¹Lucas R. Smith,^1,2Pierre Haenecour,¹Jessica J. Barnes,¹Kenneth Domanik,²Mason Neuman,^2,3Kun Wang,²Piers Koefoed,¹Elias Bloch,⁴Ryan Ogliore
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70166]
¹Lunar and Planetary Laboratory, The University of Arizona, Tucson, Arizona, USA
²Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, Missouri, USA
³McDonnell Center for the Space Sciences, Department of Physics, Washington University in St. Louis, St. Louis, Missouri,USA4 Department of Physics, University of Central Florida, Orlando, Florida, USA
Published by arrangement with John Wiley & Sons

We performed an in-depth study of the mineralogy, petrology, chemical composition, and presolar grain abundance of the C3.00-ungrouped chondrite Chwichiya 002 using a combination of in situ and bulk analytical methods. Chwichiya 002’s bulk composition is significantly enriched compared to CI chondrites (over 20 × CI for Sr, Ba, U) in rare earth and trace elements like Li, Sr, Ba, U, and Pb, indicating effects of terrestrial weathering. Concentrations of Ti and Al are similar to CI chondrites, but notably depleted relative to other carbonaceous chondrite groupings, suggesting that the parent body of Chwichiya 002 accreted from a source with a near CI composition of refractory elements, and with a low quantity of calcium–aluminum-rich inclusions. A slight reduction in Fe is linked to the predominance of FeO-poor chondrules and olivine, likely a remnant of Chwichiya 002’s formation history. Our findings uncovered phyllosilicates in the matrix and combinations of tochilinite–cronstedtite, confirming that Chwichiya 002 underwent more extensive alteration on its parent body than previously believed. We identified 12 O-anomalous presolar grains (8 Group 1, 4 Group 4) and nine presolar SiC grains, with abundances of 12.1 + 4.6/−3.5 ppm for O-rich grains and 7.8 + 3.6/−2.6 ppm for SiC grains. The relatively low occurrence of O-rich presolar grains is similar to what is seen in CM2 chondrites and samples from asteroid 162173 Ryugu, despite Chwichiya 002 being classified as type 3.00 petrologically. We conclude that Chwichiya 002 formed from a refractory-poor source similar to CM and CO chondrites, primarily consisting of FeO-poor chondrules and olivine, and underwent a moderate level of aqueous alteration on its parent body. Furthermore, the mineralogy, petrology, and compositional data reported in this study, combined with previous data on the O-isotopes of Chwichiya 002, suggest that the sample may better be classified as a CM2.8 or CM 2.9 chondrite.

¹L. Perez,¹M. Roskosz,²F. Danoix,¹L. Kern,¹V. Megevand,¹C. Brillatz,³B. Devouard,³J. Gattacceca,¹M. Gounelle
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70172]
¹IMPMC, Museum National d’Histoire Naturelle, Sorbonne Universite, Paris, France
²Groupe de Physique des Materiaux, CNRS UMR 6634, Universite de Rouen, Saint Etienne du Rouvray, France
³Aix-Marseille Universit´e, CNRS, INRA, IRD, Coll France, CEREGE UM34, Aix en Provence, France
Published by arrangement with John Wiley & Sons

This study provides the first petrographic, crystallographic, and chemical comparison between El Médano 300 (EM 300) and Northwest Africa 8155 (NWA 8155), two particular IAB-ungrouped iron meteorites. Both contain exceptionally large graphite nodules and “flowers”, providing unique insights into carbon behavior in metallic melts and cooling conditions. Despite these similarities, they differ in their petrography, crystallography, and chemical composition. Whereas EM 300 exhibits a homogeneous metallic phase with rounded kamacite grains, originating from at least two taenite crystals, NWA 8155 displays a heterogeneous composition with elongated kamacite crystals, from a unique taenite crystal, along with martensite and residual taenite. Variations in nickel and highly siderophile elements contents point to different degrees of partial melting, indicating in turn formations within two different metallic pools, most probably on separate parent bodies. Troilite textures in EM 300 (spidery), compared to NWA 8155 (bulky), suggest an impact-related origin. Abundant small schreibersite grains in EM 300 indicate faster post-impact cooling. Finally, the absence of silicates in both meteorites suggests efficient metal-silicate segregation or formation within metallic parent bodies. These results provide new insights into the diversity of thermal and collisional histories among IAB-ungrouped iron meteorites, supporting the idea that each one may represent a single parent body and therefore reflecting the diversity of early planetesimal natures and evolutions.

¹Hina Dohi,¹Minako Hashiguchi,¹Koichi Mimura
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70173]
¹Department of Earth and Environmental Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
Published by arrangement with John Wiley & Sons

A substantial fraction of organic carbon in carbonaceous chondrites has long been described as “missing,” reflecting incomplete recovery and limited resolution of operationally defined organic components. Here, we present a quantitative reassessment of the carbon budget in the Murchison meteorite using an integrated extraction–recovery mass-balance approach that constrains the distribution of carbon among operational fractions. Insoluble organic matter accounts for 69% ± 1.4% of total carbon, while acid-hydrolyzable organic matter (AOM) constitutes 15% ± 2.9%, representing a carbon pool comparable to soluble organic matter (SOM, 14% ± 2.7%). Carbonate-derived carbon accounts for 2% ± 2.0% of the total carbon inventory. The total recovered organic carbon reaches 88% ± 1.4% of bulk carbon. Carbon previously regarded as “missing” can be quantitatively reassigned to specific organic fractions, including uncollected AOM (7%) and SOM (2%), substantially reducing the previously unconstrained carbon fraction. Replicate analyses of three independently processed subsamples yield consistent residue-based carbon partitioning, supporting the robustness of the mass-balance framework. These results indicate that much of the missing carbon reflects incomplete recovery in analytical workflows rather than an unidentified reservoir, refining the organic carbon inventory of Murchison and providing a framework for reassessing carbon partitioning in primitive planetary materials.