Ryugu’s nucleosynthetic heritage from the outskirts of the Solar System

Little is known about the origin of the spectral diversity of asteroids and what it says about conditions in the protoplanetary disk. Here, we show that samples returned from Cb-type asteroid Ryugu have Fe isotopic anomalies indistinguishable from Ivuna-type (CI) chondrites, which are distinct from all other carbonaceous chondrites. Iron isotopes, therefore, demonstrate that Ryugu and CI chondrites formed in a reservoir that was different from the source regions of other carbonaceous asteroids. Growth and migration of the giant planets destabilized nearby planetesimals and ejected some inward to be implanted into the Main Belt. In this framework, most carbonaceous chondrites may have originated from regions around the birthplaces of Jupiter and Saturn, while the distinct isotopic composition of CI chondrites and Ryugu may reflect their formation further away in the disk, owing their presence in the inner Solar System to excitation by Uranus and Neptune

Oxygen isotopes of anhydrous primary minerals show kinship between asteroid Ryugu and comet 81P/Wild2

The extraterrestrial materials returned from asteroid (162173) Ryugu consist predominantly of low-temperature aqueously formed secondary minerals and are chemically and mineralogically similar to CI (Ivuna-type) carbonaceous chondrites. Here, we show that high-temperature anhydrous primary minerals in Ryugu and CI chondrites exhibit a bimodal distribution of oxygen isotopic compositions: 16O-rich (associated with refractory inclusions) and 16O-poor (associated with chondrules). Both the 16O-rich and 16O-poor minerals probably formed in the inner solar protoplanetary disk and were subsequently transported outward. The abundance ratios of the 16O-rich to 16O-poor minerals in Ryugu and CI chondrites are higher than in other carbonaceous chondrite groups but are similar to that of comet 81P/Wild2, suggesting that Ryugu and CI chondrites accreted in the outer Solar System closer to the accretion region of comets

Water circulation in Ryugu asteroid affected the distribution of nucleosynthetic isotope anomalies in returned sample

Studies of material returned from Cb asteroid Ryugu have revealed considerable mineralogical and chemical heterogeneity, stemming primarily from brecciation and aqueous alteration. Isotopic anomalies could have also been affected by delivery of exogenous clasts and aqueous mobilization of soluble elements. Here, we show that isotopic anomalies for mildly soluble Cr are highly variable in Ryugu and CI chondrites, whereas those of Ti are relatively uniform. This variation in Cr isotope ratios is most likely due to physicochemical fractionation between 54Cr-rich presolar nanoparticles and Cr-bearing secondary minerals at the millimeter-scale in the bulk samples, likely due to extensive aqueous alteration in their parent bodies that occurred 5:2þ11::84 Ma after Solar System birth. In contrast, Ti isotopes were marginally affected by this process. Our results show that isotopic heterogeneities in asteroids are not all nebular or accretionary in nature but can also reflect element redistribution by water

Oxygen isotopes in the early protoplanetary disk inferred from pyroxene in a classical type B CAI

International audienceA major unanswered question in solar system formation is the origin of the oxygen isotopic dichotomy between the Sun and the planets. Individual Calcium–Aluminum-rich inclusions (CAIs) from CV chondrites exhibit almost the full isotopic range, but how their composition evolved is still unclear, which prevents robust astrochemical conclusions. A key issue is notably the yet unsolved origin of the 16O-rich isotopic composition of pyroxene in type B CAIs. Here, I report an in-situoxygen isotope study of the archetypal type B CAI USNM-3529-Z from Allende with emphasis on the isotopic composition of pyroxene and its isotopic and petrographic relationships with other major minerals. The O isotopic composition of pyroxene is correlated with indicators of magmatic growth, indicating that the pyroxene evolved from a 16O-poor composition and became progressively enriched in 16O during its crystallization, contrary to the long held assumption that pyroxene was initially 16O-rich. This variation is well explained by isotopic exchange between a 16O-poor partial melt having the isotopic composition of melilite and a 16O-rich gas having the isotopic composition of spinel, during pyroxene crystallization.The isotopic evolution of 3529-Z is consistent with formation in an initially 16O-rich environment where spinel and gehlenitic melilite crystallized, followed by a 16O-depletion associated with melilite partial melting and recrystallization and finally a return to the initial 16O-rich environment before pyroxene crystallization. This strongly suggests that the environment of CAI formation was globally 16O-rich, with local 16O-depletions systematically associated with high temperature events. The Al/Mg isotopic systematics of 3529-Z further indicates that this suite of isotopic changes occurredin the first 150000yrof the solar system, during the main CAI formation period. A new astrophysical setting is proposed, where the 16O-depletion occurs in an optically thin surface layer of the disk and may have originated by evaporation of 16O-poor interstellar dust or non-mass-dependant isotopic fractionation

Développement de l'analyse isotopique de microparticules par sonde ionique : étude des poussières désertiques et interplanétaires

Non disponible / Not availableAu cours de cette thèse une nouvelle technique analytique a été développée pour permettre l'analyse isotopique de microparticules. Cette technique est fondée sur l'utilisation des potentialités d'imagerie de la sonde ionique IMS 1270 du CRPG. Le développement de l'imagerie isotopique a permis de mesurer le rapport 1 8 O/ 1 6 O de particules de moins de 2 [micro]m avec une précision de 3 a 4% et de carter les variations isotopiques de D/H dans des particules de 10 [micro]m avec une résolution latérale de l'ordre du micromètre. L?utilisation de cette nouvelle technique permet de résoudre le problème de l'origine des poussières sahariennes, en effet la distribution des rapports 1 8 O/ 1 6 O dans les quartzs micrométriques des poussières et des sols sahariens est une empreinte caractéristique de la géologie de la région source. La mesure des rapports isotopiques de l'oxygène de mono-grains de quartz d'une tempête de poussière collectée au dessus de l'océan atlantique permet d'attribuer l'origine de cette tempête à la zone air-Ténéré. Ce résultat a de profondes implications pour le cycle des poussières désertiques dans l'atmosphère et les processus de suspension des grains dans l'atmosphère. la cartographie des rapports D/H dans 4 poussières interplanétaires collectées dans la stratosphère par la NASA a permis de montrer que ces particules contiennent plusieurs types de matière organique d'origine interstellaire identiques a certains polymères mesures dans les chondrites carbonées et les comètes. La présence de ces polymères au sein d'une même particule semble suggérer des liens entre les matériaux les plus primitifs du système solaire

Techniques and instruments to analyze, characterize and study returned samples

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Alkali magmatism on a carbonaceous chondrite planetesimal

International audienceRecent isotopic and paleomagnetic data point to a possible connection between carbonaceous chondrites and differentiated planetary materials suggesting the existence, perhaps ephemeral, of transitional objects with a layered structure whereby a metal-rich core is enclosed by a silicate mantle which is itself overlain by a crust containing an outermost layer of primitive solar nebula materials. This idea has not received broad support mostly because of a lack of samples in the meteoritic record that document incipient melting at the onset of planetary differentiation. Here we report the discovery and the petrologic-isotopic characterization of UH154-11, a ferroan trachybasalt fragment enclosed in a CR chondrite. Its chemical and oxygen isotopic compositions are consistent with very low degree partial melting of a CV chondrite from the oxidized subgroup at a depth where fluid-assisted metamorphism enhanced the Na content. Its micro-doleritic texture indicates crystallization at an increasing cooling rate such as would occur during magma ascent through a chondritic crust. This represents the first direct evidence of magmatic activity in a carbonaceous asteroid on the verge of differentiating and demonstrates that some primitive outer solar system objects related to icy asteroids and comets underwent a phase of magmatic activity early in the solar system. With its peculiar petrology, UH154-11 can be considered the long-sought first melt produced during partial differentiation of a carbonaceous chondritic planetary body bridging a previously persistent gap in differentiation processes from icy cometary bodies to fully melted iron meteorites with isotopic affinities to carbonaceous chondrites

On the anomalous shapes of native copper crystals from the Michigan Copper Country

International audienceFor over a century, the anomalous shapes of Michigan copper crystals from the Michigan Copper Country have been acknowledged. They are well known by mineral collectors and curated in museums from all around the world; still, their particular habits remain enigmatic. These natural crystals do not seem to follow crystal shape theories, based on the internal three-dimensional crystal structure. In this article, we offer a unique perspective on the formation of Michigan copper crystals.Firstly, we review the most common theories of crystal shapes. Then, taking into account the surface reconstructions induced by adsorbed oxygen, detected by ultra-high vacuum techniques, we present evidence of a strong correlation between these oxygen-induced surface reconstructions and the anomalous shapes. Finally, in order to understand why these shapes are not found in copper at other localities, oxygen dosing was performed using NanoSIMS on different natural copper crystals as a preliminary investigation. The higher oxygen content found in the Michigan copper crystal studied compared to others supports the influence of adsorbed oxygen on the anomalous crystal shapes. This result shows which mechanisms could modify crystal shapes and allow the development of strategies to monitor them, due to the presence of oxygen impurities. This new find is of great importance in shape-dependent catalysis, sensor characteristics, or other properties of material such as nanocrystals

NanoSIMS imaging of D/H ratios on FIB sections

International audienceThe D/H ratio imaging of weakly hydrated minerals prepared as Focused Ion Beam (FIB) sections is developed in order to combine isotopic imaging by Nanoscale Secondary Ion Mass Spectrometry (NanoSIMS) of micrometer-sized grains with other nanoscale imaging techniques, such as Transmission Electron Microscopy. In order to maximize the accuracy, sensitivity, precision and reproducibility of D/H ratios at the micrometer-size, while minimizing the surface contamination at the same time, we explored all instrumental parameters known to influence the measurement of D/H ratios in situ. Optimal conditions were found to be obtained with the use of (i) a Cs$^+$ ion source and detection of H$^-$ and D$^-$at low mass resolving power, (ii) a primary beam intensity of 100 pA, and (iii) raster sizes in the range 8-15 $\mu$m. Nominally anhydrous minerals were used to evaluate the detection limits and indicate a surface contamination level of about 200 ppm equivalent H$_2$O in these conditions. With the high primary intensity used here, the dwell time is not a parameter as critical as found in previous studies and a dwell time of 1 ms/px is used to minimize dynamic contamination during analysis. Analysis of FIB sections was found to reduce significantly static contamination due to sample preparation and improved accuracy compared to using polished sections embedded not only in epoxy but in indium as well. On amphiboles, the typical overall uncertainty including reproducibility is about 20 ‰ on bulk FIB sections and about 50 ‰ at the 1.5 $\mu$m scale using image processing (1$\sigma$)

O, Mg, and Si isotope distributions in the complex ultrarefractory CAI Efremovka 101.1: Assimilation of ultrarefractory, FUN, and regular CAI precursors

International audienceOxygen, magnesium, and silicon isotopic compositions in the mineralogically complex, ultrarefractory (UR) calcium-aluminum-rich inclusion (CAI) E101.1 from the reduced CV3 chondrite Efremovka confirm that E101.1 is a compound CAI composed of several lithological units that were once individual CAIs, free-floating in the solar protoplanetary disk. Each precursor unit was found to have had its own thermal history prior to being captured and incorporated into the partially molten host CAI.Four major lithological units can be distinguished on the basis of their isotopic compositions. (1) Al-diopside-rich sinuous fragments, hereafter sinuous pyroxene, are 16O-rich (Δ17O ≤ −20‰) and have light Mg and Si isotopic compositions with mass fractionation down to −3.5‰/amu for both isotopic systems. We attribute these peculiar isotopic compositions to kinetic effects during condensation out of thermal equilibrium. (2) Spinel clusters are 16O-rich (Δ17O ∼ −22‰) and have Mg isotope systematics consistent with extensive equilibration with the host melt. This includes (i) δ25Mg values varying between + 2.6‰ and + 6.5‰ close to the typical value of host melilite at ∼+5‰, and (ii) evidence for exchange of radiogenic 26Mg with adjacent melilite as indicated by Al/Mg systematics. The spinel clusters may represent fine-grained spinel-rich proto-CAIs captured, partially melted, and recrystallized in the host melt. Al/Mg systematics indicate that both the sinuous pyroxene fragments and spinel clusters probably had canonical or near-canonical 26Al contents before partial equilibration. (3) The main CAI host (Δ17O ≤ −2‰) had a complex thermal history partially obscured by subsequent capture and assimilation events. Its formation, referred to as the “cryptic” stage, could have resulted from the partial melting and crystallization of a 16O-rich precursor that underwent 16O-depletion and a massive evaporation event characteristic of F and FUN CAIs (Fractionated with Unknown Nuclear effects). Alternatively, a 16O-rich UR precursor may have coagulated with a 16O-poor FUN CAI having 48Ca anomalies, as indicated by perovskite, before subsequent extensive melting. The Al/Mg systematics (2.4 × 10−5 ≤ 26Al/27Al)0 ≤ 5.4 × 10−5, where (26Al/27Al)'0 is a model initial 26Al/27Al ratio per analysis spot) are best understood if the FUN component was 26Al-poor, as are many FUN CAIs. (4) A complete Wark-Lovering rim (WLR) surrounds E101.1. Its Mg and Si isotopic compositions indicate that it formed by interaction of the evaporated interior CAI with an unfractionated 16O-rich condensate component. Heterogeneities in 26Al content in WLR spinels (3.7 × 10−5 ≤ 26Al/27Al)'0 ≤ 5.7 × 10−5) suggest that the previously reported age difference of as much as 300,000 years between interior CAIs and their WLRs may be an artifact resulting from Mg isotopic perturbations, possibly by solid state diffusion or mixing between the interior and condensate components.The isotopic systematics of E101.1 imply that 16O-rich and 16O-poor reservoirs co-existed in the earliest solar protoplanetary disk and that igneous CAIs experienced a 16O-depletion in an early high temperature stage. The coagulation of various lithological units in E101.1 and their partial assimilation supports models of CAI growth by competing fragmentation and coagulation in a partially molten state. Our results suggest that chemical and isotopic heterogeneities of unclear origin in regular CAIs may result from such a complex aggregation history masked by subsequent melting and recrystallization