¹Fabio Joseph,²Igor Drozdovsky,^1,3Malte Junge,¹Joanna Brau,^1,3Melanie Kaliwoda
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14381]
¹Department of Earth and Environmental Sciences, Ludwig-Maximilians-University, Munich, Germany
²Directorate of Human and Robotics Exploration, European Astronaut Centre (EAC)—European Space Agency (ESA), Troisdorf, Germany
³Mineralogical State Collection, SNSB, Bavarian State Collections of Natural History, Munich, Germany
Published by arrangement with John Wiley & Sons

Chondrules are one of the oldest objects in our solar system. Therefore, they play an important role as messengers, offering new insights into the early stage of the solar system processes and potential understanding of formation. Therefore, the investigation of all detailed structures, especially not well-known inversely zoned chondrules (IZ chondrules), is crucial. In this paper, we describe the chemical as well as the structural composition of inversely zoned chondrules with EDX, light microscopy, BSE, and Raman spectroscopy, which reveal a new process in the early solar system. Inversely zoned chondrules consist of a pyroxene core surrounded by an olivine rim. The olivines have a higher Fe content (Fa, 39%–41%) compared to those found in most other chondrules. The core displays a radial pyroxene chondrule with sometimes olivines (Fa34). These IZ chondrules have originated during the early stages of our solar system and do not show the typical known forming process of chondrules. Minor fluctuations in the SiO₂ content of chondritic melts can lead to SiO₂ depletion of the residual melt at a constant temperature due to crystallization of pyroxene, which shifts the phase equilibrium in favor of fayalite-enriched olivine, which forms a rim.

^1,2Nandita Kumari, ¹John Mustard, ³Timothy D. Glotch
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2025.116721]
¹Department of Earth, Environmental and Planetary Sciences, Brown University, USA
²Planetary Science Institute, USA
³Department of Geosciences, Stony Brook University, USA
Copyright Elsevier

Visible/near-infrared (VNIR) and thermal infrared (TIR) spectroscopy have been widely used to detect and characterize the abundances of silicates across the solar system. Recently, intermediate infrared (IMIR) reflectance spectroscopy (~4 – 6 μm) has been proposed as a tool to quantify the Mg# in olivine and pyroxene with varying iron, magnesium and calcium content. The lunar surface is composed of rocks with mixed particle sizes and thus quantifying the effects of particle size is extremely important to increase the robustness of IMIR spectroscopy as a tool for lunar surface exploration. Similarly, space weathering has been known to cause optical darkening and affect the spectra of the lunar surface materials across a broad wavelength range. In this study, we have identified the emission features of lunar analog minerals/rocks and their variations with changes in particle sizes and albedo at IMIR wavelengths in simulated lunar environment (SLE). We find that the lunar analog minerals display an increase in emissivity and striking decrease in feature contrast with an increase in particle sizes or decrease in albedo. This study shows that while this wavelength range works well in reflectance space for sample characterization, using it for emissivity measurements via orbital remote sensing or in-situ rovers requires extensive study.

^1,2Tomoko Arai, ¹Takayuki Tomiyama, ²Takafumi Niihara, ³Tatsunori Yokoyama, ⁴Miwa Yoshitake, ^2,3Hiroshi Kaiden, ^2,3Keiji Misawa, ⁴Anthony J. Irving
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2025.116715]
¹Planetary Exploration Research Center, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan
²National Institute of Polar Research, 10-3 Midoricho, Tachikawa, Tokyo 190-8518, Japan
³Graduate Institute for Advanced Studies, SOKENDAI, 10-3 Midoricho, Tachikawa, Tokyo 190-8518, Japan
⁴Department of Earth & Space Sciences, University of Washington, Seattle, WA 98195, USA
Copyright Elsevier

A lunar meteorite Northwest Africa (NWA) 4485 is a KREEP (potassium, rare earth elements and phosphorus)-rich polymict breccia, likely paired with NWA 4472. NWA 4485 includes mm-sized lithic clasts with variable textures and modal abundances. The lithic clasts share features with KREEP basalts, and consist dominantly of moderately Mg-rich pyroxene and less calcic plagioclase than those in the Apollo 17 KREEPy basalt with zircon and phosphates. Uranium‑thorium‑lead isotopic studies on zircon and baddeleyite in the lithic clasts and matrix of NWA 4485 revealed that the 207Pbsingle bond206Pb age spectrum (4350–3920 Ma) is compatible with that for apatite in the paired NWA 4472, broadly covering the ages of zircons in Apollo polymict breccia samples from multiple landing sites. The presence of a 4160 Ma zircon in a millimeter-sized lithic clast, a core of 4210 Ma in a detrital zircon with multiple rims of ~3960 Ma, and an individual zircon grain of 4350 Ma in the matrix clearly indicates that they are products of pre-mare multiple KREEP-related magmatism, predating the lunar cataclysm (~3900–4000 Ma).

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.