Rhian H. Jones

The CB (Bencubbin-like) chondrites are a metal-rich group of carbonaceous chondrites that probably formed in an impact-melt vapour plume resulting from a collision between two planetesimals. Many samples, for example the CBa-type meteorite Gujba, show evidence of secondary impact processes that occurred after formation, such as silicate-dominated impact melt veins. We investigated the texture, crystallographic microstructure and chemical composition of Fe,Ni metal particles in Gujba to distinguish primary features from those caused by secondary impact melting. We developed a qualitative classification relating the morphology of primary metal particles in Gujba to the extent that they were deformed by secondary impact melt. Electron backscatter diffraction analyses showed that less deformed Fe,Ni metal particles preserve a prior crystallographic structure, partially overprinted by recrystallization textures. Fe,Ni metal inside melt veins has been melted and recrystallized. Unmelted metal particles retain similar compositions to each other, but metal entrained in impact melt, and melted Fe,Ni metal differ slightly. Conditions on the CB parent body after secondary impact resulted in no significant equilibration between particles with primary compositions, probably as the effects of impact heating were relatively rapid. Metal–melt particles in larger systems from other planetary bodies may show more evidence of modification during impact melting.

Samples of asteroid (101955) Bennu delivered by the OSIRIS-REx mission offer the opportunity to study pristine planetary materials unchanged by exposure to the terrestrial environment. Here we use a combination of X-ray diffraction and various electron microscopy techniques to explore the detailed mineralogy of Bennu samples and determine the alteration history of the planetesimal protolith from which they originated. The samples consist largely of hydrated sheet-silicate minerals, namely nanoscale serpentine and saponite of varied grain size, which are decorated with micro- to nanoscale Fe-sulfides, magnetite and carbonates. We observe sheet silicates parallel and normal to sulfide surfaces and as inclusions in sulfides; sulfur-rich veins transecting the sheet-silicate matrix; zoned carbonates and phosphates and sulfide and magnetite grains exhibiting embayment. The mineralogical evidence indicates alteration of accreted minerals by a fluid that evolved with time, leading to etching, dissolution and reprecipitation. Sulfide compositions indicate alteration at ~25 °C, similar to conditions inferred for asteroid (162173) Ryugu and Ivuna-type (CI) chondrite meteorites. The fluid probably evolved from neutral to alkaline, culminating with the precipitation of highly soluble salts. We conclude that Bennu’s protolith comprised mainly nanometre to micrometre silicates, with fewer chondrules and calcium–aluminium-rich inclusions than those of most chondrite groups.

The “light mantle” deposit at the base of South Massif in the Moon's Taurus‐Littrow Valley was a primary science target for the Apollo 17 exploration. The possibility that it was a landslide triggered by ejecta from Tycho Crater is critical for establishing the age of Tycho and constraining recent lunar impact chronology; however, the mechanism of emplacement of the deposit has recently been questioned. The newly opened 73001/73002 double drive tube from Station 3 sampled 70.6 cm deep into the regolith and represents the first stratigraphic section of an extraterrestrial landslide deposit returned to Earth. Here we provide an overview of the stratigraphy of the 73001/73002 core based on top to bottom variations revealed by coordinated laboratory analyses and explore constraints on the emplacement of the light mantle deposit. Briefly, the upper ∼10 cm of 73002 contains a disturbed zone from space weathering and emplacement of ejecta from a nearby crater that excavated and ejected basaltic material. Below 10 cm is a nearly uniform unit of immature regolith. These data support a single event for the emplacement of the deposit at this location, followed by weathering and mixing of materials from nearby crater ejecta in the upper 10 cm. Slight variations in chemistry and clast components may reflect the relative stratigraphy of the South Massif slope, with material toward the bottom of 73001 originating from lower slopes and material from higher up in the core representing regolith from higher up the South Massif slopes.

The Apollo 17 73001/73002 double drive tube, collected at the base of the South Massif in the Taurus‐Littrow Valley, was opened in 2019 as part of the Apollo Next Generation Sample Analysis program (ANGSA). A series of continuous thin sections were prepared capturing the full length of the upper portion of the double drive tube (73002). The aim of this study was to use Quantitative Evaluation of Minerals by SCANing electron microscopy (QEMSCAN), to search for clasts of non‐lunar meteoritic origin and to analyze the mineralogy and textures within the core. By highlighting mineral groups associated with meteoritic origins, we identified 232 clasts of interest. The elemental composition of 33 clasts was analyzed using electron microprobe analysis that revealed that all clasts were of lunar origin, suggesting that any meteoritic component in the regolith material we studied is not present in the form of lithic clasts. In the process of searching for meteorite fragments, we also identified a number of clast types including a group with highly magnesian olivine compositions (Fo_92.2‐96.5). We extracted raw pixel data to investigate changes in mineralogy with depth, used QEMSCAN processors to separate and group individual clasts based on mineralogy, and determined variations in particle size with depth. Our results show a decreasing abundance of glass and agglutinate clasts with depth, associated with a higher soil maturity in the upper portion of the core. The lack of stratigraphy and dominance of non‐mare clasts is consistent with the landslide origin of the material from the South Massif.

The field of advanced curation is important for existing astromaterials collections, which includes samples returned by space missions, and meteorites and cosmic dust samples that have been recovered from here on Earth. In order to maximize the scientific return of the samples, contamination needs to be minimized at all stages of sample collection, preliminary examination, classification, and curation. Utilizing best practice methods, a detailed acquisition and curation plan was implemented during the UK's first two expeditions to collect Antarctic meteorites from two new blue icefields, Hutchison Icefields and Outer Recovery Icefields. This article documents the design and execution of the procedures used during the project's curation and classification processes. It describes two case studies showing the processes applied to the recovered meteorites, and reviews our experiences and lessons learned for the future.

Chondrules are iconic sub-millimeter spheroids representing the most abundant high-temperature dust formed during the evolution of the circumsolar disk. Chondrules have been the subject of a great deal of research, but no consensus has yet emerged as to their formation conditions. In particular, the question of whether chondrules are of nebular or planetary origin remains largely debated. Building upon decades of chondrule investigation and recent headways in combining petrographic observations and O−Ti−Cr isotopic compositions, we here propose a comprehensive vision of chondrule formation. This holistic approach points toward a nebular origin of both NC and CC chondrules, with repetitive high-temperature recycling processes controlling the petrographic and isotopic diversities shown by chondrules. Chondrule precursors correspond to mixing between (i) early-formed refractory inclusions ± NC-like dust and (ii) previous generation of chondrules ± CI-like material. Chondrule formation took place under open conditions with gas-melt interactions with multi-species gas (H₂O, Mg, SiO) playing a key role for establishing their characteristics. Petrographic and isotopic systematics do not support disk-wide transport of chondrules but point toward local formation of chondrules within their respective accretion reservoirs. Altogether, this shows that several generations of genetically-related chondrules (i.e., deriving from each other) co-exist in chondrites. In addition to supporting the nebular brand of chondrule-forming scenarios, this argues for repetitive and extremely localized heating events for producing chondrules.

Meteorites are a remarkable resource. They capture the imagination of people worldwide with their spectacular entry through Earth’s atmosphere as

Meteorites are a remarkable resource. They capture the imagination of people worldwide with their spectacular entry through Earth's atmosphere as fireballs, and their exotic character of being pieces of other worlds. Scientifically, they are critical to interpreting the early stages of formation of the Solar System, as well as the geological evolution of asteroids, the Moon, and Mars, and they are vital to understanding planetary formation processes. With the burgeoning exploration of extrasolar planetary systems, knowledge of the fundamental process of planetary growth from protoplanetary disks has taken on a new significance. Meteorites provide essential and detailed insight into the formation of planetary systems, although we must bear in mind that they only represent one reference point (our own Solar System) in what is clearly a wide spectrum of possible chemical and physical parameters governing the diverse realm of extrasolar planets. This chapter summarises the nature of our meteorite collections, and the ways in which meteorites contribute to our understanding of the formation and evolution of our own Solar System, with broader implications for planetary systems in general.