¹S.A. Singerling, ¹F.E. Brenker, ¹B. Tkalcec, ²S.S. Russell, ³T.J. Zega, ⁴T.J. McCoy, ^3,4,5H.C. Connolly Jr., ³¹D.S. Lauretta
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.06.028]
¹Schwiete Cosmochemistry Laboratory, Goethe University, Frankfurt, Germany
²Planetary Materials Group, Natural History Museum, London, UK
³Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
⁴Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
⁵Department of Geology, Rowan University, Glassboro, NJ, USA
⁶Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY, USA
Copyright Elsevier

We describe nanoscale observations obtained via transmission electron microscopy of Na,Ca carbonates in OSIRIS-REx samples of asteroid Bennu. Four Na,Ca carbonate grains were observed (including the one briefly described in McCoy and Russell et al., 2025), ranging in size from 140 nm to 2.36 µm. The stoichiometry of the grains and electron diffraction data best match gaylussite (Na2Ca(CO3)2·5H2O) or pirssonite (Na2Ca(CO3)2·2H2O). The grains rapidly amorphized under the electron beam. We also found that the grains are reactive to the terrestrial atmosphere, with their compositions and textures changing over six months of storage in a standard desiccator. NaCl salts grew on the exteriors of the grains, and the compositions of the carbonates became richer in C, F, Cl, and Ca and poorer in O and Na
Neither gaylussite nor pirssonite have been observed in planetary materials other than samples from Bennu. On Earth, these phases occur in evaporites or shales from alkali lakes and, less commonly, as veins in alkaline igneous rocks. Thermodynamic modeling has shown that both phases require a low-temperature (<55 °C), Na-rich (>140 g/kg Na2CO3) brine, and their presence in the Bennu samples supports a model of salt formation on the parent body during syndepositional back-reaction of a briny fluid (McCoy and Russell et al., 2025). We argue that these minerals have not been previously observed owing either to their rare formation conditions or their susceptibility to degradation from sample preparation and analysis (e.g., electron/ion beam imaging), terrestrial weathering, and/or storage in a terrestrial environment. This study highlights the importance of collecting and carefully preserving pristine samples from planetary bodies.

¹Marina A. Ivanova,¹Svetlana N. Teplyakova,¹Cyril A. Lorenz,²Shuying Yang,²Munir Humayun
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70005]
¹Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow, Russia
²National High Magnetic Field Laboratory and Department of Earth, Ocean & Atmospheric Science, Florida State University, Tallahassee, Florida, USA
Published by arrangement with John Wiley & Sons

Sierra Gorda 013 (SG 013) is an unusual CBa-like chondrite containing two texturally different, isotopically identical lithologies—chondritic (L1) and achondritic (L2), which should have a common origin. The metal globules of the L1 metal preserved the magmatic pattern of the siderophile element distribution that indicates they had a fractionated precursor. In this work, the trace element metal composition of lithology 2 was studied, and the revisited LA-ICP-MS data on the L1 metal was presented. Lithologies 1 and 2 have Ni and Co in the range of CB chondrites. The Ni-Co distribution in L1 and depletion in Cr of both lithologies with a negative Cr-Ni correlation are similar to that of the magmatic irons. Highly refractory siderophile element (HRSE) (W, Re, Os, Ir, Pt, Ru, Rh, and Mo) compositions of the L1 metal are highly fractionated relative to CI, but the L2 metal has a nearly uniform HRSE distribution similar to the depleted patterns of some HRSE-poor L1 metal compositions. Metal from both lithologies is depleted in volatile siderophile elements. In the L1 metal globules, the metal composition shows definite linear correlations of the HRSE elements versus Ni similar to those observed in many magmatic iron meteorites, distinct from those of the CH/CBb-zoned metal. Meanwhile, the L2 metal compositions are systematically plotted as limited clusters in the middle of the L1 trends. Based on a fractional crystallization (FC) model of the CR-like metal composition, it was shown that the distribution of siderophile elements in the metal globules of L1 can cover the full range of the fractional crystallization products of a metallic (Fe-Ni-S) liquid from the core of a differentiated body at S content 13 wt%. In contrast, the metal from L2 corresponds to a more limited range of fractional crystallization products and indicates a mixture of the fractionated metal with the primitive metal from the chondritic colliding body. Our results suggest that during a catastrophic impact event when the metallic core of a differentiated body was disrupted, the L1 lithology was quickly cooled in the impact plume, more reduced than that of CB chondrites and avoided equilibration with plume gas and preserved its fractionated HRSE patterns. The distribution of siderophile volatile elements and Au was likely overprinted by high-temperature processes of volatilization and recondensation to different degrees in the impact plume under disequilibrium conditions. The L2 metal probably avoided equilibration with the plume gas and was affected by thermal metamorphism up to 900°C in the SG 013 parent body, which possibly resulted in the higher W abundance compared to the L1 metal with a magmatic Ir-W trend due to the redox reactions with silicates under reducing conditions.

¹Kaushik Mitra,¹Lauren A. Malesky,²Michael T. Thorpe,³Ana Stevanovic
Proceedings of the National Academy of Sciences of the USA (PNAS) 122, e2504674122 Link to Article [https://doi.org/10.1073/pnas.2504674122]
¹Department of Earth & Planetary Sciences, The University of Texas at San Antonio, San Antonio, TX 78249
²University of Maryland/NASA Goddard Space Flight Center/ Center for Research and Exploration in Space and Science Technology (CRESST II), Greenbelt, MD 20771
³Kleberg Advanced Microscopy Center, The University of Texas at San Antonio, San Antonio, TX 78249

Pure siderite [FeIICO3] was recently discovered in abundant quantities (4.8 to 10.5 wt.%) by the Curiosity rover at Gale crater, Mars. Diagenetic alteration of siderite likely caused the carbonate-sequestered CO2 to be released back into the atmosphere and consequently produced ferric [Fe(III)] oxyhydr(oxide) minerals. Here, using laboratory experimentation, we demonstrate that while closed system acid diagenesis—as proposed for Gale crater—is incapable of effective siderite alteration in Mars-relevant fluids, oxyhalogen compounds (chlorate and bromate) can weather siderite not only at acidic pH but also in near-neutral Mars-relevant solutions. The ferric oxyhydroxide minerals produced as a consequence are controlled by the diagenetic fluid composition. While photooxidation is possible, the mutually exclusive products of alteration—magnetite (Fe3O4) during ultraviolet irradiation and ferric oxyhydroxide (FeOOH) by oxyhalogens—demonstrate that siderite at Gale crater underwent chemical weathering by chlorate and bromate brines owing to the complete absence of magnetite in drill samples containing siderite. We propose a top–down oxyhalogen brine percolation model to explain the iron mineralogy of the sulfate-rich unit at Gale crater. We conclude that siderite alteration by acidic fluids alone cannot explain the redox disequilibrium witnessed in Gale crater sediments as promulgated before and siderite weathering by oxyhalogen brines is the most likely explanation. It is highly likely that the halogen cycle on Mars is interlinked to the iron and the carbon cycle on early and current Mars.

¹Timothy J. Fagan,²Sachio Kobayashi,²Alexander N. Krot,²Hisayoshi Yurimoto
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70003]
¹Department of Earth Sciences, Waseda University, Tokyo, Japan
²Department of Natural History Sciences, Hokkaido University, Sapporo, Japan
³Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, Hawaii, USA
Published by arrangement with John Wiley & Sons

Oxygen isotopic compositions of minerals in three Ca-Al-rich inclusions (CAIs), one amoeboid olivine aggregate (AOA) and one Al-rich chondrule (ARC) from the pristine ungrouped carbonaceous chondrite Acfer 094 were analyzed by secondary ion mass spectrometry (SIMS), including conventional spot analyses and O-isotope imaging. Most of the ARC minerals analyzed in this study are 16O-poor (Δ17O ≥ −5.4‰), with one outlier in high-Ca pyroxene (Δ17O = −10.6 ± 2.8‰), indicating that if the ARC precursors formed initially in an 16O-rich setting, isotopic compositions were mostly reset during chondrule melting in an 16O-poor environment. The CAIs and AOA analyzed are dominated by 16O-rich compositions, consistent with previous work, but partial isotopic resetting to 16O-poor compositions has been identified. Melilite with a moderately 16O-depleted composition (Δ17O = −15.7 ± 3.0‰) was identified in an AOA, and 16O-poor diopside (Δ17O = −1.9 ± 2.5‰) was identified as the outermost layer of a Wark–Lovering-like rim of an 16O-rich CAI (Δ17O ranges from −18 to −22 ± 2.5‰). The diopside layer is bounded by an inner rim of anorthite replacing melilite, which is in turn bounded by the grossite-hibonite-perovskite-spinel-bearing core of the CAI. Isotopic imaging shows that the diopside/anorthite boundary coincides with a steep gradient in O isotopic composition. Based on modeling of O diffusion in the temperature range of 1400–1500 K, thermal events that formed the diopside and anorthite rim layers were limited to durations of no more than approximately 100 days and were probably much shorter. Given the weak metamorphic alteration of Acfer 094, the partial to nearly complete O-isotope resetting of AOA, CAI, and ARC minerals analyzed in this study occurred by short-term thermal events in the solar nebula prior to the formation of the Acfer 094 parent body. Therefore, the isotopic variations identified in this study show that at least some refractory materials were transported from 16O-rich environments, where initial crystallization took place, to 16O-poor environments in the solar nebula, where subsequent crystallization and/or isotopic resetting occurred.

¹Daiki Yamamoto, ²Aki Takigawa, ²Lily Ishizaki, ³Ryosuke Sakurai, ¹Yuki Inoue, ¹Junji Yamamoto, ⁴Sota Arakawa, ²Shogo Tachibana
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.06.010]
¹Department of Earth and Planetary Sciences, Kyushu University, Motooka, Fukuoka 819-0395, Japan
²Department of Earth and Planetary Science, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
³Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 252-5210, Japan
⁴Yokohama Institute for Earth Sciences, Japan Agency for Marine-Earth Science and Technology, Yokohama, Kanagawa 236-0001, Japan
Copyright ELsevier

Presolar silicon carbide (SiC) grains found in primitive extraterrestrial materials would preserve the pre-accretion thermal history of dust in the protosolar disk. Three series of evaporation experiments of SiC were conducted at total pressures of 0.5 and 2.5 Pa of H2-H2O gas mixture with controlled H2/H2O ratios of ∼ 52–140 and temperatures of 1523–1779 K. The STEM-EDS and Raman spectroscopic analyses of the heated samples indicated the absence of an oxide layer on the sample surface; however porous carbon-rich layers were occasionally observed. This suggests that the evaporation of SiC under the experimental conditions proceeded without the formation of a protective steady-state SiO2 layer. Under all the experimental conditions, the evaporation flux (J) has little/no dependence on temperatures typically higher than ∼1610–1670 K, while larger temperature dependences were observed at lower temperatures. The little/no temperature-dependence of J suggests that the evaporation reaction rate is controlled by the gaseous supply of H2O to the SiC surface under low-pressure conditions prevailing in the protosolar disk. The overall reaction rates would be limited by the surface chemical reactions in the large-temperature dependent regime. The large activation energies in this regime obtained in this study compared with those reported from the previous studies are likely associated with the transition regime from the SiC evaporation without continuous SiO2 formation to that accompanied by the SiO2 formation.
The survivability of presolar SiC grains was then compared with that of presolar amorphous silicate grains. We found that the lifetime of 0.1–1 μm-diameter SiC grain in the protosolar disk would have little/no temperature dependence at temperatures higher than ∼1500–1700 K, whereas it has a large temperature dependence at lower temperatures. The survival of these presolar SiC grains during the formation of igneous calcium-aluminum-rich inclusions would largely depend on the heating conditions of high-temperature events. Effective SiC evaporation would occur at ∼1200–1400 K, whereas oxygen isotopic signatures of 0.1 μm-diameter presolar amorphous silicate grains would be erased at ∼ 600–800 K in the accreting ptotosolar disk. At temperatures lower than ∼ 600–700 K, the presolar silicate/SiC number ratio normalized to its initial ratio increases with increasing the heliocentric distance from the Sun (r), reaching values of ∼ 0.7–0.9 at r > 4–5 au if the particles were released at ∼ 6–12 au. Assuming that the primitive interplanetary dust particles (IDPs) have an initial presolar silicate/SiC ratio of ∼ 6, the IDP-normalized ratios in primitive carbonaceous chondritic meteorites are in the range of ∼ 0.15–1. The high normalized presolar silicate/SiC ratios (>∼0.7) in meteorites imply that precursor materials of these meteorites originated predominantly from the regions with temperatures of < 300 K, corresponding to r of >∼4–5 au in this model. Our results indicate that the ratio of presolar silicate to SiC grains in the minimally altered primitive extraterrestrial materials may serve as a potential proxy for constraining the pre-accretional thermal history of the materials in the protosolar disk.

^1,2Daisuke Nakashima, ^2,3,4Jon M. Friedrich, ^2,5Ulrich Ott
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.06.016]
¹Department of Earth and Planetary Material Sciences, Faculty of Science, Tohoku University, Aoba, Sendai, Miyagi 980-8578, Japan
²Max-Planck Institute for Chemistry, Hahn-Meitner-Weg, 1, D-55128 Mainz, Germany
³Department of Chemistry and Biochemistry, Fordham University, 441 East Fordham Road, Bronx, NY 10458, USA
⁴Department of Earth and Planetary Sciences, American Museum of Natural History, 200 Central Park West, New York, NY 10024, USA
⁵HUN-REN Institute for Nuclear Research, Bem tér 18/c, 4026 Debrecen, Hungary
Copyright Elsevier

Noble gas isotopes and trace element abundances in five Ca-Al-rich inclusions (CAIs) from two CV3 chondrites (Allende and Axtell) were analyzed. The noble gases consist of spallogenic, radiogenic, fission, and trapped components. The old U/Th-4He ages of the CAIs (4.0 – 5.4 Ga) suggest no significant loss of radiogenic 4He and, by inference, no significant disturbance of the initial (244Pu/238U) ratios, (244Pu/238U)0, which are derived using concentrations of 244Pu-fission 136Xe. The abundances of rare earth elements and U in the CAIs suggest variable formation temperatures, which is reflected in variable (Pr/238U)0 ratios. The (244Pu/238U)0 ratios of the CAIs are variable from 0.0103 ± 0.0010 to 0.0419 ± 0.0031, which correlate with the (Pr/238U)0 ratios. The correlation suggests Pu-Pr-U fractionation during CAI formation. From the intersection between the correlation line and the calculated early Solar System Pr/238U ratio of 9.27, the 244Pu/238U ratio before Pu-Pr-U fractionation in the CAI formation region is calculated as 0.0108 ± 0.0051, which is similar to those derived using other Solar System materials such as chondrites, achondrites, chondrules, and terrestrial zircons. We thus suggest that the initial 244Pu/238U ratio has been spatially homogeneous in the inner part of the early solar nebula including the innermost solar nebula, where CAIs formed.
We also used our Xe isotope data to search for the possible presence of Xe-G, a characteristic feature of presolar silicon carbide, which has previously been reported for the CAI Curious Marie (Pravdivtseva et al., 2020). Following the same approach as those authors, we find no evidence of Xe-G in our CAIs except for possibly one (All-4). We identified a correlation, during stepped gas release, in the Curious Marie data from the literature between 130Xe-G and radiogenic 129Xe, which is surprising and not apparent in All-4. However, the exact amount of Xe-G in Curious Marie (and the very presence in All-4) sensitively depend on the applied component resolution scheme. We infer that the abundance of Xe-G in Curious Marie is about twice that previously reported and that All-4 contains Xe-HL, the characteristic Xe component of presolar nanodiamonds. While we cannot rule out the presence of presolar SiC noble gas components at a lower level than found in CAI Curious Marie as a general feature of fine-grained CAIs, Curious Marie appears to be a special case.

^1,2Laurence A. J. Garvie,³László Trif,⁴Christian G. Hoover
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70000]
¹Buseck Center for Meteorite Studies, Arizona State University, Tempe, Arizona, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
³Institute of Materials and Environmental Chemistry, HUN-REN Research Center for Natural Sciences, Budapest, Hungary
⁴School of Sustainable Engineering and the Built Environment, Ira A. Fulton Schools of Engineering, Arizona State University, Tempe, Arizona, USA
Published by arrangement with John Wiley & Sons

Meteorites arriving on Earth possess indigenous organic, isotopic, mineralogic, and magnetic properties that reveal conditions and processes from their formation. However, these properties can rapidly change when exposed to the Earth’s environment. Asteroids, which formed nearly 4.5 billion years ago, inhabit the ultrahigh vacuum of interplanetary space, with a pressure of around 1.3 × 10−11 Pa, equivalent to only a few tens of atoms per cubic centimeter. Fragments of these asteroids, which land on Earth as meteorites, immediately adsorb atmospheric gases into their pore spaces, which can subsequently adsorb into and onto the minerals. In this study, we show that adsorption of atmospheric water can significantly increase the mass of the smectite-rich Tarda (C2-ung) meteorite, with mass gains reaching around 30 wt% at 100% relative humidity (RH) and between 5 and 10 wt% under typical laboratory conditions (up to ~50% RH). In contrast, the serpentine-rich Aguas Zarcas meteorite gains approximately 11 wt% at 100% RH and around 2 wt% at ~50% RH. This water adsorption leads to observable mass fluctuations in clay-rich carbonaceous chondrites (CCs), especially those with high smectite content, which undergo a “breathing-like” process. This process involves the uptake and release of water, influenced by atmospheric humidity. Although this mass change is reversible in the short term, prolonged “breathing” can alter the mineral composition and physical properties of these materials, complicating our understanding of their origins and evolution. For instance, gypsum forms in Tarda after 10 min of exposure to 100% RH at room temperature, while the Aguas Zarcas meteorite forms significant gypsum within 24 h under similar conditions. In addition, mass changes for Tarda are measured with thermal gravimetry in a He atmosphere, by heating the sample at 100°C in a high vacuum, and after curation under an ultradry atmosphere. These experiments show that samples exposed to the atmosphere rapidly adsorb significant water that is not removed by curation under dry N2. Our findings indicate that this “breathing” process can profoundly and rapidly affect the properties of astromaterials, including samples returned from asteroids Ryugu and Bennu. Maintaining these materials in a stable, low-humidity environment can help prevent such changes and preserve their indigenous properties.

¹Coral K. Chen, ²Meng Guo, ¹Jun Korenaga, ³Simone Marchi
Earth and Planetary Science Letters 666, 119493 Link to Article [https://doi.org/10.1016/j.epsl.2025.119493]
¹Department of Earth and Planetary Sciences, Yale University, New Haven, CT 06520, United States of America
²Asian School of the Environment, Nanyang Technological University, 600259, Singapore
³Department of Space Studies, Southwest Research Institute, Boulder, CO 80302, United States of America
Copyright Elsevier

As an important reservoir for incompatible elements, the growth of the continental crust profoundly influenced the composition of the mantle and the atmosphere. The co-evolution of the continental crust, mantle, and atmosphere throughout Earth history can be traced through the transfer of argon and potassium between these three reservoirs. While many argon-constrained crustal growth models have been proposed, none of them consider the effect of late accretion (bombardment by leftover planetesimals in the several hundred million years after the Moon formed) in detail. Our model is the first of its kind to simulate both the volatile delivery and the atmospheric erosion by impacting planetesimals. Whereas the relative fraction of impactor-derived argon in the present-day atmosphere depends on the assumed impactor composition and the starting atmospheric mass, the present-day atmospheric argon originates largely from mantle degassing and crustal processing. For a range of impact parameters, our model results indicate that the early rapid growth of continental crust is required to satisfy the argon budget of the mantle and atmosphere.

¹William M. Lawrence, ¹Geoffrey A. Blake,¹John Eiler
Proceedings of the National Academy of Sciences of the USA (PNAS) 122, e2423345122 Link to Article [https://doi.org/10.1073/pnas.2423345122]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125

Macromolecular organic solids found in primitive meteorites were the main source of carbon delivered to forming planets in the early Solar System. However, the conditions under which this material formed and its subsequent incorporation into growing planetesimals remains a subject of vigorous debate. Here, we show that C isotope variations among these organics in most carbonaceous chondrites are strongly correlated with mass-independent O isotope anomalies exhibited by their host meteorites. As the latter signature has been argued to track abundances of nebular water generated from photochemical processing of CO gas, the C isotope variability of refractory organic solids may relate to this same process. We propose a framework in which CO photolysis simultaneously produces H2O and generates a pool of C+ ions that serve as precursors for C-rich organic solids, with their C isotope compositions suggesting formation over a relatively narrow and warm range of temperatures in the protoplanetary disk (~200 to 400 K). Two populations of organic precursors with different C isotope compositions became associated with distinct dust reservoirs prior to their delivery to the carbonaceous-chondrite-forming region, which likely resided at lower temperatures (<170 K). This finding places detailed constraints on the location and distribution of chemical reactions that generated both water and organic-rich reservoirs in the early Solar System.

¹Christian Liebske, ^1,3Amir Khan, ^1,2Scott M. McLennan, ¹Paolo A. Sossi
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2025.116666]
¹Institute of Geochemistry and Petrology, ETH Zürich, Switzerland
²Department of Geosciences, Stony Brook University, Stony Brook, NY, USA
³Institute of Geophysics, ETH Zürich, Switzerland
Copyright Elsevier

The terrestrial planets are believed to have accreted from chondritic meteorites of widely varying composition. Yet, making planets from known meteoritic material has proved elusive, be it their nucleosynthetic isotopic anomalies, bulk chemistry or geophysical properties. Because of the inherent non-uniqueness of meteoritic mixing models based on isotopes alone, combining geochemical and geophysical observations is key to identifying the nature of the building blocks of the terrestrial planets. Here, we integrate the recent proliferation of data in the form of geophysical measurements pertaining to Mars’s interior structure from the recent InSight mission including its astronomic-geodetic response, the chemical and isotopic compositions of undifferentiated and differentiated meteorites, and observational constraints on trace element abundances (K/Th ratio) in order to make new inferences on the constitution and provenance of Mars. Using stochastic mixing models of meteoritic material, we find that
0.02% of mixtures, consisting primarily of ordinary- and enstatite chondrites and, to a lesser extent, achondritic material, are able to reproduce the isotopic signature of Mars. Of these, however, none match the geophysical or Mg/Si and K/Th constraints, indicating that Mars is unlikely to have formed from known unmodified meteoritic material. Instead, relatively oxidised building blocks that are intrinsic to the inner solar system and underwent evaporation/condensation processes that lead to volatile-element depletion patterns unlike those in any known meteorite group, would be consistent with the isotopic, geochemical and geophysical properties of Mars.