^1,3Qi-ao Chen, ¹Wen Yu, ^2,4Hao Yan, ¹Tian Zhang, ¹Hong Tang, ¹Xiongyao Li
Earth and Planetary Science Letters, 692, 120236 (2026) Link to Article [DOI: 10.1016/j.epsl.2026.120236]

¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China
²International Center for Isotope Effects Research, State Key Laboratory of Critical Earth Material Cycling and Mineral Deposits, Nanjing University, Nanjing, 210023, China
³College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, 100049, China
⁴Frontiers Science Center for Critical Earth Material Cycling, School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210023, China
Copyright Elsevier

Solar wind implantation is widely recognized as a primary source of hydroxyl (OH) and water on the lunar surface, yet the kinetics and controlling mechanisms of this process remain poorly constrained. Here we present proton implantation experiments on San Carlos olivine conducted at 20, 90, and 130°C to quantify the kinetics and saturation behavior of OH formation. The OH abundance increases with H⁺ fluence following an exponential function and approaches a temperature-dependent saturation level. The fitted saturation concentration decreases with increasing temperature, whereas the apparent rate constant increases, indicating a decoupling between reaction kinetics and OH yield. Post-implantation heating experiments demonstrate negligible OH loss, ruling out thermal instability as the cause of reduced OH abundance at elevated temperatures. Instead, we propose a temperature-dependent branching mechanism in which implanted hydrogen partitions between OH formation and H₂ recombination. Higher temperatures enhance hydrogen mobility, promoting H-H recombination and suppressing OH formation efficiency. The conversion ratio of H⁺ to OH decreases progressively with fluence, providing a unified explanation for the large discrepancies reported in previous studies. These results provide a quantitative framework for solar wind-induced water formation and a mechanistic explanation for the latitude-dependent distribution of OH/H₂O on the Moon.

¹Dante S. Lauretta (>10)
Meteoritics & Planetary Science, 59, 9, 2453–2486 (2024) Open Source Link to Article [10.1111/maps.14227]

¹Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
Published by arrangement with John Wiley & Sons

On September 24, 2023, NASA’s OSIRIS-REx mission dropped a capsule to Earth containing ~120 g of pristine carbonaceous regolith from Bennu. We describe the delivery and initial allocation of this asteroid sample and introduce its bulk physical, chemical, and mineralogical properties from early analyses. The regolith is very dark overall, with higher-reflectance inclusions and particles interspersed. Particle sizes range from submicron dust to a stone ~3.5 cm long. Millimeter-scale and larger stones typically have hummocky or angular morphologies. Some stones appear mottled by brighter material that occurs as veins and crusts. Hummocky stones have the lowest densities and mottled stones have the highest. Remote sensing of Bennu’s surface detected hydrated phyllosilicates, magnetite, organic compounds, carbonates, and scarce anhydrous silicates, all of which the sample confirms. We also find sulfides, presolar grains, and, less expectedly, Mg,Na-rich phosphates, as well as other trace phases. The sample’s composition and mineralogy indicate substantial aqueous alteration and resemble those of Ryugu and the most chemically primitive, low-petrologic-type carbonaceous chondrites. Nevertheless, we find distinct hydrogen, nitrogen, and oxygen isotopic compositions, and some of the material we analyzed is enriched in fluid-mobile elements. Our findings underscore the value of sample return—especially for low-density material that may not readily survive atmospheric entry—and lay the groundwork for more comprehensive analyses.

¹Liam D. Peterson,²Conel M. O’D. Alexander,²Jianhua Wang,²Emma S. Bullock,^3,4Anthony J. Irving, ⁵Sune G. Nielsen
Meteoritics & Planetary Science 1–15 (in Press) Link to Article [10.1111/maps.70211]

¹Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
²Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA
³Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA
⁴Burke Museum of Natural History and Culture, University of Washington, Seattle, Washington, USA
⁵CRPG, CNRS, Université de Lorraine, Vandoeuvre l`es Nancy, France
Published by arrangement with John Wiley & Sons

Recent evidence from primitive achondrites and achondrites suggests that early-formed melted planetesimals are depleted in hydrogen relative to the bulk silicate Earth. Nevertheless, evidence from angrites, the lone oxidized group of achondrites investigated to date, suggests that oxidized planetesimals may be H-rich relative to their reduced counterparts. Additionally, we have limited constraints, derived from a few ungrouped samples, on the H budgets of outer solar system planetesimals that underwent melting. Therefore, in order to provide additional constraints on the H budgets of oxidized and outer solar system planetesimals that experienced melting, we measured the H contents of silicate minerals in brachinite and tafassite group meteorites, respectively. We found that olivine, pyroxene, and plagioclase across both groups are essentially devoid of H (<~2.6 μg/g H2OT; total H as H2O equivalents). Based upon the thermal histories of the tafassite and brachinite parent bodies as well as their petrology and mineralogy, we argue that both bodies were essentially anhydrous prior to their disruption. This result is consistent with prior work on primitive achondrites and achondrites and requires that Earth’s H budget be accounted for by accretion of thermally primitive materials, such as chondrites, comets, and ices or capture of nebular gas.