^1,2Yankun Di, ²Magdalena H. Huyskens, ²Qing-Zhu Yin, ^1,3Yuri Amelin
Geochimcia et Cosmochimica Acta (in Press) Open Access Link to Article [10.1016/j.gca.2026.06.017]
¹Research School of Earth Sciences, Australian National University, Acton, ACT 2601, Australia
²Department of Earth and Planetary Sciences, University of California Davis, Davis, CA 95616, USA
³State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
Copyright Elsevier

Compared to the Earth and inner Solar System planets, calcium–aluminium-rich inclusions (CAIs) possess nucleosynthetic Sr isotope anomalies manifested as elevated ⁸⁴Sr/⁸⁶Sr after internal normalisation using ⁸⁸Sr/⁸⁶Sr. These anomalies can be generated by heterogeneous incorporation of s-, r-, or p-process nucleosynthesis components. Accurately distinguishing between the enrichment or depletion in those components is critical for correctly understanding the timing of planetary volatile depletion, as they predict very different anomalies in ⁸⁷Sr/⁸⁶Sr and lead to disparate interpretations of ⁸⁷Rb–⁸⁷Sr chronology. Here, we constrain the origin of Sr isotope anomalies in the original Mason and Taylor (1982) set of Allende CAIs by examining their nucleosynthetic Sr and Nd isotope systems. Most CAIs analysed exhibit positive μ⁸⁴Sr and negative μ^145,148,150Nd anomalies (μ-values are defined as part-per-million deviations of isotopic ratios relative to terrestrial standards) in agreement with previous studies, but we also detected significant isotope heterogeneities among them, including discovery of CAIs with Sr and Nd isotope anomalies in directions opposite to the majority. The Nd isotope heterogeneity among CAIs is predominantly consistent with variations in the abundance of the s-process component, with a minor but clearly resolved p-process deficit on μ¹⁴²Nd_corr (μ¹⁴²Nd_corr is μ¹⁴²Nd corrected for ¹⁴⁶Sm decay). The less steep μ¹⁴²Nd_corr vs. μ¹⁴⁸Nd slope defined by the CAIs compared to that predicted by stellar models supports the recent suggestion that the accessible Earth has a small radiogenic excess in μ¹⁴²Nd relative to chondrites. Correlated Sr and Nd isotope anomalies in the CAIs suggest that (1) they formed from at least two isotopically distinct reservoirs, one with and the other without p-process Sr excesses relative to Earth, (2) the majority of CAIs formed in the p-process-Sr-enriched reservoir with additional s-process excesses, and (3) variations in r-process Sr and Nd are not observed among the CAIs. The s-process-induced ⁸⁷Sr/⁸⁶Sr anomalies in CAIs (relative to the inner Solar System) predicted based on Nd isotopes are below the typical measurement precision, negating the need for nucleosynthetic correction on CAIs’ ⁸⁷Sr/⁸⁶Sr in chronological interpretations

¹Pipasa Layak, ^1,2Nachiketa Rai, ³Kuljeet Kaur Marhas, ^4,5Hilary Downes
Geochemistry (Chemie der Erde) (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2026.126426]
¹Department of Earth Sciences, Indian Institute of Technology Roorkee, 247667, India
²Centre for Space Science and Technology, Indian Institute of Technology Roorkee, 247667, India
³Planetary Science Division, Physical Research Laboratory, Ahmedabad, 380009, India
⁴School of Natural Sciences, Birkbeck University of London, Malet Street, London, WC1E 7HX, UK
⁵Natural History Museum, Cromwell Road, London, SW7 5BD, UK
Copyright Elsevier

This study models the compositional evolution of a chondritic starting material representative of the Mesosiderite Parent Body (MSPB) under relevant pressure-temperature-redox conditions (1 bar, 1800–500 °C, fO2 = IW + 1.8), focusing exclusively on the evolution of the silicate portion of the system and not on the origin or evolution of the metallic component. The modelling framework assumes crystallization within a silicate magma ocean, and explores crystallization pathways involving varying degrees of equilibrium crystallization (EC) and fractional crystallization (FC). In addition, we present new mineral-chemistry, and phase data from two mesosiderite specimens, Estherville and Mincy.
Modelling results indicate that mesosiderite silicate mineralogy can be derived from a chondritic composition through an efficient three-stage cooling sequence: 40–50% EC, followed by FC down to 1395 °C, and then final EC of the remaining melt to 914 °C, at which point crystallization is complete. The predicted modal abundances—69 wt% pyroxenes, 26 wt% plagioclase, 1.9 wt% tridymite, and 1.6 wt% whitlockite—closely match the observed proportions in Estherville and Mincy. In both meteorites, pyroxenes and tridymites serve as robust geothermometers, stable across 870–1470 °C. The strong agreement between modelled Mg#, Fe#, density, and fO2 with published mesosiderite values further supports a chondritic starting composition of the MSPB.
The model suggests that the MSPB mantle consisted of olivine-orthopyroxene cumulates (dunitic in character), while the lower crust was dominated by pigeonite and hypersthene, forming a pyroxenitic lithology. The upper crust was enriched in plagioclase and pyroxene, reflecting a basaltic composition. Following differentiation, the MSPB likely underwent a collisional encounter with a differentiated impactor, leading to excavation of its silicate crust, followed by brecciation, remelting, and clast metamorphism. These processes ultimately produced mesosiderite meteorites as composite breccias of MSPB-derived silicates intermixed with metallic phases contributed by the impacting body.

¹Dian Ji, ¹Rajdeep Dasgupta
Earth and Planetary Science Letters 690, 120133 Link to Article [https://doi.org/10.1016/j.epsl.2026.120133]
¹Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USA
Copyright Elsevier

As the youngest returned mare basalt to date, deciphering the petrogenesis of Chang’e-5 (CE-5) basalts could assist us in understanding the late-stage lunar mantle evolution. However, the lithology of the CE-5 mantle is still controversial. Here, we present a joint study of high pressure-temperature major element phase equilibria using laboratory experiments and trace element modeling, and show that garnet is present in the source of young mare basalts on the Moon. Our high-pressure-temperature experiments approaching the multiple saturation point of the putative parental melt compositions of young CE-5 basalt show garnet and clinopyroxene coexisting with the quenched silicate melt. Trace element modeling also confirms that small amounts of garnet in the mantle source are required to reconcile the rare-earth element pattern of the CE-5 basalts, regardless of whether the CE-5 basalts were the direct mantle-melting products or produced through extensive fractional crystallization of a primitive basalt. The existence of garnet in the source either implies that lunar mantle overturn played a crucial role in contributing to the lunar mantle heterogeneity, creating a garnet-clinopyroxenitic mantle source of these young mare basalts that survived the subsequent mantle evolution, or a late-stage process introduced fertile material into the deep mantle, and such geodynamic processes within the lunar interior may have continued until 2 Ga.

¹Varun Manilal, ¹Kyusei Tsuno, ²Hideharu Kuwahara, ³Axel Wittmann, ⁴Anne Pommier, ⁵Christy Till, ¹Damanveer S. Grewal
Geochimica et Cosmochimica Acta (in Press) Link to Article [10.1016/j.gca.2026.06.018]
¹Department of Earth and Planetary Sciences, Yale University, New Haven, CT 06511, USA
²Geodynamics Research Center, Ehime University, Ehime 790-8577, Japan
³Eyring Materials Center, Arizona State University, Tempe, AZ 85281, USA
⁴Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015, USA
⁵School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85281, USA
Copyright Elsevier

Percolation is a leading mechanism for metal-silicate segregation during the earliest stages of planetesimal differentiation triggered by 26Al-heating. The efficacy of percolative core formation strongly depends on the compositions of metallic melts and co‑existing silicate mineralogies. We report results from 21 high-pressure–temperature (P = 0.5–2 GPa; T = 1350 °C) experimental charges designed to simulate percolative core formation conditions in oxidized planetesimals. These experiments equilibrated olivine aggregates having variable FeO contents (0–30 wt%) with Fe-O-S metallic melts generated from two starting compositions (eutectic-like Fe1.46S and stoichiometric FeS). Our results quantify how pressure, FeO content in olivine, and metal composition affect oxygen solubility and dihedral angles in Fe-O-S alloys. Both O solubility and dihedral angles are largely insensitive to pressure over planetesimal conditions (P < 2 GPa) but are strongly dependent on olivine FeO content and metallic composition. For eutectic systems, dihedral angles decrease from 80° to 44° for olivine containing 1 wt% and 20 wt% FeO, respectively, crossing the critical interconnection threshold near 10 wt% FeO. For FeS systems, dihedral angles decrease more gradually (67° at 5 wt% FeO to 53° at 20 wt% FeO), consistent with the lower solubility of O in FeS-rich melts and a higher FeO threshold for connectivity. We developed a Langmuir competitive adsorption framework to explain these observations: S and O compete for interfacial binding sites at the olivine-metal boundary, with their relative coverage controlled by the activities of FeO and FeS. This predictive framework explains why O solubility is systematically lower in FeS-rich melts than in eutectic melts at the same fO2 and demonstrates that both S and O act synergistically as surface-active elements that reduce dihedral angles and interfacial energies, with O exerting a stronger effect. Applying these results to differentiation of oxidized planetesimals (fO2 > IW; based on the compositions of oxidized chondrites), we find that the first-formed metallic melts would have formed interconnected networks at extremely low melt fractions and were capable of forming cores prior to widespread silicate melting in their parent bodies. Using the experimentally defined connectivity and O-solubility thresholds, we model core compositions in oxidized planetesimals as combinations of eutectic and FeS-rich Fe-O-S melts. The resulting metallic cores are predicted to be consistently O-bearing, ranging from ∼3–4 wt% O in CM-/CI-like bodies to ∼5–6 wt% O in CV-ox- and RC-like bodies. These predicted O contents are first-order estimates, as both the higher experimental temperature (1350 °C vs. ∼988–1200 °C during percolative core formation in planetesimals) and the absence of Ni in our metallic melts would likely overestimate O solubility in natural systems.

¹Ralph E. Milliken et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70179]
¹Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, Rhode Island, USA
Published by arrangement with John Wiley & Sons

Near-Earth rubble-pile asteroids Bennu and Ryugu are part of the carbonaceous taxonomic complex (C-complex), and samples returned from both bodies resemble the most aqueously altered carbonaceous chondrites. However, telescopic and spacecraft visible–near infrared (VIS–NIR) reflectance spectra of Ryugu exhibit a red (positive) spectral slope, whereas Bennu has a blue (negative) spectral slope characteristic of the rare B-type subclass of asteroids. The asteroid spectra also suggest different levels of hydration, with Ryugu dominated by OH and Bennu containing spectral evidence of more H2O. To understand what causes these differences, we acquired VIS–NIR reflectance data (~0.3–5 μm) from a variety of Bennu samples over spatial scales of 100 μm to several millimeters. No single sample reproduces the average spectral properties of Bennu, but by evaluating samples of different petrology and physical states—groups of particles, isolated particles, and larger stones—we demonstrate that primary composition, and highly hydrated Mg-rich phosphate in particular, plays a strong role in controlling the spectral slope and average hydration absorption strength of Bennu materials. Bennu and Ryugu may be dominated by different lithologies originating from different regions of a common planetesimal, thus explaining their different spectral evolution. The spectral characteristics of B-type asteroids, particularly those with blue slopes at near-infrared wavelengths and broad hydration features at ~3 μm, may indicate the presence of Mg phosphate and thus a history of complex fluid–rock interactions relevant to prebiotic chemistry.

^1,2,3Rachael Lappan,^3,4Rachel S. Kirby,⁴Andrew G. Tomkins
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70178]
¹Department of Microbiology, Biomedicine Discovery Institute, Monash University, Melbourne, Victoria, Australia
²Securing Antarctica’s Environmental Future, Monash University, Melbourne, Victoria, Australia
³School of Earth, Atmosphere and Environment, Monash University, Melbourne, Victoria, Australia
⁴Space Science and Technology Centre, School of Earth and Planetary Science, Curtin University, Perth, Western Australia,Australia
Published by arrangement with John Wiley & Sons

Since the discovery of nine meteorites near the Yamato mountains in 1969, Antarctica has been recognized as a superb location for meteorite recovery. While Antarctic recovery expeditions prioritize meteorite preservation for mineralogical and planetary studies, meteorites are not typically collected for biological applications. The LifeMet expedition was the first Australian Antarctic meteorite recovery expedition, conducted in the 2024–2025 austral summer in the Wohlthat and Orvin Mountains in Dronning Maud Land, Antarctica. The expedition had two primary objectives: (1) to examine whether Antarctic microorganisms colonize and consume nutrients from meteorites, providing insights into microbial ecosystem formation, interactions with uncommon minerals and extremophile survival strategies in Antarctica; and (2) to evaluate the practical and logistical factors influencing meteorite recovery in these regions, and the suitability of recovery approaches for biological sampling. A total of 13 stones, including one confirmed meteorite, were recovered. Adjacent environments (air, sediment, snow, ice, and terrestrial rocks) were sampled to characterize microbial sources. We found that low-altitude blue ice zones were poorly suited to meteorite recovery; however, microbe–meteorite interactions may be enhanced in these areas due to warmer temperatures and periodic ice melting. Our observations suggest that the low albedo of meteorites may promote the formation of periodically water-filled potholes and cryoconite, which may support microbial proliferation. In contrast, meteorites stranded on nunataks are minimally oxidized. Based on our observations at ~71°S, blue ice fields at altitudes above ~2000 m are better suited to meteorite recovery at current climatic conditions.

¹Kanako Yoshihara,²Akira Yoshiasa,³Huimin Shao,⁴Makoto Tokuda,⁵Ginga Kitahara,²Hiroshi Isobe
Meteoritics & Planetary Science (in Press) Open Access Link To Article [https://doi.org/10.1111/maps.70180]
¹Graduate School of Science and Technology, Kumamoto University, Kumamoto, Japan
²Department of Earth and Environmental Sciences, Faculty of Advanced Science and Technology, Kumamoto University,Kumamoto, Japan
³Chinese National Space Science Center, Beijing, China
⁴Institute of Industrial Nanomaterials, Kumamoto University, Kumamoto, Japan
⁵Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tokai, Ibaraki, Japan
Published by arrangement with John Wiley & Sons

Ni, Co, and Fe K-edge X-ray absorption fine structure (XAFS) measurements were performed, revealing an unexpected local structure around Co in well-known iron and stony-iron meteorites. Cobalt is enriched in kamacite but remains in taenite at concentrations of at least 0.3 atom%. The Co K-edge X-ray absorption near-edge structure (XANES) spectra of taenite with a face-centered cubic (FCC) structure in all examined iron meteorites exhibited an unexpected body-centered cubic (BCC)-type local coordination, with Co showing a coordination number of 8 + 6. The local FCC and BCC structures can be clearly distinguished based on their XANES patterns. In taenite, up to 20% of the local structure is inferred to be BCC in regions where three-dimensional periodicity is maintained. Moreover, local BCC structures are likely to predominate in subregions that do not contribute to three-dimensional periodicity. Co transforms into a locally ordered BCC structure within the high-temperature parent FCC phase of iron meteorites. In this phase, Co appears to have a stronger affinity for Fe than for Ni, leading to the formation of Co-Fe clusters with a regular BCC arrangement.

^1,2,3,5Hongmei Yang, ^1,2,3Xiaoju Lin, ^1,2,3Xiao Wu, ^1,2,3,4Haiyang Xian, ^1,2,3,4Jianxi Zhu, ^1,2,3,4Shan Li, ^1,2,3Jiaxin Xi, ^1,2,3Yiping Yang, ^1,2,3,4Hongping He
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.117209]
¹State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
²Center for Advanced Planetary Science, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
³Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
⁴University of Chinese Academy of Sciences, Beijing 100049, China
⁵Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China
Copyright Elsevier

Impact is one of the most crucial geological processes on the lunar surface. As the main mafic mineral in lunar mare basalts, pyroxene can be transformed into an amorphous phase under the high-temperature and high-pressure conditions triggered by impact events. However, the formation mechanism of impact-induced pyroxene glass and its implications for the impact history of the lunar surface have yet to be elicited. In this study, we investigated the formation mechanism of augite glass from a Chang’e-5 breccia using the electron pair distribution function and molecular dynamics simulations. The results show that the augite transformed into dense melt under the high-temperature and high-pressure conditions induced by impact, with subsequent quenching leading to glass formation. Atomic structural analysis indicates that the augite dense melt solidified at a temperature of approximately 4100 K and a residual pressure of about 10 GPa. The mosaicization of this augite glass in the breccia clasts indicates that it had experienced a later impact event with a shock intensity of M-S2 after its formation. By establishing the link between the atomic structure of augite glass and its formation pressure-temperature conditions, this study provides a robust method for inverting impact parameters from natural lunar glass samples. It also offers a new perspective for deciphering the multi-stage impact history of the lunar surface and the evolutionary processes of lunar regolith, and holds universal reference value for studies of impact processes on the Moon and other terrestrial planets.

¹Guillaume Leseigneur, ²Manuel Reinhardt, ¹Fatma Yesil Sahan, ³Uwe Meierhenrich
Earth and Planetary Science Letters 690, 120141 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.120141]
¹Max-Planck-Institute for Solar System Research; Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
²University of Göttingen, Geoscience Center, Department of Geobiology; Goldschmidtstraße 3, 37077 Göttingen, Germany
³Institut de Chimie de Nice (ICN), UMR 7272 CNRS, Université Côte d’Azur; 28 Avenue Valrose, 06108 Nice, France
Copright Elsevier

The isoprenoid alkanes pristane and phytane are widely detected in meteorites. As isoprenoids are considered markers of Earth’s biosphere, their presence in meteorites has led to a prevailing consensus that they represent terrestrial contamination, thereby calling into question the indigeneity of the entire meteoritic hydrocarbon inventory. Indeed, these chiral molecules are ubiquitous in biological systems, where their stereogenic centers are fixed and of the same absolute configuration. In this study we separate, for the first time, the different relevant chiral configurations of pristane and phytane in a meteorite sample, and we show that the isoprenoid alkanes detected in the Murchison meteorite are racemic. On Earth, racemization of these molecules has only been observed in oil shales and crude oils subjected to a certain degree of thermal maturation. In light of previous findings, these results strongly suggest that the Murchison meteorite was contaminated exclusively by petroleum pollutants present in Earth’s atmosphere, and categorically exclude any contribution from the biosphere at the fall site. Consequently, this work establishes a foundation for systematic investigations into the chirality of isoprenoids in other meteorite samples and the different sources of atmospheric petroleum pollution.

¹Line Colin, ¹Stéphane Labrosse, ¹Chloé Michaut, ²Adrien Morison
Earth and Planetary Science Letters 690, 120164 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.120164]
¹Laboratoire de Géologie de Lyon: Terre, Planète, Environnement, Ecole Normale Supérieure de Lyon, Université de Lyon, Université Claude Bernard Lyon 1, Lyon,France
²Research Software Engineering, MVLS SRF, University of Glasgow, Glasgow,United Kingdom
Copyright Elsevier

The Moon presents a striking asymmetry between the nearside, which concentrates the lunar mare and shows a thin crust, and the farside, composed of thick anorthosite terranes. One proposed explanation for this asymmetry is a mantle overturn, driven by the instability of a dense, ilmenite-rich layer at the top of cumulates near the end of lunar magma ocean solidification. However, thermal instabilities may arise before the crystallization of this dense layer. In particular, material exchange by melting and crystallization at the magma ocean-cumulates boundary facilitates flow through the boundary and hence the onset of convection in the cumulates. Accounting for this flow-through interface, we investigate the onset and duration of a thermal overturn using linear stability analysis and direct numerical simulations. Our results show that a thermal overturn can initiate well before the end of magma ocean solidification, lasting from ten thousand years to tens of millions of years. The dominant convective mode corresponds to a spherical harmonic of degree one and could affect crustal growth and stabilization if the top interface is sufficiently flow-through and the Rayleigh number not too large. Taking into account the thermal evolution of the core, this early overturn could generate an early lunar dynamo.