¹Chao Li et al. (>10)
Icarus (in Press) Link to Article [DOI: 10.1016/j.icarus.2026.117349]
¹Institute of Natural Resources Survey, China University of Geosciences, Wuhan 430074, China

Copyright Elsevier

The elemental geochemical characteristics analyzed by the Mars Odyssey Gamma-Ray Spectrometer (GRS) have played a key role in understanding Mars geology and geochemical processes. However, GRS data are typical compositional data with a closure effect, which may introduce uncertainty in mapping Martian elemental geochemical provinces. We present a compositional data analysis (CoDA) based on centered log-ratio (clr) and isometric log-ratio (ilr) transformations to address these problems. Based on CoDA, we sequentially applied Exploratory Data Analysis (EDA), Correlation Analysis (CA), Principal Component Analysis (PCA), and Robust Principal Component Analysis (RPCA) to process the 1451 map bins that included Al, K, Fe, Si, Ca, H₂O, Cl, and S. The EDA analysis shows that the internal structure of the data after the clr transformation is closer to a normal distribution. Only clr-based CA analysis indicates consistently negative correlations between each of the key rock-forming elements (Si, Fe, Ca, Al) and each of the volatile elements (H₂O, Cl, S) at the global scale. When considering the closure effect and outliers in the GRS data, we used ilr-based RPCA to obtain the first three robust principal components that better reflect the multivariate geochemical information of the Martian surface. In particular, the geochemical anomalies revealed by RPC1 for the H₂O-S-Cl and Ca-K-Si-Al-Fe are more closely consistent with the distribution characteristics of low thermal inertia–high albedo and high thermal inertia–low albedo, respectively. Exploratory Hierarchical Cluster Analysis (HCA) based on the first three robust principal components revealed that when the number of clusters was set to five, elemental geochemical provinces better reflected the enrichment patterns of elements on the Martian surface. The element abundance statistics and Modified Box-and-Whisker (MBW) analysis for the seven representative sub-provinces across five geochemical provinces reveal more detailed characteristics of element enrichment and depletion. Some sub-provinces have significantly higher S, Cl, H₂O, and Si contents than the global average due to volcanism (e.g., Olympus Mons, Tharsis Montes, and Elysium Mons) and historical groundwater activity regions (e.g., Meridiani Planum); some are consistent with high-density distribution regions of aqueous minerals. Martian element provinces mapped using the CoDA analysis can be combined with other types of data and geological information for further research.

^1,2Zixian Shi, ¹Zhensheng Wang, ¹Renguang Zuo, ^3,4Shijie Li, ²Yiheng Li, ^2,5Razvan Caracas
Earth and Planetary Science Letters, 696, 120392 Link to Article [DOI: 10.1016/j.epsl.2026.120392]
¹State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, 430074, China
²Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, 1, Rue Jussieu, Paris, 75005, France
³Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
⁴CAS Center for Excellence in Comparative Planetology, Hefei, China
⁵The Research Institute of the University of Bucharest (ICUB), University of Bucharest, Romania

Copyright Elsevier

The Moon-forming giant impact involved a collision between the proto-Earth and a planetary body named Theia. This resulted in the formation of a protolunar disk, where the Moon formed beyond the Roche limit, and the Earth accreted at the center. As the initial bodies are lost, reconstructing this event presents considerable challenges. Here, we place further constraints on the composition and structure of Theia by integrating improved impact numerical modeling with meteorite data. Our findings indicate that the core mass fraction (CMF) of Theia was below ∼6%, as higher values yield physically untenable mantle compositions and conflict with the Moon’s Fe-poor nature. Chemical composition constraints suggest that Theia’s mantle was composed of differentiated materials similar to aubrites, which may have derived predominantly from the mantle of a disintegrated inner Solar System planet analogous to proto-Mercury. The proto-Earth’s mantle exhibited a composition akin to that of the present-day Earth. Our research mitigates the isotope crisis in the Earth–Moon system and offers a pathway to probe Theia’s mantle mineralogy.