¹Zoë E. Wilbur (>10)
Earth and Planetary Science Letters, 695, 120296 Open Access Link to Article [DOI: 10.1016/j.epsl.2026.120296]
¹Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, WA, DC, USA
Copyright Elsevier

Exogenous fragments in brecciated planetary materials offer direct evidence of mixing among planetary bodies in the Solar System. Fragments of undifferentiated carbonaceous material are frequently identified in differentiated meteorites. However, differentiated fragments are rarely observed in carbonaceous material. An exception is the exogenous basalt observed by the OSIRIS-REx spacecraft on the carbonaceous asteroid (101955) Bennu, which motivated a search for differentiated material in the returned samples. We report a pyroxene grain in a brecciated Bennu sample that is texturally and compositionally like pyroxene from cumulate eucrites — basaltic meteorites linked to the differentiated asteroid (4) Vesta — but oxygen isotopic measurements indicate that it is likely sourced from a basaltic asteroid not clearly represented among known basaltic achondrites. This grain may have been delivered to a precursor to Bennu in the main asteroid belt. Whether this grain is representative of the pyroxene-rich boulders observed remotely on Bennu’s surface remains unconstrained. Nevertheless, extending spacecraft observations to the grain scale reveals that Bennu serves as an archive for uncharacterized basaltic asteroids, documenting a history of planetary mixing that is otherwise elusive in current meteorite records.

¹Ling-Zhi Hu, ¹Maxence Regnault, ¹Philipp Gleißner, ¹Ninja Braukmüller, ²Ashley J. King, ¹Anne Lindner, ¹Harry Becker
Earth and Planetary Science Letters, 695, 120270 Open Access Link to Article [DOI: 10.1016/j.epsl.2026.120270]
¹Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstrasse 74-100, Berlin, D-12249, Germany
²Planetary Materials Group, Natural History Museum, Cromwell Road, London, SW7 5BD, UK
Copyright Elsevier

Carbonaceous chondrites (CCs) exhibit profound non-systematic heterogeneity in their elemental and isotopic compositions, both within individual meteorite splits and among bulk samples of the same group, providing opportunities for a better understanding of early solar system processes. This variability also poses significant challenges for constraining bulk compositions of the parent bodies. We report new mass-independent Ti and Cr isotope data, integrated with major and trace element abundances for a suite of CC bulk rocks, to better understand the origin of this multiscale heterogeneity. Some bulk CCs (e.g., Yamato chondrites and Allende) exhibit elemental or isotopic compositions consistent with the literature, while others display significant differences.

Simple binary or ternary mixtures, using ε⁵⁰Ti, ε⁵⁴Cr and chemical data from the present study and literature as constraints, cannot reproduce the full range of isotopic and elemental data. The data are best explained by a multi-component mixing model with a minimum of four endmembers, involving CI-like matrix, heterogeneous non-carbonaceous (NC) dust, and two distinct refractory inclusion populations. The latter are similar to the average composition of calcium-aluminium-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs) and a CAI-like component found in some chondrules. Crucially, the model constraints reveal that NC dust, which migrated into the CC region, contained chemically fractionated material, characterized by a significant depletion in siderophile elements. This result suggests that some NC dust in CC may represent silicate-rich debris derived from the collision of early differentiated planetesimals in the inner solar system. Thus, carbonaceous chondrites record a multi-stage history of early transport of variably ⁵⁰Ti- and ⁵⁴Cr-enriched CAIs and subsequent migration of chondritic and differentiated planetary debris into CI chondrite-like icy dust of the outer disk.

¹Nicole X. Nie, ²Damanveer S. Grewal, ¹Zhe J. Zhang
Earth and Planetary Science Letters, 695, 120321 Link to Article [DOI: 10.1016/j.epsl.2026.120321]
¹Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
²Department of Earth and Planetary Sciences, Yale University, New Haven, CT, 06511, USA
Copyright Elsevier

High-temperature evaporation is a fundamental process shaping the chemical and isotopic signatures of planetary materials, yet the specific physical laws governing isotopic fractionation during evaporation remain debated. We investigated the mass-dependent isotope fractionation of Fe and Ni during vacuum evaporation of metallic melts. The residues exhibit large isotope fractionation, reaching up to 11.4 ‰ for δ^56/54Fe and 2.9 ‰ for δ^60/58Ni. Determining the isotope fractionation factors for Fe and Ni [$\alpha ={\left(m_{i1}/m_{i2}\right)}^{\beta }$] using the Rayleigh distillation model yielded a $\beta$ value of 0.5 for both Fe and Ni. Further, the evaporation coefficients of Fe and Ni were found to be similar (${\gamma }_{\text{Fe}}\simeq {\gamma }_{\text{Ni}}$). These results suggest that Fe and Ni evaporation from metallic melts is ideal and uninhibited by kinetic barriers.

We used high-precision three-isotope plots to constrain the mass fractionation law governing the evaporation process. Both Fe and Ni in the evaporation residue strictly follow the law of $n=-0.5$, distinct from the exponential law ($n=0$) typically assumed for kinetic processes. We propose a theoretical framework to reconcile this observation with kinetic gas theory: while the intrinsic instantaneous isotope fractionation between vapor and melt follows the exponential law, the apparent law observed in the residue is shifted by the Rayleigh distillation process. We derive a general relationship showing that the divergence between the apparent law and the intrinsic law during a Rayleigh distillation process is controlled by the magnitude of isotope fractionation ($\beta$), $n_{\text{appr}}\simeq \left[1+\frac{{\beta }_{i2/i1}}{2}\text{ln}\left(\frac{m_{i1}}{m_{i2}}\right)\right]n_{\text{inst}}-{\beta }_{i2/i1}$. This framework unifies conflicting observations regarding mass fractionation laws in previous evaporation experiments. The implications of these results for the evaporation history of Type-I cosmic spherules and for identifying nucleosynthetic isotopic anomalies are discussed.

^1,2Wei Dai, ¹Julien Siebert, ³Alexandre Corgne, ¹Nicolas Wehr, ⁴Yunke Song, ¹Frederic Moynier
Earth and Planetary Science Letters (in Press) Open Access Link to Article [DOI: 10.1016/j.epsl.2026.120342]
¹Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, 1 rue Jussieu, Paris, 75005, France
²Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, DK-1350 Copenhagen K, Denmark
³Instituto Ciencias de la Tierra, Universidad Austral de Chile, Valdivia, Chile
⁴Bayerisches Geoinstitut, University of Bayreuth, Bayreuth, 95440, Germany
Copyright Elsevier

Considerable isotopic variation between Earth and major chondritic materials implies a possible fractionation in the early differentiate stage of the Earth. However, it is challenging to study isotopic fractionation at the high pressures relevant to the deep Earth due to the lack of natural samples. We present Ca isotopic fractionation (Δ^44/40Ca_pv-melt) between calcium perovskite (Ca-Pv, CaTiO₃) and co-existing silicate glass (melt fraction) from experimental samples. The Δ^44/40Ca_pv-melt varies in experiments with different pressure, yields equilibrium fractionation factor [10³lnα(1000K)] of $0.{04}_{-0.08}^{+0.06}$ at 1 atm and $0.{50}_{-0.07}^{+0.07}$ at 3 GPa, respectively. The variation on Ca isotope fractionation is likely caused by Ca-Pv phase structure transition from orthorhombic/tetragonal (coordination number (CN) = 8) to cubic (CN = 12) with the increase of pressure and temperature. Our model calculation shows that Ca perovskite is enriched in heavy Ca isotopes relative to silicate melts by 0.02 to 0.08 ‰ in the lower mantle. It suggests that the Ca isotope fractionation in the deep magma ocean is less than 0.05 ‰, regardless of the variation of isotopic fractionation factor caused by phase transition. We conclude that no considerable Ca isotope variation occurred in the deep mantle and the Ca isotope composition of upper mantle could be representative of the bulk silicate Earth. Considering the Nd isotopic differences between Earth and Moon, we suggest that the Moon formed primarily from a partly molten proto-Earth with advanced crystallization of perovskites in its lower mantle.

^1,2Seamus L. Anderson (>10)
Meteoritics & Planetary Science (in Press), Link to Article [DOI: 10.1111/maps.70232]
¹Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, Perth, Western Australia, Australia
²Solar System Exploration Division, Code 690, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Published by arrangement with John Wiley & Sons

The Dingle Dell meteorite fell in the wheat belt of Western Australia on Halloween night (October 31st) in 2016 and was observed by multiple cameras from the Desert Fireball Network, being recovered less than a week later. In this paper, we report the in-depth characterization and reclassification of this meteorite, from its original LL6 class to an updated L6 chondrite. Dingle Dell is an unbrecciated L6 chondrite with low shock features (S2) and no weathering (W0). The silicate mineral chemistry is typical of an L chondrite (Fa = 24.4 ± 0.3; Fs = 20.5 ± 0.2; Wo = 1.6 ± 0.3; all mol%), while the kamacite-Co concentration is on the high end of the L-chondrite range. The measured oxygen isotopes (δ¹⁷O = 3.809 ± 0.068; δ¹⁸O = 5.102 ± 0.126; Δ¹⁷O = 1.115 ± 0.011) are slightly more consistent with an LL chondrite classification, though on the border shared by L and LL chondrites. The chromium isotopic anomaly measured in Dingle Dell also places it among both L and LL chondrites (ɛ⁵⁴Cr = −0.37 ± 0.09). Analyses of cosmogenic radionuclides and noble gases indicate that Dingle Dell existed as a small meteoroid (10–15 cm radius) for 9.3 ± 1.3 Myr before impacting the Earth. Ideal gas pycnometry indicates a grain density of 3.61 ± 0.01 g cm⁻³ and a bulk density of 3.23 ± 0.02 g cm⁻³, revealing a calculated porosity of 10.5% ± 0.5%. Dingle Dell’s likely source region near the 3:1 mean motion resonance may constitute meteoritic sampling from an asteroid not associated with the Massalia or Flora families, the proposed sources for many L chondrites.

^1,2Roger H. Hewins, ^1,3Brigitte Zanda, ¹Arnaud Duverger
Meteoritics & Planetary Science (in Press), Open Source Link to Article [DOI: 10.1111/maps.70220]
¹Muséum National d’Histoire Naturelle, Sorbonne Université, UMR CNRS 7590, Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC), Paris, France
²Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey, USA
³LTE, UMR CNRS 8255, Observatoire de Paris, Paris, France
Published by arrangement with John Wiley & Sons

Shergottites are the most abundant meteorites from Mars and a major source of information on magma reservoirs, transport, and eruption, particularly in the late Hesperian northern hemisphere. Conflicting interpretations have arisen on the crystallization conditions of pyroxene in olivine-phyric shergottites. The pyroxene Ti:Al barometer suggested deep crustal or upper mantle crystallization, while 1 bar experimental petrology yielded a similar pyroxene Al-Ti distribution but suggested near surface formation. This barometer was first calibrated for alkali basalt, in which the phases that crystallized changed as a function of pressure, and it has not been demonstrated that its application could be extended to olivine-phyric shergottites. We have confronted this question by examining the petrogenesis of NWA 6234 and NWA 10170 olivine-phyric shergottites, which we confirm are paired. Modeling of their crystallization shows that the major-element composition trend of their composite, complexly zoned pyroxene crystals cannot be reproduced, indicating disequilibrium due to rapid cooling. It also shows that, with an unchanging sequence of crystallizing phases, the partitioning of Al and Ti into pyroxene does not change with pressure. Many olivine-phyric shergottites experienced strong undercooling, as in many Apollo and terrestrial basalts, consistent with surface eruption during pyroxene crystallization.

^1,2D. K. Buckner, ²J. C. Aponte, ³A. C. Schuerger, ⁴D. I. Foustoukos, ^2,5,6F. Seguin, ⁷M. B. Wilhelm, ⁸G. Cooper, ⁹A. J. Williams
Meteoritics & Planetary Science (in Press) Open Access Link to Article [DOI: 10.1111/maps.70194]
¹NASA Postdoctoral Program, Oak Ridge Associated Universities, Oak Ridge, Tennessee, USA
²Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
³Department of Plant Pathology, University of Florida, Gainesville, Florida, USA
⁴Carnegie Institute for Science, Washington, DC, USA
⁵Center for Research and Exploration in Space Science and Technology II, Greenbelt, Maryland, USA
⁶Earth & Space Research Administration, University of Maryland—Baltimore County, Baltimore, Maryland, USA
⁷Space Science & Astrobiology Division, NASA Ames Research Center, Moffett Field, California, USA

Published by arrangement with John Wiley & Sons

In the search for life on Mars, understanding the origin of preserved organics is critical. Expected sources include exogenous delivery, endogenous synthesis, and potentially life. Environmental processing by ultraviolet (UV) irradiation can alter these organics, obscuring hallmarks of their origin. To deconvolve these effects, we conducted an experimental study subjecting the Aguas Zarcas (CM2) carbonaceous chondrite to UV–VIS–NIR (200–2500 nm) irradiation under Mars environmental conditions (8.5 mbar pressure, −4 to −7 °C temperature, Mars atmosphere mix of 95.04% CO₂, 2.59% N₂, 1.94% Ar, 0.40% O₂, and 0.03% H₂O) for 154 sols (days on Mars) equivalent exposure. We measured changes to carboxylic acid abundances and compound-specific δ¹³C isotopes and bulk carbon, nitrogen, and hydrogen weight percent and isotopes. Compared to unirradiated samples, UV-exposed samples displayed nearly a twofold increase in total carboxylic acid abundance, due to elevated quantities of formic (C₁) and acetic (C₂) acids, while indigenous longer-chained (C₃–C₆) species displayed no change in abundance. Our results suggest that on Mars, UV irradiation of carbonaceous chondrites over short time scales is unlikely to degrade indigenous carboxylic acids and additionally may represent a photochemical synthesis mechanism for producing short-chain organic acids from meteoritic insoluble organic matter (IOM), meteoritic carbonates, or atmospheric CO₂ precursors.

¹Zhi Cao, ¹Pan Yan, ¹Zhiyong Xiao, ²Yanxue Wu, ³Haiyang Xian, ¹Yunhua Wu, ⁴Lifeng Zhong, ⁵Dengfeng Li, ²Mingchao Xiong, ²Zilei Chen
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.70229]
¹Planetary Environmental and Astrobiological Research Laboratory, School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, China
²State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
³CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (CAS), Guangzhou, China
⁴Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China
⁵Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-sen University, Zhuhai, China
Published by arrangement with John Wiley & Sons

Microstructures on surfaces of lunar regolith particles record intricate processes during regolith formation and evolution. To acquire the complete morphology and composition of microstructures on surfaces of Chang’e-5 and Chang’e-6 regolith particles, the selected particles were rotated, cleaned using anhydrous ethanol, and loaded into electron microscopes for multiple rounds of analysis. During sample analysis, we noticed a few unusual features on the surfaces of the particles, including ferric-rich iron oxides and NaCl and KCl crystals. These features exhibit overlapping relationships with other microstructures, similar to those formed on the Moon. By comparing the before and after scanning electron microscope (SEM) images, we confirmed that these features resulted from the oxidation of metallic iron particles in the Earth atmosphere and the adhesion of terrestrial contaminants. Our results demonstrate that localized alteration and contamination of lunar regolith samples, although rare, may occur during a limited exposure to the Earth atmosphere, which might hamper interpretations of sample analysis. This work highlights the importance of full-process environmental protection (e.g., inert gas, constant temperature) for pretreatment, transfer and analysis of extraterrestrial samples.

¹Kana Amano (>10)
Geochimica et Cosmochimica Acta (in Press), Open Source Link to Article [DOI: 10.1016/j.gca.2026.09.011]
¹Muséum National d’Histoire Naturelle (MNHN), Institut de Minéralogie, Physique des Matériaux et Cosmochimie (IMPMC), Sorbonne Université, UMR CNRS 7590, 75005 Paris, France
Copyright Elsevier

Recent findings from sample-return missions targeting carbonaceous asteroids suggest that CI-like (Carbonaceous Ivuna-type) small bodies are more common in the solar system than previously thought. However, the general redox characteristics and variations among CI materials remain largely unexplored due to their limited availability on Earth. Moreover, CI meteorites have likely undergone irreversible terrestrial oxidation, resulting in modifications of the iron speciation and the redox states. In this context, the iron mineralogy of samples from the carbonaceous asteroid Bennu allows us to reassess the redox conditions of CI materials during its formation. We performed X-ray diffraction and Mössbauer spectroscopy of two Bennu particles from the hummocky group, as well as Oued Chebeika 002 CI meteorite. We compare their iron speciation to that of other CI and CI-like materials, including samples from the asteroid Ryugu, Orgueil CI meteorite, and Oued Chebeika 002 CI meteorite. The results show that Bennu particles contain substantial amounts of Fe sulfides (pyrrhotite, mackinawite, and pentlandite), along with Fe oxide (magnetite) and Fe-bearing (Mg-rich) phyllosilicates, similar to Ryugu samples. Cryogenic Mössbauer analysis indicates no significant contribution from ferric oxyhydroxides (i.e., ferrihydrite) in Bennu and Oued Chebeika 002 samples, confirming the previous electron microscopy observations of those samples. These observations imply that Fe³⁺ forming ferrihydrite observed in historical CI meteorites (e.g., Orgueil, Alais) results from long-term terrestrial oxidation of Fe²⁺ in sulfides, especially submicron-sized ones. This further strengthens the view that the actual CI materials and their formation environments are less oxidizing than previously estimated from old CI meteorite falls. The Fe³⁺/(Fe³⁺+Fe²⁺) ratios in phyllosilicates in the hummocky particles range from 50 to 70%, indicating local heterogeneity within individual particles. Whereas similar values have been reported for Bennu samples (determined by X-ray Absorption Near-Edge Structure spectroscopy), Ryugu samples, and Oued Chebeika 002 samples (i.e., ∼50–65% of Fe³⁺/(Fe³⁺+Fe²⁺)_{phyllosilicates}), there may be slightly Fe³⁺-rich sub-regions (close to ∼ 70%) in our Bennu particles. Furthermore, we found two distinct mineral assemblages among CI and CI-like materials: (i) relatively well-crystallized phyllosilicates without mackinawite but with pyrrhotite, and (ii) disordered phyllosilicates coexisting with mackinawite, a metastable Fe sulfide. The latter finding is consistent with recent studies of mackinawite in Bennu and Ryugu samples, which suggest its formation at the early stages of CI alteration. Together with previous studies of Bennu, Ryugu, and Orgueil samples, our results suggest that different phyllosilicate assemblages preserve distinct Fe valence states, potentially recording redox conditions associated with different stages of formation. The CI materials have conventionally been regarded as relatively equilibrated and homogeneous, however, our results demonstrate the potential of combining clay mineral crystallinity and Fe valence states to unravel formation histories at a finer scale.

¹Damanveer S. Grewal, ²Zhongtian Zhang
Geochimica et Cosmochimica Acta (in Press), Link to Article [DOI: 10.1016/j.gca.2026.08.036]
¹Department of Earth and Planetary Sciences, Yale University, New Haven, CT 06511, USA
²Department of Geosciences, Princeton University, Princeton, NJ 08544, USA
Copyright Elsevier

Water-rock reactions during aqueous alteration were critical in establishing the redox state of early Solar System planetesimals. The Urey-Craig (UC) diagram, which plots “reduced Fe” (metallic Fe + sulfide Fe) against “oxidized Fe” (silicate- and oxide-bound Fe), is the canonical framework for interpreting redox variations among chondrites. Historical CI chondrites, assumed to be metal-free with their sulfur residing in sulfate, were assigned no “reduced Fe” and long regarded as the oxidized endmember. However, the finding that the returned Ryugu and Bennu samples, along with fresh CI material, host sulfides rather than sulfates, revises their position in the UC diagram, placing them closer to the more reduced CR, L, and LL chondrites. This shift has been interpreted as evidence that CIs are more reduced, challenging their long-standing role as the oxidized endmember.

This interpretation, however, conflates two distinct Fe reservoirs. Under the low-Eh conditions of planetesimal alteration, metallic Fe oxidizes readily whereas sulfides persist, so only the non-sulfide fraction of bulk Fe is accessible to water-driven oxidation. Because bulk S content increases with matrix fraction, the proportion of non-sulfide Fe decreases, making matrix-rich CIs the group with the smallest “oxidizable” Fe reservoir. By quantifying the mean valence state and oxygen associated with the non-sulfide Fe, we show that CI chondrites, although they appear reduced in the revised UC diagram, record pervasive oxidation of the non-sulfide Fe pool, comparable to or greater than that of the most altered CM lithologies. This convergence occurs despite mineralogically distinct alteration pathways on the CM and CI parent bodies, consistent with the endpoint Fe valence being set by the redox potential of the alteration fluid rather than by specific reaction pathways. The lower total O uptake by Fe in CIs reflects not reduced conditions but a smaller initial reservoir of “oxidizable” Fe, itself limited by high bulk S. We introduce a Fe⁰-FeS-Fe_ox (metallic Fe-sulfide Fe-oxidized Fe) ternary framework that reconciles extensive oxidation in CIs with their misleading UC position and provides a more accurate basis for tracing aqueous redox pathways in carbonaceous chondrite parent bodies.