Exogenous fragments in brecciated planetary materials offer direct evidence of mixing among planetary bodies in the Solar System. Fragments of undifferentiated carbonaceous material are frequently identified in differentiated meteorites. However, differentiated fragments are rarely observed in carbonaceous material. An exception is the exogenous basalt observed by the OSIRIS-REx spacecraft on the carbonaceous asteroid (101955) Bennu, which motivated a search for differentiated material in the returned samples. We report a pyroxene grain in a brecciated Bennu sample that is texturally and compositionally like pyroxene from cumulate eucrites — basaltic meteorites linked to the differentiated asteroid (4) Vesta — but oxygen isotopic measurements indicate that it is likely sourced from a basaltic asteroid not clearly represented among known basaltic achondrites. This grain may have been delivered to a precursor to Bennu in the main asteroid belt. Whether this grain is representative of the pyroxene-rich boulders observed remotely on Bennu’s surface remains unconstrained. Nevertheless, extending spacecraft observations to the grain scale reveals that Bennu serves as an archive for uncharacterized basaltic asteroids, documenting a history of planetary mixing that is otherwise elusive in current meteorite records.

Troilite is a common phase in iron meteorites, but there are limited data available for the partitioning behavior of elements between troilite and solid metal. In this study, we present the results of experiments with coexisting Fe‐Ni solid metal, an S‐rich metallic liquid, and troilite, conducted at 800–925°C in evacuated silica tubes at 1 atm. We report solid metal–troilite partition coefficients for 22 elements commonly studied in iron meteorites. We find that elements with chalcophile behavior have an affinity for troilite and that the majority of siderophile elements are incompatible in troilite. A notable exception to this generalization is for the siderophile element Mo, which partitions roughly equally between solid metal and troilite. We find that Ni and Co are largely concentrated in the solid metal, but given their higher concentrations in iron meteorites, their partitioning behavior indicates that measurable amounts of Ni and Co should be present in iron meteorite troilite when it forms. Our work motivates the need for additional measurements of the trace element composition of iron meteorite troilite and validates the assumption made in iron meteorite crystallization models that partitioning into troilite can be neglected for the majority of siderophile elements, with the exception of Mo.

As part of the Apollo Next‐Generation Sample Analysis (ANGSA) program, we provide bulk composition, mineralogy, petrology, and noble gas assays of lunar particles and soils from the top half of the 73001/2 double‐drive tube (i.e., 73002) studied by the ANGSA consortium. The particles are derived from lithologies of the South Massif, including anorthosites, anorthositic breccias, high‐Ti basalts, noritic impact‐melt breccias, agglutinates, and regolith breccias. The impact‐melt breccias are distinguished by their inclusion of high‐Mg spinel that may extend the compositional family of pink spinel troctolites. The noble gas data provide cosmic‐ray exposure ages representing the emplacement of the light mantle unit at 60 Ma preceded by soil exposure in an avalanche‐emplaced surface around 100 Ma. These measurements provide additional insight into the geologic evolution of the Apollo 17 site and the light mantle unit sampled by the double‐drive tube.

Cosmic ray exposure (CRE) ages provide information about the parent bodies and source regions of meteorite classes. Cosmogenic noble gases are often used to quantify exposure time scales ranging from tens of ka to hundreds of Ma. The production rate of cosmogenic noble gases is primarily controlled by a meteorite's chemical composition. Historically, an average chemical composition for an entire meteorite class or subgroup was used to calculate production rates. At the scale needed for noble gas measurements, however, some meteorites exhibit mineral abundance variabilities that translate into chemical heterogeneities, necessitating subsample-specific production rates. We find that the metal and sulfide content can vary significantly between similar to 100 and 300 mg subsamples of the same enstatite (E) chondrite, leading to >10% differences in cosmogenic Ne-21 production rates between subsamples. We demonstrate an approach to determining subsample-specific production rates using E chondrites. We use electron microprobe analysis and X-ray computed microtomography to quantify the chemical composition and abundances, respectively, of metal, sulfide, and silicate minerals in six E chondrites and calculate subsample-specific production rates of He-3 and Ne-21. By applying this method to more E chondrite subsamples alongside noble gas measurements, we may begin to address broader questions, such as whether peaks in the E chondrite CRE age distribution can be attributed to distinct impact events.

Evaporation or freezing of water-rich fluids with dilute concentrations of dissolved salts can produce brines, as observed in closed basins on Earth1 and detected by remote sensing on icy bodies in the outer Solar System2,3. The mineralogical evolution of these brines is well understood in regard to terrestrial environments4, but poorly constrained for extraterrestrial systems owing to a lack of direct sampling. Here we report the occurrence of salt minerals in samples of the asteroid (101955) Bennu returned by the OSIRIS-REx mission5. These include sodium-bearing phosphates and sodium-rich carbonates, sulfates, chlorides and fluorides formed during evaporation of a late-stage brine that existed early in the history of Bennu's parent body. Discovery of diverse salts would not be possible without mission sample return and careful curation and storage, because these decompose with prolonged exposure to Earth's atmosphere. Similar brines probably still occur in the interior of icy bodies Ceres and Enceladus, as indicated by spectra or measurement of sodium carbonate on the surface or in plumes2,3.

The OSIRIS‐REx mission returned a sample of regolith from the carbonaceous asteroid Bennu in September 2023. We present preliminary in situ investigations of the petrology and petrography of selected particles ranging in size from 0.5 to 3 mm. Using a combination of optical and electron beam techniques, we investigate whole specimens and polished sections belonging to morphologically and visually distinct categories of particles. We find that morphological differences in the particles are reflective of petrographic and petrologic differences, leading to the conclusion that we have at least two distinct major lithologies in the bulk sample. Our findings support predictions from remote sensing, suggesting that the morphological differences observed in the boulder population of Bennu correspond to petrologic differences. Our data provide insight into the geologic activity on Bennu's parent body and the petrographic framework needed to contextualize the detailed analyses of this pristine asteroidal material.

Orbital observations of Bennu revealed a surface covered in boulders that are most similar among meteorites in our collections to aqueously altered carbonaceous chondrites, and initial analyses of the returned Bennu sample have begun to reveal insights into Bennu's origins. We identified a suite of paired CM2 chondrite meteorites that have a finely layered texture and bear a striking similarity, although at a different scale, to rugged, layered boulders on Bennu. We investigated the nature and potential origin of this layered texture by performing a petrofabric analysis on samples MET 00431, 00434, and 00435. We developed a micro-geospatial mapping framework that is more commonly used for landscape-scale investigations. Our results reveal a pervasive fracture network that exhibits a similar orientation to flattened particles dominated by tochilinite-cronstedtite intergrowths (TCI). We propose that their petrofabrics originated from a low-energy impact on the parent body that occurred after the main period of aqueous alteration halted. The impactdeformed TCI (which formed during earlier aqueous alteration) and generated the fractures. We propose that the sample from Bennu may contain particles with similar layered textures to these meteorites which, if present, would likewise indicate the dominant role of impacts and aqueous alteration on Bennu's parent body.

We have carried out a SEM-EPMA-TEM study to determine the textures and compositions of relict primary iron sulfides and their alteration products in a suite of moderately to heavily-altered CM1 carbonaceous chondrites. We observed four textural groups of altered primary iron sulfides: 1) pentlandite+phyllosilicate (2P) grains, characterized by pentlandite with submicron lenses of phyllosilicates, 2) pyrrhotite+pentlandite+magnetite (PPM) grains, characterized by pyrrhotite-pentlandite exsolution textures with magnetite veining and secondary pentlandite, 3) pentlandite+serpentine (PS) grains, characterized by relict pentlandite exsolution, serpentine, and secondary pentlandite, and 4) pyrrhotite+pentlandite+magnetite+serpentine (PPMS) grains, characterized by features of both the PPM and PS grains. We have determined that all four groups were initially primary iron sulfides, which formed from crystallization of immiscible sulfide melts within silicate chondrules in the solar nebula. The fact that such different alteration products could result from the same precursor sulfides within even the same meteorite sample further underscores the complexity of the aqueous alteration environment for the CM chondrites. The different alteration reactions for each textural group place constraints on the mechanisms and conditions of alteration with evidence for acidic environments, oxidizing environments, and changing fluid compositions (Ni-bearing and Si-Mg-bearing).

Enstatite meteorites, both aubrites and enstatite chondrites, formed under exceptionally reducing conditions, similar to the planet Mercury. Despite being reduced, the MESSENGER mission showed that the surface of Mercury is more enriched in volatiles (e.g., S, Na, K, Cl) than previously thought. To better understand the mineral hosts of these volatiles and how they formed, this work examines the chemistry and petrographic settings of a rare, K-bearing sulfide called djerfisherite within enstatite chondrites and aubrites. The petrographic settings of djerfisherite within aubrites suggest this critical host of Cl formed after both the crystallization of troilite and exsolution of daubr & eacute;elite. Djerfisherite is commonly observed as a rim on other sulfides and in contact with metal. We present an alteration model for djerfisherite formation in aubrite meteorites, whereby troilite and Fe-Ni metal are altered through anhydrous, alkali- and Cl-rich fluid metasomatism on the aubrite parent body to produce secondary djerfisherite. Moreover, we observe a loss of volatiles in djerfisherite within impact melted regions of the Miller Range 07139 EH3 chondrite and the Bishopville aubrite and explore the potential for impact devolatilization changes to sulfide chemistry on other reduced bodies in the Solar System. Vapor or fluid phase interactions are likely important in the formation of volatile-rich phases in reduced systems. While most Na and K on the mercurian surface is expected to be hosted in feldspar, djerfisherite is likely a minor, but critical, reservoir for K, Na, and Cl. Djerfisherite present on reduced bodies, such as Mercury, may represent sulfides formed via late-stage, primary metasomatism.

Journal Article Vapor Phase Metasomatism on the Aubrite Parent Body Evidenced by the Volatile-Bearing Sulfide Djerfisherite Get access Zoë Wilbur, Zoë Wilbur Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, United States Corresponding author: zewilbur@arizona.edu Search for other works by this author on: Oxford Academic Google Scholar Timothy McCoy, Timothy McCoy Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, United States Search for other works by this author on: Oxford Academic Google Scholar Catherine Corrigan, Catherine Corrigan Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, United States Search for other works by this author on: Oxford Academic Google Scholar Jessica Barnes Jessica Barnes Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, United States Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 830–831, https://doi.org/10.1093/micmic/ozad067.412 Published: 22 July 2023

Evidence of impact-induced compaction in the carbonaceous chondrites, specifically CMs and CVs, has been widely investigated utilizing microscopy techniques and impact experiments. Here, we use high-resolution photography and large area and high-resolution electron backscattered diffraction (EBSD) mapping analyses in tandem, to explore the effects of impact-induced compaction at both the meso- and micro-scales in the Allende CV3.6 carbonaceous chondrite. Macro-scale photography images of a similar to 25 cm slab of Allende captured meso-scale features including calcium-aluminum inclusions (CAIs) and chondrules. CAIs have a long-axis shape-preferred orientation (SPO). Examination of such meso-scale features in thin section revealed the same trend. Matrix grains from this section display a large amount of heterogeneity in petrofabric orientation; microscale, high-resolution, large area EBSD mapping of similar to 300,000 olivine matrix grains; high-resolution large area EBSD map across an elongate CAI; and a series of high-resolution EBSD maps around two chondrules and around the CAI revealed crystallographic preferred orientations (CPOs) in different directions. Finally, internal grains of the CAI were found to demonstrate a weak lineation CPO, the first crystallographic detection of possible CAI "flow." All results are consistent with multiple, gentle impacts on the Allende parent body causing hemispheric compaction. The larger, more resistant components are likely to have been compressed and oriented by earlier impacts, and the matrix region petrofabrics and CAI "flow" likely occurred during subsequent impacts. Meteoritic components respond differently to impact events, and consequently, it is likely that different components would retain evidence of different impact events and angles.

Northwest Africa (NWA) 8418 is an unusual chondrite whose properties do not exactly match those of any other known chondrite. It has similarities to the CV (Vigarano group), CK (Karoonda group), and CL (Loongana group) chondrites, but its abundance of large calcium‐aluminum‐rich inclusions (CAIs) and the low NiO content (<0.2 wt%) of its matrix olivine ally it most closely with the CV group. The absence of grossular, monticellite, wollastonite, and sodalite from the alteration products of the CAIs; the magnesium‐rich nature of the matrix olivines (Fa 38 ) relative to that of the CV3 chondrites (~Fa 50 ); and the presence of secondary Na‐bearing plagioclase and chlorapatite indicate a metamorphic temperature >600 °C. NWA 8418 contains kamacite, taenite, and troilite, and lacks magnetite and pentlandite. We propose that NWA 8418 be reclassified as a reduced CV4 chondrite, which makes it the first CV chondrite of petrologic type 4.