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In order to provide spectral ground truth data for remote sensing applications, we have measured mid-infrared spectra (2–18 µm) of three typical, well-defined lithologies from the Chelyabinsk meteorite that fell on February 15, 2013, near the city of Chelyabinsk, southern Urals, Russia. These lithologies are classified as (a) moderately shocked, light lithology, (b) shock-darkened lithology, and (c) impact melt lithology. Analyses were made from bulk material in four size fractions (0–25 µm, 25–63 µm, 63–125 µm, and 125–250 µm), and from additional thin sections. Characteristic infrared features in the powdered bulk material of the moderately shocked, light lithology, dominated by olivine, pyroxene and feldspathic glass, are a Christiansen feature (CF) between 8.5 and 8.8 µm; a transparency feature (TF) in the finest size fraction at ∼13 µm, and strong reststrahlen bands (RB) at ∼9.1 µm, 9.5 µm, 10.3 µm, 10.8 µm, 11.2–11.3 µm, 12 µm, and between 16 and 17 µm. The ranges of spectral features for the micro-FTIR spots show a wider range than those obtained in diffuse reflectance, but are generally similar. With increasing influence of impact shock from ‘pristine’ LL5 (or LL6) material (which have a low or moderate degree of shock) to the shock-darkened lithology and the impact melt lithology as endmembers, we observe the fading/disappearing of spectral features. Most prominent is the loss of a ‘twin peak’ feature between 10.8 and 11.3 µm, which turns into a single peak. In addition, in the ‘pure’ impact melt “endmember lithology” features at ∼9.6 µm and ∼9.1 µm are also lost. These losses are most likely correlated with decreasing amounts of crystal structure as the degree of shock melting increases. These changes could connect mid-infrared features with stages for shock metamorphism (Stoffler et al., 1991): Changes up to shock stage S4 would be minor, the shock darkened lithology could represent S5 and the impact melt lithology S6 and higher. Similarities of the Chelyabinsk spectra to those of other LL chondrites indicate that the findings of this study could be related to this group of meteorites in general.

On July 15, 2021, a huge fireball was visible over Poland. After the possible strewn field was calculated, the first and so far only sample, with a mass of 350 g, was discovered 18 days after the fireball event. The Antonin meteorite was found August 3, 2021, on the edge of a forest close to a dirt road near Helenow, a small suburb of the city of Mikstat. The rock is an ordinary chondrite breccia and consists of equilibrated and recrystallized lithologies. The boundaries between different fragments are difficult to detect, and the lithologies are of petrologic type 5 and type 4. The rock is moderately shocked (S4) and contains local impact melt areas and thin shock veins. The low-Ca pyroxene and olivine are equilibrated (Fs20.6 and Fa24.0, respectively), typical of L chondrites. The L chondrite classification is also supported by O isotope data and the results of bulk chemical analysis. The Ti isotope characteristics confirm that Antonin is related to the noncarbonaceous (NC) meteorites. One of the studied thin sections shows an unusual metal–chondrule assemblage, perhaps indicating that the metal in the chondrite is heterogeneously distributed, which is, however, not clearly visible in the element abundances.

Carbon is of fundamental interest for constraining the volatile element inventory of terrestrial planets. In some meteorites, like ureilites and enstatite chondrites, graphite is the major carbon-carrier. Here, we report the in-situ analyses of graphite in 19 ureilites, 11 enstatite chondrites, and 3 graphite-bearing clasts in ordinary chondrites by secondary ion mass spectrometry (SIMS). In coarse-grained ureilites the obtained carbon-compositions of graphite range from –9.2‰ to –0.1‰ (δ13C). The carbon-composition tends to be homogeneous within a sample and correlates with the Fa content in olivine. In contrast, fine-grained ureilites exhibit considerable intra-sample heterogeneity, and graphite tends towards 13C-enriched compositions (up to +10.4‰). Isotopic and petrographic differences are presumably a result of post-igneous shock processing, including annealing during impact smelting. Enstatite chondrites host a variety of graphite morphologies, occurring in two distinct assemblages: Silicate-associated graphite (SAG) and metal-associated graphite (MAG). These assemblages show diverging carbon-compositions: SAG consistently exhibits δ13C in a narrow range between –4‰ and +1‰, very similar to the bulk silicate Earth value. In contrast, diverse compositions from –19.7‰ to +13.7‰ were observed for MAG. These differences are likely pre-accretionary in origin and potentially point towards isotopically distinct precursors. If Earth accreted from enstatite-chondrite-like material, carbon potentially hosted by Earth's core may have an isotopically light signature when compared to the mantle. Although graphite-bearing clasts in unequilibrated ordinary chondrites (UOCs) are extraordinarily rare, these clasts are of particular interest as they might represent materials, not corresponding to known meteorites. Graphite from these clasts show coinciding carbon-compositions with a mean δ13C close to –1‰. Although the coinciding compositions might argue for a genetic relationship among the clasts, petrographic evidence suggests they have experienced distinct thermal histories.

On April 23, 2019, a meteorite fall occurred in Aguas Zarcas, Costa Rica. According to the Meteoritical Bulletin, Aguas Zarcas is a brecciated CM2 chondrite dominated by two lithologies. Our X‐ray computed tomography (XCT) results show many different lithologies. In this paper, we describe the petrographic and mineralogical investigation of five different lithologies of the Aguas Zarcas meteorite. The bulk oxygen isotope compositions of some lithologies were also measured. The Aguas Zarcas meteorite is a breccia at all scales. From two small fragments, we have noted five main lithologies, including (1) Met‐1: a metal‐rich lithology; (2) Met‐2: a second metal‐rich lithology which is distinct from Met‐1; (3) a brecciated CM lithology with clasts of different petrologic subtypes; (4) a C1/2 lithology; and (5) a C1 lithology. The Met‐1 lithology is a new and unique carbonaceous chondrite which bears similarities to CR and CM chondrite groups, but is distinct from both based on oxygen isotope data. Met‐2 also represents a new type of carbonaceous chondrite, but it is more similar to the CM chondrite group, albeit with a very high abundance of metal. We have noted some similarities between the Met‐1 and Met‐2 lithologies and will explore possible genetic relationships. We have also identified a brecciated CM lithology with two primary components: a chondrule‐poor lithology and a chondrule‐rich lithology showing different petrologic subtypes. The other two lithologies, C1 and C1/2, are very altered and possibly related to the CM chondrite group. In this article, we describe all the lithologies in detail and attempt a classification of each in order to understand the origin and the history of formation of the Aguas Zarcas parent body., ProjektDEAL, Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, Japan Society for the Promotion of Science http://dx.doi.org/10.13039/501100001691

WOS:000600550100030; International audience; Chromium (Cr) isotopes play an important role in cosmochemistry and planetary science because they are powerful tools for dating (Mn-53-Cr-53 short-lived chronometry), tracing (Cr-54 nucleosynthetic anomalies) the origins of the materials, and studying the processes involved in volatile element fractionation and planetary differentiation (Cr stable isotopic fractionation). To use Cr isotopes for these purposes, it is essential to precisely know the compositions of the various chondritic reservoirs. However, the Cr isotope composition of Rumuruti (R) chondrites remains unknown. Here, we report high-precision mass-independent (average 2SE uncertainty of similar to 0.02 and similar to 0.06 for epsilon Cr-53 and epsilon Cr-54, respectively; epsilon indicates 10,000 deviation) and mass-dependent (uncertainty of average 0.03 parts per thousand for delta Cr-53; .delta indicates 1000 deviation) Cr isotope data for 12 bulk R chondrites of petrologic types 3-6 (including R chondrite breccias), and one R chondrite-like clast (MS-CH) in the Almahata Sitta polymict ureilite. All the R chondrites show homogeneous bulk epsilon Cr-54 values, -0.06 +/- 0.08 (2SD), similar only to those of the Earth-Moon system and enstatite chondrites. This first epsilon Cr-54 dataset for R chondrites provides significant addition to the epsilon Cr-54-A, Delta O-17 diagram, and positions them as a potential endmember for planetary precursors. The R chondrites possess a higher Mn-55/Cr-52 of 0.68 +/- 0.04 relative to most of carbonaceous chondrites and higher epsilon Cr-53 values 0.23 +/- 0.05 (2SD) relative to most of chondrite groups. This likely results from the lower chondrule abundance in R chondrites compared to that of ordinary and enstatite chondrites. The stable Cr isotope composition of R chondrites is homogeneous with a delta Cr-53 = -0.12 +/- 0.03%e (2SD). Combined with previous data of other groups of chondrites, we show that the stable Cr isotopic composition of all the chondrites is homogeneous with delta Cr-53 of -0.12 +/- 0.04%e (2SD, N = 42) and is independent of the petrologic type and redox conditions. The lack of mass-dependent fractionation between all groups of chondrites suggests that the average chondrite delta Cr-53 value is also representative for the initial composition of all differentiated planets in the Solar System. Finally, the MS-CH clast in Almahata Sitta has a Cr isotopic composition (epsilon Cr-53 = 0.18 +/- 0.04, epsilon Cr-54 = 0.16 +/- 0.07, and delta Cr-53 = -0.11 +/- 0.05%e) that is consistent (within error) with it being an R chondrite-like clast. (C) 2020 Elsevier Ltd. All rights reserved.

The nature of oxygen-isotope heterogeneity in refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)] from weakly metamorphosed chondrites is one of the outstanding problems in cosmochemistry. To obtain insights into possible processes resulting in O-isotope heterogeneity of refractory inclusions, we investigated the mineralogy, petrology, and oxygen isotopic compositions of six CAIs and two AOAs and aqueously formed fayalite grains within the matrix of the H3.1 chondrite Northwest Africa (NWA) 3358. Most of the refractory inclusions studied appear to be unmolten solar nebula condensates; some may have experienced partial melting and/or high-temperature annealing. The NWA 3358 refractory inclusions nearly completely avoided metasomatic alteration on the H-chondrite parent body: nepheline grains replacing anorthite and/or melilite are either very minor or absent. Five out of eight refractory inclusions studied have heterogeneous O-isotope composition: Δ17O ranges from ∼− 25‰ to ∼3.5 ± 2‰ (2σ). This O-isotope heterogeneity appears to be mineralogically controlled with melilite and anorthite being systematically 16O-depleted compared to hibonite, spinel, Al,Ti-diopside, and forsterite all having similar solar-like Δ17O of ∼−24 ± 2‰. In contrast to NWA 3358 refractory inclusions, the previously studied AOAs and a fine-grained CAI from the LL3.00 chondrite Semarkona have uniform Δ17O of ∼−25‰ ( Itoh et al., 2007 , McKeegan et al., 1998 ). Because the mineralogically-controlled O-isotope heterogeneity in refractory inclusions from ordinary chondrites appears to correlate with petrologic type of a host meteorite experienced by aqueous alteration, we suggest O-isotope exchange in NWA 3358 CAIs and AOAs resulted from aqueous fluid-rock interaction on the H-chondrite parent asteroids. This is supported by the presence of 16O-depleted anorthite (Δ17O ∼ 3.5 ± 2‰) and aqueously formed fayalite similar depleted in 16O (Δ17O ∼ 4 ± 2‰). The Δ17O of NWA 3358 fayalite is comparable to that of magnetite and fayalite in Semarkona and other weakly metamorphosed L3 and LL3 chondrites ( Choi et al., 1998 , Doyle et al., 2015 ) suggesting similar Δ17O of aqueous fluids on the H, L, and LL chondrite parent asteroids.

Warkite (IMA 2013-129) is a new Sc-rich ultrarefractory mineral in the rhonite group of the sapphirine supergroup. It has a P 1 ¯ aenigmatite-type structure with a = 10.367 A, b = 10.756 A, c = 8.895 A, α = 106°, β = 96°, γ = 125°, and Z = 2, and general formula of Ca2(Sc,Ti,Al,Mg,Zr)6Al6O20. Warkite occurs as micrometer-sized crystals in eleven ultrarefractory Ca,Al-rich inclusions (UR CAIs) from the CM, CV, CO, and CH chondrites. In the CM, CO, and CV CAIs, warkite in the cores coexists with a Ti-rich oxide, either perovskite or kangite; the cores are generally mantled and rimmed by davisite and/or Sc-diopside. In the CH CAIs and one CO CAI, warkite in the cores coexists with perovskite and grossite; the cores are mantled by grossite ± gehlenite, and rimmed by low-Sc, Al-diopside. Therefore, there are two basic families of warkite-bearing inclusions, those containing Sc-rich clinopyroxene but no grossite and those containing grossite but no Sc-rich clinopyroxene. Scandian clinopyroxene in warkite-bearing CAIs generally formed by the reaction of warkite, which supplied most or all of the Sc, Ti, and Al, and a nebular gas that supplied much of the Ca and O and virtually all of the Mg and Si. The presence of Sc-rich clinopyroxenes may reflect exposure of some warkite-bearing CAIs to a dust-rich environment, which would enhance partial pressures of Si-, Mg-, and Ca-bearing species in the vapor and make it oxidizing relative to a dust-poor gas. Warkite in grossite-bearing inclusions is generally Ti3+-enriched relative to those in davisite-bearing inclusions, consistent with their formation in relatively dust-poor, more-reducing environments. Warkite compositions are sensitive to the presence or absence of spinel, melilite, Sc-rich clinopyroxenes, and grossite. Compositional variations of perovskite and warkite grains indicate a connection but, except for late-stage Fe exchange, they did not equilibrate with each other. The presence of at least two trends in Y-Sc among perovskites without corresponding trends in warkite suggests that at least some perovskite formed separately. Warkite-bearing CAIs from CM2s and CO3.0s are uniformly 16O-rich (Δ17O ∼ −23‰), whereas those from metamorphosed COs and CVs are isotopically heterogeneous: warkite, kangite, perovskite, melilite, and davisite are 16O-depleted to various degrees (Δ17O range from −22 to −2‰) relative to hibonite, spinel, and forsterite, all having 16O-rich compositions (Δ17O ∼ − 25 to −20‰). We infer that warkite-bearing CAIs originated in an 16O-rich nebular gas. Subsequently, CAIs from metamorphosed CVs and COs experienced O-isotope exchange with an 16O-depleted external reservoir, most likely aqueous fluids on the CV and CO chondrite parent asteroids; however, O-isotope exchange in the solar nebula cannot be excluded.

Volatile-rich, CI- and CM-like clasts occur in different brecciated achondrite and chondrite groups. The CI-like clasts in HEDs, polymict ureilites, as well as ordinary, CR, and CB chondrites have a similar mineralogy, indicating a similar alteration history. However, when viewed in detail, their mineral chemistry shows some minor differences between the clasts from different meteorite groups. For CM-like clasts found in HED meteorites, the clasts are, based on their mineralogy, clearly fragments of CM chondrites. To be able to decipher whether CI- (or CM-)like clasts from different meteorite groups are related to certain meteorite classes known to contain volatiles, we obtained D/H ratios of several clasts from the meteorite groups mentioned above and compared them with those of CI and CM chondrites as well as to unique carbonaceous chondrites such as Bells, Essebi, and Tagish Lake. Considering the δD-values, CM-like clasts in HEDs span a similar range compared to bulk values of CM chondrites, further indicating that CM-like clasts are fragments of CM chondrites. For CI-like clasts a clear distinction can be made: While CI-like clasts in HEDs and ordinary chondrites show a very similar range in their δD-signatures compared to “common” CI chondrites, meaning that these clasts are likely related to CI chondrites, the CI-like clasts in polymict ureilites are enriched in D up to 3000‰; a similarly high enrichment is found for the CI-like clasts in CR chondrites. Thus, although the CI-like clasts in ureilites and CR chondrites likely experienced similar alteration histories as the CI-like clasts found in the other meteorite types, these clasts probably formed in a different region than the CI chondrites and, thus, are more accurately referred to as C1 clasts. Overall, the existence and isotopic signatures of the C1 clasts in several meteorite groups proves the existence of additional primitive, volatile-rich material in the (early) Solar System besides the matter we study as the CI, CM, and CR chondrites. This material was distributed throughout the Solar System very early and might have played an important role for the volatile inventory of the terrestrial planets.

International audience; On April 23rd, 2019, the Aguas Zarcas meteorite fall occurred in Costa Rica. Because the meteorite was quickly recovered, it contains valuable extraterrestrial materials that have not been contaminated by terrestrial processes. Our X-ray computed tomography (XCT) and scanning electron microscopy (SEM) results on various pre-rain fragments from earlier work (Kerraouch et al., 2020; 2021) revealed several distinct lithologies: Two distinct metal-rich lithologies (Met-1 and Met-2), a CM1/2 lithology, a C1 lithology, and a brecciated CM2 lithology consisting of different petrologic types. Here, we further examined these lithologies in the brecciated Aguas Zarcas meteorite and report new detailed mineralogical, chemical, isotopic, and organic matter characteristics. In addition to petrographic differences, the lithologies also display different chemical and isotopic compositions. The variations in their bulk oxygen isotopic compositions indicate that the various lithologies formed in different environments and/or under diverse conditions (e.g., water/rock ratios). Each lithology experienced a different hydration period during its evolution. Together, this suggests that multiple precursor parent bodies may have been involved in these processes of impact brecciation, mixing, and re-assembly. The Cr and Ti isotopic data for both the CM1/2 and Met-1 lithology are consistent with those of other CM chondrites, even though Met-1 displays a significantly lower ε50Ti isotopic composition that may be attributable to sample heterogeneities on the bulk meteorite scale and may reflect variable abundances of refractory phases in the different lithologies of Aguas Zarcas. Finally, examination of the organic matter of the various lithologies also suggests no strong evidence of thermal events, but a short-term heating cannot completely be excluded. Raman parameters indicate that the peak temperature has been lower than that for Yamato-793321 (CM2, ∼400 °C). Considering the new information presented in this study, we now better understand the origin and formation history of the Aguas Zarcas daughter body.

In the last 7 years, three meteorites (Blaubeuren, Cloppenburg, and Machtenstein) found in Germany were identified as chondrites. Two of these rocks had been recovered from the impact sites decades ago but were not considered to be meteorites. The aim of this study is to fully characterize these three meteorites. Based on the compositional data on the silicates, namely olivine and low‐Ca pyroxene, these meteorites fit nicely within the H‐group ordinary chondrites. The brecciated texture of Blaubeuren and Cloppenburg (both H4‐5) is perfectly visible, whereas that of Machtenstein, officially classified as an H5 chondrite, is less obvious but was detected and described in this study. Considering chondrites in general, brecciated rocks are very common rather than an exception. The bulk rock degree of shock is S2 for Blaubeuren and Machtenstein and S3 for Cloppenburg. All samples show significant features of weathering. They have lost their original fusion crust and more than half (W3) or about half (W2‐3) of their original metal abundances. The oxygen isotope compositions of the three chondrites are consistent with those of other H chondrites; however, the Cloppenburg values are heavily disturbed and influenced by terrestrial weathering. This is supported by the occurrence of the very rare hydrated iron phosphate mineral vivianite (Fe2+Fe2+2[PO4]2·8H2O), which indicates that the chondrite was weathered in a very wet environment. The terrestrial ages of Blaubeuren (~9.2 ka), Cloppenburg (~5.4 ka), and Machtenstein (~1.8 ka) show that these chondrites are very similar in their degree of alteration and terrestrial age compared to meteorite finds from relatively wet terrestrial environments. They still contain abundant metal, although, as noted, the oxygen isotope data indicate substantial weathering of Cloppenburg. The bulk compositions of the three meteorites are typical for H chondrites, although terrestrial alteration has slightly modified the concentrations, leading in general to a loss of Fe, Co, and Ni due to preferential alteration of metals and sulfides. As exceptions, Co and Ni concentrations in Machtenstein, which has the shortest terrestrial age, are typical for H chondrites. The chemical data show no enrichments in Ba and Sr, as is often observed in different meteorite groups of desert finds., European Regional Development Fund http://dx.doi.org/10.13039/501100008530, Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

Deciphering aspects of the solar system’s formation process and the origin of planetary bodies can be achieved by examining primitive solar system materials, as these materials reflect the early solar system composition and may represent the building blocks of planetary bodies. Along these lines, knowing the original composition of carbonaceous chondrite meteorites is a valuable asset for determining the conditions in the parent bodies where they formed. Therefore, to determine the key characteristics of the parent bodies from which the carbonaceous chondrites and primitive materials are derived, we examined chemical and sulfur isotope compositions of sulfides in CM, CI and C2ung carbonaceous chondrites as well as from CM- and CI-like volatile-rich clasts; such an investigation allows us to explore the origin of these sulfides and to determine the primordial S composition of their parent body source region. In this study, sulfides from 7 CM, CI, and C2ung carbonaceous chondrites and 16 chondritic and achondritic breccias containing volatile-rich clasts were analyzed by electron microprobe and SIMS. Different sulfides were found, which shows evidence of different formation origins. Based on compositions and exsolution textures, we suggest that one fraction of the sulfides in both clasts and chondrites formed at high temperatures prior to incorporation into the parent body. The other sulfides most likely have a secondary origin and precipitated during fluid–rock interaction. Furthermore, differences in the S isotopic signature of the sulfides in chondrites correlate with the degree of aqueous alteration of the carbonaceous host rocks (CM or CI). Studying the sulfides of the volatile-rich clasts in brecciated chondrites and achondrites, a similar fractionation cannot be seen. Even though the mineralogy of CI chondrites and CI-like clasts is similar, the sulfides in CI chondrites appear to be enriched in heavy isotopes compared to those in the clasts (δ34S + 1‰ (CI) vs −2‰ (CI-like clast). This could have been caused by different alteration conditions, or it represents a different sampling reservoir. In this study a large S isotopic fractionation between pentlandite and pyrrhotite was found in large primarily formed sulfides showing exsolution textures, indicating that pentlandite prefers to incorporate light S isotopes. Considering the S isotope composition of the exsolved phase which can be found in CM- and CI-like clasts, the pristine δ34S value of the original monosulfide solid solution (mss) is estimated to be ∼−2‰. This value possibly resembles the sampling reservoir from which the sulfides formed, indicating that both CM- and CI-like clasts derived from a similar reservoir, and this reservoir is different from the formation reservoir of the CI chondrites.

The enriched basaltic (martian) shergottite Ksar Ghilane (KG) 002, discovered in 2010, is exceptionally rich in coexisting but discrete apatite and merrillite crystals. It has been selected to better constrain the formation conditions and post-crystallization processes, and thus the evolution of martian rocks based on Ca-phosphates. A petrological, chemical, chronological and microstructural approach using a series of high-spatial resolution techniques including Raman spectroscopy, electron microscopy (SEM, EPMA, CL-imaging) and secondary ion mass spectrometry (SIMS) analysis has been applied to a representative number of Ca-phosphate grains. Analytical results for apatite and merrillite reveal: (i) zoning in F, Cl, Br and I concentrations, (ii) elevated Cl concentrations in the range of ∼11,900–35,300 µg/g and halogen ratios, i.e., Cl/Br and Cl/I, as well as stable chlorine isotope composition, reported as δ37Cl values rel. to Standard Mean Ocean Chloride (SMOC, defined as 0‰) with a value of +0.67 ± 0.14‰ (1σ), distinguishing KG 002 phosphates from that of other enriched and depleted shergottites. The halogen and heavier δ37Cl record indicate a slightly higher degree of ∼3.5% assimilation of Cl-rich and isotopically heavier crustal reservoir on Mars when compared to other enriched shergottites. (iii) Structural investigations together with the chemical and petrological context of the grains confirm the occurrence of hydroxyl-poor merrillite, indicate weak if any alteration effects induced by metamictization, only minor structural modifications due to shock metamorphism, and absence of replacement reactions. Therefore, igneous crystallization of Ca-phosphates from a fractionated, hydrous and ferrous mantle source, rich in volatiles including the halogens and Na and lithophile rare earth-elements, and absence of interaction with crustal fluids/brines of the sample is deduced. (iv) The Pb isotopic composition of six apatite and three merrillite grains is highly unradiogenic and the 238U-206Pb record yields a phosphate crystallization time at 395 ± 240 Ma (2σ), which is similar to those of other enriched shergottites.

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

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 -9 m³/kg). The rock consists of relict chondrules and clusters of sulfide and magnetite grains set in a fine-grained matrix. The most abundant phases are phyllosilicates. Carbonates (~3.9 vol.%) occur as calcites, dolomites, and a Na-rich phase. The relict chondrules (often surrounded by sulfide laths) are free of anhydrous silicates and contain abundant serpentine. Lithic clasts are also surrounded by similar sulfide laths partly intergrown with carbonates. ⁵³Mn-⁵³Cr ages of carbonates in Flensburg indicate that brecciation and contemporaneous formation of the pyrrhotite-carbonate intergrowths by hydrothermal activities happened no later than 4564.6±1.0 Ma (using D'Orbigny as Mn-Cr anchor). This corresponds to 2.6±1.0 or 3.4±1.0 Ma after CAIs, depending on the exact age CAI age. This is the oldest dated evidence for brecciation and carbonate formation, which likely occurred during parent body growth and incipient heating due to ²⁶Al. The O isotope composition of Flensburg reveals that it plots at the ¹⁶O-rich end of the CM chondrite field and in the transition field to the CV-CK-CR chondrites. This is unexpected since the O-isotope compositions of strongly aqueously-altered chondrites are generally found to be at the ¹⁶O-poor end of the CM range. The mass-dependent Te isotopic compositionof Flensburg is slightly different from mean CM chondrites and is most similar to those of the ungrouped C2 chondrite Tagish Lake. On the other hand, the 50Ti and 54Cr isotope nomalies indicate that Flensburg is similar to CM chondrites, as do the ~10 wt.% H₂O. Yet, the bulk Zn, Cu, and Pb concentrations are about 30% lower than those of mean CM chondrites. The He, Ne and, Ar isotopes of Flensburg show no solar wind contribution; its trapped noble gas signature is similar to that of CMs with a slightly lower concentration of ²⁰Netr. Based on the bulk H, C and N elemental abundances and isotopic compositions, Flensburg is clearly unique among the analyzed chondrites as it has the lightest bulk H and N isotopic compositions of any type 1 or 2 chondrite. The number of soluble organic compounds in Flensburg is even lower than that of the brecciated CI chondrite Orgueil. The extraordinary significance of Flensburg is given by the observation that it represents the oldest chondrite sample, in which the contemporaneous episodes of aqueous alteration and brecciation are 81 perfectly visible. The characterization of a large variety of carbonaceous chondrites with different alteration histories is important for interpreting returned samples from the OSIRIS-REx and Hayabusa 2 missions.

Aubrites Peña Blanca Spring and Norton County were studied in the mid-infrared reflectance as part of a database for the MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) instrument on the ESA/JAXA BepiColombo mission to Mercury. Spectra of bulk powder size fractions from Peña Blanca Spring show enstatite Reststrahlen bands (RB) at 9 µm, 9.3 µm, 9.9 µm, 10.4 µm, and 11.6 µm. The transparency feature (TF) is at 12.7 µm, the Christiansen feature (CF) at 8.1–8.4 µm. Micro-FTIR of spots with enstatite composition in Norton County and Peña Blanca Spring shows four types: Types I and II are similar to the bulk powder spectra but vary in band shape and probably display axis orientation. Type III has characteristic strong RB at 9.2 µm, 10.4 µm, and 10.5 µm, and at 11.3 µm. Type IV is characterized by a strong RB at 10.8−11.1 µm. Types III and IV could show signs of incipient shock metamorphism. Bulk results of this study confirm earlier spectral studies of aubrites that indicate a high degree of homogeneity and probably make the results of this study representative for spectral studies of an aubrite parent body. Spectral types I and II occur in all mineralogical settings (mineral clasts, matrix, melt, fragments in melt vein), while spectral type III was only observed among the clasts, and type IV in the melt. Comparison with surface spectra of Mercury does not obtain a suitable fit, only type IV spectra from quenched impact glass show similarity, in particular the 11 µm feature. Results of this study will be available upon request or via the IRIS database (Münster) and the Berlin Emissivity Database (BED).

CM chondrites are complex impact (mostly regolith) breccias, in which lithic clasts show various degrees of aqueous alteration. Here, we investigated the degree of alteration of individual clasts within 19 different CM chondrites and CM-like clasts in three achondrites by chemical analysis of the tochilinite-cronstedtite-intergrowths (TCIs; formerly named “poorly characterized phases”). To identify TCIs in various chondritic lithologies, we used backscattered electron (BSE) overview images of polished thin sections, after which appropriate samples underwent electron microprobe measurements. Thus, 75 lithic clasts were classified. In general, the excellent work and specific criteria of Rubin et al. (2007) were used and considered to classify CM breccias in a similar way as ordinary chondrite breccias (e.g., CM2.2-2.7). In BSE images, TCIs in strongly altered fragments in CM chondrites (CM2.0-CM2.2) appear dark grayish and show a low contrast to the surrounding material (typically clastic matrix), and can be distinguished from TCIs in moderately (CM2.4-CM2.6) or less altered fragments (CM2.7-CM2.9); the latter are bright and have high contrast to the surroundings. We found that an accurate subclassification can be obtained by considering only the “FeO”/SiO2 ratio of the TCI chemistry. One could also consider the TCIs’ S/SiO2 ratio and the metal abundance, but these were not used for classification due to several disadvantages. Most of the CM chondrites are finds that have suffered terrestrial weathering in hot and cold deserts. Thus, the observed abundance of metal is susceptible to weathering and may not be a reliable indicator of subtype classification. This study proposes an extended classification scheme based on Rubin’s scale from subtypes CM2.0-CM2.9 that takes the brecciation into account and includes the minimum to maximum degree of alteration of individual clasts. The range of aqueous alteration in CM chondrites and small spatial scale of mixing of clasts with different alteration histories will be important for interpreting returned samples from the OSIRIS-REx and Hayabusa 2 missions in the future.

An important question regarding the formation of the solar system is how planetary bodies developed from dust and ice into the planets and planetary bodies. A particularly interesting topic is the thermal evolution of carbonaceous chondrites and volatile-rich clasts that could have originated from CM- and CI-like parent bodies. Two types of these volatile-rich clasts, which are a particular type of dark clasts, can be found. These clasts are mineralogically very similar to CM and CI chondrites and can occasionally be found in achondritic meteorites. Mineral assemblages suggest that both CM and CI chondrites as well as volatile-rich clasts experienced low peak temperatures. However, these mineral assemblages only offer large estimated temperature ranges to describe the thermal history of CM and CI chondrites, and the thermal history of volatile-rich clasts has not been previously described. In this study, to gain a better understanding of the thermal history of both CM and CI chondrites and volatile-rich clasts, we estimated peak temperatures of 30 volatile-rich clasts (16 CI-, and 14 CM-like) in 10 different host meteorites (4 polymict ureilites, 5 polymict eucrites and 1 howardite) by Raman carbon thermometry. An automated method was developed in order to describe over 4000 collected Raman spectra using four pseudovoigt functions. The full width half maximum (FWHM) of the D1-band was then used to calculate peak temperatures. Results were then compared to Raman data of 8 different well-studied carbonaceous chondrites (including CI and CM chondrites) to evaluate the suggestion that volatile-rich clasts are composed of similar material to the equivalent CI and CM chondrites. Our results show that the peak temperatures experienced by CI-like clasts range between 30–110 °C with an average of about 65 ± 25 °C; the peak temperatures experienced by CM-like clasts range from 50 to 110 °C with an average of about 70 ± 25 °C. Six of the 8 studied carbonaceous chondrites (CM, CI, CR or C2ungr) also plot in the same low-temperature range between 50 °C and 75 °C and can thus be considered to have formed under similar temperature conditions as the volatile-rich clasts. This is in agreement with previous suggestions, based on their mineral compositions that volatile-rich clasts and CI and CM carbonaceous chondrites are composed of similar materials. The peak temperatures for carbonaceous chondrites determined in this study considerably reduce the range of temperature estimates proposed previously for these chondrites by different methods. By highlighting the ability of our methodology to evaluate data in an automated way, this study shows that Raman carbon thermometry is a good analytical technique for obtaining information about peak temperatures in small and delicate samples.

After accretion of meteorite parent bodies, larger and smaller collisions have led to significant modifications of these bodies. Involved processes include excavation of material, thermal metamorphism, melting, mixing of different materials, re-accretion, and re-lithification. All these processes can be repeated several times. In this study polished thin sections (PTS) of 2280 chondrites (1193 H, 947 L, and 140 LL chondrites) were investigated in order to obtain the abundance of brecciated rocks among the ordinary chondrites. In addition, we have determined the abundance and characteristics of shock vein-bearing H, L, and LL chondrites and of impact melt rock clasts. We also recognized xenolithic components based on O-isotope studies. Noble gas data were considered in order to detect regolith breccias and to discuss late impact histories. The investigation of 2280 samples shows that 23% (276 of 1193) of the H chondrites, 23% (220 of 947) of the L chondrites, and 79 % (110 of 140) of the LL chondrites are brecciated. Considering the heavily-brecciated LL chondrites in 63 of the 140 chondrites (45%) shock veins were clearly detected. 57 of these 63 chondrites are brecciated rocks. The investigation of the H and L chondrites has shown that about 26% (310 of 1193) of the H chondrites and 40% (379 of 947) of the L chondrites contain shock veins. In our data-set 20% of the H chondrites and 8.3% of the LL chondrites, but only 3.0% of the L chondrites contain solar noble gases. Remarkably, about 62% of all brecciated H chondrites (with noble gases analyzed) contain solar noble gases compared to only around 11% and 10% of the brecciated L and LL chondrites, respectively. The identification of xenolithic clasts (e.g., CI-, CM-, and ureilite-like lithologies) in primitive type 3 chondrites indicates simultaneous accretion of clasts and chondrules. These clasts must have been formed early within the first 2 Ma on subsequently-destroyed precursor, first generation parent bodies. The formation of complex breccias witnesses the collisions between asteroids of very different lithologies and heritage. Although the onion-shell configuration of primordial parent bodies is necessary in order to form the chondrites with different degrees of metamorphic overprint (petrologic types 3–6) subsequent catastrophic fragmentation and reassembly to form asteroids with a rubble-pile structure are required to explain certain features discussed in this work. However, distinct peaks in the cosmic ray exposure age distributions indicate that not too many impacts in the last 100 Ma were responsible to deliver the majority of the ordinary chondritic meteoroids to Earth. Yet, this certainly does not tell anything about the number of “last-generation” parent bodies that exist in the asteroid belt, since S-type asteroids are the most abundant type of asteroid in the inner main belt and thought to be the parent bodies of ordinary chondrites.

Understanding the relationships between and among chondritic components of various chondrite groups is of prime importance for deciphering the dynamics of material transport and planetary accretion in the early Solar System. Here we obtain insights into these processes and the reservoirs present by investigating the nucleosynthetic Ti isotopic signatures of individual Ca,Al-rich inclusions (CAIs) and Na–Al-rich chondrules from ordinary and CO chondrites. This specific type of chondrule is of interest as it is thought to have incorporated refractory, CAI-like material as precursors. Our data show that CAIs from ordinary and CO chondrites exhibit 50Ti excesses that are indistinguishable from CV CAIs, and thus indicate a common source reservoir for refractory inclusions in ordinary, CO, and CV chondrites. Na–Al-rich chondrules from CO chondrites also show 50Ti excesses, indicating the presence of CAIs from this reservoir in the precursor materials of CO chondrules. In contrast, Na–Al-rich chondrules from ordinary chondrites show no 50Ti excesses and are indistinguishable from the bulk values for ordinary chondrites. Thus, known CAIs cannot have been the refractory precursor of the Na–Al-rich chondrules in ordinary chondrites. Consequently, within the accretion region of the ordinary chondrites, two different types of refractory components must have existed: (1) a 50Ti-enriched refractory component that is present as CAIs and either arrived at the accretion region of the ordinary chondrites after chondrule formation, or was only present in insignificant amounts, and (2) another type of refractory material without a 50Ti excess, which was involved as precursor in the chondrule formation process. Our data thus imply that refractory components with condensation signatures must have formed in at least two isotopically distinct nebular regions. These may be related to non-carbonaceous and carbonaceous source regions, that is, the inner and outer Solar System, divided by the early formation of Jupiter.

The complimentary chemical composition of chondrules and matrix has so far only been studied in carbonaceous chondrites. We have extended these studies to the matrix-rich Rumurutis We have determined the chemical composition of 27 bulk chondrules and 100 matrix spots in unequilibrated fragments of three different Rumuruti (R) chondrites (NWA 2446, NWA 753, Hughes 030). Also, the bulk chemical composition of NWA 753 was determined. Bulk R chondrites have about CI chondritic (= solar) ratios of Fe/Mg (1.89), Al/Ti (18.62), and Al/Ca (0.94), while chondrules and matrix are complementary to each other. Mean Fe/Mg ratios in chondrules are 0.43 (NWA 2446), 0.36 (NWA 753), and 0.34 (Hughes). Chondrules are depleted in Fe, while matrices are enriched in Fe with respective values of 2.59, 2.45, and 2.39. Bulk Fe/Mg ratio of NWA 753, the only sample which is unaffected by terrestrial weathering, is reproduced by careful mass balance calculations using compositions and abundances of chondrules, matrix and sulphides from the same thin section. Refractory element ratios are also complementary: Al/Ti and Al/Ca are sub-chondritic in chondrules (Al/Ti: 10.43 in NWA 753, 12.24 in NWA 2446 and 11.47 in Hughes 030; Al/Ca: 0.66 in NWA 2446, 0.53 in NWA 753, and 0.46 in Hughes 030), while matrices generally have super-chondritic Al/Ca and Al/Ti ratios (Al/Ti: 28.00 in NWA 2446, 23.20 in NWA 753 and 19.00 in Hughes 030; Al/Ca: 2.30 in NWA 2446, 1.90 in NWA 753, and 0.41 in Hughes 030). Calcium is enriched in the Hughes 030 matrix due to terrestrial weathering. These complementary element ratios and the CI chondritic bulk strongly suggest a common reservoir from which all R chondrite components formed, similar to carbonaceous chondrites. Further, super-chondritic Si/Mg, and CI chondritic Fe/Mg ratios in bulk R chondrites require addition of Si to their reservoir, most probably before chondrule formation.

Mars probably accreted within the first 10 million years of Solar System formation and likely underwent magma ocean crystallization and crust formation soon thereafter. To assess the nature and timescales of these large-scale mantle differentiation processes we applied the short-lived 182 Hf– 182 W and 146 Sm– 142 Nd chronometers to a comprehensive suite of martian meteorites, including several shergottites, augite basalt NWA 8159, orthopyroxenite ALH 84001 and polymict breccia NWA 7034. Compared to previous studies the 182 W data are significantly more precise and have been obtained for a more diverse suite of martian meteorites, ranging from samples from highly depleted to highly enriched mantle and crustal sources. Our results show that martian meteorites exhibit widespread 182 W/ 184 W variations that are broadly correlated with 142 Nd/ 144 Nd, implying that silicate differentiation (and not core formation) is the main cause of the observed 182 W/ 184 W differences. The combined 182 W– 142 Nd systematics are best explained by magma ocean crystallization on Mars within ∼20–25 million years after Solar System formation, followed by crust formation ∼15 million years later. These ages are indistinguishable from the I–Pu–Xe age for the formation of Mars' atmosphere, indicating that the major differentiation of Mars into mantle, crust, and atmosphere occurred between 20 and 40 million years after Solar System formation and, hence, earlier than previously inferred based on Sm–Nd chronometry alone.

On February 6, 2016 at 21:07:19 UT, a very bright fireball was seen over the eastern part of Denmark. The weather was cloudy over eastern Denmark, but many people saw the sky light up-even in the heavily illuminated Copenhagen. Two hundred and thirty three reports of the associated sound and light phenomena were received by the Danish fireball network. We have formed a consortium to describe the meteorite and the circumstances of the fall and the results are presented in this paper. The first fragment of the meteorite was found the day after the fall, and in the following weeks, a total of 11 fragments with a total weight of 8982 g were found. The meteorite is an unbrecciated, weakly shocked (S2), ordinary H chondrite of petrologic type 5/6 (Bouvier et al. 2017). The concentration of the cosmogenic radionuclides suggests that the preatmospheric radius was rather small similar to 20 cm. The cosmic ray exposure age of Ejby (83 +/- 11 Ma) is the highest of an H chondrite and the second highest age for an ordinary chondrite. Using the preatmospheric orbit of the Ejby meteoroid (Spurny et al. 2017) locations of the recovered fragments, and wind data from the date of the fall, we have modeled the dark flight (below 18 km) of the fragments. The recovery location of the largest fragment can only be explained if aerodynamic effects during the dark flight phase are included. The recovery location of all other fragments are consistent with the dark flight modeling.

The Ureilite Parent Body (UPB) was a C-rich planetary embryo disrupted by impact. Ureilites are fragments of the UPB mantle and among the most numerous achondrites. Zinc isotopic data are presented for 26 unbrecciated ureilites and a trachyandesite (ALM-A) from the same parent body. The δ66Zn values of ureilites range from 0.40 to 2.71‰ including literature results. Zinc isotopic compositions do not correlate with the compositions of olivine cores, with C and O isotopic compositions, with Zn abundances, nor with shock grades. The wide range of δ66Zn displayed by the ureilites is chiefly explained by evaporation processes that took place during the catastrophic breakup of the UPB. During breakup, the high temperatures of the UPB mantle allowed Zn to evaporate, regardless of the intensity the shock suffered by the ureilitic debris. For the most shocked of them, post-shock heating permitted greater evaporation, and heavier Zn isotopic compositions. The surface of the UPB was certainly much colder than the mantle before the breakup. Therefore, crustal rocks were probably less prone to Zn evaporation. ALM-A, the sole crustal rock analyzed at present, has a δ66Zn value (0.67‰) significantly higher than those of regular chondrites. This result indicates that its mantle source displayed already non-chondritic Zn isotopic compositions before the breakup of the UPB.

International audience; Based on the high abundance of fine-grained material and its dark appearance, NWA 11024 was recognized as a CM chondrite, which is also confirmed by oxygen isotope measurements. But contrary to known CM chondrites, the typical phases indicating aqueous alteration (e.g., phyllosilicates, carbonates) are missing. Using multiple analytical techniques, this study reveals the differences and similarities to known CM chondrites and will discuss the possibility that NWA 11024 is the first type 3 CM chondrite. During the investigation, two texturally apparent tochilinite-cronstedtite intergrowths were identified within two thin sections. However, the former phyllosilicates were recrystallized to Fe-rich olivine during a heating event without changing the textural appearance. A peak temperature of 400-600 degrees C is estimated, which is not high enough to destroy or recrystallize calcite grains. Thus, calcites were never constituents of the mineral paragenesis. Another remarkable feature of NWA 11024 is the occurrence of unknown clot-like inclusions (UCLIs) within fine-grained rims, which are unique in this clarity. Their density and S concentration are significantly higher than of the surrounding fine-grained rim and UCLIs can be seen as primary objects that were not formed by secondary alteration processes inside the rims. Similarities to chondritic and cometary interplanetary dust particles suggest an ice-rich first-generation planetesimal for their origin. In the earliest evolution, NWA 11024 experienced the lowest degree of aqueous alteration of all known CM chondrites and subsequently, a heating event dehydrated the sample. We suggest to classify the meteorite NWA 11024 as the first type 3 CM chondrite similar to the classification of CV3 chondrites (like Allende) that could also have lost their matrix phyllosilicates by thermal dehydration.

The asteroid 4 Vesta is the second most massive planetesimal in the Solar System and a rare example of a planetary object that possibly can be linked to a specific group of differentiated meteorites, the howardite–eucrite–diogenite suite. The 182Hf–182W chronometry of individual zircon grains from six basaltic eucrites revealed distinct growth episodes ranging from 4532 − 11 / + 6 Ma to 4565.0 ± 0.9 Ma and constrains the early thermal history of 4 Vesta, indicating that its mantle generated basaltic melts for at least 35 million years (Myr). Initially, the energy needed for melting was provided by decay of short-lived isotopes, mostly 26Al. The long duration of magmatism despite the short lifetime of 26Al implies that the asteroid must have accreted within the first ∼4 Myr of Solar System formation, similar to the formation of iron meteorite parent bodies, and that its interior must have been thermally well insulated by an early-formed crust that prevented heat loss.

Al-rich objects (Ca,Al-rich inclusions (CAIs), Al-rich chondrules, Al-rich fragments) occur in all chondrite classes. These objects can be centimeter-sized in CV3 carbonaceous chondrites, but they are generally much smaller in other chondrite groups and classes. Within the ordinary chondrites, most Al-rich objects are chondrules that vary from Ca- to Na-rich. Here, we have investigated the mineralogy and major element chemistry of 32 Na-rich chondrules and 3 Na-rich fragments from 15 different chondrites. Most objects (chondrules and chondrule fragments) are from ordinary chondrites (petrologic types 3.2–3.8), but two of the chondrules are from two CO3 chondrites, and three of the chondrules are from one Rumuruti (R)-chondrite. We found that these Na-rich objects have bulk Na 2 O-concentrations between 4.3 and 15.2 wt%. Texturally, they typically consist of euhedral to subhedral (often skeletal) mafic minerals (olivine and pyroxenes) embedded within a nepheline-normative, glassy mesostasis, which is brownish in transmitted light. In addition, some chondrules contain euhedral to subhedral spinel. Bulk chondrule compositions show group II, group III, and ultrarefractory rare earth element (REE) patterns similar to those found in CAIs. These results clearly demonstrate that the Na-rich chondrules must have been formed by melting of precursors containing an (ultra-)refractory element-rich component and Na-rich constituents. The Na-rich chondrules showed Sm and Eu anomalies, indicating that they must have formed at low oxygen fugacities. Based on the chemical composition of the Na-rich objects, we can rule out that they were formed as a result of planetary formation due to metasomatic processes or processes related to collisions between molten planetesimals.

Two samples of a unique achondritic lithology of the Almahata Sitta meteorite (MS-MU-019 and MS-MU-036) contain three coexisting pyroxene species: orthoenstatite, clinoenstatite and augite. The silicate assemblage appears to be the restite after extraction of melts of broadly basaltic and metal-sulfide composition from an enstatite chondrite protolith. Transmission electron microscopy (TEM) provides evidence that clinoenstatite within the lithology formed from earlier protoenstatite. The absence of pigeonite despite the successful nucleation of augite and the persistence of orthoenstatite during cooling suggests that the sub-solidus formation of the three coexisting pyroxenes occurred at a pressure of about 0.1 GPa. Rapid cooling at >1 K/h below 1260°C is documented by the cessation of augite equilibration, preservation of the 3-pyroxene assemblage and a low volume fraction of nanoscale orthoenstatite lamellae formed during the transformation of protoenstatite to clinoenstatite. The pressure implies a diameter of roughly 500 km of the differentiated parent body, putting petrological constraints on the size of planetesimals that may have contributed to the accretion of the terrestrial planets including Earth. The high cooling rate indicates a catastrophic disruption of this large planetesimal early in its history. The lithology studied here underlines that planetesimals which existed in the inner Solar System were more diverse than previously thought, and included potentially large differentiated bodies with very FeO-poor, enstatite-dominated mantles. Remains of these bodies are poorly represented in meteorite collections, which points to efficient accretion in the inner Solar System or to removal and little re-distribution of material into the present-day asteroid belt.

A key process in the early solar system that significantly affects the further evolution and transport of highly volatile elements throughout the solar system hydrothermal parent body alteration. To determine whether hydrothermal alteration in outer solar system parent bodies occurred more or less simultaneously or due to a sequence of multiple different events, we investigated low-temperature hydrothermally altered CM and CI chondrites along with volatile-rich CM-like clasts and C1 clasts with abundant mineral phases that contain volatiles. In this respect, C1 clasts are particularly important as they closely resemble the CI chondrites but originate from isotopically different parent bodies. Specifically, we applied the SIMS-based Mn/Cr in situ dating technique to carbonates, a common hydrothermally formed phase in low-temperature hydrothermally altered meteorites. The Mn/Cr ages of dolomites in CI chondrites and C1 clasts as well as calcites in CM chondrites and CM-like clasts reveal that nearly all carbonates in low-temperature hydrothermally altered clasts and chondrites were formed within a brief period between 2-6 Ma after CAI formation. Given this sharp separation, and that hardly any material contains carbonates formed later than ∼6 Ma after CAI formation, hydrothermal alteration likely occurred near-contemporaneously among different parent bodies in the outer solar system. Further, the timing of hydrothermal alteration matches peak heating of 26Al decay that ceased at ∼5 Ma after CAI formation. Hereby, these results are consistent with a model in which the carbonates in low-temperature hydrothermally altered parent bodies precipitated from the fluid produced by melting ice. The results also show that other potential heating events (e.g., impacts) only negligibly contributed to creating environments where fluid-mediated dissolution and precipitation of carbonates was possible. Additionally, the isotopic (H, O, Cr, and S) differences between C1 clasts and CI chondrites are most likely not caused by differences in timing of hydrothermal aqueous alteration and, thus, are best explained by spatially different isotopic reservoirs.

We compare the solar wind (SW) He Ne and Ar compositions collected during the Apollo Solar Wind Composition (SWC) experiments (1969 1972; Al Pt foils) and the Genesis mission (2002 2004; so called DOS targets considered here). While published SW Ne 20/Ne 22 and Ar 36/Ar 38 ratios of both data sets agree differences exist in the He 4/He 3 He 4/Ne 20 and Ne 20/Ar 36 ratios. However Ne 20/Ar 36 ratios from Apollo 16 Pt foils exclusively adopted as SW values by the SWC team are consistent with the Genesis results. We investigate if the differences indicate a variability of the SW over the course of about 30 yr or systematic biases of the two data sets which were collected in different environments and measured several decades apart in different laboratories (University of Bern; ETH Zurich). New measurements of Apollo 15 SWC aluminum foils in Zurich generally agree with the original measurements performed in Bern. Zurich samples show slightly lower He 4 concentrations suggesting a few percent of diffusive loss of He 4 during storage of the foils. A 3 difference between the He isotopic ratios measured in Bern and in Zurich possibly represents an analytical bias between the laboratories. The low SW He 4/Ne 20 and Ne 20/Ar 36 ratios in Apollo 15 Al foils compared to Genesis data are consistent with a mixture of Genesis like SW and noble gases from small amounts of lunar dust. Our data suggest that the mean SW He Ne and Ar isotopic and elemental compositions have not significantly changed between the overall Apollo and Genesis mission collection periods.

The Almahata Sitta strewn field is dominated by ureilites, but contains a large fraction of chondritic fragments of various types. We analyzed stable isotopes of He, Ne, Ar, Kr, and Xe, and the cosmogenic radionuclides 10Be, 26Al, and 36Cl in six chondritic Almahata Sitta fragments (EL6 breccia, EL6, EL3-5, CB, LL4/5, R-like). The cosmic-ray exposure (CRE) ages of five of the six samples have an average of 19.2 ± 3.3 Ma, close to the average of 19.5 ± 2.5 Ma for four ureilites. The cosmogenic radionuclide concentrations in the chondrites indicate a preatmospheric size consistent with Almahata Sitta. This corroborates that Almahata Sitta chondrite samples were part of the same asteroid as the ureilites. However, MS-179 has a lower CRE age of 11.0 ± 1.4 Ma. Further analysis of short-lived radionuclides in fragment MS-179 showed that it fell around the same time, and from an object of similar size as Almahata Sitta, making it almost certain that MS-179 is an Almahata Sitta fragment. Instead, its low CRE age could be due to gas loss, chemical heterogeneity that may have led to an erroneous 21Ne production-rate, or, perhaps most likely, MS-179 could represent the true 4π exposure age of Almahata Sitta (or an upper limit thereof), while all other samples analyzed so far experienced exposure on the parent body of similar lengths. Finally, MS-179 had an extraordinarily high activity of neutron-capture 36Cl, ~600 dpm kg−1, the highest activity observed in any meteorite to date, related to a high abundance of the Cl-bearing mineral lawrencite.

On March 6, 2016 at 21:36:51 UT, extended areas of Upper Austria, Bavaria (Germany) and the southwestern part of the Czech Republic were illuminated by a very bright bolide. This bolide was recorded by instruments in the Czech part of the European Fireball Network and it enabled complex and precise description of this event including prediction of the impact area. So far six meteorites totaling 1473 g have been found in the predicted area. The first pieces were recovered on March 12, 2016 on a field close to the village of Stubenberg (Bavaria). Stubenberg is a weakly shocked (S3) fragmental breccia consisting of abundant highly recrystallized rock fragments embedded in a clastic matrix. The texture, the large grain size of plagioclase, and the homogeneous compositions of olivine (Fa31.4) and pyroxene (Fs25.4) clearly indicate that Stubenberg is an LL6 chondrite breccia. This is consistent with the data on O, Ti, and Cr isotopes. Stubenberg does not contain solar wind-implanted noble gases. Data on the bulk chemistry, IR spectroscopy, cosmogenic nuclides, and organic components also indicate similarities to other metamorphosed LL chondrites. Noble gas studies reveal that the meteorite has a cosmic ray exposure (CRE) age of 36 ± 3 Ma and that most of the cosmogenic gases were produced in a meteoroid with a radius of at least 35 cm. This is larger than the size of the meteoroid which entered the Earth's atmosphere, which is constrained to

Most extraterrestrial samples feature the two accessory Ca-phosphates (apatite-group minerals and merrillite), which are important carrier phases of the rare earth elements (REE). The trace-element concentrations (REE, Sc, Ti, V, Cr, Mn, Co, As, Rb, Sr, Y, Zr, Nb, Ba, Hf, Ta, Pb, Th, and U) of selected grains were analyzed by LA-ICP-MS and/or SIMS (REE only). This systematic investigation includes 99 apatite and 149 merrillite analyses from meteorites deriving from various asteroidal bodies including 1 carbonaceous chondrite, 8 ordinary chondrites, 3 acapulcoites, 1 winonaite, 2 eucrites, 5 shergottites, 1 ureilitic trachyandesite, 2 mesosiderites, and 1 silicate-bearing IAB iron meteorite. Although Ca-phosphates predominantly form in metamorphic and/or metasomatic reactions, some are of igneous origin. As late-stage phases that often incorporate the vast majority of their host’s bulk REE budget, the investigated Ca-phosphates have REE enrichments of up to two orders of magnitude compared to the host rock’s bulk concentrations. Within a single sample, each phosphate species displays a uniform REE-pattern, and variations are mainly restricted to their enrichment, therefore indicating similar formation conditions. Exceptions are brecciated samples, i.e., the Adzhi-Bogdo (LL3-6) ordinary chondrite. Despite this uniformity within single samples, distinct meteorite groups do not necessarily have unique REE-patterns. Four basic shapes dominate the REE patterns of meteoritic Ca-phosphates: (1) flat patterns, smoothly decreasing from La-Lu with prominent negative Eu anomalies (acapulcoites, eucrites, apatite from the winonaite and the ureilitic trachyandesite, merrillite from ordinary chondrites); (2) unfractionated patterns, with only minor or no anomalies (mesosiderites, enriched shergottites, IAB-iron meteorite); (3) LREE-enriched patterns, with either positive or slightly negative Eu anomalies (chondritic apatite); and (4) strongly LREE-depleted patterns, with negative Eu anomalies (depleted shergottites). The patterns do not correlate with the grade of metamorphism (petrologic type), specific adjacent mineral assemblages or with Ca-phosphate grain size. Neither the proportions of different REE, nor particular REE patterns themselves are universally correlated to a specific formation mechanism yet Eu (i.e., magnitude of the Eu anomaly) is a sensitive indicator to evaluate the timing of plagioclase and phosphate crystallization. Based on our data, U and Th abundances in apatite increase (almost linearly) with the grade of metamorphism, as well as with the differentiation of their host rock.

In common with the remarkable variation in the bulk rock Zr content of distinct meteorite groups, ranging from 800 ppm, the occurrence and abundance of accessory zircon is also highly diverse and limited to certain meteorite classes. A detailed literature study on the occurrence of meteoritic zircon, along with other Zr-bearing phases reveals that lunar rocks, eucrites and mesosiderites are the prime sources of meteoritic zircon. Rare zircon grains occur in chondrites, silicate-bearing iron meteorites and Martian meteorites, with grain sizes of >5 μm allowing chemical and chronological studies at high spatial resolution using secondary ion mass spectrometry (SIMS) technique. Grain sizes, crystal habits, structural and chemical characteristics of zircon grains derived from various meteorite types, including their REE abundances, minor element concentrations, and Zr/Hf values is diverse. Superchondritic Zr/Hf values (47 ± 8; s.d. with n = 97), i.e., typical for zircon in eucrites and mesosiderites, indicate crystallization from a fractionated, incompatible-element-rich (residual) melt. Differences in REE abundances, occurrence or absence of Ce- and Eu-anomalies, and overall REE patterns that are often fractionated with a depletion in LREE, might be primarily controlled by variable formation conditions of individual grains and/or differences in the residual melt compositions on a small, local scale within single samples. Subsequent fractionation/modification of the chemical fingerprint of meteoritic zircon can involve high-temperature annealing processes during thermal metamorphic reactions and/or impact events along with mixing of lithic fragments since many samples are breccias.

Enstatite (E) chondrites are a group of texturally highly variable meteorites formed under strongly reducing conditions giving rise to unique mineral and chemical characteristics (e.g., high abundances of various sulfides and Si-bearing metal). In particular the abundant metal comprises a range of textures in E chondrites of different petrologic type, but available in situ siderophile trace element data on metal are limited. Nine samples of E chondrites from the recent Almahata Sitta fall [one EH3, two EL3/4, two EL6, two EL impact melt rocks (IMR), two EH IMR] were investigated in this study in addition to St. Mark’s (EH5) and Grein 002 (EL4/5), with a focus on the nature of their metal constituents. Special attention was given to metal–silicate intergrowths (MSSI) that occur in many primitive E chondrites, which have been interpreted as post-accretionary asteroidal impact melts or primitive nebular condensates. This study shows that siderophile trace element systematics in E chondrite metal are independent of petrologic type of the host rock and distinct from condensation signatures. Three basic types of siderophile trace element signatures can be distinguished, indicating crystallization from a melt, thermal equilibration upon metamorphism/complete melting, and exsolution of schreibersite–perryite–sulfide. Textural and mineral–chemical constraints from EL3/4s are used to evaluate previously proposed formation processes of MSSI (impact melting vs. nebular condensation) and elucidate which other formation scenarios are feasible. It is shown that post-accretionary (in situ) impact melting or metallic melt injection forming MSSI on the thin section scale, and nebular condensation, are unlikely formation processes. This leads to the conclusion that MSSIs are pre-accretionary melt objects that were formed during melting processes prior to the accretion of the primitive E chondrites. The same can be concluded for metal nodules in the EH3 chondrite examined. The pre-accretionary origin of MSSIs in E chondrites is consistent with a growing body of evidence for early differentiation followed by impact disruption of early formed planetesimals in all major chondrite types.

International audience; Volcanism is a substantial process during crustal growth on plane-tary bodies and well documented to have occurred in the early Solar System from the recognition of numerous basaltic meteorites. Considering the ureilite parent body (UPB), the compositions of magmas that formed a potential UPB crust and were complemen-tary to the ultramafic ureilite mantle rocks are poorly constrained. Among the Almahata Sitta meteorites, a unique trachyandesite lava (with an oxygen isotope composition identical to that of common ureilites) documents the presence of volatile-and SiO 2 -rich magmas on the UPB. The magma was extracted at low degrees of disequilib-rium partial melting of the UPB mantle. This trachyandesite extends the range of known ancient volcanic, crust-forming rocks and docu-ments that volcanic rocks, similar in composition to trachyandesites on Earth, also formed on small planetary bodies ∼4.56 billion years ago. It also extends the volcanic activity on the UPB by ∼1 million years (Ma) and thus constrains the time of disruption of the body to later than 6.5 Ma after the formation of Ca–Al-rich inclusions. differentiation | meteorite parent body | achondrites | differentiated