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Tarda is an ungrouped, hydrated carbonaceous chondrite (C2‐ung) that was seen to fall in Morocco in 2020. Early studies showed that Tarda chemically resembles another ungrouped chondrite, Tagish Lake (C2‐ung), which has previously been linked to the dark D‐type asteroids. Samples of D‐type asteroids provide an important opportunity to investigate primitive conditions in the outer solar system. We show that Tarda contains few intact chondrules and refractory inclusions and that its composition is dominated by secondary Mg‐rich phyllosilicates (>70 vol%), carbonates, oxides, and Fe‐sulfides that formed during extensive water–rock reactions. Quantitative assessment of first‐order reversal curve (FORC) diagrams shows that Tarda's magnetic mineralogy (i.e., framboidal magnetite) is comparable to that of the CI chondrites and differs notably from that of most CM chondrites. These traits support a common formation process for magnetite in Tarda and the CI chondrites. Furthermore, Tarda's pre‐terrestrial paleomagnetic remanence is similar to that of Tagish Lake and samples returned from asteroid Ryugu, with a very weak paleointensity (<0.6 μT) suggesting that Tarda's parent body accreted more distally than that of the CM chondrites, possibly at a distance of >5.4–8.3 AU. An origin in the cold, outer regions of the solar system is further supported by the presence of distinct, porous clasts enriched in aliphatic‐rich organics that potentially retain a pristine interstellar composition. Together, our observations support a genetic relationship between Tarda and Tagish Lake. [ABSTRACT FROM AUTHOR]

On the microscale, the Winchcombe CM carbonaceous chondrite contains a number of lithological units with a variety of degrees of aqueous alteration. However, an understanding of the average hydration state is useful when comparing to other meteorites and remote observations of airless bodies. We report correlated bulk analyses on multiple subsamples of the Winchcombe meteorite, determining an average phyllosilicate fraction petrologic type of 1.2 and an average water content of 11.9 wt%. We show the elemental composition and distribution of iron and iron oxidation state are consistent with measurements from other CM chondrites; however, Winchcombe shows a low Hg concentration of 58.1 ± 0.5 ng g−1. We demonstrate that infrared reflectance spectra of Winchcombe are consistent with its bulk modal mineralogy, and comparable to other CM chondrites with similar average petrologic types. Finally, we also evaluate whether spectral parameters can estimate H/Si ratios and water abundances, finding generally spectral parameters underestimate water abundance compared to measured values. [ABSTRACT FROM AUTHOR]

A laboratory study was performed using the Visible Oxford Space Environment Goniometer in which the broadband (350–1250 nm) bidirectional reflectance distribution function (BRDF) of the Winchcombe meteorite was measured, across a range of viewing angles—reflectance: 0°–70°, in steps of 5°; incidence: 15°, 30°, 45°, and 60°; and azimuthal: 0°, 90°, and 180°. The BRDF dataset was fitted using the Hapke BRDF model to (1) provide a method of comparison to other meteorites and asteroids, and (2) to produce Hapke parameter values that can be used to extrapolate the BRDF to all angles. The study deduced the following Hapke parameters for Winchcombe: w = 0.152 ± 0.030, b = 0.633 ± 0.064, and hS = 0.016 ± 0.008, demonstrating that it has a similar w value to Tagish Lake (0.157 ± 0.020) and a similar b value to Orgueil (0.671 ± 0.090). Importantly, the surface profile of the sample was characterized using an Alicona 3D® instrument, allowing two of the free parameters within the Hapke model φ and θ¯, which represent porosity and surface roughness, respectively, to be constrained as φ = 0.649 ± 0.023 and θ¯ = 16.113° (at 500 μm size scale). This work serves as part of the characterization process for Winchcombe and provides a reference photometry dataset for current and future asteroid missions. [ABSTRACT FROM AUTHOR]

The highly hydrated, petrologic type 1 CM and CI carbonaceous chondrites likely derived from primitive, water‐rich asteroids, two of which are the targets for JAXA's Hayabusa2 and NASA's OSIRIS‐REx missions. We have collected visible and near‐infrared (VNIR) and mid infrared (MIR) reflectance spectra from well‐characterized CM1/2, CM1, and CI1 chondrites and identified trends related to their mineralogy and degree of secondary processing. The spectral slope between 0.65 and 1.05 μm decreases with increasing total phyllosilicate abundance and increasing magnetite abundance, both of which are associated with more extensive aqueous alteration. Furthermore, features at ~3 μm shift from centers near 2.80 μm in the intermediately altered CM1/2 chondrites to near 2.73 μm in the highly altered CM1 chondrites. The Christiansen features (CF) and the transparency features shift to shorter wavelengths as the phyllosilicate composition of the meteorites becomes more Mg‐rich, which occurs as aqueous alteration proceeds. Spectra also show a feature near 6 μm, which is related to the presence of phyllosilicates, but is not a reliable parameter for estimating the degree of aqueous alteration. The observed trends can be used to estimate the surface mineralogy and the degree of aqueous alteration in remote observations of asteroids. For example, (1) Ceres has a sharp feature near 2.72 μm, which is similar in both position and shape to the same feature in the spectra of the highly altered CM1 MIL 05137, suggesting abundant Mg‐rich phyllosilicates on the surface. Notably, both OSIRIS‐REx and Hayabusa2 have onboard instruments which cover the VNIR and MIR wavelength ranges, so the results presented here will help in corroborating initial results from Bennu and Ryugu. [ABSTRACT FROM AUTHOR]

Introduction: The Winchcombe meteorite fell on the 28th February, 2021 in Glouscestershire, UK [1]. Following the fall, samples were quickly collected by several members of the public and scientific community, allowing minimal terrestrial alteration to occur [1]. Based on its petrographic and chemical characteristics, the Winchcombe meteorite has been classified as a CM2 chondrite [1]. Four of the collected samples were analysed in the Mössbauer Spectroscopy laboratory for Earth and Environment (MoSEE) at the University of Stirling. This analysis gave information on the Winchcombe meteorite's iron mineralogy and oxidation states, which constrain alteration processes on its parent body. Method: A powder sample (BM.2022,M3-4;138.7 ± 5 mg) was placed into an acrylic glass sample holder (~1.3 cm circular diameter), loaded into a standard Wissenschaftliche Elektronik transmission spectrometer and measured at 3 different temperatures (room temperature, 77 and, 4.2 K). Low temperatures were achieved with an ICEoxford Dry ICE 4K closed-cycle helium gas cryostat. Spectra from the powder sample were evaluated with Recoil software using Lorentzian line profiles. Three rock chip samples (BM.2022,M1-1, BM.2022,M3-27 and BM.2022,M8-14) were measured without any further sample preparation at room temperature with a Miniturised Mössbauer spectrometer MIMOS II [2], which is set up in backscattering geometry. Spectra from this were evaluated with an in-house software routine (Mbfit) using Lorentzian line profiles. Mbfit is based on the least-squares minimization routine MINUIT. No f-factor correction was applied. Results: Spectra obtained from the rock chips indicated the presence of Mg- and Fe-rich serpentine (cronstedtite as the Fe-rich phase) and tochilinite. The same phases are seen in the room temperature transmission spectrum, along with the addition of two magnetite sextets (Fig. 1). As the temperature is decreased to 77 K, we see an additional sextet appear which could indicate the presence of an Fe,Ni sulfide (Fe2+). When the temperature is decreased further to 4.2 K, magnetic ordering occurs, resulting in a complex spectrum (Fig. 1). As the spectrum is complex, only locations of peaks characteristic for cronstedtite and Fe2+ were identified. Discussion: Temperature dependent transmission spectra are similar to other reported CM2 chondrites: Mighei [3], Murchison [3,4], Cold Bokkeveld [5], and Mukundpura [6,7]. As the spectra show no evidence of metallic Fe, it can be concluded that any metallic Fe originally present in these samples has been altered into tochilinite but, with the exception of minor magnetite, not into iron (hydr)oxides. Ferric iron is exclusively hosted in the clay mineral cronstedtite. Ferric iron abundances range from 25 to 30% of the total iron. This is lower than the values between 49 and 71 % reported for other CM2 chondrites [3,7-9], but these studies included spectral features that we have attributed to tochilinite in their calculations. Cronstedtite and serpentine formed from the aqueous alteration of olivine and pyroxene, while the initial presence of metallic iron might have played a role in the serpentinization process. [ABSTRACT FROM AUTHOR]

Introduction: The Winchcombe meteorite fell on 28th February 2021. At 21.54, the fireball was witnessed across the UK and recorded by 16 stations operated by the six meteor camera networks of the UK Fireball Alliance (UKFAll), allowing for calculation of its strewn field and main belt source [1]. The event was widely observed by eyewitnesses and soon attracted considerable media attention. The first carbonaceous chondrite recovered in the UK, Winchcombe joins a short list of only 17 British falls for which material is known [2]. Recovery: The recovered material was initially examined by team members in the field, conducting home visits to potential finds and systematically searching the local area. Permission for minimally destructive analysis on the material was sought from all landowners. The largest mass landed on the driveway and lawn of a fortunate family who collected much of the material with rubber gloves and a stainless steel knife, storing it in cleaned supermarket cottage cheese/cream pots, and polyethylene sandwich bags. Some material was collected as soon as 12 hours after the fall. Additional material was collected at this site by the recovery team who, using nitrile gloves, tweezers, paintbrushes and a toothbrush, transferred the material directly into conservation-grade storage materials (aluminium foil, glass vials and polyethylene sample bags) provided by the Natural History Museum (NHM) meteorite collection [3]. The largest single stone was found in a field of Rushbury House Farm, during a search by the recovery team on 6th March, and collected using nitrile gloves and geological sample bags. The quick response of UKFAll and associated media campaign was critical in raising awareness of how to identify a meteorite and how to handle specimens appropriately, resulting in many enquiries from the public. In total, approximately 602 g have been recovered from sites, such as driveways, gardens, fields and a solar farm, across an 8.5 km strewnfield. Immediate curation: The first samples were received and placed into a desiccator at the NHM on the 4th. In the following fortnight, 709 g of material (including mud containing small meteorite fragments), from six sites, had been visually examined and documented under the NHM object entry process to enable investigation prior to official acquistion. Samples were quickly curated, and are stored in glass vials with polyethylene lids, with fragments > ~100 mg individually weighed. Twenty-three of the largest fragments have been encased in high purity Al foil, placed in acid-free cardboard trays and stored in heat-sealed Escal enclosures with Mitsubishi RPK system oxygen scavengers. The largest piece is stored in an individual dessicator and is currently on display in the Vault gallery in the NHM. Two stones (BM.2022,M1-85 and BM.2022,M1-86) were taken directly from the field to the Open University to facilitate swift oxygen isotope measurements and are stored in a nitrogen cabinet in a class 100 cleanroom, under long-term loan from the NHM. Additionally, some material has been returned to the landowners for donation to local museums and thus not accessioned into the NHM collection. Tracking subsamples: Thanks to the generosity of the local community, a total of 518.3 g have now been donated into the NHM collection. Specimens have been designated according to their find location and collection date. The subsamples are tracked with sequential numbers, similar to the NASA curatorial numbering system. The subsample relationship of any given fragment can be provided upon request to the curator. Thus far, 47 loans, a total of approximately 80 g (including non-destructive analyes) and 20 polished sections have been made available to the Winchcombe consortium, covering analyses including bulk properties, mineralogy and petrology of the different lithologies, fusion crust, organics, magnetics, reflectance spectroscopy, and terrestrial alteration, as well as C, N, O, Ti, Cr, H, Ne isotopic systems [1, 3-16]. Long term curation: A nitrogen glove box (MBraun Labstar) with built-in microscope is on order and will be used for the permanent storage of the Winchcombe meteorite, funded by the Science and Technology Facilities Council (STFC), UK. Samples of the mud, lawn, and the original collecting vessels are all available as witness material. We welcome requests for scientific loans once the initial consortium work is published in a special issue of Meteoritics and Planetary Science. [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: Fusion crusts form during the atmospheric entry heating of meteorites and preserve a record of the conditions that occurred in the last few seconds of their deceleration in the atmosphere [1]. Although fusion crusts are ubiquitous they are rarely characterised and studied because they obscure the primary features of meteorites. Here we report the results of a study of the fusion crust of the Winchcombe CM2 chondrite. The Winchcombe meteorite fell at 21:54 hours on 28 February 2021 in Gloucestershire in the UK and was recovered over the next week. The fall was observed on UKFAll network cameras and recorded by CCTV. The meteoroid had a low entry velocity compared to other observed falls of 13.5 km/s. Study of the fusion crust reveals unique textural features that testify to previously unknown processes related to vigorous degassing of this intensely altered CM2 chondrite. Methods: Six polished blocks of Winchcombe were studied using backscattered electron imaging, elemental mapping, energy dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD) and micro-X-ray fluorescence (XRF). Apparent size distributions and abundances were obtained by threshold analysis using ImageJ. Results: The fusion crust consists of an inner thermally altered substrate and outer melted crust. The altered substrate exhibits unusually abundant dehydration cracks extending up to 5 mm into the meteorite. The crack network encompasses fragments up to 70 μm in diameter (dense rock equivalent) with increasing abundance with decreasing size. Loss of sheet-like habits for phyllosilicates and tochilinite testifies to progressive dehydration towards the exterior. The outer melted crust has a vesicular porphyritic texture with olivine phenocrysts and magnetite in a glassy mesostasis. Grain-size and magnetite abundance increase outwards similar to other CI/CM2 fusion crusts [2]. High Ni (<80 wt%) sulphide-metal droplets occur - often as menisci on vesicles. A magnetite rim occurs on the exterior surface and some vesicles, and include some tabular, rim-parallel magnetite crystals. Unique features in the fusion crust are oscillatory zoned olivine crystals, monolayers of magnetite and silicate warts. Monolayers form chains of magnetite crystals within the mesostasis that have tabular crystals similar to magnetite rims. EBSD data reveals [111] is parallel to the length of tabular crystals and is layer parallel in rims and monolayers. Oscillatory zoned crystals are equant with up to 4 Mg-rich zones. Silicate warts form lenticular features on the surface of the fusion crust and contain dendritic olivine - their compositions are, however, similar to the rest of the crust. Magnetite monolayers lie between warts and the underlying crust. Discussion: The unusualy high abundance of dehydration cracks suggests the tochlinite-rich matrix of the Winchcombe meteorite is particularly sensitive to dehydration, owing to the low decomposition temperature of this mineral (250oC [3]). Mechanical failure of the substrate, in part driven by gas pressure, is likely to inject large abundances of particulates into the meteoroid gas stream. Observations of episodic pulsed plasma in the trail of the fireball may be a phenomena associated with calving of the dehydrated substrate and generate thermal pulses explaining the presence of oscillatory zoning. Other features also are consistent with vigorous degassing. Magnetite monolayers appear to have formed as surface magnetite rims - owing to their similar alignment of tabular crystals. Trapping of surface magneite rims through collapse of melt protrusions is likely to explain how these layers become buried within the crust and is probably driven by perturbation of surface melt by rapid vesicle loss. Finally, silicate warts are likely to be droplets attached to the crust surface. Their dendritic textures suggest higher peak temperatures and strongly suggest they represent droplets removed from other stones in the shower. Warts represent the first discovery of intershower transport of ablation materials, possibly owing to enhanced ablation as a result of vigorous degassing. Implications: The fusion crust of the Winchcombe meteorite illustrates the complexity of processes affecting meteorites during atmospheric flight. Features such as magnetite monolayers and silicate warts have not previously been described, and may be unique to tochlinite-rich CM2 chondrites, which experience vigorous degassing. They may also allow ablation debris to be related to particular types of meteorite, thus providing a distributed record of the meteorite flux. Winchcombe underlines the utility of fusion crust, which should be routinely characterised in addition to meteorite interiors. [ABSTRACT FROM AUTHOR]

Introduction: The Winchcombe fall was observed on the 28th of February 2021 and ~600 g of meteoritic material was recovered over the following month [1]. Winchcombe is classified as a CM2 chondrite, though several lithologies are represented in the recovered material showing variations in petrologic type and degree of aqueous alteration. Analyses have been performed to gain a comprehensive understanding of its bulk material properties as part of a nationwide collaboration [e.g. 1, 2]. Here we discuss spectral analyses conducted at the Planetary Spectroscopy Facility at the University of Oxford. These measurements include visible to near-infrared (VNIR; 0.7-5 um) and mid-infrared (MIR; 5-25 um) reflectance measurements of two Winchcombe samples, as well as multi-angle VNIR Bidirectional Reflectance Distribution Function (BRDF) measurements made using the Visible Oxford Space Environment Goniometer [3]. The BRDF was measured for a powdered sample characterized in terms of porosity and surface roughness, and this dataset was used to determine the broadband albedo (0.35-1.25 um) of Winchcombe in [1]. IR Spectroscopy: Reflectance spectra of two samples (BM.2022,M1-91; BM.2022,M2-41) were measured with a Bruker VERTEX 70v Fourier Transform Infrared spectrometer, using a diffuse reflectance accessory under vacuum (~2 hPa) at 4 cm-1 resolution and an average of 150 scans calibrated to a diffuse gold target. The shortest wavelength range (0.8-2 μm) was acquired using an InGaAs detector coupled with a VIS/Quartz beamsplitter, while a RTDLaTGS detector and wide range beamsplitter were used for the near- and mid-infrared (2-25 μm). We correlate the spectra with modal mineralogy as determined using position-sensitive-detector X-ray diffraction (PSD-XRD) [1] and water abundance using thermogravimetric analysis (TGA) [2] for the same samples. A strong feature near 2.7 μm is attributed to OH-stretching, which indicates the aqueously altered mineralogy of the meteorite. It can also be affected by terrestrial alteration products and adsorbed water. Several studies [4,5,6] have used reflectance near this feature to estimate water content of asteroids and meteorites. We compared water abundances as measured through TGA to calculated water abundance using reflectance parameters and found reflectance measurements generally underestimated measured water abundance. The Christiansen feature (reflectance minimum) is located near 9 μm and indicates poor silicate polymerization. The shift in position between the two Winchcombe spectra (~0.1 um) correlates to slightly different olivine contents. The positions in the Winchcombe spectra are consistent with spectra of other CM chondrites [e.g. 7]. The transparency feature (reflectance maximum) near 11.5 um is another compositional indicator and has been shown to correlate to aqueous alteration in CM chondrites [7]. Shifts in this feature indicate BM.2022,M2-41 is more aqueously altered than BM.2022,M1-91. This is consistent with the determined mineralogy [1]. Bidirectional Reflectance Distribution Function (BRDF): The BRDF was measured for a powdered sample of the Winchcombe meteorite (BM.2022,M1-22) across 0 - 70° reflectance angles, in steps of 5°; at 15°, 30°, 45° and 60° incidence angles; and at 0°, 90° and 180° azimuthal angles. The dataset was then fitted using the Hapke BRDF model to enable constraints to be placed on the bulk scattering properties of the meteorite sample [8]. Importantly, the surface profile of the sample was characterized using an Alicona 3D® instrument. Therefore, two of the free parameters within the model - the filling factor, φ; and the RMS slope angle, θ - could be set, as φ = 0.65 ± 0.02 and θ = 16.11° (at 500 μm size-scale). This enabled w, b and hS to be set as the three open parameters within the Hapke BRDF model Least-Squares Levenberg-Marquardt fitting function. The best fit Hapke parameters were determined to be w = 0.152 ± 0.030, b = 0.633 ± 0.064 and hS = 0.016 ± 0.008. From the BRDF dataset, the broadband albedo value was calculated to be A = 4.09 ± 0.18 %, which can be converted to hemispheric albedo by multiplying by π [8]. As with the reflectance samples (previous section), modal mineralogy and water abundance were obtained for BM.2022,M1-22 [2]. Summary: VNIR and MIR spectroscopy are highly effective tools used in planetary remote sensing to determine the composition and physical properties of rocks and minerals. Here we are able to catalog several important spectral features and derived properties of the Winchcombe material for comparison to other meteorites and asteroids. The laboratory measured Winchcombe BRDF provides a reference photometric dataset for use in remote sensing studies of similar airless bodies, and by combining the IR spectra of the pristine Winchcombe material with other measurements on Earth, we can better understand and interpret data from Solar System objects and, in turn, learn more about their origins and evolution. [ABSTRACT FROM AUTHOR]

Introduction: Thermal and aqueous alteration are common occurrences in the lifetime of carbonaceous chondrites. These alteration processes must be well understood in order to unravel the history of these meteorites. Alteration leads to the breakdown, formation, and modification of several magnetic minerals, i.e., Fe-Ni metal, magnetite, and pyrrhotite [1-4]. Crucially, the bulk magnetic properties of carbonaceous chondrites are governed by the abundance, morphology, size, and chemistry of these phases. As such, their bulk magnetic properties can be used to recover novel information regarding their thermal and aqueous history. A particularly informative set of bulk magnetic measurements that can provide such insights are first order reversal curve (FORC) diagrams [5]. Here, we utilize this approach to investigate the parent body histories of a suite of CO, CI and CM chondrites. Methods: We measured FORC diagrams of: 2 CO chondrite powders (petrologic type 3.0 and 3.1); 2 CI chondrite powders (petrologic type 1.0); 2 chips of the ungrouped C2 chondrite WIS 91600 (petrologic type ~1.4); and 46 CM chondrite powders including 25 that experienced some degree of transient metamorphism (petrologic type 1.1 - 2.4; ranging from unheated to stage IV, <300 - >750 °C). These measurements were conducted using an alternating gradient magnetometer (AGM), and the FORC diagrams were processed using the VARIFORC approach in the FORCinel software package [6]. Principal component analysis (PCA) was used to identify variations in magnetic mineralogy in these carbonaceous chondrites [7]. Results: PCA of the FORC diagrams indicates that there are distinct and systematic variations in magnetic mineralogy with increasing aqueous alteration, and/or metamorphism of CM chondrites. These differences are reflected in the morphology of magnetite and the abundance of metal. Aqueous alteration: FORC-PCA of CI and ungrouped C2 chondrites plot in distinct principal component space compared to 'unheated' CM chondrites. FORC diagrams of CI and ungrouped C2 chondrites (petrologic types 1.0 - 1.4) indicate the presence of framboids and plaquettes of magnetite formed during alteration, while CM and CO chondrites of similar aqueous alteration extents contain isolated <0.1-5µm magnetite grains. Thermal alteration: FORC-PCA is able to distinguish 3 different stages of heating (I/II, III, IV) from 'unheated' CM chondrites. FORC diagrams reveal populations of magnetically interacting, < 0.1µm magnetite grains upon heating to stage I/II (150 - 500 °C, likely due to the thermal breakdown of tochilinite on heating), and the formation of metal from magnetite and Fe-sulfides upon heating to stage III & IV (>500 °C). Discussion: Differences in the morphology of the magnetite formed during aqueous alteration between carbonaceous chondrite groups is most readily attributed to changes in the chemistry of the ice accreted into the CM parent body compared to CI & C2-ung parent bodies. This could then feasibly facilitate the formation of magnetite framboids and plaquettes in the CI and C2-ung chondrites [8]. FORC-PCA also provides a unique perspective on the systematic changes in mineralogy associated with the formation and destruction of metal and magnetite during increased thermal alteration of the carbonaceous chondrites. This extensive bulk magnetism study demonstrates that FORC-PCA is a powerful tool for the analysis of carbonaceous chondrites. It is a quick, non-destructive technique which requires little to no sample preparation, making it ideal for the study of meteoritic material. FORC-PCA can classify the extent of heating among CM chondrites and can help identify the mineralogical and morphological changes that magnetic minerals experience during aqueous alteration. Crucially, this approach targets the magnetic mineralogy of a sample, so provides complementary information to that gleaned from other indicators of aqueous and thermal history, e.g., X-ray diffraction and spectroscopy (which target Si-O bonding) [2], thermogravimetric analysis (which targets H2O abundance) [9], and chemical composition [10]. As such, FORC diagrams can serve as a novel tool, which in combination with a suite of other techniques, will unlock a comprehensive understanding of the processes that modify chondritic asteroids. [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]

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]