across entire scenes. In this study, linear spectral unmixing (LSU) with Iterative Error Analysis (IEA) endmember extraction was applied to M³ Level 2 reflectance data for sub-pixel mineral mapping of Theophilus crater. After noise reduction via Minimum Noise Fraction (MNF) and enhancement of absorption features through continuum removal, IEA extracted five image-derived endmembers without prior mineralogical information or reference libraries. The extracted endmembers were subsequently identified against 23 reference spectra from the RELAB and USGS spectral libraries using explicit criteria based on diagnostic absorption-band positions and Pearson correlation (r = 0.87–0.97 for the assigned minerals). Four endmembers were identified as spinel, plagioclase, pyroxene, and OH/H₂O-bearing materials, while the fifth remains unassigned and likely reflects space-weathering effects or mosaicking artifacts. The five-endmember model reconstructs the observed continuum-removed spectra with a mean RMSE of 0.010, and the derived relative abundance maps show a reasonable spatial correspondence with independent Kaguya Multiband Imager mineral maps (Spearman ρ up to 0.63). The resulting maps show spinel concentrated at the central peak, plagioclase dominating the peak and crater walls, and broadly distributed pyroxene, consistent with previous studies. Notably, the unmixing results reveal spatially distinct abundance maxima for spinel and plagioclase within the central peak, suggesting sub-kilometer compositional gradients within the Pink Spinel Anorthosite (PSA) lithology. This sub-pixel approach yields fractional abundance maps that complement conventional per-pixel methods. The combination of library-independent endmember extraction and library-based identification demonstrates that LSU with IEA provides an effective sub-pixel mapping framework for lunar regions where prior mineralogical knowledge is limited.

^1,2Angel Mojarro, ²José C. Aponte, ²Daniel P. Glavin, ²Jamie E. Elsila, ^1,2Jason P. Dworkin, ^3,4,5Harold C. Connolly Jr.
Geochimica et Cosmochimica Acta (in Press)
Open Access
Link to Article [DOI: 10.1016/j.gca.2026.10.003]
¹University of Maryland Baltimore County and Center for Research and Exploration in Space Science and Technology, NASA GSFC, Greenbelt, MD, USA
²Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
³Department of Geology, School of Earth and Environment, Rowan University, Glassboro, New Jersey, USA
⁴Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
⁵Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA

Copyright Elsevier

The return of pristine samples from carbonaceous asteroids Ryugu by JAXA’s Hayabusa2 mission and Bennu by NASA’s OSIRIS-REx mission has enabled the direct comparative study of prebiotic organic compounds across the two primitive bodies. Using pyrolysis, thermochemolysis, and one-pot derivatization coupled to gas chromatography-triple quadrupole-mass spectrometry, we analyzed free volatile, insoluble, and soluble organic matter in a Ryugu aggregate and compared results to a Bennu aggregate and stones of interest. Pyrolysis of the Ryugu sample revealed polycyclic aromatic hydrocarbons, their alkylated homologues, and sulfur-, oxygen-, and nitrogen-bearing heterocyclic aromatic compounds consistent with aqueous alteration of the parent body. One-pot derivatization of the Ryugu aggregate yielded only tentative detections of β-alanine and 2,4-diaminopyrimidine. This is in contrast to the 14 proteinogenic α-amino acids and five canonical nucleobases previously detected across Bennu samples using the same technique. Thermochemolysis of the Ryugu sample revealed limited methylated derivatives while Bennu samples did not yield compounds above the procedural blank. The sparse thermochemolysis detections in samples from both asteroids are notable given that diverse methylated derivatives have been reported from the Orguiel (CI1) and Murchison (CM2) meteorites. We interpret these results as most likely originating from reagent-mineral interactions suppressing TMAH yields. Overall, contrasting organic inventories reflect divergent-parent body histories. Results from the Ryugu samples are consistent with a CI1-like classification, displaying increased alkylation of insoluble organic matter alongside depleted soluble organic matter abundances. In contrast, Bennu preserves heterogeneous organic signatures across stones recording multiple distinct alteration episodes. The presence of prebiotic molecules including amino acids and nucleobases across both asteroids further highlights the significance of carbonaceous bodies in contributing the chemical building blocks of life throughout the early Solar System.