Water in planetary interiors and regoliths: Distribut ion, origin, and geochemical implications

초록

Water is a key volatile compound that influences planetary differentiation, magmatism, and surface evolution throughout the Solar System. Once considered anhydrous, the Moon and most asteroids are now known to host structurally bound hydroxyl and molecular H2O within minerals, glasses, and regolith materials. This review integrates sample-based and orbital evidence to summarize the distribution, storage, and geochemical behavior of water across representative planetary bodies such as the Moon, Mars and carbonaceous asteroids such as Ceres, Ryugu, and Bennu. Analytical and isotopic studies using Secondary Ion Mass Spectrometry (SIMS), Fourier-transform infrared spectroscopy (FTIR), and orbital spectroscopy reveal water content ranging from tens of ppm in lunar magmas to several wt % in hydrated asteroids, accompanied by systematic variations in deuterium/protium (D/H) and d18O ratios that record distinct volatile reservoirs and delivery pathways. Water retention and loss are jointly controlled by planetary size, oxidation state, and thermal evolution, according to qualitative synthesis and comparative analysis of published research. Geochemically, even minute amounts of water can mediate regolith alteration and crustal evolution, greatly lower melted viscosity, and affect mantle rheology, which may improve convective processes. Its presence or depletion fundamentally affects planetary habitability and volatile cycling within the inner solar system. Significant uncertainties (analytical, interpretational, and sampling) still exist despite significant advancements in the quantification of hidden reservoirs within deep interiors and in differentiating between endogenous and exogenous sources. Future missions, Artemis, Chang'e-7/8, and Mars Sample Return as well as developments in isotopic microanalysis and data-driven spectral unmixing methods (including machine learning techniques) have the potential to improve our comprehension of planetary hydration and the volatile evolution of terrestrial bodies. (c) 2026 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

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