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.

¹G. Florin, ¹P. Gleißner, ¹H. Becker
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.06.006]
¹Freie Universität Berlin, Institut für Geologische Wissenschaften, Malteserstr. 74-100, 12249 Berlin, Germany
Copyright Elsevier

In the last decade, several studies have reported enrichments of the heavy isotopes of moderately volatile elements in lunar mare basalts. However, the mechanisms controlling the isotope fractionation are still debated and may differ for elements with variable geochemical behaviour. Here, we present a new comprehensive dataset of mass-dependent copper isotope compositions (δ65Cu) of 30 mare basalts sampled during the Apollo missions. The new δ65Cu data range from +0.14 ‰ to +1.28 ‰ (with the exception of two samples at 0.01 ‰ and –1.42 ‰), significantly heavier than chondrites and the bulk silicate Earth. A comparison with mass fractions of major and trace elements and thermodynamic constraints reveals that Cu isotopic variations within different mare basalt suites are mostly unrelated to fractional crystallisation of silicates or oxides and late-stage magmatic degassing. Instead, we propose that the δ65Cu average of each suite is representative of the composition of its respective mantle source. The observed differences across geographically and temporally distinct mare basalt suites, suggest that this variation relates to large-scale processes that formed isotopically distinct mantle sources. Based on a Cu isotope fractionation model during metal melt saturation in crystal mush zones of the lunar magma ocean, we propose that distinct δ65Cu compositions and Cu abundances of mare basalt mantle sources reflect local metal melt–silicate equilibration and trapping of metal in mantle cumulates during lunar magma ocean solidification. Differences in δ65Cu and mass fractions and ratios of siderophile elements between low- and high-Ti mare basalt sources reflect the evolving compositions of both metal and silicate melt during the late cooling stages of the lunar magma ocean.

^1,2S. Benaroya,^2,3,4J. Gross
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14379]
¹Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada
²Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey, USA
³Astromaterials Acquisition and Curation Office, NASA JSC, Houston, Texas, USA
⁴Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
Published by arrangement with John Wiley & Sons

Shergottites span a textural, mineralogical, and geochemical range, and finding links between the various petrologic and geochemical groups is of great interest as it provides insight into the conditions of the Martian interior. Here, we compare the texture, mineralogy, mineral chemistry, and geochemistry of REE-enriched intrusive shergottite groups, including poikilitic shergottites, olivine–gabbroic shergottites, and gabbroic shergottites. Due to the similarities of olivine–gabbroic samples to poikilitic and gabbroic shergottites, we suggest that the former may represent an intermediary petrologic type. We suggest a shared magmatic history for these sample groups via a shared stratified magma chamber. Thermodynamic modeling of the proposed shared magmatic history using Magma Chamber Simulator (MCS) and MELTS was able to reproduce the mineralogies and general crystallization histories of samples using a parental melt of bulk silicate mars (BSM) composition and the compositions of olivine–phyric shergottites LAR 06319 and NWA 6234.

¹Yuchen Xu,²Yangting Lin,²Jialong Hao,²Sen Hu,²Wei Yang,¹Yongliao Zou,¹Yang Liu
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14380]
¹State Key Laboratory of Solar Activity and Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, China
²Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

NWA 10493 and NWA 10498, two hot desert finds, are classified as the CO3.0 meteorites based on the Cr2O3 contents in ferroan olivines, representing some of the most primitive chondrites from the CO parent body. The abundances of presolar grains are known to be sensitive to the degree of aqueous alteration and thermal metamorphism. Therefore, an in situ investigation of presolar grains was conducted in the fine-grained matrix of NWA 10493 and NWA 10498 using NanoSIMS C- and O-isotopic image mapping. The matrix-normalized abundance of presolar SiC grains in NWA 10493 is
ppm, which declines to
ppm when the much larger (>1000 nm) grain is excluded. This lower presolar SiC abundance is comparable to the presolar SiC abundance of
ppm calculated in NWA 10498, similar to those from the most aqueously altered CM chondrites based on in situ studies of the fine-grained rims of chondrules. The abundances of O-anomalous grains in both NWA 10493 (54 ± 15 ppm) and NWA 10498 (42 ± 13 ppm) are lower than those reported for the most primitive CO meteorites, indicating slightly higher degrees of thermal alterations. These findings are consistent with the previously observed variations in Cr content within the respective chondrule olivine and point toward classification grades of 3.02–3.05.

¹E. Quirico, ²H. Yabuta, ¹P. Beck, ¹L. Bonal, ^3,5A. Bardyn, ^3,4L.R. Nittler, ³C.M.O’D. Alexander
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.05.046]
¹Université Grenoble Alpes, CNRS, Institut de Planétologie et Astrophysique de Grenoble (IPAG), UMR 5274, Grenoble F-38041, France
²Graduate School of Advanced Science and Engineering, Hiroshima University, Hiroshima, Japan
³Earth and Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road, N.W., Washington, DC 20015, USA
⁴School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
⁵Brin Mathematics Research Center, The University of Maryland, 4146 CSIC Bldg. #406, 8169 Paint Branch Drive, College Park, MD 20742-3289, USA
Copyright Elsevier

A significant population of primitive carbonaceous chondrites experienced short-duration heating, which is usually attributed to either impact or solar heating. Shock recovery experiments performed on carbonaceous chondrites have successfully reproduce the typical evolution in the petrographies and mineralogical compositions of natural samples. However, only few studies focused on the chemical and structural transformations of insoluble organic matter (IOM). We report here on shock recovery experiments conducted on two chondrites: Murchison (CM2) and Elephant Moraine EET 90628 (L3.0). Experiments on Murchison show carbonization and oxidation of IOM at all shock intensities (5–50 GPa) and a pronounced structural evolution at 40 GPa associated with complete dehydroxylation of serpentines, as well as formation of olivine and amorphous silicates. The δD value of Murchison IOM (initial δD = 1636 ± 529 ‰) evolves significantly, with the rapid disappearance of isotopic hot spots and a bulk δD of −79 ‰ at 40 GPa. At 40 GPa, the extent of dehydroxylation of serpentines is consistent with stage III heated chondrites, but the structural characteristics of the IOM resembles material from stage II meteorites, i.e. a slight modification of the IOM in a matrix dominated by serpentines.
These experiments only partially reproduce the characteristics of natural samples, and they show that the IOM evolution in short-duration heated C2 chondrites is essentially controlled by the post-shock cooling episode, which lasts from hours to years, compared to < ∼1 µs for the shock peak pressure. The high pressure conditions in the shock do not catalyze the carbonization process and the maturation of IOM. In contrast, the IOM evolution in heated C2 chondrites is better simulated by conventional heating experiments under controlled redox conditions over durations of hours. Shock recovery experiments, however, could be interesting to assess the effect of hypervelocity impacts by small impactors on the surface of airless bodies. Experiments performed on EET 90628 show a structural evolution consistent with natural objects. In particular, the co-evolution of the width and ratio of the peak intensities of the D-band (FWHM-D and ID/IG, respectively) in the Raman spectra of the IOM from the shocked samples is consistent with those measured on type 3 ordinary and carbonaceous chondrites. An interesting finding is that the G-band width and position parameters (FWHM-G and ωG) do not correlate with the shock intensity, just as these parameters do not correlate with the intensity of thermal metamorphism in the case of type 3 chondrites. This lack of correlation is not observed on Earth in the case of coals and kerogens that experienced a progressive thermal history.