Meteoritics & Planetary Science最新文献

Analyzing primitive extraterrestrial samples from asteroids is key to understanding the evolution of the early solar system. The OSIRIS-REx mission returned samples from the B-type asteroid Bennu, providing a valuable opportunity to compare them with the Ryugu samples collected by the Hayabusa2 mission. This study examines the representativeness of a fraction of the Bennu samples, which was allocated from NASA to JAXA, by nondestructive characterization of their physical and spectral properties without atmospheric exposure. The reflectance and observed spectral features in the visible-to-infrared range of the Bennu sample resemble those from the spectroscopic analysis of different fractions. Additionally, we found differences in the slope of the visible range and band-center of ~2.7 μm band between the samples and the asteroid surface, which could be explained by the degree of space weathering. A comparative analysis of the Bennu and Ryugu samples revealed spectral similarities, including absorption features indicative of Mg-rich phyllosilicates, organics, and carbonates, without any evidence of sampling bias or terrestrial alteration. This finding can be used as a benchmark for subsequent Ryugu–Bennu comparative studies.

Analyzing primitive extraterrestrial samples from asteroids is key to understanding the evolution of the early solar system. The OSIRIS-REx mission returned samples from the B-type asteroid Bennu, providing a valuable opportunity to compare them with the Ryugu samples collected by the Hayabusa2 mission. This study examines the representativeness of a fraction of the Bennu samples, which was allocated from NASA to JAXA, by nondestructive characterization of their physical and spectral properties without atmospheric exposure. The reflectance and observed spectral features in the visible-to-infrared range of the Bennu sample resemble those from the spectroscopic analysis of different fractions. Additionally, we found differences in the slope of the visible range and band-center of ~2.7 μm band between the samples and the asteroid surface, which could be explained by the degree of space weathering. A comparative analysis of the Bennu and Ryugu samples revealed spectral similarities, including absorption features indicative of Mg-rich phyllosilicates, organics, and carbonates, without any evidence of sampling bias or terrestrial alteration. This finding can be used as a benchmark for subsequent Ryugu–Bennu comparative studies.

A bright fireball was seen at 4:46 a.m. CET on November 19, 2020, over Austria, and also eye witnessed in Italy and Germany. The resulting Kindberg meteorite was the fifth well-approved meteorite fall in Austria, and all rocks represent ordinary chondrites. One specimen of Kindberg, measuring 233.08 g, was recovered on July 4, 2021, largely covered by a dark brownish fusion crust. The meteorite is an L6 ordinary chondrite (OC) breccia; Kindberg's highly equilibrated type 6 character is also supported by the large-sized plagioclase grains (An_9-12; with grains >100 μm) and the homogeneous compositions of olivine (Fa_24.4±0.4) and low-Ca pyroxene (Fs_20.6±0.3). The meteorite shows remarkable shock effects in the form of easily visible dark shock veins cross-cutting the bulk rock. The olivine in Kindberg is dominated by grains with undulous extinction or planar fractures, indicating a weakly shocked (S3 [C-S3]) chondritic rock. Close to the shock veins, olivine can also show mosaicism. In addition, wadsleyite, a high-pressure polymorph of olivine, was identified by Raman and IR spectroscopy. Wadsleyite, sometimes in paragenesis with maskelynite and locally part of an intergrowth with majorite and perhaps ringwoodite, was found within and close to the veins. The occurrence of high-pressure phases of olivine and maskelynite in a weakly shocked bulk rock clearly indicates their formation at relatively low equilibrium shock pressures of <20 GPa (S3/S4 transition). Equilibrium shock pressures consistent with those experienced by bulk rocks shocked to S5 (>30–35 GPa) and S6 (>45 GPa; S5/S6 transition) are not required to form high-pressure polymorphs of olivine. The L-chondrite classification is confirmed by O isotope data. The bulk chemical composition also supports L-group membership.

NASA's OSIRIS-REx mission successfully collected and returned ~121.6 g of bulk samples from the B-type, near-Earth asteroid (101955) Bennu to Earth in September 2023. Upon returning to Earth, the samples were transported to the NASA Johnson Space Center where most of the samples have been stored and processed. On August 22, 2024, 0.5 wt% of Bennu samples (0.663 g) and a contact pad that collected particles from the surface of Bennu were permanently transferred to JAXA from NASA based on a Memorandum of Understanding and a letter of agreement between the two agencies. Following this, all the Bennu samples have been curated under nitrogen-purged gloveboxes, called clean chambers in a clean room at the Extraterrestrial Sample Curation Center in Sagamihara. While maintaining the pristinity of samples at the curation, we conduct a series of nondestructive analyses, including near-infrared spectroscopy within the clean chambers. Bennu curation was conceptualized primarily based on the Hayabusa2 curation, whereas lessons learned from the Hayabusa2 curation were integrated into designing Bennu curation. Here, we describe preparations for the Bennu curation, with an emphasis on the differences from the Hayabusa2 curation.

CM chondrites have undergone varying degrees of aqueous alteration and thermal metamorphism on their parent bodies. Consequently, the petrologic grade of CM chondrites spans the entire type 2 scale (e.g., types 2.0–2.9). A 12236 is a very primitive petrologic type 2.9 carbonaceous chondrite that offers a unique window into the complex formation and evolution histories of CM chondrites. Based on its chemical composition, it is one of the least altered CM chondrites identified to date and one of the most primitive meteorites. Here, we present a comprehensive characterization of the organic and inorganic constituents of A 12236, determined through electron microscopy, micro-Raman, and s-SNOM nano-FT-IR spectroscopy. We identified FeNiS phases, including pentlandite, pyrrhotite, and troilite, within a fine-grained matrix composed predominantly of crystalline and amorphous silicates, including phyllosilicates. Raman spectroscopic results suggest that A 12236 experienced less thermal metamorphism than type 3 carbonaceous chondrites and contains polyaromatic organic matter with slightly differing structural order. Nano-FT-IR spectroscopy revealed chemically distinct aliphatic and aromatic organic phases, with observed compositional heterogeneity indicating variations in organic precursors and accreted materials. Correlation analysis highlights the complex associations between organic matter and phyllosilicates, along with evidence of differing aromatic compositions within the matrix. The varying abundances of nanoscale organics in different areas of A 12236 suggest that the organic matter is highly heterogeneously distributed within the matrix. Our findings demonstrate the effectiveness of nano-FT-IR spectroscopy for high-resolution, nondestructive analysis of extraterrestrial samples.

Ureilites are carbon-rich ultramafic achondrites that display unique textures, including strips of metal and carbon phases situated along grain boundaries and in fractures. Shock metamorphism observed in ureilites suggests an episode of brittle deformation caused by impact disruption of their parent body. The origin of carbon and metal has long been debated; in particular, whether either is endogenous or at least partly exogenous. We conducted experiments to simulate the metal-carbon textures and constrain their origin. Two model systems were investigated: (A) intrusion of FeS melt (analog for metal) into an olivine matrix containing dispersed graphite and (B) intrusion of graphite into a matrix containing dispersed FeS. After static annealing at 0.5–2 GPa and 1300°C, the samples were deformed at high strain rates to simulate an impact event. The microstructures of system A most closely resembled the textures observed in medium to low-shock main group ureilites, supporting an endogenous origin of carbon and a largely exogenous origin of metal. The grain boundary linings of ureilites were formed by impactor metal that intruded along grain boundaries and mixed with locally mobilized carbon. Hence, we establish a direct connection between the metal-carbon textures in ureilites and the collision history of their parent body.

Main group pallasite meteorites (PMG) are samples of an early, highly differentiated magmatic planetesimal dominated by olivine and metal-sulfide-phosphide assemblages with accessory chromite among other phases. This mineralogy reflects mantle- and core-related reservoirs, but the relative contributions of each and the overall petrogenesis are obscured by high degrees of protolith melting. Here, we present new data on the chemistry of chromite in these meteorites and review previous datasets. The purely lithophile elements Mg and Al partition into chromite via (Mg,Fe)(Al,Cr)₂O₄ and mainly reflect interactions with olivine and basaltic melt, respectively. Chromite cores are virtually always more aluminous than rims, and while MgO contents were likely reset during slow cooling, their Al₂O₃ contents are more robust and were largely set during the period of silicate magmatism. Main group pallasite chromites display bimodality in Al₂O₃ contents, with peak concentrations at ~7.7 wt% and below 6 wt%, which is unlike any other achondrite chromite population. Some chromites have very low Al₂O₃ contents (~0.01 wt%) due to formation in the absence of silicate melt, that is, via exsolution of Cr from cooling liquid metal. High-, low-, and very low-Al₂O₃ chromites in these meteorites broadly reflect relict, prograde, and retrograde periods of planetesimal heating followed by cooling. The Al₂O₃ contents of the chromites in many other achondrites and equilibrated chondrites are similar to the higher values in pallasites, with most greater than 3 wt%. This suggests that meteoritic chromite is a significant sink for ²⁶Al during its life as a heat source for planetesimal differentiation. To first order, it may be responsible for ~25%–50% (i.e., about one third) of heating in partially depleted mantles.

On October 24, 2024, an impressive fireball was visible over Austria. After the possible strewn field was calculated, the first sample of the Haag meteorite, with a mass of 8.76 g, was discovered on November 2, 2024, 8 days after the fireball event. Four more samples were found afterward putting the total sample mass at about 151 g. Short-lived radionuclides were measured shortly after recovery on a small sample, which was also used for almost all analyses presented here. Results confirm that the Haag meteorite derived from the bolide fireball event. Haag is a severely fragmented ordinary chondrite breccia and consists of typical equilibrated and recrystallized lithologies (LL4-6) as well as impact-related lithic clasts, such as dark, fine-grained impact breccias. Most fragments are highly recrystallized (type 6), but some show a well-preserved chondritic texture, which is of petrologic type 4 since the olivines are equilibrated. The olivines in the bulk rock have Fa contents of 29.5 ± 0.5 mol%, whereas the low-Ca pyroxenes have compositions of Fs_23.9±1.4Wo_1.6±0.7 with slightly variable Fs contents up to 28 mol%. However, the occurrence of type 3 fragments in other parts of the rock cannot completely be ruled out. Many clasts are moderately shocked (S4; C-S4). Using the fragment with the lowest degree of shock to determine the bulk rock's shock degree, Haag has an overall shock degree of S2 (C-S2). The LL chondrite classification is also supported by O isotope data, the results of bulk chemical analysis, and the physical properties of density and magnetic susceptibility. The nucleosynthetic Ti and Cr isotope data confirm that Haag is an ordinary chondrite, related to the noncarbonaceous (NC) meteorites. Haag does not contain detectable amounts of solar wind-implanted noble gases, and we rule out any substantial exposure at the direct surface of the parent body. Based on noble gases, Haag has an exposure age of 21–24 Ma and a pre-atmospheric meteoroid radius of 20–85 cm with a sample depth between 4 and 5 cm below the meteoroid surface, consistent with constraints from cosmogenic radionuclides. The soluble organic compositions of Haag are consistent with the profiles of the Stubenberg (LL6) breccia and show characteristics consistent with the complex shock, brecciation, and lithification history of the breccia. Haag and Stubenberg fell near each other (110 km away) within just 8 years. Since only 8.5% (about 110) of meteorite falls worldwide are LL chondrites, it is remarkable that two LL chondrites fell near each other in such a short time.

We conducted a scanning electron microscopy (SEM) and transmission electron microscopy (TEM) study of sulfide–metal assemblages (SMAs) in minimally to moderately altered CR2 chondrites. The assemblages occur on chondrule rims and consist of kamacite cores rimmed by pyrrhotite. The kamacite and pyrrhotite share orientation relationships, arguing for a genetic link. The SMAs contain secondary alteration products, including nanoscale magnetite at the sulfide–metal interface (minimally altered SMAs) and magnetite, serpentine, nanoscale Ni-rich metal at metal–magnetite interfaces, and Ni,S-bearing reaction fronts within magnetite (moderately altered SMAs). We argue the SMAs initially formed in the solar nebula from the separation of immiscible metal and silicate melts followed by sulfidization of the metal. Aqueous alteration on the asteroidal parent body caused the kamacite to transform into magnetite and the magnetite to transform into serpentine. Alteration of kamacite to magnetite occurred under oxidizing and alkaline conditions, whereas alteration of magnetite to serpentine occurred under reducing, alkaline, and higher aSiO₂ conditions. Serpentinization of magnetite appears to be a relatively common process in some carbonaceous chondrites. Additionally, theoretical and experimental studies are needed that simulate the oxidation of metal by H₂O gas and water and also serpentinization of magnetite to form serpentine with variable Mg-Fe contents.