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Reckling Peak (RKP) 17085 is a newly classified Antarctic CM chondrite that preserves a complex alteration history characterized by mild aqueous alteration (CM2.7), overprinted by a short‐lived thermal metamorphic event (heating stage III [<750°C]), and affected by low‐grade terrestrial weathering. This meteorite contains abundant Fe‐rich bands within the fine‐grained matrix, composed of micron‐scale Fe‐oxyhydroxide minerals. They are interpreted as "alteration fronts" arising due to the dissolution and transport of Fe (typically <500 μm) before being abruptly deposited. This alteration texture is relatively rare among hydrated carbonaceous chondrites, with only five reported instances to date (Murchison, Murray, Allan Hills 81002, Miller Range 07687, and Northwest Africa 5958). Evidence from RKP 17085 suggests that early aqueous alteration operated as multiple geochemically isolated microenvironments, which moved outwards from local point sources within the matrix. Low permeability fine‐grained rims on chondrules appear to have acted as barriers to fluid flow, controlling the migration of fluid across the parent body. Furthermore, the higher porosity regions within the altered fine‐grained matrix represent either void space generated by the dehydration of hydrated minerals during post‐hydration metamorphism and/or sites of ice accretion (water‐ice or C‐bearing ices) preserved within a mildly altered primitive matrix. [ABSTRACT FROM AUTHOR]

The Winchcombe meteorite is a CM chondrite breccia composed of eight distinct lithological units plus a cataclastic matrix. The degree of aqueous alteration varies between intensely altered CM2.0 and moderately altered CM2.6. Although no lithology dominates, three heavily altered rock types (CM2.1–2.3) represent >70 area%. Tochilinite–cronstedtite intergrowths (TCIs) are common in several lithologies. Their compositions can vary significantly, even within a single lithology, which can prevent a clear assessment of alteration extent if only TCI composition is considered. We suggest that this is due to early alteration under localized geochemical microenvironments creating a diversity of compositions and because later reprocessing was incomplete, leaving a record of the parent body's fluid history. In Winchcombe, the fragments of primary accretionary rock are held within a cataclastic matrix (~15 area%). This material is impact‐derived fallback debris. Its grain size and texture suggest that the disruption of the original parent asteroid responded by intergranular fracture at grain sizes <100 μm, while larger phases, such as whole chondrules, splintered apart. Re‐accretion formed a poorly lithified body. During atmospheric entry, the Winchcombe meteoroid broke apart with new fractures preferentially cutting through the weaker cataclastic matrix and separating the breccia into its component clasts. The strength of the cataclastic matrix imparts a control on the survival of CM chondrite meteoroids. Winchcombe's unweathered state and diversity of lithologies make it an ideal sample for exploring the geological history of the CM chondrite group. [ABSTRACT FROM AUTHOR]

As part of an integrated consortium study, we have undertaken O, Cd, Cr, Si, Te, Ti, and Zn whole rock isotopic measurements of the Winchcombe CM2 meteorite. δ66Zn values determined for two Winchcombe aliquots are +0.29 ± 0.05‰ (2SD) and +0.45 ± 0.05‰ (2SD). The difference between these analyses likely reflects sample heterogeneity. Zn isotope compositions for Winchcombe show excellent agreement with published CM2 data. δ114Cd for a single Winchcombe aliquot is +0.29 ± 0.04‰ (2SD), which is close to a previous result for Murchison. δ130Te values for three aliquots gave indistinguishable results, with a mean value of +0.62 ± 0.01‰ (2SD) and are essentially identical to published values for CM2s. ε53Cr and ε54Cr for Winchcombe are 0.319 ± 0.029 (2SE) and 0.775 ± 0.067 (2SE), respectively. Based on its Cr isotopic composition, Winchcombe plots close to other CM2 chondrites. ε50Ti and ε46Ti values for Winchcombe are 3.21 ± 0.09 (2SE) and 0.46 ± 0.08 (2SE), respectively, and are in line with recently published data for CM2s. The δ30Si composition of Winchcombe is −0.50 ± 0.06‰ (2SD, n = 11) and is essentially indistinguishable from measurements obtained on other CM2 chondrites. In conformity with petrographic observations, oxygen isotope analyses of both bulk and micromilled fractions from Winchcombe clearly demonstrate that its parent body experienced extensive aqueous alteration. The style of alteration exhibited by Winchcombe is consistent with relatively closed system processes. Analysis of different fractions within Winchcombe broadly support the view that, while different lithologies within an individual CM2 meteorite can be highly variable, each meteorite is characterized by a predominant alteration type. Mixing of different lithologies within a regolith environment to form cataclastic matrix is supported by oxygen isotope analysis of micromilled fractions from Winchcombe. Previously unpublished bulk oxygen isotope data for 12 CM2 chondrites, when combined with published data, define a well‐constrained regression line with a slope of 0.77. Winchcombe analyses define a more limited linear trend at the isotopically heavy, more aqueously altered, end of the slope 0.77 CM2 array. The CM2 slope 0.77 array intersects the oxygen isotope field of CO3 falls, indicating that the unaltered precursor material to the CMs was essentially identical in oxygen isotope composition to the CO3 falls. Our data are consistent with earlier suggestions that the main differences between the CO3s and CM2s reflect differing amounts of water ice that co‐accreted into their respective parent bodies, being high in the case of CM2s and low in the case of CO3s. The small difference in Si isotope compositions between the CM and CO meteorites can be explained by different proportions of matrix versus refractory silicates. CMs and COs may also be indistinguishable with respect to Ti and Cr isotopes; however, further analysis is required to test this possibility. The close relationship between CO3 and CM2 chondrites revealed by our data supports the emerging view that the snow line within protoplanetary disks marks an important zone of planetesimal accretion. [ABSTRACT FROM AUTHOR]

We review the mineralogy, petrology, and abundance of petrological type 1 extraterrestrial material. Such material has been completely altered by aqueous processing on its parent bodies. As well as the four meteorite groups that contain type 1 members (CI, CM, CR, and CY), we summarize data from the 2019 fall Flensburg and a recent reanalysis of the "meteorite" Bench Crater found on the Moon, along with fine‐grained micrometeorites, interplanetary dust particles, and xenoliths in meteorites. Type 1 materials exhibit a remarkably high diversity of alteration conditions (temperature, water‐to‐rock [W/R] ratios, and fluid composition) and starting mineralogy. Type 1 material comprises a significant component of the modern extraterrestrial flux to the Earth and was likely common throughout the solar system during the whole course of its history, pointing to both widespread accretion with ices and heating of parent bodies. Type 1 materials are composed predominantly of various phyllosilicates, carbonates, sulfides, and magnetite. Some type 1 materials appear to be part of a "CM clan" typified by serpentine‐rich phyllosilicate compositions and an oxygen isotope composition that falls in the 16O‐rich part of the CM field. Others span a wide range in δ18O (>30‰) and fall on or above the terrestrial fractionation line (+ve Δ17O). Positive Δ17O values are unusual for carbonaceous meteorites but are relatively common in type 1 materials. The wide variation in oxygen isotopes, as well as in textures, mineralogy, and bulk chemistry, points to multiple parent bodies that may originate in the inner and/or outer solar system. Cometary materials, or transition objects such as Main Belt comets or type D asteroids, are likely the source of much of the type 1 materials on Earth but relating them to specific parents requires more study. [ABSTRACT FROM AUTHOR]

TAM5.29 is an extraterrestrial dust grain, collected on the Transantarctic Mountains (TAM). Its mineralogy is dominated by an Fe‐rich matrix composed of platy fayalitic olivines and clasts of andradite surrounded by diopside‐jarosite mantles; chondrules are absent. TAM5.29 records a complex geological history with evidence of extensive thermal metamorphism in the presence of fluids at T < 300 °C. Alteration was terminated by an impact, resulting in shock melt veins and compaction‐orientated foliation of olivine. A second episode of alteration at lower temperatures (<100 °C) occurred postimpact and is either parent body or terrestrial in origin and resulted in the formation of iddingsite. The lack of chondrules is explained by random subsampling of the parent body, with TAM5.29 representing a matrix‐only fragment. On the basis of bulk chemical composition, mineralogy, and geological history TAM5.29 demonstrates affinities to the CVox group with a mineralogical assemblage in between the Allende‐like and Bali‐like subgroups (CVoxA and TAM5.29 are rich in andradite, magnetite, and FeNiS, but CVoxA lacks hydrated minerals, common in TAM5.29; conversely, CVoxB are rich in hydrated phyllosilicates but contain almost pure fayalite, not found in TAM5.29). In addition, TAM5.29 has a slightly different metasomatic history, in between the oxidized and reduced CV metamorphic grades while also recording higher oxidizing conditions as compared to the known CV chondrites. This study represents the third CV‐like cosmic dust particle, containing a unique composition, mineralogy, and fabric, demonstrating variation in the thermal metamorphic history of the CV parent body(‐ies). [ABSTRACT FROM AUTHOR]

The early stages of atmospheric entry are investigated in four large (250–950 μm) unmelted micrometeorites (three fine‐grained and one composite), derived from the Transantarctic Mountain micrometeorite collection. These particles have abundant, interconnected, secondary pore spaces which form branching channels and show evidence of enhanced heating along their channel walls. Additionally, a micrometeorite with a double‐walled igneous rim is described, suggesting that some particles undergo volume expansion during entry. This study provides new textural data which links together entry heating processes known to operate inside micrometeoroids, thereby generating a more comprehensive model of their petrographic evolution. Initially, flash heated micrometeorites develop a melt layer on their exterior; this igneous rim migrates inwards. Meanwhile, the particle core is heated by the decomposition of low‐temperature phases and by volatile gas release. Where the igneous rim acts as a seal, gas pressures rise, resulting in the formation of interconnected voids and higher particle porosities. Eventually, the igneous rim is breached and gas exchange with the atmosphere occurs. This mechanism replaces inefficient conductive rim‐to‐core thermal gradients with more efficient particle‐wide heating, driven by convective gas flow. Interconnected voids also increase the likelihood of particle fragmentation during entry and, may therefore explain the rarity of large fine‐grained micrometeorites among collections. [ABSTRACT FROM AUTHOR]

Introduction: CM carbonaceous chondrites are among the most chemically primitive meteorites, yet are also some of the most aqueously altered [1,2]. This pervasive parent body processing destroys much of the primary mineralogy and texture [2]. Nano-scale investigations indicate that the permeability of aqueously altered carbonaceous chondrites is low, permitting fluid flow only over distances <100 µm [3], and that aqueous alteration is locally heterogeneous [4]. In contrast, recent observations of large veins of carbonate on the B-type asteroid Bennu [5], which has spectroscopic similarities to CMs [6], suggest macro-scale movement of fluids. On the 28th February 2021 a bright fireball was observed by the UK Fireball Alliance (UKFall) [7]. This resulted in the recovery of the Winchcombe meteorite 12 hours later [7]. It is a CM chondrite breccia with eight distinct lithologies, with variable alteration histories ranging from CM2.0-CM 2.6 plus a cataclastic matrix [8]. The limited terrestrial alteration of Winchcombe, combined with the orbital parameters determined by UKFAll [7], make it an ideal sample to explore macro-nanoscale constraints on aqueous alteration of CM chondrites. Here, we present the key results of the investigations undertaken by the fine-grained sub-team of the Winchcombe consortium study. Methods: Several rock chips and petrographic sections of the Winchcombe meteorite were analysed using X-ray computed tomography (XCT), electron probe microanalysis (EPMA), scanning electron microscopy (SEM) techniques (including secondary electron (SE) and backscatter electron (BSE) imaging, energy dispersive X-ray spectrometry (EDS), QEMSCAN, electron backscatter diffraction (EBSD)), focused ion beam (FIB) microscopy (including FIB based time of flight secondary ion mass spectrometry (TOF-SIMS) transmission electron microscopy (TEM) techniques (including, HAADF, EELS, STEM, EDS, XANES), atom probe tomography (APT). Permeability at the macroscale were established via numerical simulations. Key results: XCT data indicate that some Winchcombe lithologies have a preferred alignment of relic ellipsoidal chondrules defining a foliation fabric. These foliations are in separate orientations in different lithologies from the same rock chip. Some lithologies also exhibit a 'fracture cleavage' defined by sub-parallel fracture sets. Numerical simulations indicate that Winchcombe has an anisotropic permeability with a much lower permeability along one axis. SEM imaging reveals a range from complete to incomplete replacement of carbonate and silicate phases in some tochilinite cronstedtite intergrowths (TCIs) with some carbonate-TCI grains separated by only a few 100 µm. EPMA data show a moderate spread of compositions within the matrix, fine-grained rims (FGR), and TCIs within each lithology. TEM investigations of an FGR around a chondrule within a subtype 2.2 lithology reveal the presence of inclusions that resemble glass with embedded metal and sulphide (GEMS). Coordinated TOF-SIMS and APT data indicate that Na is concentrated at the boundary between Mg-rich and Fe-rich serpentine intergrowths in TCIs. Discussion and conclusions: At the macro-scale, XCT results and numerical simulations show that fluids flowed more readily along a 2D plane and less-readily along the pole to that plane. Such an anisotropic permeability network may be generated via compaction or through precipitation of minerals during aqueous alteration, and would serve to limit fluid transfer, resulting in the segregation of fluid compositions which may enhance the preservation of pockets of unaltered material. At the nanoscale, the survival of both GEMS-like phases that are readily altered by minor degrees of aqueous alteration, and the heterogeneity in the extent of carbonate alteration to TCIs over short distances, suggest that regions within otherwise severely aqueously altered regions of the Winchcombe meteorite experienced little fluid interaction. This was likely caused by local variations in permeability on the Winchcombe parent. The cause of this lower permeability that limited fluid migration to reactive surfaces could be a primary texture, a compaction texture, an impact texture, or generated by progressive alteration. Therefore, even in pervasively aqueously altered meteorites it is likely that some nano-macro scale volumes can preserve their primary mineralogy and texture. [ABSTRACT FROM AUTHOR]

Introduction: The Mighei-like (CM) carbonaceous chondrites are the largest class of hydrated meteorites, representing collisionally derived fragments of water-rich asteroids [1,2]. Most (>95%) are breccias, whose clasts sample a range of aqueous alteration extents [3]. They can therefore act as "snapshots" recording the progression of fluidrock interaction on the CM parent body. Conversely, analysis of the material between clasts (termed cataclastic matrix) provides an opportunity to study the post-hydration history of the CM parent body, specifically its fragmentation and re-accretion. Here, we investigate both aspects of the CM chondrites' geological history through study of the newly recovered fall: Winchcombe [4, 5]. Methods: Sixteen polished sections with a total area of 190 mm2 were generated for this work. They were studied under scanning electron microscopy (SEM) using backscattered electron (BSE) imaging, energy dispersive X-ray spectroscopy (EDX) and electron microprobe analysis (EMPA). These sections sample the two largest masses (the main mass [320 g] and the agricultural field stone [152 g]) recovered from the Winchcombe strewnfield [4]. Results: Winchcombe is a breccia, composed of lithological clasts held within a cataclastic matrix. We identified eight distinct lithologies. Their aqueous alteration extents vary between intensely altered CM2.0 and moderately altered CM2.6 [6]. Although no lithology dominates, three rock types represent >70% of the studied area. Several lithologies contain abundant tochilinite-cronstedtite intergrowths (TCIs). Type-II forms with zoned textures are most common, typically they have Fe-rich rims ("FeO"/SiO2 wt.%: 1-5) and Mg-rich cores ("FeO"/SiO2 wt.%: < 1), however, forms with hollow cores or cores containing a mix of phyllosilicate and calcite or phyllosilciates and anhydrous silicate are also found. The cataclastic matrix represents ~15% of the studied area. It has a coarse, heterogenous texture and includes abundant subangular fragments. Fragments include the full range of CM chondrite components (e.g. Fe-sulphides, whole chondrules with or without fine-grained rims, olivine and pyroxene grains, serpentine, carbonate grains, TCI clusters, as well as coherent blocks of fine-grained matrix). The cataclastic matrix is, therefore, a complex mix of components, with both heavily altered and mildly altered phases found in close association. Another striking feature is the apparent low abundance (< 3 area%) of identifiable whole chondrules. Discussion and conclusions: Our data suggest that both anhydrous silicates and carbonates (T1a calcites) act as precursor phases for type-II TCI formation. Cross-cutting relationships allow the sequence of mineralization to be reconstructed. Initially, inward dissolution by Fe-rich and S-rich fluids forms rims composed of intermixed tochilinite and cronstedtite. In the intermediate stages of type-II TCI formation, further dissolution continues without concurrent precipitation, resulting in the formation of hollow structures. These voids were later infilled, most often by Mg-rich phyllosilicates. As alteration advanced, early-formed secondary phases became unstable and were either dissolved (e.g. T1a calcites) or chemically altered (e.g. TCI rims). The presence of numerous lithological clasts with variable aqueous alteration extents and abrupt boundaries found in close juxtaposition indicates that the cataclastic matrix formed by the deposition of fines, alongside larger fragments (the clasts), on or near the surface of the parent asteroid. Furthermore, the composition of the cataclastic matrix is consistent with formation by fragmentation and mixing of debris derived from the entire clast population. The cataclastic matrix is, therefore, interpreted as an impact-derived fallback breccia. Analysis of grain size and texture suggests that disruption of the original parent asteroid responded by intergranular fracture at grain sizes <100 µm, while larger phases, such as whole chondrules, splintered apart. Re-accretion formed a poorly lithified rubble-pile body. During atmospheric entry, the meteoroid broke apart with new fractures preferentially cutting through the weaker cataclastic matrix and thereby separating the Winchcombe meteoroid into its component-lithological clasts. Thus, the strength of the cataclastic matrix imparts a significant control on the survival of CM chondrite meteoroids. [ABSTRACT FROM AUTHOR]

Introduction: Micrometeorites (MMs) are millimeter to sub-millimeter-sized dust particles that are liberated as debris tails from asteroids and comets and are constantly captured by Earth. They are decelerated at high altitudes, often heated and partially melted, yet survive atmospheric entry to be recovered from Earth's surface environments. They have been successfully separated from Antarctic ice and investigated in detail using numerous analytical techniques, which has improved our understanding of the source population of small bodies, their compositions and aqueous processing of materials [1-4]. Additionally, the study of MMs provides a complementary perspective on meteorite studies as well as regolith samples obtained from sample return missions like Hayabusa2 and OSIRIS-REx. Identifying the parent bodies of MMs and understanding their relationship to known meteorite groups improves our knowledge of solar system geological diversity during the age of early planetesimals. Such a classification requires a detailed investigation of the MM mineralogy, chemical characteristics, and oxygen isotope compositions. Here, we report on a quantitative and semi-quantitative analysis of the mineralogy of several unmelted MMs from Antarctica. We focus on the textural setting of P-bearing minerals with surrounding phases, which has not received particular attention. Furthermore, selected MMs will be investigated for O-isotopes. Samples and Methods: We investigated a subset of small (<150 µm) MMs from the Cap Prud'homme MM collection [4]. These are blue-ice derived particles, hand-picked from filter papers in 1994. Mineralogy of the particles was ascertained using energy dispersive spectroscopy (EDS) and wavelength dispersive spectroscopy (WDS) on the JEOL JXA-8530F electron microprobe (EPMA) at Arizona State University. Analyses were conducted with a beam current of 15 nA, an acceleration voltage of 15 keV, and a beam size of 1 to 5 µm. High-resolution elemental maps of K, P, Si, Al, Na, Mg, Cl, S, Ti, Fe, Mn, Ca were collected. Results: CP94-050 epoxy mount has 80 MMs; data on sixty-seven MMs, often with CI and CM-like characteristics have been previously published [4-7]. The remaining MMs range in size from ~80 µm to ~135 µm in diameter and are primarily irregular in shape. Of these, four are fine-grained MMs (FgMMs), two are scoriaceous fine-grained MMs, and seven are coarse-grained MMs. Of the FgMMs, three are type C2 (compact and chemically heterogenous), and one is type C3 (highly porous) based on the classification scheme of [4]. We conducted sixty-nine WDS spot analyses of about 5×5 µm2 regions in the MM suite. Thirty-one of these target regions are from MMs previously unstudied in this capacity. These regions are either fine-grained matrix or larger coarse grains. Individual grains vary from spherical to irregular to elongated. WDS analyses outside the range of 97 to 101 wt. % were rejected, unless the spot was taken from a porous, fine-grained matrix, in which case a threshold of >94 wt. % was used (e.g., [4]). Twenty-four grain analyses met the former criteria. Eight of these spots are olivine (Fo85.1-99.3), 12 are pyroxene (En88.5-97.4Fs1.5-7.8Wo0.6-4.2), one is Ca-rich augite (En55.5Fs0.8Wo43. 7), and two are SiO2 grains. The remaining grain is non-stoichiometric with a Si/O ratio is 1/3 and with Mg and Al enrichments. Sixty-nine spots were analyzed for P with WDS. Considering 97 to 101 wt. % totals, we identified two grains that are olivine while 2 are pyroxene; the remaining grains show non-stoichiometric compositions. The P content of these silicate grains vary from >0.01 to 0.035 wt.%. We also found five fine-grained, porous regions with lower totals (>94 wt. % criteria) that contain P (0.012-0.0127 wt.%). Several of these contain Mg and Ca, suggestive of thermally metamorphosed apatite minerals. Elemental maps show that P is evenly distributed in most MMs, although a few MMs show hotspots. For example, one MM displays a 5×5 µm2 hotspot, contains elevated levels of Fe (18.3 wt. %) and S (1.07 wt. %), and exhibits non-stoichiometric elemental composition. Several P hotspots contain Fe and are either Fe-phosphide inclusions or Fe-Ni metal altered to ferrihydrite. Discussion: The study of the phases containing S and P can provide valuable insights into (1) element reservoirs and (2) redistribution during metasomatic fluid processing on asteroid parent bodies. Phosphorus is present in Fe-Ni metal in the most primitive carbonaceous chondrites [8]. Secondary processes oxidize P to form phosphates and phosphides [9]. We identify P in olivine and pyroxene minerals, and in grains that contain P in association with S, Mg, and Ca in non-stoichiometric proportions. We argue that fluid-mediated processing occurred in these MM parent bodies and P is not completely lost from the MMs during re-entry through Earth's atmosphere. [ABSTRACT FROM AUTHOR]

Recovery: At 21:54 (UTC) on the 28th February 2021 a bright fireball was observed over the United Kingdom. The fireball, which lasted ~8 seconds, was widely reported on social media and recorded by 16 stations operated by the six meteor camera networks that collaborate as the UK Fireball Alliance (UKFAll). The main mass (~320 g) of the meteorite was discovered the next morning by the Wilcock family on their driveway in the town of Winchcombe, Gloucestershire. Upon landing, the stone shattered into a pile of dark mm- to cm-sized fragments and powder, most of which was collected using rubber gloves and sealed within polyethylene bags ~12 hours after the fall. In total, >500 g of material was recovered from the local area by members of the public and the UK planetary science community within seven days of the fall, during which time there was no rainfall [1]. The largest intact piece of the Winchcombe meteorite is a 152 g fusion-crusted stone found on nearby farmland on the 6th March. Fireball: The entry velocity of the Winchcombe meteoroid was ~14 kms-1 and the recordings clearly show several fragmentation events. Analysis of the video footage combined with the measurement of short-lived radionuclides suggest that the original body was small (<70 kg). The pre-atmospheric orbit of the Winchcombe meteoroid is similar to those previously reported for the Sutter's Mill (C/CM) [2] and Maribo (CM) chondrites [3]. Petrography: A consortium was quickly established to study the Winchcombe meteorite. Petrographic observations of polished samples indicate that Winchcombe is a CM ("Mighei-like") carbonaceous chondrite [4, 5]. It consists of chondrules [6] and calcium-aluminium-rich inclusions (CAIs) [7] set within a matrix of phyllosilicates, tochilinite-cronstedtite intergrowths (TCIs) [8, 9], carbonates [10], magnetite, and sulphides. Many of the samples show evidence for brecciation and contain multiple distinct lithologies with sharp boundaries. Most lithologies are intermediately to highly aqueously altered (CM2.4 - 2.0), although a rare lithology containing unaltered chondrules and metal has also been identified (~CM2.6). The presence of an unusual Zn-Fe sulphide hints at metasomatism on the parent body [11]. Reflectance spectra of the Winchcombe meteorite show absorption features at ~3 µm and in the mid-infrared (IR) region that are consistent with abundant phyllosilicates [12], while it's fusion crust displays several unique textures related to degassing during atmospheric entry [13]. Composition: The classification of Winchcombe as a CM chondrite is further supported by major and minor element abundances [e.g., 14], and oxygen, titanium, and chromium isotopic compositions [15]. The bulk water content of Winchcombe measured within one month of the fall was ~11 wt.%. Analysis by stepped combustion yielded carbon, nitrogen, and noble gas abundances and isotopic compositions largely consistent with other highly altered CM chondrites [16, 17]. Low voltage SEM characterisation less than a week after the fall of fresh, unpolished fragments located several small (~10's µm) carbon- and nitrogen-bearing regions with "globule-like" morphologies. Carbon K-edge spectra of organic matter in the Winchcombe meteorite show a strong absorption feature at ~285 eV that is assigned to aromatic C=C [18]. Initial analysis by both both liquid (LC-) and gas chromatography-mass spectrometry (GC-MS) revealed extraterrestrial organic components including lipids, fatty acids, and amino acids [19]. Outlook: The Winchcombe meteorite is only the fifth carbonaceous chondrite fall with a known preatmospheric orbit, and due to its rapid recovery is likely the most pristine member of the CM group. The mineralogical, elemental, and organic properties of the Winchcombe meteorite provide a snapshot of conditions in the outer regions of the protoplanetary disk and new insights into the chemical and dynamic evolution of volatiles in the early solar system. The nature and timing of the Winchcombe meteorite fall also makes it complementary to samples of asteroids Ryugu and Bennu collected by the Hayabusa2 and OSIRIS-REx missions, offering an opportunity to develop and rehearse curation and analytical protocols on fresh, carbonaceous materials [20]. [ABSTRACT FROM AUTHOR]

Introduction: Micrometeorites have been identified in deep sea sediments, polar regions, urban environments, and increasingly as relatively abundant fossilized particles in the geological record [1,2,3]. Fossil micrometeorites in ancient rocks can provide a record of the past extraterrestrial flux to Earth; while their chemical, textural and mineralogical features allow us to investigate atmospheric processes at the time of atmospheric entry and post-depositional and diagenetic processes after impact and incorporation into sediments [4,5]. In this project we utilized a collection of acid-digestion residues from a suite of late Silurian, Devonian and early Carboniferous rocks from the Ural Mountains, covering the period from ~420-350 Ma. The well-constrained chronostratigraphy from previous micropalaentological studies of this section provide insights into the extraterrestrial flux during this period and potential atmospheric changes across the Devonian. Methods: Deep-sea limestones from the Komi River area of the Ural Mountains were collected as part of micropalaentological fieldwork between 2000 and 2002. Approximately 1 kg of each rock sample was dissolved in 10% acetic acid and the residual material retained and separated using heavy liquids (sodium polytungstage). For this micrometeorite project, these leftover micropalaentological collection materials were re-used to extract Iton-dominated micrometeorites (I-types) and other cosmic spherules. These resistant micrometeorite types were extracted using magnetic separation and visual identification. The extracted particles were analysed and confirmed as extrerrestrial [4,5] using a combination of scanning electron microscopy (SEM), quantitative energy-dispersive X-ray spectroscopy (EDS), and electron microprobe analysis (EMPA) techniques. Findings: Thus far a total of 40 micrometeorites have been identified. Chemical analysis shows that these micrometeorites are primarily composed of magnetite and Mn-bearing magnetite, similar to previous studies of fossil micrometeorites from ancient sediments (e.g., [3]). Ongoing textural and geochemical analysis will be used to infer changes in the atmospheric oxidation during this crucial period in Earth's history. Evolution of plants and the colonisation of the land during the Devonian led to an increase in atmospheric O2 concentrations and a decrease of CO2 in the Devonian atmosphere[6]. Constraining the relative degree of oxidation in these meteorites will shed light on the atmospheric evolution during this period and potentially provide a new climate proxy based on micrometeorites. Comparison between these fossil micrometeorites, and prisine, geologically modern samples will provide constraints on the poorly-understood processes that may alter the micrometeorites during storage on the seafloor and during lithification [3]. Conclusions: Developing this fossil micrometeorite collection will enhance an existing world-leading repository of extraterrestrial material at the Natural History Museum; and this work shows that previously overlooked samples from micropalaeontological collections, can be easily repurposed to extract micrometeorites, unlocking a wealth of information and enhancing both collections simultaneously. Future sample return missions such as Hayabusa2 and OSIRIS-REx [7,8] will also return small particulate material from asteroids, and hence there is additional benefit to establishing a dedicated micrometeorite collection to study both modern and fossil micrometeorites as analogues and prepare protocols for future sample return material. [ABSTRACT FROM AUTHOR]

Introduction: On 28th February 2021 a bright fireball was observed across the UK; its trajectory, orbit and strewn field were subsequently defined by image and video capture from the UK Fireball Alliance [1,2]. The main mass of the resulting meteorite was recovered within 12 hours of its fall in the town of Winchcombe [1,2]. This meteorite was subsequently classified as a CM2 chondrite breccia with numerous distinct lithologies displaying a range of aqueous alteration from CM2.0 to CM2.6 [3]. This pristine sample had severely restricted opportunity for terrestrial alteration, thus making it ideal for trace level chemistry studies of its aqueous alteration microstructures derived from water rock reactions on the meteorite's parent body. Of particular interest are tochilinite cronstedtite intergrowths (TCIs) that form during aqueous alteration and whose chemistry and structure are used as indicators for the nature and extent of hydration in CM chondrites [4]. Methods: A sample of the Winchcombe meteorite set within a polished resin block on loan from the NHM, UK, was examined using scanning electron microscopy (SEM). Multiple TCI features were selected as specific targets for more detailed study. The selection of the specific TCIs for study was based on their differing extent of alteration textures and chemistry. SEM-energy dispersive X-ray spectroscopy (EDS) was used to define a range of TCI inclusions with point analysis composition data and mapping data to show elemental distributions. Focused Ion Beam (FIB)-SEM based Time of Flight Secondary Ion Mass Spectrometry (TOFSIMS) was then applied to these same areas to give much higher resolution major, minor, and trace elemental maps, as well as isotope maps gathered as two and three dimensional datasets. Methods: A sample of the Winchcombe meteorite set within a polished resin block on loan from the NHM, UK, was examined using scanning electron microscopy (SEM). Multiple TCI features were selected as specific targets for more detailed study. The selection of the specific TCIs for study was based on their differing extent of alteration textures and chemistry. SEM-energy dispersive X-ray spectroscopy (EDS) was used to define a range of TCI inclusions with point analysis composition data and mapping data to show elemental distributions. Focused Ion Beam (FIB)-SEM based Time of Flight Secondary Ion Mass Spectrometry (TOFSIMS) was then applied to these same areas to give much higher resolution major, minor, and trace elemental maps, as well as isotope maps gathered as two and three dimensional datasets. Discussion and Conclusions: FIBSEM based TOFSIMS is a very useful in-situ analytical technique to characterise two and three dimensional microstructures in meteorites. The aqueous alteration structures that formed within the Winchcombe meteorite parent body have localized variations that most probably relate to changes in its permeability. Further research is planned to explore these results producing data sets with transmission electron microscopy (TEM) and transmission Kikuchi diffraction (TKD) of the exact same study target sites within this sample, to reveal the nanoscale growth structures and infer growth mechanics. [ABSTRACT FROM AUTHOR]

Introduction: On the evening of Sunday 28th February 2021 a bright fireball was witnessed from many parts of southern England and adjacent areas [1, 2]. The main mass of over 300 g was recovered the following morning by the Wilcock family from their driveway in Winchcombe, Gloucestershire and stored in clean plastic bags [1, 2]. Two days later, the material collected from the driveway was tentatively identified as a CM2 chondrite, with similarities to the historic Cold Bokkeveld (CM2) meteorite. In order to provide additional corroboration for this initial identification, O-isotope analysis was undertaken on 5th March, with the results confirming that the Winchcombe material did have a composition consistent with a CM2, and was indeed close to that of Cold Bokkeveld. The O-isotope analysis was completed within 5 days of the meteorite's fall - perhaps a record? Subsequent detailed petrographic and geochemical studies confirmed the initial identification and the meteorite is now officially classified as a CM2 [1, 2, 3]. In order to investigate Winchcombe in greater detail a consortium study is ongoing and the results discussed here summarize the initial findings of the "Winchcombe Isotope Team" (WIT). The initial remit of WIT was to undertake high-precision isotopic analysis on a range of elements (Ca, Cd, Cr, K, Li Mg, Mo, Ni, O, Si, Ti, Te, U, W, and Zn) and to also undertake presolar grain studies. Noble gas and light stable isotope analysis (Ne, Ar, Xe, H, C, N) is being covered by another team [1]. Presolar grain studies are ongoing and the results will be reported at a later date. Here we discuss the initial results of our measurements of the Cd, Cr, O, Te, Ti and Zn isotopic composition of the Winchcombe meteorite. Si isotope data is currently being collected and the results will be discussed at the meeting. Methods: O-isotopes: Analyses were undertaken by laser fluorination [4] at the Open University on powdered 100 - 150 mg chips of Winchcombe. Zn, Cd and Te-isotopes: Analyses were undertaken at Imperial College on a 1.94 g sample of Winchcombe. Cr isotopes: Analyses were undertaken at the University of St. Andrews on 20 mg of Winchcombe material. Ti isotopes: Analyses were undertaken at the University of Bristol on a 101 mg sample of Winchcombe. Full analytical details for O-isotope analysis are given in [1, 5] and for Cd, Cr, Si, Te, Ti and Zn in [5]. Results: O-isotope analyses of two Winchcombe fragments have distinct O-isotope compositions: δ17O 2.75 ± 0.40‰; δ18O 9.48 ± 0.50‰; Δ17O -2.18 ± 0.14‰ (2SD, n=2) and δ17O 0.98 ± 0.31‰; δ18O 7.29 ± 0.62‰; Δ17O - 2.23 ± 0.00‰ (2SD, n=2); with both plotting at the isotopically heavy, more aqueously altered, end of the CM2 array close to Cold Bokkeveld and Murchison [5]. Our analysed fragments sample the two most abundant lithologies in Winchcombe. These are both highly altered (66Zn values determined for two Winchcombe aliquots are +0.29 ± 0.05‰ (2SD) and +0.45 ± 0.05‰ (2SD). The small difference between these analyses likely reflects minor sample heterogeneity. Zn isotope compositions for Winchcombe show excellent agreement with published CM2 data [7, 8, 9]. δ114Cd for a single Winchcombe aliquot was +0.29 ± 0.04‰ (2SD), which is close to a previous result for Murchison [10]. A higher δ114Cd value for Cold Bokkeveld [10] may reflect parent body processing [11]. δ130Te values for three aliquots gave indistinguishable results, with a mean value of +0.62 ± 0.01‰, and are essentially identical to published values for five CM2s [12]. ε53Cr and ε54Cr for Winchcombe were 0.319 ± 0.029 (2SE) and 0.775 ± 0.067 (2SE) respectively. Based on its Cr isotopic composition, Winchcombe plots close to other CM2 chondrites [13]. ε50Ti values for Winchcombe are in line with recently published data for CM2s [13] Discussion and conclusions: Zn, Cd, Te, Ti and Cr isotope data are consistent with a CM2 classification for Winchcombe. O-isotope analysis indicates that it experienced extensive parent body aqueous alteration. However, like other CM2s, Winchcombe displays significant lithological variation [6]. Further O-isotope analysis will be undertaken on the less altered material from Winchcombe to better constrain the extent of hydration on its parent body. In addition, we will be undertaking leaching experiments (Ni, Cr and Zn) following the methodology outlined by [14]. [ABSTRACT FROM AUTHOR]

Introduction: Following low temperature aqueous alteration (<200 °C), a number of CM carbonaceous chondrites experienced post-hydration heating (>300 °C) on their parent body [1-3]. However, the timing, duration and mechanism of the dehydration events remain poorly defined. Constraining the thermal history of the carbonaceous chondrites is an important step to understanding the evolution of water-rich C-complex asteroids, and the distribution and transport of volatiles in the early solar system. Iron sulfides are widespread in carbonaceous chondrites and are highly sensitive to both aqueous alteration and thermal metamorphism. Dehydrated CM chondrites contain a generation of recrystallized sulfides with compositions and textural features diagnostic of their metamorphic heating [4-6]. Here, we have systematically characterized Fesulfide grains within the matrices of dehydrated CM chondrites that experienced a range of peak temperatures (~300 - >750 °C) to constrain the timescales of metamorphism and infer the thermal history of the parent body. Samples & Methods: The composition and morphology of coarse (10 -150 µm) Fe-sulfide grains within polished sections of Jbilet Winselwan (CM2, Stage II, ~300 - 500°C), Dhofar (Dho) 1434 (CMan, Stage III, ~500 - 750°C) and Pecora Escarpment (PCA) 02012 (CM2, Stage IV, >750°C) were characterized using a ZEISS EVO 15LS scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). Backscattered electron (BSE) images, element maps and spot analyses were acquired at 20 kV and 1.5 nA. Results: In Jbilet Winselwan, most (~80%) of the analysed grains are pyrrhotite with inclusions of pentlandite (PoPn), which form either ~5 µm sized oriented laths or patches 10 - 50 µm in size. The pentlandite patches themselves appear to contain ~1 µm sized pyrrhotite inclusions. We also observed individual grains of pyrrhotite (Po) and pentlandite (Pn) in Jbilet Winselwan. In Dho 1434, the grains are either PoPn, pentlandite with inclusions of metal (PnM), or pyrrhotite with inclusions of both pentlandite and metal (PoPnM). The majority of Fe-sulfide grains within PCA 02012 are PoPn and PoPnM grains, although we also found one individual Po grain, and one pyrrhotite grain with metal inclusions (PoM). Unlike the oriented laths observed in Jbilet Winselwan, all of the metal and pentlandite inclusions within Dho 1434 and PCA 02012 are irregular in shape, randomly oriented, and <~15 µm in size. Discussion: Kimura et al. [5] used Fe-sulfide textures and compositions to classify the dehydrated CM chondrites into three categories: A) unheated meteorites, with pentlandite commonly occuring along the boundary of pyrrhotite grains; B) mildly heated (~Stage II-III), characterized by blebs or lamellae of pentlandite in all pyrrhotite grains; C) severely heated (~Stage III-IV), with abundant Ni-rich metal inclusions and an absence of pentlandite exsolution textures. The evolving Fe-sulfide assemblages with increasing peak metamorphic temperature reflect exsolution of pentlandite from a monosulfide solid solution ([Fe,Ni]1-xS) at temperatures <610 °C, and thermal decompositon of pentlandite into Ni-rich metal at temperatures >610 °C [5,6]. The PoPn grains within Jbilet Winselwan are consistent with the mildly heated Category B Fe-sulfides. However, the small pyrrhotite inclusions within the larger patches of pentlandite are similar to the "snowflake texture" in CM and CR chondrites described by Singerling and Brearley [7], who interpreted them as primary Fe-sulfides that condensed from the solar nebula prior to accretion. We therefore suggest that Jbilet Winselwan contains distinct lithologies that experienced varying degrees of metamorphism [2], including at least one lithology that was never heated to temperatures >300°C and still retains primary Fe-sulfide grains from the nebula. In Dho 1434 and PCA 02012, the Fe-sulfide textures are consistent with both the mildly heated Category B and strongly heated Category C sulfides. This does not appear to be attributable to brecciation as the Fe-sulfide grains of different categories are not associated with a particular lithology in either of the sections. Instead, the range of Fesulfide textures could either result from different Fe-sulfide compositions prior to heating, or indicate localized variations (on the order of 1000's of µm) in peak metamorphic temperature. The presence of PnM and PoPnM grains, where pentlandite has only partially broken down into metal, suggests the metamorphic event was too rapid to allow for equilibrium to be maintained. Rapid and potentially heterogeneous heating is more consistent with impact heating rather than heating via solar radiation or radiogenic decay. [ABSTRACT FROM AUTHOR]

We report the discovery of significant numbers (500) of large micrometeorites (>100 μm) from rooftops in urban areas. The identification of particles as micrometeorites is achieved on the basis of their compositions, mineralogies, and textures. All particles are silicate-dominated (S type) cosmic spherules with subspherical shapes that form by melting during atmospheric entry and consist of quench crystals of magnesian olivine, relict crystals of forsterite, and iron-bearing olivine within glass. Four particles also contain Ni-rich metal-sulfide beads. Bulk compositions are chondritic apart from depletions in the volatile, moderately volatile, and siderophile elements, as observed in micrometeorites from other sources. The reported particles are likely to have fallen on Earth in the past 6 yr and thus represent the youngest large micrometeorites collected to date. The relative abundance ratio of barred olivine to cryptocrystalline spherule types in the urban particles of 1.45 is shown to be higher than a Quaternary average of ∼0.9, suggesting variations in the extraterrestrial dust flux over the past 800 k.y. Changes in the entry velocities of dust caused by quasi-periodic gravitational perturbation during transport to Earth are suggested to be responsible. Variations in cosmic spherule abundance within the geologic column are thus unavoidable and can be a consequence of dust transport as well as major dust production events. [ABSTRACT FROM AUTHOR]

The origin of micrometeorites (MMs) from asteroids and comets is well-established, but the relative contribution from these two classes remains poorly resolved. Likewise, determining the precise origin of individual MMs is an open challenge. Here, cosmic-ray exposure ages are used to resolve the spatial origins of 12 MMs collected from urban areas and Antarctica. Their 26 Al and 10 Be concentration, produced during cosmic-ray irradiation in space, were measured by accelerator mass spectrometry. These data are compared to results from a model simulating the transport and irradiation of the MM precursors in space. This model, for the first time, considers a variety of orbits, precursor particle sizes, compositions and densities and incorporates non-isotropic solar and galactic cosmic-ray flux profiles, depth-dependent production rates, as well as spherical evaporation during atmospheric entry. While the origin for six MMs remains ambiguous, two MMs show a preferential tendency towards an origin in the Inner Solar System (Near Earth Objects to the Asteroid Belt) and four towards an origin in the Outer Solar System (Jupiter Family Comets to the Kuiper Belt). These findings challenge the notion that dust originating from the Outer Solar System is unlikely to survive long-term transport and delivery to the terrestrial planets. This article is part of the theme issue 'Dust in the Solar System and beyond'.