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We report on the detection of primordial organic matter within the carbonaceous chondrite Maribo that is distinct from the majority of organics found in extraterrestrial samples. We have applied high-spatial resolution techniques to obtain C-N isotopic compositions, chemical, and structural information of this material. The organic matter is depleted in ^15N relative to the terrestrial value at around δ^15N ~ -200‰, close to compositions in the local interstellar medium. Morphological investigations by electron microscopy revealed that the material consists of µm- to sub-µm-sized diffuse particles dispersed within the meteorite matrix. Electron energy loss and synchrotron X-ray absorption near-edge structure spectroscopies show that the carbon functional chemistry is dominated by aromatic and C=O bonding environments similar to primordial organics from other carbonaceous chondrites. The nitrogen functional chemistry is characterized by C-N double and triple bonding environments distinct from what is usually found in ^15N-enriched organics from aqueously altered carbonaceous chondrites. Our investigations demonstrate that Maribo represents one of the least altered CM chondrite breccias found to date and contains primordial organic matter, probably originating in the interstellar medium., Finanziert über die DEAL-Vereinbarung mit Wiley 2019-2022.

Funding: This study was supported by urgency funding from the U.K.’s Science and Technology Facilities Council (STFC) as part of the project “Curation and Preliminary Examination of the Winchcombe Carbonaceous Chondrite Fall.” Additional work was funded by STFC through grants ST/N000846/1, ST/T002328/1, ST/T506096/1, and ST/W001128/1 (to L.D., M.R.L., and L.J.Ha.); ST/V000675/1 (to K.H.J. and R.H.J.); ST/P005225/1 (to R.T.); ST/S000348/1 (to M.V.G., P.J.W., and M.J.B.); ST/R00143X/1 (to J.B. and L.J.Hi.); ST/S000615/1 (to G.S.C.); ST/V000799/1 (to P.G.); and ST/V000888/1 (to T.E.). A.J.K. and H.C.B. acknowledge funding support from UK Research and Innovation (UKRI) grant MR/T020261/1. P.L.C. acknowledges funding support from UKRI grant MR/S03465X/1. K.H.J. acknowledges funding support from the Royal Society, grant URF\R\201009. L.J.Ha. and M.R.L. acknowledge funding from Natural Environment Research Council (NERC) National Environmental Isotope Facility (NEIF) grant no. 2406.0321. L.D., M.R.L., and L.J.Ha. acknowledge COVID-19 funding support from the University of Glasgow, UK. D.V. was supported in part by NASA cooperative agreement 80NSSC21M0073. P.P. and I.Sy. acknowledge funding from the VEGA agency, project no.1/0421/20. A.J.T.J. acknowledges support from the European Union and the State of Hungary, cofinanced by the European Regional Development Fund in the project of GINOP-2.3.2-15-2016-00009 “ICER.” P.M.S. acknowledges support from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 945298. FRIPON was initiated by funding from ANR (grant N.13-BS05-0009-03), carried out by the Paris Observatory, Muséum National d’Histoire Naturelle, Paris-Saclay University, and Institut Pythéas (LAM-CEREGE). FRIPON data are hosted and processed at Institut Pythéas SIP (Service Informatique Pythéas). The Desert Fireball Network team and Global Fireball Observatory are funded by the Australian Research Council (DP200102073). Direct links between carbonaceous chondrites and their parent bodies in the solar system are rare. The Winchcombe meteorite is the most accurately recorded carbonaceous chondrite fall. Its pre-atmospheric orbit and cosmic-ray exposure age confirm that it arrived on Earth shortly after ejection from a primitive asteroid. Recovered only hours after falling, the composition of the Winchcombe meteorite is largely unmodified by the terrestrial environment. It contains abundant hydrated silicates formed during fluid-rock reactions, and carbon- and nitrogen-bearing organic matter including soluble protein amino acids. The near-pristine hydrogen isotopic composition of the Winchcombe meteorite is comparable to the terrestrial hydrosphere, providing further evidence that volatile-rich carbonaceous asteroids played an important role in the origin of Earth's water. Publisher PDF

The isotopic and chemical properties of organic matter (OM) in extraterrestrial samples record a combination of presolar, nebular, parent-body, and terrestrial processes, which can be disentangled by high-spatial resolution studies [e.g., 1]. These studies have the advantage that they also allow for analysis of the petrographic relationship to the matrix and require only minimal chemical treatment. Here we have investigated OM properties within two recent observed falls, Tarda and Winchcombe, by combined “in-situ” techniques. Carbon and nitrogen isotopic compositions were studied by NanoSIMS. OM was sectioned by the focused ion beam (FIB) technique (Hitachi Ethos NX5000). Scanning Transmission X-Ray Microscopy (STXM) was performed at the I08 beamline of Diamond Light Source. Low-kV electron energy loss spectroscopy (EELS) in the vibrational and core loss regimes was performed with a monochromated, aberration-corrected Nion UltraSTEM 100MC. Nitrogen and carbon isotopic compositions of OM aggregates and nanoglobules in Tarda show a range of δ15N values from close-to-terrestrial to ~600‰ with close-to-terrestrial or slightly heavy δ13C values. Single hotspots reach >1000‰ in δ15N and ~80‰ in δ13C, but no negative δ15N values similar to Maribo OM have been detected [2]. STXM analyses at the C K-edge show that OM in Winchcombe is typical for OM in primitive meteorites, with strong absorption at the aromatic C=C (~285 eV) and the ketone/aldehyde (~286.6 eV) bands. The presence of reactive double and triple C-N bonding is a strong indicator that some OM is still pristine. [1] Van Kooten et al. GCA 2018, [2] Vollmer et al. SciRep 2020.

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Elephant Moraine (EET) 96029 is a CM carbonaceous chondrite regolith breccia with evidence for unusually mild aqueous alteration, a later phase of heating and terrestrial weathering. The presence of phyllosilicates and carbonates within chondrules and the fine-grained matrix indicates that this meteorite was aqueously altered in its parent body. Features showing that water-mediated processing was arrested at a very early stage include a matrix with a low magnesium/iron ratio, chondrules whose mesostasis contains glass and/or quench crystallites, and a gehlenite-bearing calcium- and aluminium-rich inclusion. EET 96029 is also rich in Fe,Ni metal relative to other CM chondrites, and more was present prior to its partial replacement by goethite during Antarctic weathering. In combination, these properties indicate that EET 96029 is one of the least aqueously altered CMs yet described (CM2.7) and so provides new insights into the original composition of its parent body. Following aqueous alteration, and whilst still in the parent body regolith, the meteorite was heated to ~400-600 °C by impacts or solar radiation. Heating led to the amorphisation and dehydroxylation of serpentine, replacement of tochilinite by magnetite, loss of sulphur from the matrix, and modification to the structure of organic matter that includes organic nanoglobules. Significant differences between samples in oxygen isotope compositions, and water/hydroxyl contents, suggests that the meteorite contains lithologies that have undergone different intensities of heating. EET 96029 may be more representative of the true nature of parent body regoliths than many other CM meteorites, and as such can help interpret results from the forthcoming missions to study and return samples from C-complex asteroids.

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On September 12, 2019 at 12:49:48 (UT) a bolide was observed by hundreds of eye-witnesses from the Netherlands, Germany, Belgium, Denmark and the UK. One day later a small meteorite stone was found by accident in Flensburg. The presence of short-lived cosmogenic radionuclides with half-lives as short as 16 days proves the recent exposure of the found object to cosmic rays in space linking it clearly to the bolide event. An exceptionally short exposure time of ∼5000 years was determined. The 24.5 g stone has a fresh black fusion crust, a low density of, Geochimica et Cosmochimica Acta, 293, ISSN:0016-7037, ISSN:1872-9533

Like most primitive carbonaceous chondrites, the CM chondrites experienced varying degrees of asteroidal aqueous alteration, which may have overprinted pre-accretionary processing. Several aqueous alteration scales for CM chondrites (and other carbonaceous chondrites) have been proposed based on alteration-dependent changes in various petrological and geochemical characteristics. Given the possibility that the intensity of aqueous alteration could be recorded in the primordial noble gas compositions, we test potential correlations between petrologic, geochemical and noble gas characteristics in a detailed study on 39 CM chondrites, including some of the most pristine CM chondrites identified to date, and 4 CM-related carbonaceous chondrites. We mainly compare our noble gas data with the alteration schemes proposed by Alexander et al. (2013) and Howard et al. (2015). In addition to the noble gas analyses, we determined the phyllosilicate fractions of 17 of the CM chondrites using X-ray diffraction (XRD) to complement missing data points in the Howard alteration scheme. The influence of post-hydration thermal modification on noble gases in CM chondrites is investigated by comparison of heated and unheated samples. Cosmic-ray exposure (CRE) ages are determined for all samples in this study as well as for 26 more samples based on CM chondrite literature noble gas data. The noble gas inventory in CM chondrites represents a mixture of cosmogenic, radiogenic, and abundant primordially trapped noble gases. Additionally, about 50 % of our CM bulk samples contain detectable solar wind (SW), which implies that many but not all CM chondrites are regolith breccias or carry SW from a pre-accretion irradiation phase. Aqueous alteration affects primordial noble gas abundances and elemental and isotopic compositions in CM chondrites. In particular, the process causes loss of an Ar-rich component, different in elemental and isotopic composition to known noble gas components. This component is lost during the early stages of aqueous alteration until complete degassing of its carrier material (possibly upon at least partial destruction) below petrologic type of ~1.5 on the Howard et al. (2015) scale. Likely, small amounts of Q gases were additionally released by aqueous alteration. Strong thermal modification at >750 °C results in a significant additional loss of noble gases, whereas peak temperatures, Geochimica et Cosmochimica Acta, 310, ISSN:0016-7037, ISSN:1872-9533