Search

Initial analyses showed that asteroid Ryugu's composition is close to CI (Ivuna-like) carbonaceous chondrites (CCs) - the chemically most primitive meteorites, characterized by near-solar abundances for most elements. However, some isotopic signatures (for example, Ti, Cr) overlap with other CC groups, so the details of the link between Ryugu and the CI chondrites are not yet fully clear. Here we show that Ryugu and CI chondrites have the same zinc and copper isotopic composition. As the various chondrite groups have very distinct Zn and Cu isotopic signatures, our results point at a common genetic heritage between Ryugu and CI chondrites, ruling out any affinity with other CC groups. Since Ryugu's pristine samples match the solar elemental composition for many elements, their Zn and Cu isotopic compositions likely represent the best estimates of the solar composition. Earth's mass-independent Zn isotopic composition is intermediate between Ryugu/CC and non-carbonaceous chondrites (NCs), suggesting a contribution of Ryugu-like material to Earth's budgets of Zn and other moderately volatile elements.

Fusion crusts form during the atmospheric entry heating of meteorites and preserve a record of the conditions that occurred during deceleration in the atmosphere. The fusion crust of the Winchcombe meteorite closely resembles that of other stony meteorites, and in particular CM2 chondrites, since it is dominated by olivine phenocrysts set in a glassy mesostasis with magnetite, and is highly vesicular. Dehydration cracks are unusually abundant in Winchcombe. Failure of this weak layer is an additional ablation mechanism to produce large numbers of particles during deceleration, consistent with the observation of pulses of plasma in videos of the Winchcombe fireball. Calving events might provide an observable phenomenon related to meteorites that are particularly susceptible to dehydration. Oscillatory zoning is observed within olivine phenocrysts in the fusion crust, in contrast to other meteorites, perhaps owing to temperature fluctuations resulting from calving events. Magnetite monolayers are found in the crust, and have also not been previously reported, and form discontinuous strata. These features grade into magnetite rims formed on the external surface of the crust and suggest the trapping of surface magnetite by collapse of melt. Magnetite monolayers may be a feature of meteorites that undergo significant degassing. Silicate warts with dendritic textures were observed and are suggested to be droplets ablated from another stone in the shower. They, therefore, represent the first evidence for intershower transfer of ablation materials and are consistent with the other evidence in the Winchcombe meteorite for unusually intense gas loss and ablation, despite its low entry velocity. Science and Technology Facilities Council (STFC): ST/V000799/1

Correction to: Nature Astronomy https://doi.org/10.1038/s41550-022-01846-1. Published online 12 December 2022.

Determining compositional trends among individual minerals is key to understanding the thermodynamic conditions under which they formed and altered, and is also essential to maximizing the scientific value of small extraterrestrial samples, including returned samples and meteorites. Here we report the chemical compositions of Fe-sulfides, focusing on the pyrrhotite-group sulfides, which are ubiquitous in chondrites and are sensitive indicators of formation and alteration conditions in the protoplanetary disk and in small Solar System bodies. Our data show that while there are trends with the at.% Fe/S ratio of pyrrhotite with thermal and aqueous alteration in some meteorite groups, there is a universal trend between the Fe/S ratio and degree of oxidation. Relatively reducing conditions led to the formation of troilite during: (1) chondrule formation in the protoplanetary disk (i.e., pristine chondrites) and (2) parent body thermal alteration (i.e., LL4 to LL6, CR1, CM, and CY chondrites). Oxidizing and sulfidizing conditions led to the formation of Fe-depleted pyrrhotite with low Fe/S ratios during: (1) aqueous alteration (i.e., CM and CI chondrites), and (2) thermal alteration (i.e., CK and R chondrites). The presence of troilite in highly aqueously altered carbonaceous chondrites (e.g., CY, CR1, and some CM chondrites) indicates they were heated after aqueous alteration. The presence of troilite, Fe-depleted pyrrhotite, or pyrite in a chondrite can provide an estimate of the oxygen and sulfur fugacities at which it was formed or altered. The data reported here can be used to estimate the oxygen fugacity of formation and potentially the aqueous and/or thermal histories of sulfides in extraterrestrial samples, including those returned by the Hayabusa2 mission and due to be returned by the OSIRIS-REx mission in the near future.

Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measured the mineralogy and bulk chemical and isotopic compositions of Ryugu samples. The samples are mainly composed of materials similar to those of carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37° ± 10°C, about 5.2 − 0.7 + 0.8 million (statistical) or 5.2 − 2.1 + 1.6 million (systematic) years after the formation of the first solids in the Solar System. After aqueous alteration, the Ryugu samples were likely never heated above ~100°C. The samples have a chemical composition that more closely resembles that of the Sun’s photosphere than other natural samples do.

The CM chondrites are samples of primitive water-rich asteroids formed during the early solar system. They record significant interaction between liquid water and silicate rock, resulting in a mineralogy dominated by hydrated secondary phases. Their similarity to the near-Earth asteroids Bennu and Ryugu – targets of current sample return space missions – makes the analysis of CM chondrites essential to the interpretation of these enigmatic bodies. Here, we review the aqueous alteration history of the CM chondrite group. Initially, amorphous silicate, metal and sulphides within the matrix were converted into Fe-cronstedtite and tochilinite. Later, the serpentinization of refractory coarse-grained inclusions led to the addition of Mg to the fluid phase. This is reflected in the cation composition of secondary phases which evolved from Fe-rich to Mg-rich. Although most CM meteorites are classified as CM2 chondrites and retain some unaltered anhydrous silicates, a few completely altered CM1s exist (∼4.2% [Meteoritical Bulletin, 2021]). The extent of aqueous alteration can be quantified through various techniques, all of which trace the progression of secondary mineralization. Early attempts employed petrographic criteria to assign subtypes – most notably the Browning and Rubin scales have been widely adopted. Alternatively, bulk techniques evaluate alteration either by measuring the ratio of phyllosilicate to anhydrous silicate (this can be with X-ray diffraction [XRD] or infrared spectroscopy [IR]) or by measuring the combined H abundance/δD compositions. The degree of aqueous alteration appears to correlate with petrofabric strength (most likely arising due to shock deformation). This indicates that aqueous alteration may have been driven primarily by impact rather than by radiogenic heating. Alteration extent and bulk O-isotope compositions show a complex relationship. Among CM2 chondrites higher initial water contents correspond to more advanced alteration. However, the CM1s have lighter-than-expected bulk compositions. Although further analyses are needed these findings could suggest either differences in alteration conditions or initial isotopic compositions – the latter scenario implies that the CM1 chondrites formed on a separate asteroid from the CM2 chondrites. Secondary phases (primarily calcite) act as proxies for the conditions of aqueous alteration and demonstrate that alteration was prograde, with an early period at low temperatures (

We provide the first detailed analysis of the carbonaceous chondrite Dhofar (Dho) 1988. This meteorite find was recovered in 2011 from the Zufar desert region of Oman and initially classified as a C2 ungrouped chondrite. Dho 1988 is a monomict breccia composed of millimetre-sized clasts, between which large (∼50–250 µm) intermixed sulphide-Ca-carbonate veins formed. It has high sulphide abundances (∼14 vol%), medium-sized chondrules (avg. 530 µm, N = 33), relatively low chondrule/CAI abundances ( Dho 1988 experienced advanced aqueous alteration [petrologic subtype 1.3 in the scheme of Howard et al. (2015)]. Alteration style and extent are similar to the CM chondrite group, with the matrix having been replaced by tochilinite-cronstedtite intergrowths and chondrules progressively pseudomorphed by phyllosilicates, sulphides and in one instance Ca-carbonates. However, departures from CM-like alteration include the replacement of chondrule cores with Al-rich, Na-saponite and upon which Cr-spinel and Mg-ilmenite grains precipitated. These late-stage aqueous alteration features are common among the CY chondrites. Fractures in Dho 1988 that are infilled by phyllosilicates, sulphides and carbonates attest to post-brecciation aqueous alteration. However, whether aqueous alteration was also active prior to brecciation remains unclear. Veins are polymineralic with a layered structure, allowing their relative chronology to be reconstructed: intermixed phyllosilicate-sulphide growth transitioned to sulphide-carbonate deposition. We estimate temperatures during aqueous alteration to have been between 110 °C Dho 1988 was later overprinted by thermal metamorphism. Peak temperatures are estimated between 700 °C and 770 °C, based on the thermal decomposition of phyllosilicates (both serpentine and saponite) combined with the survival of calcite. As temperatures rose during metamorphism the thermal decomposition of pyrrhotite produced troilite. Sulphur gas was liberated in this reaction and flowed through the chondrite reacting with magnetite (previously formed during aqueous alteration) to form a second generation of troilite grains. The presence of both troilite and Ni-rich metal in Dho 1988 (and other CY chondrites) demonstrate that conditions were constrained at the iron-troilite buffer.

A ∼175 µm refractory inclusion, A-COR-01 from one of the least altered carbonaceous chondrites, ALHA 77307 (CO3.0), has been found to bear unique characteristics that indicate that it is one of the first solids to have formed at the very birth of the solar system while isotopic reservoirs were still evolving rapidly. Its core is composed mainly of hibonite and corundum, the two phases predicted to condense first from a gas of solar composition, and like many common types of Calcium-, Aluminium-rich Inclusions (CAIs) is surrounded by a rim of diopside. Core minerals in A-COR-01 are very 16O-rich (Δ17OCore = −32.5 ± 3.3 (2SD) ‰) while those in the rim display an O isotopic composition (Δ17ORim = −24.8 ± 0.5 (2SD) ‰) indistinguishable from that found in the vast majority of the least altered CAIs. These observations indicate that this CAI formed in a very 16O-rich reservoir and either recorded the subsequent evolution of this reservoir or the transit to another reservoir. The origin of A-COR-01in a primitive reservoir is consistent with the very low content of excess of radiogenic 26Mg in its core minerals corresponding to the inferred initial 26Al/27Al ratio ((26Al/27Al)0 = (1.67 ± 0.31) × 10−7), supporting a very early formation before injection and/or homogenisation of 26Al in the protoplanetary disk. Possible reservoir evolution and short-lived radionuclide (SLRs) injection scenarios are discussed and it is suggested that the observed isotope composition resulted from mixing of a previously un-observed early reservoir with the rest of the disk., Geochimica et Cosmochimica Acta, 286, ISSN:0016-7037, ISSN:1872-9533

We present the first high-precision vanadium (V) isotope data for lunar basalts. Terrestrial magmatic rock measurements can display significant V isotopic fractionation (particularly during (Fe, Ti)oxide crystallisation), but the Earth displays heavy V (i.e. higher 51V/50V) isotopic compositions compared to meteorites. This has been attributed to early irradiation of meteorite components or nucleosynthetic heterogeneity. The Moon is isotopically-indistinguishable from the silicate Earth for many refractory elements and is expected to be similar in its V isotopic composition. Vanadium isotope ratios and trace element concentrations were measured for 19 lunar basalt samples. Isotopic compositions are more variable (∼2.5‰) than has been found thus far for terrestrial igneous rocks and extend to lighter values. Magmatic processes do not appear to control the V isotopic composition, despite the large range in oxide proportions in the suite. Instead, the V isotopic compositions of the lunar samples are lighter with increasing exposure age ( t e ). Modelling nuclear cross-sections for V production and burnout demonstrates that cosmogenic production may affect V isotope ratios via a number of channels but strong correlations between V isotope ratios and t e ⁎ [Fe]/[V] implicate Fe as the primary target element of importance. Similar correlations are found in the latest data for chondrites, providing evidence that most V isotope variation in chondrites is due to recent cosmogenic production via Fe spallation. Contrary to previous suggestions, there is no evidence for resolvable differences between the primary V isotopic compositions of the Earth, Moon, chondrites and Mars.

Chondritic meteorites, and especially the most volatile-rich chondrites, the carbonaceous chondrites, preserve a record of the solar protoplanetary disk dust component and how it has been changed both in the disk environment itself and in its asteroidal parent body. Here we review some of the key features of carbonaceous chondrites and report some new data on their organics component. These show that the nebula reached temperature of >10000C, but only very locally, to produce chondrules. Most meteoritic material underwent thermal and/or aqueous processing, but some retain delicate nebular components such as complex organic molecules and amorphous silicates.

We present spectral measurements of a suite of mineral mixtures and meteorites that are possible analogs for asteroid (101955) Bennu, the target asteroid for NASA's Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) mission. The sample suite, which includes anhydrous and hydrated mineral mixtures and a suite of chondritic meteorites (CM, CI, CV, CR, and L5), was chosen to characterize the spectral effects due to varying amounts of aqueous alteration and minor amounts of organic material. Our results demonstrate the utility of mineral mixtures for understanding the mixing behavior of meteoritic materials and identifying spectrally dominant species across the visible to near-infrared (VNIR) and thermal infrared (TIR) spectral ranges. Our measurements demonstrate that, even with subtle signatures in the spectra of chondritic meteorites, we can identify diagnostic features related to the minerals comprising each of the samples. Also, the complementary nature of the two spectral ranges regarding their ability to detect different mixture and meteorite components can be used to characterize analog sample compositions better. However, we observe differences in the VNIR and TIR spectra between the mineral mixtures and the meteorites. These differences likely result from (1) differences in the types and physical disposition of constituents in the mixtures versus in meteorites, (2) missing phases observed in meteorites that we did not add to the mixtures, and (3) albedo differences among the samples. In addition to the initial characterization of the analog samples, we will use these spectral measurements to test phase detection and abundance determination algorithms in anticipation of mapping Bennu's surface properties and selecting a sampling site.

The practical limitations inherent to human and robotic planetary exploration necessitate the development of specific protocols and methods. This non-standard approach requires testing and validation phases in order to optimise instrumental setups and improve data interpretation; this can occur prior to, during, or even after a mission. Flight instruments, and/or their spare models, may be evaluated using relevant terrestrial materials and/or locations. These materials are called analogues: “analogue sites” for large-scale locations, and “analogue samples” for smaller-scale materials. Depending on the scientific domain, the word “analogue” may carry different meanings but is invariably used to denote objects having compositions and/or physical properties similar to specific extraterrestrial objects. However, due to the variability in composition and properties of natural materials, there are always – inevitably – some differences between the analogue and the object(s) to which it refers. In analogue studies, it is, thus, important to focus on the specific properties that need to be imitated and to consider analogue properties rather than analogue sites or samples alone. Here, we introduce the concept of “functional analogues”. We first make an overview of the different types of analogues and sort them according to their utility. We then describe how different types of functional analogues can be used throughout the timeline of space missions, from the evaluation of different methods in the definition of a mission to understanding the results acquired by probes exploring extraterrestrial bodies. Finally, logical pathways are outlined that facilitate the selection of the best-suited functional analogue(s) according to their intended use and taking into account practical limitations., SCOPUS: ar.j, info:eu-repo/semantics/published

The last thirty years of cosmochemistry and planetary science have shown that one major Solar System reservoir is vastly undersampled in the available suite of extra-terrestrial materials, namely small bodies that formed in the outer Solar System (>10 AU). Because various dynamical evolutionary processes have modified their initial orbits (e.g., giant planet migration, resonances), these objects can be found today across the entire Solar System as P/D near-Earth and main-belt asteroids, Jupiter and Neptune Trojans, comets, Centaurs, and small (diameter < 200 km) trans-Neptunian objects. This reservoir is of tremendous interest, as it is recognized as the least processed since the dawn of the Solar System and thus the closest to the starting materials from which the Solar System formed. Some of the next major breakthroughs in planetary science will come from studying outer Solar System samples (volatiles and refractory constituents) in the laboratory. Yet, this can only be achieved by an L-class mission that directly collects and returns to Earth materials from this reservoir. It is thus not surprising that two White Papers advocating a sample return mission of a primitive Solar System small body (ideally a comet) were submitted to ESA in response to its Voyage 2050 call for ideas for future L-class missions in the 2035-2050 time frame. One of these two White Papers is presented in this article., Experimental Astronomy, 54 (2-3), ISSN:0922-6435, ISSN:1572-9508

Recovery and transport of returned samples is a crucial importance issue, because it has the fundamental duty to avoid forward contamination (i.e., contamination of the sample from the terrestrial environment) and, in the case of samples returned from a planetary body possibly hosting any life form, backward contamination (i.e., contamination of non-terrestrial organisms to humans). This chapter reviews how sample return missions dealt with this issue, through description of: i) landing sites and their influence on recovery and transport operations; ii) analysis of techniques and technologies used so far to transport extra-terrestrial samples from landing sites to curation facilities as well as among laboratory environments; iii) regulatory issues for packaging and transport of restricted samples, i.e., potentially hosting biological molecules.

The CM carbonaceous chondrite meteorites provide a record of low temperature aqueous reactions in the early solar system. A number of CM chondrites also experienced short-lived, post-hydration thermal metamorphism at temperatures of 200C to over 750C. The exact conditions of thermal metamorphism and the relationship between the unheated and heated CM chondrites are not well constrained but are crucial to understanding the formation and evolution of hydrous asteroids. Here we have used position-sensitive-detector X-ray diffraction (PSD-XRD), thermogravimetric analysis (TGA) and transmission infrared (IR) spectroscopy to characterise the mineralogy and water contents of 14 heated CM and ungrouped carbonaceous chondrites. We show that heated CM chondrites underwent the same degree of aqueous alteration as the unheated CMs, however upon thermal metamorphism their mineralogy initially (300 to 500C) changed from hydrated phyllosilicates to a dehydrated amorphous phyllosilicate phase. At higher temperatures (over 500C) we observe recrystallisation of olivine and Fe-sulphides and the formation of metal. Thermal metamorphism also caused the water contents of heated CM chondrites to decrease from 13 wt percent to 3 wt percent and a subsequent reduction in the intensity of the 3 micron feature in IR spectra. We estimate that the heated CM chondrites have lost 15 to 65 percent of the water they contained at the end of aqueous alteration. If impacts were the main cause of metamorphism, this is consistent with shock pressures of 20 to 50 GPa. However, not all heated CM chondrites retain shock features suggesting that some were instead heated by solar radiation. Evidence from the Hayabusa2 and ORSIRS-REx missions suggest that dehydrated materials may be common on the surfaces of primitive asteroids and our results will support upcoming analysis of samples returned from asteroids Ryugu and Bennu., Comment: Accepted for publication in Geochimica et Cosmochimica Acta

Sample return missions are among the most exciting space missions, providing both scientifically unique information and an unparalleled mechanism for the inspiring the public. Returned samples allow us to make critical ground truth measurements that can calibrate remote sensing measurements from spacecraft. Some scientific studies can only be done in laboratories rather than remotely or with landed spacecraft. Currently Europe does not have a facility suitable for the curation of returned extra-terrestrial samples. This not only hinders European Space Agency (ESA) missions, but also renders European institutions and Principal Investigators unable to fully participate as equal participants in missions implemented by other countries. The EURO CARES project was the first European attempt to review and evaluate the current state-of-the-art in curatorial practice for sample return missions, and determine the different and necessary steps in order to create a fully functional European Extra-terrestrial Sample Curation Facility to match the ESA requirements.

The 11th Symposium on Polar Science/Ordinary sessions: [OA] Antarctic meteorites, Poster presentations, Mon. 16 Nov. - Fri. 18 Dec.

International audience

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.

Primordial refractory silicates record evidence that aluminum-26 was efficiently mixed across different solar system sources., Understanding the spatial variability of initial 26Al/27Al in the solar system, i.e., (26Al/27Al)0, is of prime importance to meteorite chronology, planetary heat production, and protoplanetary disc mixing dynamics. The (26Al/27Al)0 of calcium-aluminum–rich inclusions (CAIs) in primitive meteorites (~5 × 10−5) is frequently assumed to reflect the (26Al/27Al)0 of the entire protoplanetary disc, and predicts its initial 26Mg/24Mg to be ~35 parts per million (ppm) less radiogenic than modern Earth (i.e., Δ′26Mg0 = −35 ppm). Others argue for spatially heterogeneous (26Al/27Al)0, where the source reservoirs of most primitive meteorite components have lower (26Al/27Al)0 at ~2.7 × 10−5 and Δ′26Mg0 of −16 ppm. We measured the magnesium isotope compositions of primitive meteoritic olivine, which originated outside of the CAI-forming reservoir(s), and report five grains whose Δ′26Mg0 are within uncertainty of −35 ppm. Our data thus affirm a model of a largely homogeneous protoplanetary disc with (26Al/27Al)0 of ~5 × 10−5, supporting the accuracy of the 26Al→26Mg chronometer.

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.

The aqueously altered CM carbonaceous chondrite meteorites can be used to investigate the nature and transport of volatiles in the early solar system. We present the preliminary results of an effort to collect 2D infrared (IR) spectral maps from the matrix and fine-grained rims (FGRs) of material that surround chondrules and inclusions in the Murchison CM2 meteorite using synchrotron IR micro-spectroscopy. The main features in mid-IR spectra of the matrix and FGRs occur at ∼3500 cm−1 and ∼1000 cm−1 and are attributed to OH/H2O and Si O bonds in phyllosilicates and anhydrous silicates. Minor features in the spectra are attributed to organic species (3000–2800 cm−1), CO2 (2400–2000 cm−1), and carbonates (1500–1380 cm−1). In both the matrix and FGRs we observe correlations between the OH/H2O and phyllosilicate/silicate features confirming that phyllosilicates dominate the mineralogy. This is consistent with previous studies showing that Murchison contains ∼70 vol% phyllosilicates following aqueous alteration on an asteroid parent body. The presence of anhydrous silicates in the matrix indicates that the alteration was heterogeneous at the micron-scale and that the reactions did not reach completion. We highlight a possible correlation between the phyllosilicates and organic species in the matrix, supporting the hypothesis that phyllosilicates may have played an important role in the formation and preservation of simple organic molecules and compounds. In the FGRs variations in the distribution of the phyllosilicate minerals cronstedtite and Mg-serpentine/saponite likely reflect differences in the local geochemical conditions during aqueous alteration on the asteroid.

We report new mineralogical, petrographic and noble gas analyses of the carbonaceous chondrite meteorites Y-82162 (C1/2ung), Y-980115 (CI1), Y-86029 (CI1), Y-86720 (C2ung), Y-86789 (C2ung), and B-7904 (C2ung). Combining our results with literature data we show that these meteorites experienced varying degrees of aqueous alteration followed by short-lived thermal metamorphism at temperatures of >500 °C. These meteorites have similar mineralogy, textures and chemical characteristics suggesting that they are genetically related, and we strongly support the conclusion of Ikeda (1992) that they form a distinct group, the CYs (“Yamato-type”). The CY chondrites have the heaviest oxygen isotopic compositions (δ17O ˜12‰, δ18O ˜22‰) of any meteorite group, high abundances of Fe-sulphides (˜10 ‒ 30 vol%) and phosphates, and contain large grains of periclase and unusual objects of secondary minerals not reported in other carbonaceous chondrites. These features cannot be attributed to parent body processes alone, and indicate that the CYs had a different starting mineralogy and/or alteration history to other chondrite groups, perhaps because they formed in a different region of the protoplanetary disk. The short cosmic-ray exposure ages (≤1.3 Ma) of the CY chondrites suggest that they are derived from a near-Earth source, with recent observations by the Hayabusa2 spacecraft highlighting a possible link to the rubble-pile asteroid Ryugu., Geochemistry, 79 (4)

We have analysed the petrography, major element abundances and bulk Al-Mg isotope systematics of 19 ferromagnesian chondrules from the CV3 chondrites Allende, Mokoia, and Vigarano, together with an Al-rich chondrule and refractory olivine from Mokoia. Co-variations of Al/Mg with Na/Mg and Ti/Mg in our bulk chondrules suggest their compositions are dominantly controlled by reworking of different proportions of chondrule components (e.g. mafic minerals and mesostatis); their precursors are thus fragments from prior generations of chondrules. Our samples show a range in fractionation corrected 26Mg/24Mg (Δ′26Mg) ∼ 60 ppm, relative to precisions 27Al/24Mg. The data can be used to calculate model initial 26Al/27Al, or (26Al/27Al)0, of the chondrule precursors. Our resolvably radiogenic chondrules yield model (26Al/27Al)0 ∼ 1–2 × 10−5, equivalent to model “ages” of precursor formation ≦1 Ma post CAI. However, many of our chondrules show near solar Δ′26Mg and no variability despite a range in 27Al/24Mg. This suggests their derivation either from younger precursor chondrules or open system behaviour once 26Al was effectively extinct ((26Al/27Al)0 < 0.8 × 10−5, given the resolution here). Evidence for the latter explanation is provided by marked rims of orthopyroxene replacing olivine, indicating reaction of chondrules with a surrounding silicate vapour. Concurrent isotopic exchange of Mg with a near chondritic vapour during late reworking could explain their isotopic systematics. One ferromagnesian object is dominated by a high Mg# olivine with elevated Ti and Ca abundances. This refractory olivine has a markedly negative Δ′26Mg = −16 ± 3 ppm (2se), reflecting its early removal (model age of 26Mg. If representative of the chondrule forming region, this grain defines a minimum interval of radiogenic ingrowth for CV chondrites commensurate with (26Al/27Al)0 > 3.4 ± 0.6 × 10−5. Overall, our samples record a sequence of events from the formation of ferromagnesian objects within 0.5 Ma of CAI to re-equilibration of chondrules and silicate vapour >2 Ma post CAI, assuming an initially homogeneous 26Al/27Al. Metamorphism on the asteroid parent body may have played a subsequent role in affecting Mg isotope composition, but we argue this had a minor influence on the observations here.

We analysed 44 fine-grained and scoriaceous micrometeorites. A bulk mid-IR spectrum (8–13 μm) for each grain was collected and the entire micrometeorite population classified into 5 spectral groups, based on the positions of their absorption bands. Corresponding carbonaceous Raman spectra, textural observations from SEM-BSE and bulk geochemical data via EMPA were collected to aid in the interpretation of mid-IR spectra. The 5 spectral groups identified correspond to progressive thermal decomposition. Unheated hydrated chondritic matrix, composed predominantly of phyllosilicates, exhibit smooth, asymmetric spectra with a peak at ∼10 μm. Thermal decomposition of sheet silicates evolves through dehydration, dehydroxylation, annealing and finally by the onset of partial melting. Both CI-like and CM-like micrometeorites are shown to pass through the same decomposition stages and produce similar mid-IR spectra. Using known temperature thresholds for each decomposition stage it is possible to assign a peak temperature range to a given micrometeorite. Since the temperature thresholds for decomposition reactions are defined by the phyllosilicate species and the cation composition and that these variables are markedly different between CM and CI classes, atmospheric entry should bias the dust flux to favour the survival of CI-like grains, whilst preferentially melting most CM-like dust. However, this hypothesis is inconsistent with empirical observations and instead requires that the source ratio of CI:CM dust is heavily skewed in favour of CM material. In addition, a small population of anomalous grains are identified whose carbonaceous and petrographic characteristics suggest in-space heating and dehydroxylation have occurred. These grains may therefore represent regolith micrometeorites derived from the surface of C-type asteroids. Since the spectroscopic signatures of dehydroxylates are distinctive, i.e. characterised by a reflectance peak at 9.0–9.5 μm, and since the surfaces of C-type asteroids are expected to be heated via impact gardening, we suggest that future spectroscopic investigations should attempt to identify dehydroxylate signatures in the reflectance spectra of young carbonaceous asteroid families.

We report the mineralogy, petrology, major, minor and trace element geochemistry, O and Si isotopes of a complex compound chondrule from the Allende meteorite. The chondrule contains zones of refractory (Ca, Al-rich) regions along with regions more similar to ferromagnesian chondrules. The bulk silicon isotopic composition of the object is δ30Si = –0.71 ± 0.03‰. The oxygen isotopic composition of the different phases within the compound chondrules fall along the Allende chondrule line and range from Δ17O – 12.5 to –2‰. Rare earth element abundances are enriched compared to chondritic levels by up to 15× CI, and show a nebular condensate signature with depletions in Eu and Yb. Our data show that the object evolved in oxygen isotopes in a nebular environment, most likely due to formation from a mixture of diverse components combined with interaction with nebular gas. In addition, differences in olivine composition across the inclusion suggest isotopically distinct oxygen regions also existed in dust in the protoplanetary disk. This object and other compound objects demonstrate that CAIs were present in the chondrule forming region, however they are not found in the majority of chondrules. We speculate that the bulk of the CAIs may have been added into the CV parent body after initial accretion of the body.

The rare CI carbonaceous chondrites are the most aqueously altered and chemically primitive meteorites but due to their porous nature and high abundance of volatile elements are susceptible to terrestrial weathering. The Ivuna meteorite, type specimen for the CI chondrites, is the largest twentieth-century CI fall and least affected by terrestrial alteration. The main mass of Ivuna (BM2008 M1) has been stored in a nitrogen atmosphere at least since 2008 and is the most pristine CI chondrite stone. We report the mineralogy, petrography and bulk elemental composition of BM2008 M1 and a second Ivuna stone (BM1996 M4) stored in air. Both Ivuna stones are breccias consisting of multiple rounded, phyllosilicate-rich clasts formed through aqueous alteration followed by impact processing. A polished thin section of BM2008 M1 analysed immediately after preparation was found to contain sulphate-bearing veins formed when primary sulphides reacted with oxygen and atmospheric water. A section of BM1996 M4 lacked veins but had sulphate grains on the surface recently formed (last 6 years). Differences in the extent of terrestrial alteration recorded by BM2008 M1 and BM1996 M4 probably reflect variations in the post-recovery curation history of the stones before entering the NHM collection, and indicate that where possible pristine samples of hydrated carbonaceous should be kept out of the terrestrial environment in a stable environment to avoid modification. The bulk elemental composition of the two Ivuna stones show some variability due to their heterogeneous nature but in general are similar to previous analyses of CI chondrites. We combine our elemental abundances with literature values to calculate a new average composition for the Ivuna meteorite, which is in good agreement with existing compilations of CI chondrites and the most recent solar photospheric abundances., Geochimica et Cosmochimica Acta (to be published)

EURO-CARES (European Curation of Astromaterials Returned from the Exploration of Space) was a three-year multinational project (2015-2017) funded by the European Commission's Horizon 2020 research programme. The objective of EURO-CARES was to create a roadmap for the implementation of a European Extra-terrestrial Sample Curation Facility (ESCF). This facility was intended to be suitable for the curation of samples from return missions from the Moon, asteroids, Mars, and other bodies of the Solar System. The EURO-CARES project covered five technical areas, led by scientists and engineers from institutions across Europe. 1. Planetary Protection: Planetary protection requirements and implementation approaches were assessed by experts and guided by international policy. Existing sterilization methods and techniques were reviewed. It was found that measures already employed for high containment biosafety facilities are suitable for a restricted sample return mission. However, the development of certain technologies, such as a 'double walled' isolator, remote manipulation, integration of scientific analytical instruments, etc. is also required. 2. Facilities and Infrastructure: Aspects from building design to storage of the samples were examined in the project. Requirements for the facility included that it contained a receiving laboratory, a cleaning and opening laboratory, a bio-assessment laboratory, a curation laboratory, and sample storage. Different design solutions were prepared in collaboration with architects. 3. Instruments and Methods: The methodology of characterisation of returned samples and the instrument base required at the ESCF were determined. The analyses provide an appropriate level of characterisation while ensuring minimal contamination and minimal alteration of the sample. When the samples are returned to Earth, several stages of studies would be conducted. 4. Analogue Samples: Analogue proxy samples were considered critical for testing sample handling, preparation techniques, storage conditions, planetary protection measures, as well as to validate new analytical methods. A list of useful analogue samples has been assembled. 5. Sample Transport: The Earth re-entry capsule from a sample return mission is targeted at a specific landing ellipse on Earth and must then be transported safely to the ESCF in an appropriate transport container. Lessons learned from past sample return missions show that preparations for recovery included: training of the recovery team for every possible scenario, possible temporary facilities nearby the landing site, environmental measurements and collection of samples at the landing site, added to this if necessary, would be planetary protection measures. In conclusion, long-term curation of extra-terrestrial samples requires that the samples are kept clean to minimize the risk of Earth contaminants, at the same time as contained, in case of a restricted sample return. This work describes a roadmap for a combined high containment and ultraclean European sample curation facility and the development of the necessary novel scientific and engineering methods and techniques., SCOPUS: cp.p, info:eu-repo/semantics/published

We report the discovery of a partially altered microchondrule within a fine-grained micrometeorite.This object is circular

This study explores the petrology of five giant (>400 μm) hydrated fine-grained micrometeorites from the Transantarctic Mountain (TAM) micrometeorite collection. For the first time, the extent and mechanisms of aqueous alteration in unmelted cosmic dust are evaluated and quantified. We use a range of criteria, previously defined for use on hydrated chondrites, including phyllosilicate fraction, matrix geochemistry and micro textures. Collectively, these micrometeorites represent ∼2.22 mm2 of intensely altered hydrated chondritic matrix (with petrologic subtypes of