Meteoritics & Planetary Science最新文献

Phosphate minerals are significant carriers of volatiles (e.g., OH) and halogens in chondritic material; however, their origin in most groups of carbonaceous chondrites remains poorly characterized. We have determined the abundance, morphology, texture, and composition of phosphate grains in aqueously altered CI chondrites and in hydrated and thermally metamorphosed Antarctic CY chondrites using scanning electron microscopy and electron probe microanalysis. Phosphates include apatite (formula Ca5(PO₄)3X, where X = F-, Cl-, OH- or other anions) and sodium-bearing magnesium phosphate, both of which formed during episodes of aqueous alteration on the CI and CY parent bodies. Apatite grains in the CI chondrites range up to 40 μm in size with a modal abundance of ~0.10 area%, while in the CYs, the largest grains are ~50 μm in size and the modal abundance is ≤0.70 area%. Analysis by secondary ion mass spectrometry (SIMS) indicates that apatite in the CYs contains ~1.0–1.8 wt% H2O, with δD values of −84‰ to 393‰ likely reflecting aqueous and thermal processing. Apatite in both the CI and CY chondrites is rich in fluorine, with fluorine abundances that range from 20 to 80 mole% of the X (anion) site. This contrasts with apatite in other chondrite groups, which is predominantly Cl-rich. Estimated bulk chondrite F abundances based on F abundance in apatite are 12–21 ppm F for the CI chondrites and 61 ppm F for the CY chondrites. This is comparable to bulk CI chondrite F abundances in the literature, suggesting that most fluorine is hosted in apatite. However, the chlorine content of CI chondrite apatite (<0.05 wt%) is too low to account for the bulk chondrite Cl abundance, indicating that Cl is hosted in other phases. Mg,Na-phosphate, a rare extraterrestrial mineral, has a modal abundance of ~0.02 area% in both the CI and CY chondrites. Mg,Na-phosphates in the CI and CY chondrites are halogen-poor (<0.15 wt%) and are typically hydrated in the CIs (analytical totals as low as 67 wt%) and dehydrated in the CYs (analytical totals >96.0 wt%). The occurrence of Mg,Na-phosphates in the CI and Antarctic CY chondrites is indicative of brines on their respective parent bodies. Similarities between the two groups, as well as with the phosphate mineral assemblage in asteroids Ryugu and Bennu, indicate that comparable fluid compositions and environmental conditions were prevalent on numerous parent bodies in the early Solar System.

Mesosiderites are rare, differentiated meteorites, so-called stony-iron meteorites—they are impact breccias composed of an unusual mix of crustal basalt and pyroxenite, core-derived metal, but no mantle materials. This odd mixture makes their origin enigmatic and has inspired many different formation theories over the last several decades. Some of the outstanding questions have regarded the origin of the metal, whether it came from another celestial body or from within the main parent body, and the puzzlingly low abundance, or absence, of mantle material in mesosiderites. The role of impacts has been central to most of the suggested theories, but mesosiderites show little to no evidence of shock metamorphism. The mystery of the origin of mesosiderites is further compounded by the relatively limited amount of published data, as well as the restricted number of samples available for research. With the detailed investigation and reclassification of the mesosiderites Lamont, Acfer 265, Queen Alexandra Range 86900 (QUE 86900), and MacAlpine Hills 88102 (MAC 88102) presented herein, our new observations shine some much-needed light on this meteorite group. Based on their petrologic and metamorphic characteristics, Lamont is classified as a B3/4, Acfer 265 and QUE 86900 as A1, and MAC 88102 as an A4 mesosiderite. The observation of multiple sets of parallel thin lamellae in high-Ca plagioclase and cristobalite in Lamont, and a silicate emulsion in QUE 86900 is proposed to be shock-related features. In both Lamont and QUE 86900, these features are interpreted to be subsequent to the initial impact, which mixed crustal and core material, and prior to deep burial. No shock-related features were noted in Acfer 265 and MAC 88102.

Angrites and eucrites are among the oldest basaltic rocks in the solar system. However, the shock histories of these meteorite groups differ markedly, as most angrites show little to no evidence of shock metamorphism. While some angrites exhibit weak wavy extinction in olivine, indicative of low-level shock, only two—Northwest Africa (NWA) 1670 and NWA 7203—are known to preserve significant shock features such as shock melt veins. To better constrain the shock history of angrites, we performed noble gas analyses on the rare shock-metamorphosed angrite NWA 7203 to determine its cosmic ray exposure and gas retention ages. Neon in NWA 7203 is entirely cosmogenic, and combined neon and argon data yield a cosmic ray exposure age of 22.7 ± 3.1 Ma (2σ). This age nominally differs from that of the other shocked angrite, NWA 1670, but is comparable to that of the unshocked angrite NWA 7812. NWA 7203 may have been ejected from a rubble pile-like asteroid composed of both shocked and unshocked materials. Two distinct ⁴⁰Ar/³⁹Ar apparent ages, 3.38 ± 0.10 Ga and 1.41 ± 0.11 Ga, were obtained, likely reflecting variable argon loss during a single impact-induced thermal event that occurred no earlier than 1.41 ± 0.11 Ga (2σ). This is the first report for the shock metamorphic age of an angrite. Our results reinforce the view that even shocked angrites lack clear evidence of a catastrophic disruption of their parent body (>100 km) hypothesized to have occurred in the early solar system. To resolve this conundrum, we propose that angrites may have experienced extensive melting during such an event, which suppressed or erased conventional shock features. If this impact occurred near the time of their crystallization (>4564 Ma), it may have been a “hot shock” event driven by heat from short-lived radionuclides. Such an event could have generated large volumes of shock melt, from which quenched angrites subsequently formed. We suggest that differentiated planetary bodies may have commonly undergone such early-stage disruption events during the formative epoch of the solar system.

The lunar regolith contains a rich history of Solar System impact events and solar activity. Many future missions will land in the south polar region of the Moon, a heavily impact cratered highland terrain, similar to the Apollo 16 landing site. In preparation, it is important to understand regolith processes and the upper stratigraphy of the regolith in typical highlands regions. In this study, we used a nondestructive scanning electron microscope with the QEMSCAN software to analyze the mineralogical compositions and maturities of regolith samples from various depths within four Apollo 16 double drive tubes. Our results support previous analyses made using other techniques that there is a lack of stratigraphic correlation across the central and southern regions of the Apollo 16 landing site, where the cores show lateral and vertical heterogeneities. Our results also show that QEMSCAN is a powerful tool for rapid, quantitative assessment of regolith characteristics. Our findings can serve as an analog for south polar regolith, providing context for upcoming missions looking to sample the subsurface regolith in the south polar region.

Instrumentally determined pre-atmospheric orbits of meteorites offer crucial constraints on the provenance of extraterrestrial material and the dynamical pathways that deliver it to Earth. However, recovery efforts are focused on larger and slower impacts due to their higher survival probabilities and ease of detection. In this study, we investigate the prevalence of these biases in the population of recovered meteorites with known orbits. We compiled a data set of 75 meteorites with triangulated trajectories and compared their orbits to 538 potential $��>�$1 g meteorite-dropping fireballs detected by the Global Fireball Observatory, the European Fireball Network, and the Fireball Recovery and InterPlanetary Observation Network. Our results reveal that objects with small semi-major axis values (a$��<�$1.8 au) appear 2–3$��\times �$ more often than expected. The current sample of meteorites with known orbits does not reflect the sources of meteorites in our collections, and it is essential to account for search and recovery biases to obtain a more representative understanding of meteorite source contributions.

Saper, L., Liu, Y., Kipp, M. A., Burney, D., Ma, C., Tissot, F. L. H., Young, E., Treffkorn, J. and Farley, K. A. (2025) Chemical, Isotopic (O, He, U), and Petrological Characteristics of a Slowly Cooled Enriched Gabbroic Shergottite, Northwest Africa 13134. Meteoritics & Planetary Science, 60: 1119–1150. https://doi.org/10.1111/maps.14345

In Table 6, the two glasses analyzed using the phosphate EPMA routine had Na₂O contents erroneously reported as K₂O contents. We have provided an updated Table 6 corrected for these two entries.

We apologize for this error.

Climate change is inducing a global atmospheric contraction above the tropopause (~10 km), leading to systematic decrease in neutral air density. The impact of climate change on small meteoroids has already been observed over the last two decades, with documented shifts in their ablation altitudes in the mesosphere (~50–85 km) and lower thermosphere (~85–120 km). This study evaluates the potential effect of these changes on meteorite-dropping fireballs, which typically penetrate the stratosphere (~10–50 km). As a case study, we simulate the atmospheric entry of the fragile Winchcombe carbonaceous chondrite under projected atmospheric conditions for the year 2100 assuming a moderate future emission scenario. Using a semi-empirical fragmentation and ablation model, we compare the meteoroid's light curve and deceleration under present and future atmospheric density profiles. The results indicate a modest variation of the ablation heights, with the catastrophic fragmentation occurring 300 m lower and the luminous flight terminating 190 m higher. The absolute magnitude peak remains unchanged, but the fireball would appear 0.5 dimmer above ~120 km. The surviving meteorite mass is reduced by only 0.1 g. Our findings indicate that century-scale variations in atmospheric density caused by climate change moderately influence bright fireballs and have a minimal impact on meteorite survival.