^1,2Naoya Imae,¹Makoto Kimura,^1,2Akira Yamaguchi
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14348]
¹Antarctic Meteorite Research Center, National Institute of Polar Research, Tokyo, Japan
²Department of Polar Science, The Graduate University for Advanced Studies, SOKENDAI, Tokyo, Japan
Published by arrangement with John Wiley & Sons

The in-plane rotation method is used to obtain X-ray random diffraction (XRD) patterns of polished thin sections of 10 CM chondrites. The samples include five intermediately altered CM chondrites with subtypes 2.6–2.3, two heavily altered CM chondrites with subtype 2.0 and three with secondary heating after hydration (Y 980036, Y 980051, and Jbilet Winselwan). These CM chondrites are compared to each other as well as four previously analyzed CM meteorites of subtypes 3.0–2.8 and 2.0. The same thin sections also underwent textural observations and compositional analyses. Unheated CM chondrites display systematic mineralogical changes. As the alteration degree increases from subtypes 3.0–2.0, the presence of olivine and clinoenstatite decreases, while that of serpentines increases. The abundance of tochilinite significantly increases from 2.7 to 2.3 but then decreases from 2.3 to 2.0. Subtype 2.0 consists of relatively more Mg-rich serpentine than Fe-rich serpentine (cronstedtite). The XRD identified only Mg-serpentine from Jbilet Winselwan, suggesting selective decomposition of Fe-rich serpentine (cronstedtite), while all hydrous minerals in Y 980036 and Y 980051 decomposed. Additionally, all three CM chondrites with secondary heating after hydration show stage II or category B heating by the peak metamorphic temperature of 300–750°C. Compared to previous studies using XRD, the combination of XRD with the textural and compositional analyses using the same polished thin section, avoiding the preparation for powder samples, is a straightforward approach to characterize hydrated chondritic samples. The approach is nondestructive and can be correlated with SEM/EPMA, unlike previous XRD studies that required powdered samples.

^1,2K.Righter et al. (> 10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14353]
¹Dept. Earth and Environmental Sciences, University of Rochester, Rochester, New York, USA
²ARES, NASA Johnson Space Center, Houston, Texas, USA
Published by arrangement with John Wiley & Sons

The Meteorite Hills dense collection area in the Transantarctic Mountains has yielded 1130 meteorites over several ANSMET field seasons. Twenty-three CM carbonaceous chondrites were recovered as part of the 2000–2001 and 2001–2002 field seasons. Many of these CMs have unique or rare features, but most are small (<50 g), making their preservation of highest priority, so material can be available for future researchers. One major contributor to preservation is knowing which samples are paired with others. Because CM chondrites are fine grained and petrographic features are subtle, standard petrography is not as helpful in classification. To strengthen the understanding of pairing and classification, we initiated a focused study of the 23 CM chondrites recovered from Meteorite Hills. Combining magnetic susceptibility (MS), modal mineralogy as determined using X-ray diffraction (XRD), and published information about a subset of samples, we have reassessed the classification and pairing. Many samples have MS log χ values between 3.7 and 3.9, but there are a few exceptions such as MET 00432 (4.85), MET 01076 and 77 (4.06 and 4.63, respectively), and MET 01073 (3.21). Fifteen of the samples exhibit intermediate to high levels of aqueous alteration with phyllosilicate fractions (PSF) of 0.88–0.93. A trio of samples exhibit even higher levels of alteration with PSFs of 0.96–0.98. Find locations and cosmic ray exposure (CRE) ages of these two groups are similar and the latter very short at 0.1–0.2 Ma, raising the possibility that they are all part of the same heterogeneous fall. Since the three heavily altered samples are rare and have distinctive mineralogy relative to other MET CMs, they should be preserved regardless of whether they are from one large fall or two separate falls. Two samples (MET 01076 and MET 01077) contain a much greater fraction of olivine and pyroxene, have longer CRE ages, and most likely are heated CM chondrites. Three samples are unpaired and have unique characteristics: MET 00432 has a high magnetite fraction and other mineralogical and chemical properties comparable to C2 ungrouped chondrites such as Tagish Lake and Tarda, while MET 001087 (PSF = 0.77) and MET 00633 (PSF = 0.76) are less aqueously altered than the other meteorites, with the former in particular showing a significant tochilinite peak in its XRD pattern. Although MET 00633 could arguably be part of the larger pairing group of samples given its similar find location, we recommend keeping it unpaired given its distinct mineralogy.

¹Robert W. Nicklas,¹Melody Z.-A. Chen,¹Evan J. Saltman,¹Ethan F. Baxter,¹Andrew J. Lonero,¹Anthony B. Love
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14356]
¹Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, Massachusetts, USA
Published by arrangement with John Wiley & Sons

Brachinites, brachinite-like achondrites (BLA), and other similar primitive achondrites offer important constraints on differentiation processes of the earliest formed planetesimals, as they quenched amidst early differentiation processes on their parent body. Geochemical data for all major mineral phases in two previously poorly characterized meteorites, El Medano (EM) 395 and Northwest Africa (NWA) 12532, show that while EM 395 is a typical brachinite, NWA 12532 is more unusual, containing a high abundance of non-equilibrated apatite (1.26%) likely formed by a late-stage metasomatic event. These new data demonstrate that metasomatism by a P-Cl-Ca-rich fluid probably occurred on the brachinite parent body. This metasomatism may have occurred either during normal cooling of the asteroid or during later impact-related heating, consistent with the late formation of apatite in the paired andesitic achondrites Graves Nunatak (GRA) 06128 and 06129. These conclusions highlight that, while magmatism on small parent bodies ceased shortly after solar system formation, subsolidus processes may have continued much longer, and that metasomatism must be considered when interpreting bulk rock geochemical signatures of primitive achondrites.

¹Mohammad Tauseef,¹Ingo Leya,²Jérôme Gattacceca,³Sönke Szidat,²Régis Braucher,⁴Pascal M. Kruttasch,⁴Anna Zappatini,²ASTER Team
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14355]
¹Physics Institute, Space Research and Planetology, University of Bern, Bern, Switzerland
²CNRS, Aix Marseille Université, IRD, INRAE, CEREGE, Aix-en-Provence, France
³Department of Chemistry, Biochemistry and Pharmaceutical Sciences & Oeschger Center for Climate Change
Research, University of Bern, Bern, Switzerland
⁴Institute of Geological Sciences, University of Bern, Bern, Switzerland
Published by arrangment with John Wiley & Sons

This study presents a refined approach to determine 14C saturation activities and 14C/10Be saturation activity ratios in chondritic meteorites with the goal to improve terrestrial age dating. By combining new model calculations for 10Be, 14C, and cosmogenic (22Ne/21Ne)cos, along with experimental data from 17 freshly fallen chondrites, we established reliable correlations for 14C production rates and 14C/10Be production rate ratios as a function of (22Ne/21Ne)cos. The experimental data agree with the model calculations, and they fully confirm that 14C production rates and 14C/10Be production rate ratios depend on shielding. Constrained correlations describe the experimental data for all shielding conditions and all ordinary chondrites mostly within the uncertainties given by the model. The new correlations therefore provide a significant improvement compared to the earlier approaches, in which average meteorite-type-dependent 14C production rates and average 14C/10Be production rate ratios were assumed. Ignoring the shielding dependence introduces a size-dependent bias into the terrestrial age database. This study enables the determination of shielding-corrected 14C saturation activities and 14C/10Be production rate ratios to calculate shielding-corrected terrestrial ages for meteorites reducing or eliminating a size bias in the database. In addition, this novel approach enables to give reliable uncertainty estimates of within 15% for the 14C and 14C-10Be terrestrial ages.

^1,2A. L. Knight,^1,2S. J. VanBommel,³R. Gellert,⁴J. A. Berger,^1,2J. G. Catalano,^5,6J. Gross,^1,2J. R. Christian
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2024JE008569]
¹Department of Earth, Environmental, and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, USA
²McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, MO, USA
³Department of Physics, University of Guelph, Guelph, ON, Canada
⁴Jacobs JETSII at NASA Johnson Space Center, Houston, TX, USA
⁵NASA Johnson Space Center, Houston, TX, USA
⁶Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ, USA
Published by arrangement with John Wiley & Sons

The Mars Exploration Rovers (MER) Spirit and Opportunity, sent to Gusev crater and Meridiani Planum, respectively, determined the chemical composition of martian materials with their Alpha Particle X-ray Spectrometers (APXS). The MER APXS was effective at routinely quantifying major, minor, and select (Ni, Zn, Br) trace elements at levels down to ∼50 ppm but often reached detection limits for other trace elements (e.g., Ga and Ge during typical individual analyses of a single sample). To enable precise quantification of additional trace elements, a database of MER APXS target properties (e.g., location, feature, target, formation, target type, sample preparation) was created, enabling the construction of a library of composite (i.e., summed) spectra with improved statistics. Composite spectra generated from individual spectra with shared characteristics have a higher potential for resolving and thus quantifying trace element peaks. Analyses of composite spectra from Meridiani Planum and Gusev crater indicate that the molar Ga to Al ratio is relatively constant throughout both regions and is in line with predicted values for the martian crust and measured values in martian meteorites. Gallium and aluminum likely do not volatilize and instead remain together during volcanism and aqueous alteration. In contrast, Ge is enriched at least an order of magnitude relative to martian meteorites, and the molar Ge to Si ratio is much more variable across Meridiani Planum and Gusev crater. Enrichment of Ge may be a global phenomenon resulting from volcanic outgassing of volatiles and subsequent overprinting by local mobilization and enrichment via hydrothermal fluids.

^1,2K. Hirata,¹T. Usui,^3,4E. Caminiti,⁵J. Wright,⁶S. Besse
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008788]
¹Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara, Japan
²Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
³LIRA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, Meudon, France
⁴Université Grenoble Alpes, CNRS, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), Saint-Martin-d’Hères, France
⁵School of Physical Sciences, The Open University Walton Hall, Milton Keynes, UK
⁶European Space Astronomy Centre (ESAC), European Space Agency (ESA), Madrid, Spain
Published by arrangement with John Wiley & Sons

The observed geochemical heterogeneity on the surface of Mercury is key to understanding the planet’s volcanic activity and mantle conditions. The Caloris basin shows a diversity in elemental composition, spectral properties, and geomorphology, both within and around it. However, the relationship among these characteristics has not been well understood due to the mismatch in spatial resolutions of the available observation data. This study investigates the geochemical end-members around the Caloris basin, overcoming the limitation of the low spatial resolution of MESSENGER’s X-Ray Spectrometer (XRS) data. End-member units are defined using spectral and geomorphological units from MESSENGER’s VIS-NIR spectral data and high-resolution images, with the assumption of homogeneous elemental compositions within each unit. A mixing model is constructed to reproduce the XRS data by mixing the end-members, and we solve the inverse problem to calculate the respective end-member compositions. Five end-member compositions were determined, including those corresponding to the post-Caloris volcanic smooth plains interior and exterior to the basin and surrounding pre-Caloris crust. Two smooth plains units, which are geomorphologically indistinguishable but spectrally distinct, showed a compositional variation consistent with magma evolution through fractional crystallization. This suggests that they originated from parent magmas with a common composition. The pre-Caloris crust units showed a large compositional variation, ranging from low- to high-Mg content, implying the potential existence of high-Mg crusts comparable to the HMR. The observed crustal diversity could be explained by relatively minor heterogeneity in source mantle compositions and/or conditions of partial melting within the mantle.

^1,2Ronghua Pang,^1,3Zhuang Guo,¹Chen Li,^1,4Sizhe Zhao,^1,5Xiongyao Li,¹Yuanyun Wen,⁶Shuangyu Wang,¹Rui Li,^1,5Yang Li
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2024JE008611]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
²University of Chinese Academy of Sciences, Beijing, China
³Department of Geology, NWU-HKU Joint Center of Earth and Planetary Sciences, Northwest University, Xi’an, China
⁴State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
⁵Center for Excellence in Comparative Planetology, Chinese Academy of Sciences, Hefei, China
⁶Laboratory for Space Environment and Physical Sciences, Harbin Institute of Technology, Harbin, China
Published by arrangement with John Wiley & Sons

Due to the lack of an atmosphere and a global magnetic field on the Moon, its surface is extensively subject to space weathering. One of the important products of space weathering is the iron particle, which has significant impacts for planetary exploration. Research on Apollo samples suggests that iron particles primarily form through vapor deposition processes during meteorite impacts. The Chang’e-5 (CE5) samples are the youngest samples collected so far, and the phenomenon of surface vapor deposition has not been studied in depth. Anorthite stoichiometrically free of Fe minerals, is highly suitable for studying the vapor deposition process of iron particles. Five anorthite grains from CE5 were analyzed using transmission electron microscope (TEM). Results show that the iron particle on the surface of anorthite formed from impact sputtering glass, and lack vapor-deposited nanophase iron particles (np-Fe0, <100 nm) on its surface. Additionally, residual Fe from Fe-Mg silicate impactors on the anorthite surface did not form np-Fe0. The dominant mechanism of np-Fe0 formation due to space weathering differs between the CE5 and Apollo landing sites. Impact melting rather than vapor deposition may be the dominant mechanism of np-Fe0 formation at the CE5 landing site due to impact. This indicates that the meteorite impact environment of CE5 landing site is weak. It is not possible to generate a large amount of vapor deposition-derived np-Fe0 like in Apollo samples.

¹Baoliang Wang, ¹Frédéric Moynier, ²Yan Hu
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.04.007]
¹Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, 1 Rue Jussieu, 75005 Paris, France
²Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, NV 89154, USA
Copyright Elsevier

Enstatite meteorites, including enstatite chondrites and enstatite achondrites (e.g., aubrites), formed under highly reducing conditions in the solar system. Enstatite chondrites underwent progressive thermal metamorphism from petrologic type 3 to type 6, potentially leading to vaporization and redistribution of volatile elements. Coupled Rb and K isotopic analyses of enstatite meteorites could provide complementary insights into the inherent isotopic variability and volatile depletion processes. In this study, we present Rb and K isotopic compositions for a suite of enstatite meteorites, including sixteen enstatite chondrites spanning metamorphic grades from 3 to 6, as well as four aubrites. Type 3 enstatite chondrites exhibit isotopic compositions similar to those of Earth for both Rb and K, which further underscores the isotopic resemblance between Earth and enstatite chondrites. From type 3–4 to type 5–6, the examined enstatite chondrites generally show a trend towards heavier Rb and K isotopic compositions, indicating volatilization and redistribution of Rb and K during open system thermal metamorphism of the parent body(ies). One EH5 (St. Marks) and two EL6 (Pillistfer and Atlanta) samples deviate from this trend with light K isotope compositions, which may result from an interplay of evaporation, vapor transport and recondensation. On the other hand, the Rb and K isotopic variations in aubrites—which originated from the melting and fractional crystallization of enstatite chondrite-like parent body(ies)—likely reflect more complex processes, possibly involving a combination of plagioclase-bearing melt extraction, magmatic differentiation, core segregation, and the back-condensation of volatiles after impact volatilization.

¹William S. Cassata
Earth and Planetary Science Letters 660, 119307 Link to Article [https://doi.org/10.1016/j.epsl.2025.119307]
¹Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA
Copyright Elsevier

The origins of Earth’s volatiles, including water, remain uncertain. Noble gases can be used to constrain volatile sources as they exhibit significant chemical and isotopic variations amongst Solar System materials that Earth may have accreted. Here, I refine the isotopic composition of cometary xenon (Xe) measured during the Rosetta mission by optimizing its fit to isotopically similar presolar grains in meteorites. Using this composition, I show that Earth’s atmosphere can be explained as a mixture of 83.6 ± 3.2% meteoritic, 15.3 ± 2.8% cometary, and 1.1 ± 0.7% fission Xe (1σ; percentages are with respect to 132Xe). This same approach applied to Kr indicates Earth’s atmosphere is 72.1 ± 9.5% meteoritic and 27.9 ± 9.5% cometary Kr (1σ; percentages are with respect to 84Kr). Carbonaceous chondrites are likely the predominant source of meteoritic Xe. A carbonaceous chondrite accretion mass of 1.8– 5.2 wt.-% of Earth at the 95% confidence interval explains the relative abundances of meteoritic and fission Xe in Earth’s atmosphere. Such accretion may have delivered up to 6 – 18 oceans of water to Earth. Conversely, a cometary ice accretion mass of less than 5 × 10–5 wt.-% of Earth explains the relative abundance of cometary Xe. This would have delivered less than 0.2% of Earth’s water. The data further imply a more linear temporal variation in the mass dependent fractionation of atmospheric Xe throughout the first two billion years of Earth history than previously thought.

^1,2Lixin Gu, ^1,3Yangting Lin, ⁴Yongjin Chen, ⁵Yuchen Xu,^1,2Xu Tang, ^1,3Jinhua Li
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.04.004]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
²Institutional Center for Shared Technologies and Facilities, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
³College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
⁴Center for High Pressure Science and Technology Advanced Research, Beijing 100094, China
⁵State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China
Copyright Elsevier

Hyper-velocity impacts are dominant agents in the physical and chemical alteration of lunar surface materials. Natural small-scale craters on lunar soils provide an opportunity to understand the impact process and specific space weathering effects on minerals, however, they have not been systematically studied. Here, we report the morphology and microstructure of submicron-scale craters on Chang’e-5 lunar soils. Craters are found only on a few soil grains. Most identified craters exhibit large diameter-to-depth (D/d) ratios (>3) or are spatially clustered, indicating that they are formed by secondary ejecta rather than primary micrometeoroid impacts. Advanced electron microscopy investigations revealed that the microstructures of these craters are complex. Craters on the surfaces of two pyroxenes and one olivine have continuous nanophase iron (npFe0)-bearing rims that extend over the crater and beyond over the crystal substrate, even when covered by an impact-produced redeposition layer. These features provide reliable evidence of solar wind exposure prior to the impact events that formed the craters. The possibility cannot be ruled out that the npFe0 particles present in these craters were previously produced by solar wind irradiation and not by impact. However, no clear signs are observed to establish the chronological order of formation of npFe0 particles in other craters studied. Furthermore, a crater on ilmenite has a minimum D/d value of 2.6, suggesting that this crater is likely formed by a primary micrometeoroid impact. Some unusual euhedral and elongated npFe0 particles observed on the crater floor may also have been produced earlier by solar wind irradiation and retained in the crater during subsequent impact. Shock melting and vapor deposition may also contribute to npFe0 formation by reduction during impact. Our findings imply that secondary impacts can also have a high velocity (1–2.38 km/s lunar escape velocity) and play a more crucial role in the microstructural and chemical changes of lunar soils than previously recognized. Moreover, the formation of npFe0 particles in submicron-scale craters may involve multiple processes, such as solar wind irradiation, shock melting, and vapor deposition, and their effects can be superimposed. These new formation processes of npFe0 particles are universal and fundamental to the evolution of materials on the Moon and other airless planetary bodies.