Meteoritics & Planetary Science最新文献

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 $��{94}_{�-�45�}^{�+�74�}�$ ppm, which declines to $��{17}_{�-�9�}^{�+�16�}�$ ppm when the much larger (>1000 nm) grain is excluded. This lower presolar SiC abundance is comparable to the presolar SiC abundance of $��{10}_{�-�6�}^{�+�13�}�$ 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.

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.

The El Ali meteorite, a colossal 15.2 t iron meteorite, was discovered in an area characterized by bushy calcareous evaporates (sedimentary distinctive textures, which align with the description of the meteorite's find location) near the town of El Ali in West Hiran, Somalia. This paper delves into the fascinating history of this meteorite, tracing its path from obscurity to international prominence and then to the tragedy of losing a local people's symbol and heritage. For centuries, nomadic local people have used the rusty brown rock as a humble whetstone or honing stone. However, over time it has transformed into a symbol of local heritage and resilience named the “Shiid-birood.” In 2022, a pivotal moment occurred when the meteorite was classified and three previously unknown minerals—elaliite, elkinstantonite, and olsenite—were identified in the meteorite. These findings sparked international media attention to the El Ali meteorite, leading to its official recognition by the Meteoritical Society. Almaas University researchers were the first to interact with the meteorite in Mogadishu, Somalia, and provided initial descriptions, properties, and measurements of the meteorite. Remarkably, the El Ali meteorite ranks as the ninth largest meteorite globally, weighing an impressive 15.2 t. However, secrecy and uncertainty surround its fate. The meteorite has been exported to China, leaving Somalia bereft of its cultural and natural heritage significance. Will it be cut into pieces or preserved intact for exhibitions and future scientific studies? Perhaps, there is still some hope to ensure its return to its rightful place of origin—Somalia.

We report the discovery of (Al,Cu)-bearing metallic alloys in two micrometeorites found in the Project Stardust collection gathered from urban rooftop environments in Norway. Most of the alloys are the same as those found in the Khatyrka meteorite and other micrometeorites, though one has a composition that has not been reported previously. Oxygen isotope ratio measurements using secondary ion mass spectrometry show that the Project Stardust samples reported here, like all earlier examples of natural (Al,Cu)-bearing alloys, contain material of chondritic affinity.

To understand chemical variability within individual martian meteorites, we report major, minor, trace, and highly siderophile element abundances, as well as ¹⁸⁷Re-¹⁸⁷Os, for four separate rock fragments of gabbroic shergottite Northwest Africa (NWA) 6963. The compositions of these aliquots are consistent with data for NWA 6963 from Filiberto et al. (2018). Data reported for NWA 6963 in Day et al. (2018) and Tait and Day (2018) should no longer be used due to doubt in provenance of the sample fragment used in those studies. Genuine fragments of NWA 6963 show significant variability in elements due to different modal proportions of minerals. Terrestrial weathering effects appear to be most pronounced for Ba and Pb. The age and composition of NWA 6963 indicate that it may be related to enriched basaltic shergottites and some olivine–phyric and poikilitic shergottites that are referred to here as the “enriched shergottite group.” The ¹⁸⁷Re-¹⁸⁷Os systematics of the enriched shergottite group all conform to generation at ~180 million years from the same or similar mantle sources with long-term Re/Os enrichment on Mars. They show coherent fractional crystallization trends in plots of compatible elements with the possibility for impact-contaminated regolith assimilation in NWA 6963. The enriched shergottite group may represent magmatism akin to terrestrial continental flood basalt provinces. Entrainment of incompatible trace element enriched upper mantle in an otherwise deeply-derived incompatible trace element depleted mantle plume head in Mars at 180 million years ago may explain the similar crystallization ages of both enriched shergottites and some intermediate shergottites.

Meteoritical Bulletin 113 contains the 3646 meteorites approved by the Nomenclature Committee of the Meteoritical Society in 2024. It includes 17 falls, 2964 ordinary chondrites, 218 HED, 158 carbonaceous chondrites (including 7 ungrouped), 59 lunar meteorites, 38 iron meteorites (9 ungrouped), 30 ureilites, 31 primitive achondrites (3 ungrouped), 28 mesosiderites, 24 enstatite chondrites, 21 martian meteorites, 24 ungrouped stony achondrites, 20 Rumuruti chondrites, 17 pallasites, 8 angrites, 5 enstatite achondrites (one ungrouped), and 1 ungrouped chondrite. Of the meteorites approved in 2024, 1250 were collected in Antarctica, 1102 in Africa, 689 in Asia, 575 in South America, 17 in North America, 11 in Europe, and 2 in Oceania.

The aim of this work is to provide a model-backed hypothesis for the formation of evaporites—sulfates, borates—in Gale crater using thermochemical modeling to determine constraints on their formation. We test the hypothesis that primary evaporites required multiple wet–dry cycles to form, akin to how evaporite assemblages form on Earth. Starting with a basalt-equilibrated Mars fluid, Mars-relevant concentrations of B and Li were added, and then equilibrated with Gale lacustrine bedrock. We simulated the cycles of evaporation followed by groundwater recharge/dilution to establish an approximate minimum number of wet–dry cycles required to form primary evaporites. We determine that a minimum of 250 wet–dry cycles may be required to start forming primary evaporites that consist of borates and Ca-sulfates. We estimate that ~14,250 annual cycles (~25.6 k Earth years) of wet and dry periods may form primary borates and Ca-sulfates in Gale crater. These primary evaporites could have been remobilized during secondary diagenesis to form the veins that the Curiosity rover observes in Gale crater. No Li salts form after 14,250 cycles modeled for the Gale-relevant scenario (approximately 10⁶ cycles would be needed) which implies Li may be leftover in a groundwater brine after the time of the lake. No major deposits of borates are observed to date in Gale crater which also implies that B may be leftover in the subsequent groundwater brine that formed after evaporites were remobilized into Ca-sulfate veins.

We reevaluated pairing relationships among 56 Antarctic howardites, eucrites, and diogenites (HED) from the Miller Range ice fields (MIL) based on new measurements of cosmogenic radionuclides and bulk composition of 28 HED samples and one HED-related dunite. These measurements were combined with petrographic examinations and find locations of the majority of the HED samples at MIL. During these studies, we reclassified 1 howardite, MIL 07665, as a brecciated diogenite and eight howardites as brecciated eucrites. We conclude that 18 of the 23 diogenites belong to a single large pairing group of brecciated diogenites. This pairing group includes at least seven samples with bulk compositions that indicate they contain 10%–25% of eucritic material, so technically the meteorites of this pairing group cross the boundary between diogenites and howardites. We also identified several smaller pairing groups (of 2–5 members each) among the eucrites and two paired samples among the howardites. The pairing relationships among the Miller Range eucrites are not fully resolved yet, as the collection contains many small specimens (<10 g) that were not included in this study. Altogether, we conclude that the 56 HED meteorites at Miller Range represent between 19 and 26 individual falls.

Pentlandite (Fe, Ni)₉S₈ is an important accessory mineral on asteroidal surfaces. It has been identified in returned regolith samples from asteroids Itokawa, Ryugu, and Bennu. Currently, systematic studies to understand the response of this mineral phase under space weathering conditions are lacking. In this work, we performed pulsed laser irradiation to simulate micrometeoroid impacts, and ion irradiation with 1 keV H⁺ and 4 keV He⁺ to simulate solar wind exposure for pentlandite. To understand the chemical, microstructural, and spectral alterations resulting from simulated space weathering, we conducted X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and reflectance spectroscopy across the visible to near-infrared wavelengths. Our results reveal S depletion and a change in the Fe:Ni ratio at the sample surface with continuing ion irradiation. Ion irradiation also created compositionally distinct rims in the pentlandite samples, while laser irradiation produced a surface melt. Additionally, we identified hillocks protruding from the pentlandite rim after He⁺ irradiation. Our findings also show that laser and H⁺-irradiation cause the sample to brighten, while He⁺ ion irradiation causes darkening. The change in spectral slope for samples irradiated with the laser and He⁺ is minimal, while H⁺ causes the sample to redden slightly. This work will enable the identification of space weathering signatures on pentlandite grains present in the recently returned samples from asteroids Ryugu and Bennu.