¹E.A. Cloutis et al. (>10)
Icarus (in Press) Link to Article [DOI: 10.1016/j.icarus.2026.117289]
¹Centre for Terrestrial and Planetary Exploration (C-TAPE), University of Winnipeg, 515 Portage Avenue, Winnipeg R3B 2E9, Manitoba, Canada
Copyright Elsevier

We measured reflectance spectra (250–2500 nm) of a 200 mg aliquot (sample id OREX-800029-0) of aggregate (unsorted) regolith particles returned from asteroid Bennu by the OSIRIS-REx mission). Our measurements include spots centered on small (<0.5 mm), medium (0.5–1 mm), and large particles (1–2 mm), as well as spots dominated by larger individual particles, including angular, hummocky, and mottled examples. The ultraviolet (UV) spectra (250–450 nm) are characterized by low reflectance (<3%), slightly red spectral slopes, absorption features near 270 and 320 nm attributable to Fe²⁺-O charge transfers, and Fe³⁺-associated absorption features, respectively. The 450–2500 nm region spectra are of low reflectance (<3% at 550 nm), red-sloped, and exhibit variable but weak absorption features, the most ubiquitous being a broad region of absorption in the 1000 nm region (<~2%), attributable to magnetite and Fe²⁺-bearing phyllosilicates. The low albedo, weak absorption features, and red-sloped spectra can be attributed to the presence of carbonaceous components. Overall, we confirm the spectral similarities between Bennu aggregate material and powders of the rare CI1 chondrite meteorites. The spectra we measured are generally red-sloped, in contrast to the blue-sloped global-average spectra measured by ground-based telescopes and the OSIRIS-REx spacecraft. This difference is consistent with Bennu’s boulder-dominated surface and limited fine-grained dust, in combination with compositional contributions from optically efficient minor phases.

¹Poula Eyðbjørnsdóttir, ¹Anders Johansen, ¹Elishevah van Kooten
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [DOI: 10.1016/j.gca.2026.07.028]
¹Center for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen, Denmark.
Copyright Elsevier

Chondrules and their associated fine-grained rims (FGRs) record fundamental processes operating in the early protoplanetary disk, yet the relationship between chondrule chemistry, morphology, and matrix complementarity remains incompletely understood. Here we investigate the major, minor, and trace element compositions of 66 chondrules and associated FGRs from relatively unaltered CM carbonaceous chondrites Asuka 12236, Paris and Maribo in relation to their three-dimensional morphology, using a multi-analytical approach including femtosecond LA-ICP-MS and X-ray tomography. Our results show that CM chondrules record a systematic process of metal loss and evaporation of Si-rich mesostasis, driving initially CI-like precursor compositions toward more Mg- and Si-rich bulk compositions along the CI ratio line and toward increasingly Si-poor forsteritic mineral assemblages. GEMS-like materials in pristine CM matrices appear to mirror chondrule compositions and likely represent complementary condensates derived from evaporated Si-rich mesostasis. The dust accreted to chondrules is dominantly CI-like but incorporates ∼ 14 wt% complementary condensate material represented by chondritic amorphous silicates, reconciling the observed Mg/Si complementarity between chondrules and matrix with the preservation of primordial organics and presolar grains.

Morphological observations further reveal no significant sectioning bias in chondrule size or plane, consistent with CM chondrule populations being dominated by agglomerates of ∼ 100 μm sized microspherules rather than larger primary melt droplets. Many chondrules display grape-bunch textures formed by welding of smaller primary chondrules with metal-rich or CI-like rims. This structure may explain the moderate volatile element plateau at ∼ 0.3 × CI observed for average CM chondrule compositions, reflecting incorporation of primary fine-grained rim material into these aggregates. We propose a “micro-chondrule-first” formation scenario in which localized heating events produced small molten droplets that subsequently accreted CI-like dust and ice, aggregated, and experienced limited in situ aqueous alteration. These observations place new constraints on chondrule formation mechanisms in the outer disk and highlight the importance of localized melting and aggregation processes.

^1,2Shuya Tan et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [DOI: 10.1016/j.gca.2026.06.034]
¹Earth and Space Exploration Center, Ritsumeikan University, Kusatsu, Japan
²Institute for Extra-cutting-edge Science and Technology Avantgarde Research of Life (X-star),
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
Copyright Elsevier

The geochemical effects of freezing are becoming important in the investigation of closed aqueous environments, such as inland water on Earth and early Mars, and liquid water on planetesimals. Carbonate-bearing alkaline saline lakes in Mongolia are frozen in the cold season, with chemical species being partitioned among surface ice, lake water, and sediments. Freezing of the lakes leads to the accumulation of dissolved carbonate species, thereby decreasing the pH. The lakes are enriched not only in heavy metals, such as As, Mo, and U, but also in phosphorus. However, little is known about how metals and phosphorus are affected by chemical changes during freezing. Moreover, the mechanisms of major chemical changes are poorly understood and reproduced. Here we performed field surveys to investigate the behavior of these elements during lake freezing. Heavy metals and phosphorus accumulate in lake water during freezing, similar to major elements such as Cl−, with Mo and U concentrations reaching ∼1 mg/L. On the other hand, As and P accumulations are limited. Concentrations of heavy metals and phosphorus in ice increase with depth in the ice. We interpret the observed behavior using a geochemical model that accounts for their adsorption reactions coupled with water removal by freezing and carbonate precipitation. The model successfully reproduces the major chemical changes, including the decrease in pH, achieving quantitative accuracy by accounting for the combined effects of freezing and the revised solubility of carbonate minerals. The pH decrease promotes the adsorptions of As and P on sedimentary ferrihydrite particles, suppressing their accumulation in lake water. However, the decrease in pH is insufficient to promote adsorptions of Mo and U, resulting in their accumulations as major dissolved species. Adsorptions of heavy metals and phosphorus by iron oxides may be an important factor in their behaviors at low temperatures near the freezing point of water. Based on our model and observations, we discuss phosphate/carbonate precipitation in freezing porewater of icy planetesimals and phosphate availability in lake water on early Mars.

¹Valentine Megevand, ¹Sylvain Bernard, ²Corentin Le Guillou, ²Roberto Conconi, ¹François Guyot
Meteoritics & Planetary Science (in Press) Open Source Link to Article [DOI: 10.1111/maps.70214]
¹Institut de Minéralogie, Physique des Matériaux et Cosmochimie, Muséum National d’Histoire Naturelle, Centre National de la Recherche Scientifique UMR 7590, Sorbonne Université, Paris, France
²Université de Lille, CNRS, INRA, Centrale Lille, UMR 8207 – UMET – Unité Matériaux et Transformations, Villeneuve d’Ascq, France
Published by arrangement with John Wiley & Sons

Carbonaceous chondrites contain phosphorus, whose speciation and thus history remain to be investigated. Phosphorus/sulfur-bearing assemblages have been reported in carbonaceous CM chondrites, but there is no consensus about their exact compositions and origins. Here, we present submicrometer-scale investigations by analytical transmission electron microscopy of phosphorus/sulfur-bearing assemblages from the CM chondrites Murray and Murchison. Results indicate that, in CM chondrites, phosphorus associated with sulfides occurs under distinct oxidation states. In Murray, we identified a pyrrhotite–schreibersite nanocrystalline assemblage associated with carlsbergite and chromite. Its reduced nature and petrographic context are indicative of a nebular formation mechanism, possibly through kamacite sulfidation. In contrast, Murchison contains nanocrystalline pentlandite assemblages associated with carlsbergite and likely with phosphate phases that we interpret as being produced via interactions with an oxidizing fluid under asteroidal conditions. Thermodynamic modeling suggests that such complex assemblages hosting reactive forms of both phosphorus and nitrogen could promote the synthesis of activated phosphate species such as diamidophosphate, an efficient phosphorylation reagent, thereby underscoring their potential prebiotic significance.

^1,2Kyusei Tsuno, ³Hideharu Kuwahara, ¹Varun Manilal, ²Axel Wittmann, ^2,4Kurt Leinenweber, ³Tetsuo Irifune, ¹Damanveer S Grewal
Earth and Planetary Science Letters (in Press) Link to Article [DOI: 10.1016/j.epsl.2026.120246]
¹Department of Earth and Planetary Sciences, Yale University, New Haven, CT, 06511, United States
²Eyring Materials Center, Arizona State University, Tempe, AZ, 85287, United States
³Geodynamic Research Center, Ehime University, Matsuyama, 790-8577, Japan
⁴School of Molecular Sciences, Arizona State University, Tempe, AZ, 85287, United State
Copyright Elsevier

Geochemical constraints imply that a solid silicate layer existed between the base of the Martian magma ocean (∼14 GPa) and the core-mantle boundary (∼18–20 GPa) during early differentiation. Both S-poor metallic melts segregated during core formation and S-rich sulfide melts exsolved upon subsequent magma ocean cooling must have percolated through this layer to the core, but the efficiency of this process is poorly constrained. At ∼18 GPa, this layer comprises roughly equal proportions of ringwoodite and majorite garnet, yet no dihedral angles in majorite garnet have been reported. We conducted experiments at 18 GPa and 1723–2200 K to determine dihedral angles between Fe(-Ni)-S-O alloy melts (25–46 mol% S+O) and both ringwoodite and majorite garnet. Dihedral angles decrease with increasing temperature, S+O content, and oxygen fugacity, while Ni has no effect. Dihedral angles in majorite garnet are systematically ∼10° lower than in ringwoodite under comparable conditions. Despite this, all dihedral angles (89°-126°) remain above the 60° threshold for melt interconnection, so the entire mineral assemblage acts as a percolation barrier. Because our experimental S+O contents exceed those of the S-poor core-forming alloy (∼15 mol% S), the measured angles represent a lower bound; the barrier for core-forming metal was even more severe. Theoretical models predict that for such angles, a few (> ∼1–2) vol.% of melt remains trapped as isolated pockets upon network disconnection. Such melts constitute a hidden deep mantle reservoir of highly siderophile elements (HSEs) and siderophile volatiles (C, N), explaining their abundances in bulk silicate Mars without requiring a late veneer.

¹Fabrice Gaillard, ²Yves Marrocchi, ¹Gregory Rogerie, ³Mohamed A. Bouhif, ¹Camille Bernard, ⁴Mathieu Roskosz
Earth and Planetary Science Letters, 692, 120245 Link to Article [DOI: 10.1016/j.epsl.2026.120245]

¹Institut Des Sciences de la Terre d’Orléans, CNRS/Université d’Orléans/BRGM, 1a Rue de la Férollerie 2, Orléans, 45071 CEDEX, France
²Université de Lorraine, CNRS, CRPG, Nancy, F-54000, France
³Laboratoire Magmas et Volcans, Université Clermont Auvergne, CNRS, IRD, OPGC, Clermont-Ferrand, F-63000, France
⁴IMPMC, MNHN, CNRS, UMR 7590, Muséum National d’Histoire Naturelle, Sorbonne Universités, CP 52, 57 rue Cuvier, Paris, F-75231, France
Copyright Elsevier

The Mercury-Venus-Earth-Mars-Vesta planetary suite exhibits large variations in oxidation state as defined by the Fe to FeO ratio (i.e. core to silicate ratio), with increasingly oxygen-depleted bodies toward the centre of the solar system. As undifferentiated materials (i.e., chondrites) likely display a similar heliocentric FeO-gradient, planetary and chondritic oxidation states should be related in this respect. We develop an approach wherein, the equilibrium oxygen redistribution during gas – silicate melt – molten metal alloy during differentiation is resolved for bodies of various compositions and sizes. As a case study, three chondritic end-members were considered: enstatite, ordinary, and carbonaceous. A broad range of planetary oxidation states are obtained that encompass the above-mentioned planetary suite. The oxidation state during the growth of small bodies (<2000 km in radius) of constant bulk composition is affected by metal-vapour carbon redistribution, whereas on larger bodies, the incorporation of hydrogen, oxygen and silicon in the core prevails, causing the convergence toward a putative universal magma ocean FeO content. A dual regime is observed for the water content in the silicate magma ocean, which increases up to a planetary radius of ∼3000 km, whereas in larger bodies, hydrogen incorporation into the core brings about dehydration of the complementary silicate mantles. The accretion of ordinary chondrites perfectly matches the oxidation state of Mars and produces a core with C-H-S-N contents matching the Martian core density as suggested by the Insight missions. Finally, Vesta’s oxidation state seemingly requires an H2O-rich oxidizing component during the formation of planetesimals.

^1,2,6Ranjan Sarkar, ³Ed Cloutis, ³Daniel Applin, ³Nathalie Turenne, ⁴Daniel Mège, ⁵Andreas Beinlich, ⁵Stanley A. Mertzman
Icarus (in Press) Link to Article [DOI: 10.1016/j.icarus.2026.117282]
¹Max Planck Institute for Solar System Research, Göttingen, Germany
²Indian Institute of Technology, Kharagpur, India
³Department of Geography, University of Winnipeg, Winnipeg, MB, Canada R3B 2E9
⁴Centrum Badań Kosmicznych Polskiej Akademii Nauk (CBK PAN), ul. Bartycka 18a, 00-716, Warszawa, Poland
⁵Institut für Geologische Wissenschaften, Freie Universität Berlin, Kaiserswerther Str. 16-18, 14195 Berlin, Germany.
⁶Department of Earth and Environment, Franklin and Marshall College, Lancaster, PA 17604, USA.
Copyright Elsevier

Listvenites are extensively carbonated ultramafic rocks such as peridotites and serpentinites that commonly containing carbonates (magnesite, dolomite), quartz, and often the accessory mineral fuchsite—a green, chromium-bearing variety of muscovite. Listvenites form distinctive yellow-orange ridges in areal views due to their mechanically-resistant carbonate-silica mineralogy and iron oxidation. They form when an ultramafic protolith comes into contact with CO₂-rich fluids and undergoes a progressive replacement of the Fe/Mg-bearing olivines and pyroxenes or serpentinites into increasingly carbonate-rich assemblages, and ultimately to carbonate-quartz rocks. We analyzed listvenite samples from the Atlin area, British Columbia, Canada using a variety of analytical techniques, including X-ray diffraction (XRD), X-ray fluorescence (XRF), wet chemistry (WC), visible-near infrared (VNIR) reflectance spectroscopy (0.35-2.5 μm), and Raman spectroscopy. VNIR and Raman spectroscopies were able to successfully identify all major mineral phases through their diagnostic absorption (VNIR) or emission (Raman) features. We found that listvenite composition is readily derivable from VNIR reflectance and Raman spectra, with fuchsite providing a diagnostic signature in VNIR spectra due to its unique Cr³⁺ absorption bands that remain detectable even at low concentrations. These findings establish a spectroscopic framework for identifying listvenites in remote sensing applications, relevant for exploration of Solar System bodies, particularly Mars, where such carbonated ultramafic rocks can produce H₂ and CH₄, and may preserve biosignatures and might indicate past habitable conditions associated with their low-temperature formation.

^1,2Oleg I. Siidra, ³Artem S. Borisov, ⁴Victoria A. Ginga, ¹Veronika R. Abdulina, ⁵Dmitri O. Charkin, ⁶Anatoly V. Kasatkin, ³Astrid Holzheid, ⁴Annette Setzer, ⁷Vladimir N. Bocharov
Icarus (in Press) Link to Article [DOI: 10.1016/j.icarus.2026.117275]
¹Department of Crystallography, St. Petersburg State University, University Emb. 7/9, 199034 St. Petersburg, Russia
²Kola Science Center, Russian Academy of Sciences, Apatity 184200, Murmansk Region, Russia
³Institut für Geowissenschaften der Universität Kiel, Olshausenstr. 40, D-24098 Kiel, Germany
⁴Felix Bloch Institute for Solid-State Physics, Leipzig University, Linnestrasse 5, D-04103 Leipzig, Germany
⁵Chemistry Department, Moscow State University, Vorobievy Gory 1-3, Moscow 119991 Russia
⁶Fersman Mineralogical Museum of the Russian Academy of Sciences, Leninsky Prospekt 18-2, 119071 Moscow, Russia
⁷Geomodel Resource Center, St. Petersburg State University, University Emb. 7/9, 199034 St. Petersburg, Russia
Copyright Elsevier

Copiapite-group minerals are among the most common hydrated iron sulfate minerals in a variety of geological environments on Earth. They are also believed to be widespread on the Martian surface. The transformation and stability of the copiapite-group minerals are examined in this study using a diverse array of methods, including low- (LT) and high-temperature (HT) single-crystal X-ray diffraction (SCXRD), LT- and HT-powder X-ray diffraction (PXRD), vacuum powder X-ray diffraction, HT-Raman spectroscopy, magnetization and heat capacity measurements. The research is conducted over a broad temperature range (−175–740 °C) and under vacuum (~ 600 Pa) conditions that are partially similar to those found on the Martian surface (from −153 °C to over 20 °C and ~ 600 Pa). The obtained results indicate that aluminocopiapite, (Al0.54Fe3+0.13)Σ0.67Fe3+4(SO4)6(OH)2(H2O)20, is unstable under low vacuum conditions and undergoes a structural transition to a post-aluminocopiapite phase, (Al0.63Fe3+0.04)Σ0.67Fe3+4(SO4)6(OH)2(H2O)12.44 with a significantly lower water and iron content and a higher aluminum content. Schwertmannite, Fe3+16O16(OH)9.6(SO4)3.2·10H2O is formed as a film/shell on the crystal surface of post-aluminocopiapite via a single crystal-to-single crystal (SC-SC) topotactic transformation and exsolution. After 14 days of exposure to air, the post-aluminocopiapite crystal with schwertmannite shell undergoes a reversible process, reverting to its initial aluminocopiapite state. A closely analogous transformation, involving partial dehydration, was observed for copiapite, Fe2+Fe3+4(SO4)6(OH)2(H2O)20, demonstrating that this behavior is a general feature of the copiapite group.
It is therefore unlikely that copiapite-group minerals would exist on the surface of Mars and in comparable extraterrestrial environments in their initial form. Instead, under Mars surface conditions with low vacuum, post-copiapites and schwertmannite may be among the most common minerals in hydrated iron sulfate mineral associations. This is relevant for decoding past geo- and climatic environments on Mars and for selecting the conditions for the return of intact samples collected by rovers to Earth.

¹Jillian Kirk, ¹Myriam Telus, ¹Pranvera Hyseni, ¹Fatima Jorge-Chavez, ²Vanessa Mendoza, ³Steven J. Desch, ⁴Dale Burns, ⁵Steven Simon
Icarus (in Press) Open Access Link to Article [DOI: 10.1016/j.icarus.2026.117263]
¹University of California Santa Cruz, Department of Earth and Planetary Sciences, 1156 High Street, Santa Cruz, 95064, CA, USA
²Western Washington University, Geology Department, 516 High St, Bellingham, 98225, WA, USA
³Arizona State University, School of Earth and Space Exploration, 781 Terrace Mall, Tempe, 85287, AZ, USA
⁴Stanford University, Department of Geological Sciences, 450 Jane Stanford Way, Stanford, 94305, CA, USA
⁵University of New Mexico, Institute of Meteoritics, 221 Yale Blvd NE MSC03 2050, Albuquerque, 87131, NM, USA
Copyright Elsevier

Chondrules are small igneous particles that formed in the protoplanetary disk and make up the bulk of chondrites. Chondrule rims offer insights into the composition of dust in the solar nebula and the conditions and heating mechanisms associated with chondrule formation. High-resolution elemental mapping of pristine CO3 chondrite thin sections revealed igneous chondrule rims enriched in manganese, a moderately volatile element (MVE), which is sensitive to thermal processing. These chondrule rims have not previously been characterized, in part due to their small thicknesses (
30
m). Characterization of Mn-rich rims in CO3 chondrites reveals that this enrichment exists in a variety of textures, some of which are associated with non-igneous fine-grained rims, while many clearly formed from a melt. Mn-rich pyroxenes in CO3 chondrule rims are also enriched in Na, K, and Cr, as compared to pyroxene in host chondrules (i.e., chondrules hosting the Mn-rich rims) and no-rim chondrules (chondrules without Mn-rich rims). These enrichments seem to be the result of nebular processing of chondrules as opposed to parent-body processing, as enrichments do not correlate with petrologic subtypes. Pyroxene with similar enrichments in these elements occur within igneous chondrule rims seen in CR chondrites, indicating that these rims may have formed across different locations and times in the nebula. Previous studies have suggested that MVE enrichment of chondrule rims occurred during interaction with MVE-enriched nebular gas. Our results could support an alternative scenario involving accretion of MVE-enriched dust onto solidified chondrules, which subsequently experienced varying degrees of thermal processing, possibly facilitated by a planetesimal or planetary embryo bow shock, resulting in MVE-enriched chondrule rims. Future work is needed to validate this idea. This study highlights the potential role of outgassing planetesimals and/or planetary embryos as a source of MVE-rich dust in the solar nebula.

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