¹R. J. Windmill, ¹I. A. Franchi, ¹X. Zhao, ¹R. C. Greenwood, ¹M. Anand
Meteoritics & Planetary Science (in Press) Open Source Link to Article [DOI: 10.1111/maps.70210]
¹Planetary and Space Sciences, School of Physical Sciences, The Open University, Milton Keynes, UK
Published by arrangement with John Wiley & Sons

The light element distribution in planetary cores and the processes driving core evolution in rocky planets are poorly understood. Magmatic iron meteorites are samples from the cores of ancient embryonic planetesimals and therefore provide a window into the processes governing core evolution. We performed high precision oxygen isotope analyses on chromite from IIIAB iron meteorites to investigate the oxygen isotopic evolution across a protoplanetary core using laser-assisted fluorination. We identify three unexpected and hitherto unreported discrete isotopic subgroups within the IIIAB chemical group and discuss possible causes for their existence. The most likely explanation is that they may be sampling multiple parent bodies, either completely unrelated or mixed during an impact. This would have significant implications for the use of the chemical classification scheme for iron meteorites as well as models for IIIAB core evolution. Second, that they may be evidence that oxygen mobility across the core was controlled by diffusion. If this is the case, they may represent homogenized melt pools in a wider core context, recording oxygen diffusion into a planetary core, which could help explain the density deficit observed in Earth’s core. Third, we discuss whether core rain out through a heterogeneous IIIAB mantle and inefficient mixing in the core could explain the isotopic results. Finally, we compare these IIIAB oxygen isotopic signatures to published data for main group pallasite minerals and conclude that the meteorite groups cannot be from a common parent body, answering a long-standing question in meteoritical science.

I

¹Yasuaki Tsuruoka, ^1,5Hideto Yoshida, ^2,6Yuki Inoue, ²Daiki Yamamoto, ³Hiroyuki Kagi, ⁴Akira Miyake, ¹Shogo Tachibana
Meteoritics & Planetary Science (in Press) Open Source Link to Article [DOI: 10.1111/maps.70213]

¹Department of Earth and Planetary Science, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
²Department of Earth and Planetary Sciences, Kyushu University, Nishi-ku, Fukuoka, Japan
³Geochemical Research Center, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
⁴Department of Geology and Mineralogy, Kyoto University, Sakyo-ku, Kyoto, Japan
⁵The Kiso Observatory, Institute of Astronomy, The University of Tokyo, Kiso-machi, Nagano, Japan
⁶Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa-shi, Chiba, Japan
Published by arrangement with John Wiley & Sons

Dmisteinbergite is a metastable polymorph of CaAl₂Si₂O₈, which has been found in calcium−aluminum-rich inclusions (CAIs) in chondrites, although anorthite is the predominant CaAl₂Si₂O₈ phase in natural type B CAIs. The occurrence/absence of igneous dmisteinbergite would put tighter constraints on the thermal history of CAIs. However, little attention has been paid for crystallization of dmisteinbergite in CAI melts even though its kinetically controlled crystallization (i.e., crystallization from a supercooled melt) has been proposed. In this study, we conducted dynamic crystallization experiments on CAI analogs in the presence of low-pressure hydrogen gas (1–10 Pa) to simulate the formation of igneous CAIs and to understand crystallization behavior of CaAl₂Si₂O₈ phases. Dmisteinbergite was found in samples cooled at rates of 1–20 °C h⁻¹, while anorthite was found in samples cooled at 5 °C h⁻¹, suggesting that the slow cooling (likely slower than on the order of 1 °C h⁻¹) might promote the formation of anorthite. Because the slow cooling rates during the final stage of crystallization of CAIs likely reflect conditions approaching the background temperature of CAI-forming regions, CaAl₂Si₂O₈ phases in type B CAIs could constrain the thermal history and formation environment of those regions.

Dmisteinbergite is a metastable polymorph of CaAl₂Si₂O₈, which has been found in calcium−aluminum-rich inclusions (CAIs) in chondrites, although anorthite is the predominant CaAl₂Si₂O₈ phase in natural type B CAIs. The occurrence/absence of igneous dmisteinbergite would put tighter constraints on the thermal history of CAIs. However, little attention has been paid for crystallization of dmisteinbergite in CAI melts even though its kinetically controlled crystallization (i.e., crystallization from a supercooled melt) has been proposed. In this study, we conducted dynamic crystallization experiments on CAI analogs in the presence of low-pressure hydrogen gas (1–10 Pa) to simulate the formation of igneous CAIs and to understand crystallization behavior of CaAl₂Si₂O₈ phases. Dmisteinbergite was found in samples cooled at rates of 1–20 °C h⁻¹, while anorthite was found in samples cooled at 5 °C h⁻¹, suggesting that the slow cooling (likely slower than on the order of 1 °C h⁻¹) might promote the formation of anorthite. Because the slow cooling rates during the final stage of crystallization of CAIs likely reflect conditions approaching the background temperature of CAI-forming regions, CaAl₂Si₂O₈ phases in type B CAIs could constrain the thermal history and formation environment of those regions.

¹Giovanna Agrosì, ²Paola Manzari, ¹Daniela Mele, ^3,4Johan Villeneuve, ⁵Tiziano Catelani, ⁶Mattew J. Genge, ⁷Luca Bindi
Meteoritics & Planetary Science (in Press) Open Source Link to Article [DOI: 10.1111/maps.70215]

¹Dipartimento di Scienze della Terra e Geoambientali, Università di Bari, Bari, Italy ²Agenzia Spaziale Italiana, Centro Spaziale Giuseppe Colombo, Matera, Italy
³Centre de Recherches Pétrographiques et Géochimiques, CNRS, Nancy, France
⁴Universite Paris-Cite, Institut de Physique du Globe de Paris, CNRS, Paris, France ⁵Centro di Servizi di Microscopia Elettronica e Microanalisi, Università di Firenze, Florence, Italy
⁶Department of Earth Science and Engineering, Imperial College London, London, UK ⁷Dipartimento di Scienze della Terra, Università di Firenze, Florence, Italy
Published by arrangement with John Wiley & Sons

We report the discovery of the second (Al,Cu)-alloy–bearing micrometeorite, FB-A2, recovered from Mount Gariglione (southern Italy), representing the sixth such occurrence worldwide. Although chondritic in nature, FB-A2 differs markedly from previously described microspherules. It is a scoriaceous micrometeorite dominated by silicates and contains a relict clast composed of Mg-rich olivine and pyroxene phenocrysts set in a Fe-rich silicate matrix. The particle rim hosts fine aggregates of phosphates, magnetite, Ni-bearing magnetite, and sulfides, whereas the interior contains nepheline crystals. A 120 μm (Al,Cu)-alloy grain occurs at one corner of the particle. The porphyritic texture of the clast indicates a chondrule fragment—the first identified in an (Al,Cu)-bearing micrometeorite—while polyhedral sub-grain boundaries and metal–sulfide veins record shock metamorphism. Iron-rich alteration of relict silicates is consistent with high-temperature (<560 °C) metasomatism typical of CV3 chondrites and is supported by oxygen isotope compositions close to the Carbonaceous Chondrite Anhydrous Mineral Line. Brecciation of chondrule olivine suggests impact-induced fluid pressure excursions during early Solar System metasomatism, whereas impact melt enveloping elongate olivines indicates a later impact that introduced the (Al,Cu)-alloys. Overall, the texture, mineralogy, and isotopic composition of FB-A2 provide the most detailed constraints yet on the origin of (Al,Cu)-bearing micrometeorites and confirm a genetic link to the Khatyrka meteorite.

¹Jin-Young Lee, ²Jeongmin Kim, ¹Sei-Sun Hong
Meteoritics & Planetary Science (in Press) Open Source Link to Article [DOI: 10.1111/maps.70216]

¹Quaternary Geological Research Center, Korea Institute of Geoscience and Mineral Resources, Daejeon, Korea
²Research Center of Earth and Environmental Sciences, Korea Basic Science Institute, Cheongju, Korea
Published by arrangement with John Wiley & Sons

We present the first micrometer-scale, phase-resolved compositional characterization of impact melt glass from the Hapcheon crater (~1.4 km apparent diameter), the first confirmed impact structure on the Korean Peninsula, integrating EPMA-WDS (5 μm spot), confocal Raman spectroscopy (<1 μm spot), XRD, and 40Ar/39Ar step-heating geochronology. EPMA of 37 points resolves three compositionally distinct groups separated by a clear compositional gap: silica-glass cores (CORE; n = 23; 98.4 wt% SiO2, K2O 0.023 wt%), feldspathic–mafic mantling glass (MANTLE; n = 6; ~55 wt% SiO2, K2O 2.24 wt%), and feldspathic glass clasts (UNCERTAIN; n = 8; ~61 wt% SiO2, K2O 3.10 wt%), demonstrating phase-segregated melting of the quartz and feldspathic–mafic fractions of the Cretaceous Dongmyeong target rock rather than whole-rock homogenization. Confocal Raman spectroscopy confirms coesite in 74% of 34 spectra and identifies diaplectic quartz glass, documenting micrometer-scale shock heterogeneity; a 30-point colocation data set confirms coesite within the ultralow-K2O glass phase. The ultralow K2O causes systematic 40Ar/39Ar age overestimation through inherited 40Ar; all seven plateau ages (1.8–5.6 Ma) exceed the independent 10Be burial age of 1.33 Ma. Step-heating Ca/K systematics confirm multiphase assemblages, and inverse-isochron 40Ar/36Ar intercepts independently corroborate inherited 40Ar. The youngest compositionally anchored age brackets the impact at 1.33–3.07 Ma (Plio-Pleistocene).

^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.

^1,2Martin Cordiner et al. (>10)
Nature 655, 870–874 Open Access Link to Article [10.1038/s41586-026-10771-6]

¹Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA
²Department of Physics, Catholic University of America, Washington DC, USA

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Haoyu Li,¹Ren T. C. Marquez,^1,2Gerrit Budde,³Haolan Tang,⁴Alexander N. Krot,⁵Marina A. Ivanova,⁶Johan Villeneuve,¹ François L. H. Tissot
Proceedings of the National Academy of Sciences 123, 29 Open Access Link to Article [10.1073/pnas.2529765123]

¹The Isotoparium, Division of Geological and Planetary Sciences, Caltech, Pasadena, CA 91125
²Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912
³National Key Laboratory of Deep Space Exploration/State Key Laboratory of Lithospheric and Environmental Coevolution, University of Science and Technology of China, Hefei 230026, China
⁴Hawaii Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, Honolulu, HI 96822
⁵Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow 119991, Russia
⁶Centre de Recherches Pétrographiques et Géochimiques, CNRS, Université de Lorraine, UMR7358, Nancy F-54000, France

The 26Al-26Mg systematics in calcium–aluminum-rich inclusions (CAIs)—the oldest known Solar System solids—has traditionally been used to provide high-resolution temporal constraints on the early Solar System evolution. More recently, the study of variations in the initial Mg isotope composition has emerged as a means to probe for potential compositional heterogeneity in the nascent solar nebula. Here, we report high-precision magnesium isotope data for a collection of 19 CAIs that captures the diversity of refractory inclusions. The data reveal widespread Mg isotope heterogeneity prior to 26Al decay, covering a large range from −0.285 to +0.088‰. Combined with literature data, the distribution of Mg isotope heterogeneity in CAIs forms a continuum and no longer defines distinct populations. Our findings therefore suggest a continuous CAI formation process that captured a rapid temporal change in the composition of infalling material from the parental molecular cloud of the Solar System.

¹M. C. Benner,¹B. S. Prince,¹D. L. Schrader,¹T. J. Zega
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70212]

¹Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
²Astromaterials Research and Exploration Science (ARES) Division, XI
³Research Office, NASA Johnson Space Center,Houston, Texas, USA3Department of Materials Science & Engineering, University of Arizona, Tucson, Arizona, USA
Published by arrangement with John Wiley & Sons

Here we report on the microstructure and chemistry of sulfide minerals returned from asteroid (162173) Ryugu. We identify a unique sulfide population in particle A0016 composed of violarite (FeNi₂S₄), pyrite (FeS₂), chalcopyrite (CuFeS₂), pyrrhotite (Fe_1-xS), and pentlandite ([Fe,Ni]₉S₈). Violarite, pyrrhotite, and pyrite reveal evidence of formation from a fluid including porosity, phyllosilicate inclusions, and gaps along grain boundaries due to volume change. Violarite grains are polycrystalline with spatially correlated Ni and Co enrichments and contain pyrrhotite lamellae measuring 100s nanometers across. Pyrite assemblages are polycrystalline with spatially anticorrelated Ni and Co enrichments. In comparison, the chalcopyrite grain is a compositionally homogeneous single crystal spatially associated with rutile (TiO₂). The data suggest that particle A0016 experienced multiple generations of fluid flow. The first generation of fluid flow occurred at low temperatures (25 to 100 °C) under alkaline (pH > 8) conditions, leading to the precipitation of pyrrhotite and pentlandite. In comparison, the second generation of fluid flow was acidic (pH < 6.5) and reducing (−0.14 ≤ Eh ≤ −0.36) at elevated temperatures (230 to 300 °C), leading to formation of pyrite, violarite, and chalcopyrite. The elevated temperatures required to produce this sulfide population are consistent with heating from an impact on Ryugu’s parent body.