Shober, P.M., Vaubaillon, J., Devillepoix, H.A., Sansom, E.K., Deam, S.E., Anghel, S., Colas, F., Vernazza, P., Zanda, B., Bouley, S. What Falls Versus What We Recover: Quantifying Search and Recovery Bias for Orbital Meteorites. Meteoritics & Planetary Science. 2025.
The final coauthor, Sylvain Bouley, a core member of the FRIPON project, was accidentally omitted from the original publication.
We apologize for this error.
Alteration of historic CI1 meteorite falls during their curation demonstrates the susceptibility of smectite-rich carbonaceous chondrites to terrestrial exposure. The discovery of Oued Chebeika 002 in Morocco in June 2024 presents a unique opportunity to document the earliest stages of weathering of a CI1 find. We studied 10–30 mg fragments that had been recovered by September 2024. Grains of quartz and feldspar were implanted into the fragments by wind action whilst on the desert floor. Gypsum is the main product of terrestrial weathering. It encrusts their outer surfaces, in one case covering 5.3% of a fragment, and has filled voids within both fractures and phyllosilicate clasts. Other products of terrestrial weathering are Ca-carbonate grains that have grown within a sand-filled fracture, and rock inhabiting fungi colonizing the surface of a fragment. Chemical weathering was facilitated by water that had been adsorbed by smectite from the humid desert air, and crystallization of gypsum was driven by evaporation from the surfaces of those fragments that were exposed to direct sunlight. The gypsum and Ca-carbonate grew over a period of 3 or 4 months, approximately between June and September 2024, whereas the time scale of fungal colonization can only be constrained to a year or less. The rapid interaction of Oued Chebeika 002 with the Earth's atmosphere, lithosphere, and biosphere underscores the importance of prompt recovery and careful curation of CI1 and other smectite-rich meteorites.
At ~66 Ma, the Cretaceous–Paleogene Boundary (KPB) sections at Anjar and Um Sohryngkew (India) were 14,333 and 16,549 km, respectively, from Chicxulub, making them the farthest distal KPBs. The spatial and temporal proximity of the sites to Deccan volcanism makes them important locations to better understand the impact-volcanism debate. This study integrates petrological, mineralogical, and geochemical techniques to distinguish signatures of the instantaneous Chicxulub impact from those of the prolonged Deccan volcanism (lasting ~10 my). The sites contained two ejecta components: a potential spherule (Um Sohryngkew) and Ir-anomalies. The poorly preserved spherule (~240 μm diameter) exhibited mineral dendrites. At Anjar, two Ir-anomalies are noted: 8.50 ppb (SGA-2; ~3.19 m below Flow IV) and 1.16 ppb (SGA-12). Four Ir-anomalies are noted at Um Sohryngkew: 1.36 ppb (SMU-19; 28.44 m from the oldest layer), 3.17 (SMU-14), 7.00 (SMU-7), and 1.19 ppb (SMU-6). Multiple Ir-anomalies, elevated background-Ir, and glass shards at both sites highlight a greater influence of Deccan volcanism than previously recognized. Deccan magma-based Ir-enrichment is unlikely as such values were not reported in Deccan basalts, but higher Ir-concentrations in sedimentary layers point to indirect contributions from Deccan outgassing. Thus, the findings of the study underscore the complex interplay of Deccan volcanism and Chicxulub impact across the Indian Subcontinent.
On Mars, neighboring craters of similar diameter show variations in rim thermal inertia. In this study, thermal inertia (TI) was calculated using Mars Odyssey Thermal Emission Imaging System (THEMIS) nighttime images acquired during the southern hemisphere Martian autumn, a period with minimal fine dust influence. One hundred and thirty-seven craters of different diameters across 21 TI scenes were analyzed, encompassing Gale Crater and its surroundings. Morphological parameters such as depth-diameter ratio (d/D), radii variation (RV), rim irregularity (RI), and mantle rim percentage (MRP) were derived using Mars Reconnaissance Orbiter (MRO) Context camera (CTX) images. Two hypotheses were tested: Hypothesis I—Crater rim thermal inertia influenced by crater degradation during the southern hemisphere Martian autumn, and Hypothesis II—Crater rim thermal inertia influenced by crater rim regolith mantling during the southern hemisphere Martian autumn. Multilevel regression models were used to test the hypotheses. Hypothesis I was rejected, and Hypothesis II was found to be statistically significant (p < 0.05), indicating crater rim TI variations are largely influenced by regolith mantling, reflecting dominant depositional activity. During the southern hemisphere autumn on Mars, atmospheric dust levels are relatively low; however, significant surface dust remains, likely redistributed by dust storms from the preceding summer season.
Samples returned from asteroid Ryugu by the Hayabusa2 mission are dominated by fine-grained matrix material made of phyllosilicates and nanosulfides. Here, we report the mineralogical, textural, and chemical characteristics of nanosulfide-rich regions identified in Ryugu particles. High-resolution scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy reveal nanoscale heterogeneities in sulfide composition and morphology, indicating formation under variable conditions. Nanosulfide-rich regions are dominated by the presence of mackinawite (FeS) and pyrrhotite (Fe1-xS), in different proportions. Mackinawite, identified for the first time in Ryugu, occurs as well-crystallized lamellar crystals with some areas containing greigite (Fe3S4) and others showing signs of oxidation. In contrast, pyrrhotite appears either as euhedral nanocrystals or as structurally complex grains composed of stacked platy segments, which are characterized by numerous defects, including inclusions and planar defects. The distribution and associations of these phases are consistent with low-temperature aqueous alteration under alkaline and reducing conditions, likely occurring in Ryugu's parent body. The presence of mackinawite implies complex thermodynamic and kinetic constraints and suggests the presence of localized fluids in which Fe concentrations exceeded those of S by an order of magnitude.
The O-, N-, Mo-, Ru-, Os-, Cr-, Ti-, Ni-, Fe-, Nd-, Ca-, Zn-, Sr-, and Mg-isotopic compositions of enstatite chondrites are essentially identical to those of the Earth and Moon. These correspondences suggest enstatite chondrites formed at ≈1 AU as the only known chondrite groups that accreted in the vicinity of a major planet. Bulk Earth has a higher Mg/Si weight ratio (1.09) than enstatite chondrites (0.63–0.76) and aubrites (0.84). Earth could have accreted from a mixture of these materials along with forsterite (Mg/Si = 1.73) and niningerite [(Mg,Fe)S] from the lower mantles of aubritic parent asteroids whose crusts and upper mantles were stripped off by hit-and-run collisions. The highly reducing conditions in which enstatite chondrites formed resulted from the dehydration of the inner regions of the nebula caused by outward diffusion of water vapor; this lowered the H2O/H2 ratio of the gas. The minor fraction of oxidized material in enstatite chondrites formed earlier—when the H2O/H2 ratio was briefly enhanced by inward-migrating ice particles. Enstatite chondrites are the most shocked chondrite groups, exhibiting a large variety of shock features—for example, deformed silicate lattices; petrofabrics; brecciation; shock veins; metal globules; coesite; impact-melt textures; impact-produced phases (keilite, sinoite, graphite and F-rich minerals); and fractionated bulk REE patterns. The Ar-Ar, Rb-Sr and I-Xe ages of enstatite chondrites indicate many of these rocks were shocked early in Solar System history, 4520–4563 Ma ago. This interval stretches back to the period of giant-planet migration, when the 1 AU region became dynamically excited.
With a size of 51.2 × 7.2 km, the 10.9 ± 1.7 ka old Jiddat al Harasis 091 L5 chondrite strewn field is the largest known in Oman. It consists of more than 700 meteorites with a total mass of >4.5 tons from which the largest six stones of >100 kg to 1.5 tons make up two thirds of the total mass. Small stones are underrepresented, consistent with a fracturing behavior of a meteor with low shock level. Modeling yields that a bolide with 28 ± 12 tons (115 ± 15 cm radius) entered the atmosphere at a shallow angle of 22° ± 2° with a velocity of about 16 kms−1. For ~16 s, it produced a spectacular meteor along a luminous path of ~200 km length. Mass mixing within the rather straight and narrow strewn field indicates a sequence of multiple fragmentations from below 50 km down to 7 km altitude. This can be resolved adopting a wind profile from nowadays winter season, as the weather patterns with alternating Monsoon and Passat winds in the region are rather well known and repeatable since the last ice age. The largest masses with 1447 and 842 kg, respectively, produced impact breccia consisting of limestone and meteorite fragments. According to the model, the biggest mass hit the ground at a velocity of 175 ms−1 and released an impact energy of 22 MJ, corresponding to 5.3 kg TNT. This may have produced an impact crater of ~1 m diameter which, however, is not preserved. Breccia found below a much smaller mass of 68 kg deserves an explanation beyond impact energy.
Apollo sample 67015 has been classified as a fragmental breccia comprised of highlands-type clasts and is proposed to be the most complex Apollo 16 sample. 67015 is dominated by impact melt rock clasts that display a variety of textures, which have been previously interpreted to be indicative of multiple impact events. Recent modeling has indicated that the Apollo 16 regolith may contain impact basin ejecta from Nectaris, Serenitatis, Imbrium, and Orientale. Here, the textural, mineralogical, and geochemical diversity of impact melt rock clasts in several thin sections of 67015 was assessed to evaluate the provenance of these impact melts and attempt to constrain the basin ejecta emplacement at the Apollo 16 site. The petrography and mineral chemistry of the melt rock clasts is highly diverse and may indicate a variety of sources, supporting previous evidence that the Apollo 16 regolith received ejecta from numerous large impact cratering events including Imbrium and Serenitatis. The diversity of clast types observed in 67015 and textural variability of thin sections prompts discussion into the most appropriate classification of this sample as well as the nomenclature used to describe lunar melt-bearing breccia samples.
Mesosiderites are widely believed to have originated from a metal-silicate mixing event triggered by planetesimal collisions in the early solar system. However, a key unresolved issue in this model is the physical state (liquid vs solid) of the metallic materials involved, which complicates our understanding of mesosiderite formation. Melt pockets and comb plessites in the Dong Ujimqin Qi mesosiderite provide critical insights into this issue. The melt pockets exhibit quenched textures of dendritic troilite-metal intergrowths, typically cooled at a rate of >9500°C s−1 above 950°C. In contrast, the Ni profile in kamacite, pentlandite, taenite, and cordierite inside melt pockets points to a subsequent burial-induced slow cooling process, which starts below 780°C with a maximal estimated rate of ~2°C Myr−1. The two-stage cooling pathway of melt pockets aligns well with thermal fingerprints expected from the catastrophic disruption and reassembly of the mesosiderite parent body. More importantly, the impact has led to shock deformation of metal nodules to varying degrees, as reflected by the extension of kamacite polygonization associated with melt pockets into some comb plessite domains. This provides vital evidence that the metal nodules remained partially solid during the mixing process. Accordingly, we propose a revised mesosiderite formation model that involves an impact mixing with a partially solidified metal planetesimal. The revised model better accounts for several issues regarding the formation of mesosiderites, such as three-orders-of-magnitude variations of bulk Ir concentrations, slow metallographic cooling rates, bimodal size distribution of the metallic nodule and matrix, and deficient olivine materials.
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