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We present here an investigation of Ryugu particles recovered by the Hayabusa2 space mission and their extracted carbonaceous acid residues using Raman spectroscopy. Raman parameters of Ryugu intact grains and their acid residues are characterized by broad D (defect induced) and G (graphite) band widths, indicating the presence of polyaromatic carbonaceous matter with low thermal maturity. Raman spectra of Ryugu particles and CI (type 1) chondrites exhibit stronger laser‐induced fluorescence backgrounds compared to Type 2 and Type 3 carbonaceous chondrites. The high fluorescence signatures and wide bandwidths of the D and G bands of Ryugu intact grains are similar to the Raman spectra observed in CI chondrites, reflecting the low structural order of their aromatic carbonaceous matter, and strengthening the link between Ryugu particles and CI chondrites. The high fluorescence background intensity of the Ryugu particles is due to multiple causes, but it is likely that the relative abundance of geometry‐bearing macromolecular organic matter in total organic carbon contents makes a large contribution to the fluorescence intensities. Locally observed high fluorescence in the acid‐extracted residues of Ryugu is due to nitrogen‐bearing outlier phase. The high fluorescence signature is one consequence of the low degree of thermal maturity of the organic matter and supports evidence that the Ryugu particles have escaped significant parent body thermal metamorphism. [ABSTRACT FROM AUTHOR]

The dynamics of collisional events have been studied for three highly shocked L chondrites (Tenham, Sixiangkou, and Acfer 040). Crystal growth rates of high‐pressure polymorphs of olivines and pyroxenes and diffusion‐driven redistribution of Mn, Ca, Fe, and Na associated with these polymorphic transitions were studied independently. These two approaches were then applied on the same samples, and for meteorites that underwent different collisional histories. The relevance of the use of pyroxene polymorphs (e.g., akimotoite) is demonstrated. Combined analysis of the exact same ringwoodite and akimotoite crystals by scanning transmission electron microscopy (STEM) and NanoSIMS demonstrate that while STEM has a better lateral resolution, the 40 nm maximum resolution of the NanoSIMS is sufficient to distinguish and analyze diffusion profiles. With STEM chemical and structural information concerning the nucleation mechanisms of ringwoodite and akimotoite, the concentration profiles derived from NanoSIMS images were used to derive the shock pulse duration and impactor size for these three meteorites. The two approaches (crystal growth kinetics and elemental diffusion) provide comparable durations assuming that diffusion coefficients are carefully selected. We obtain shock time scales of 1, 7, and 4 s for Tenham, Sixiangkou, and Acfer 040, respectively. Corresponding impactor sizes are also calculated, and the results point toward either (i) an early separation of the L chondrites from the parent body, and secondary impacts resulting in the observed meteorites or (ii) the meteorites all originate from different depths in the parent body. [ABSTRACT FROM AUTHOR]

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- The insoluble organic matter (IOM) of an unequilibrated enstatite chondrite Sahara (SAH) 97096 has been investigated using a battery of analytical techniques. As the enstatite chondrites are thought to have formed in a reduced environment at higher temperatures than carbonaceous chondrites, they constitute an interesting comparative material to test the heterogeneities of the IOM in the solar system and to constrain the processes that could affect IOM during solar system evolution. The SAH 97096 IOM is found in situ: as submicrometer grains in the network of fine-grained matrix occurring mostly around chondrules and as inclusions in metallic nodules, where the carbonaceous matter appears to be more graphitized. IOM in these two settings has very similar δ15N and δ13C; this supports the idea that graphitized inclusions in metal could be formed by metal catalytic graphitization of matrix IOM. A detailed comparison between the IOM extracted from a fresh part and a terrestrially weathered part of SAH 97096 shows the similarity between both IOM samples in spite of the high degree of mineral alteration in the latter. The isolated IOM exhibits a heterogeneous polyaromatic macromolecular structure, sometimes highly graphitized, without any detectable free radicals and deuterium-heterogeneity and having mean H- and N-isotopic compositions in the range of values observed for carbonaceous chondrites. It contains some submicrometer-sized areas highly enriched in 15N (δ15N up to 1600‰). These observations reinforce the idea that the IOM found in carbonaceous chondrites is a common component widespread in the solar system. Most of the features of SAH 97096 IOM could be explained by the thermal modification of this main component. [ABSTRACT FROM AUTHOR]

Abstract: We performed the first NanoSIMS study on melt inclusions (MI) hosted in olivine from type-II chondrules in the Semarkona chondrite. At this nanometric scale, a one- to two-micrometre smooth contact has been discovered between the host crystal (olivine) and the melt inclusion. All profiles show smooth concentration gradients linking two plateaus (one for olivine and the other for the melt inclusion), and some of them also show bumps and valleys in several elements (Fe and Si for example). Different processes can be envisaged to explain those smooth profiles, more or less successfully. [Copyright &y& Elsevier]

• Mn-Cr systematics of sphalerite in five E chondrites was established by SIMS. • Mn-Cr system appears affected by weathering processes in MAC 88136. • Other disturbances could relate to complex thermal histories. • Substantial variation in initial 53Mn/55Mn still limits chronologic applications. • Chronologic potential is recognizable but requires additional research. We investigated the 53Mn-53Cr isotopic composition of a suite of enstatite chondrites by in situ analyses of various mineral phases with the Cameca IMS 1280-HR ion probe at Heidelberg, Germany, and a Cameca NanoSIMS at Paris, France. Only in sphalerite we found anomalies in 53Cr/52Cr-ratios correlating with 55Mn/52Cr which are due to decay of short-lived 53Mn (t 1/2 = 3.7 Ma). A sphalerite in the EH-impact melt LAP 02225 showed the largest excess of 53Cr, with 53Cr/52Cr-ratios ranging up to 2.2. The calculated initial 53Mn/55Mn-ratios are within the range of previous Mn-Cr studies. We observed a spatial variation within a large sphalerite in LAP 02225, translating in distinct initial 53Mn/55Mn values. In case of the EL3 chondrite MAC 88136 the initial 53Mn/55Mn derived for one sphalerite is at the lower end of previously reported values and may reflect a variable influence of alteration-induced exchange of common Cr. This is supported by the total reset of the 53Cr/52Cr-ratio in another sphalerite in contact with an alteration vein irrespective of high Mn/Cr-ratios. Our observed initial 53Mn/55Mn-ratios of Sahara 97158, Indarch and EET 96135 correspond to the I-Xe systematics and hence, show that sphalerites can preserve reasonable age information. For Indarch however, if compared with other initial 53Mn/55Mn values from literature, a considerable scatter is obvious. This clearly demonstrates that the Mn-Cr system in sphalerite can be disturbed by various, still poorly investigated, processes (e.g., by thermal events, weathering, diffusion-controlled remobilization). Future application of Mn-Cr dating to sphalerite in enstatite chondrites thus requires a better understanding of how such processes influence the Mn-Cr systematics and demands for tools to identify the undoubtly present sphalerites carrying a true chronologic information. [ABSTRACT FROM AUTHOR]