Multiscale correlated analysis of the Aguas Zarcas CM chondrite

In this paper, we report the results of a campaign of measurements on four fragments of the CM Aguas Zarcas (AZ) meteorite, combining X‐ray computed tomography analysis and Fourier‐transform infrared (FT‐IR) spectroscopy. We estimated a petrologic type for our sampled CM lithology using the two independent techniques, and obtained a type CM2.5, in agreement with previous estimations. By comparing the Si‐O 10‐µm signature of the AZ average FT‐IR spectra with other well‐studied CMs, we place AZ in the context of aqueous alteration of CM parent bodies. Morphological characterization reveals that AZ has heterogeneous distribution of pores and a global porosity of 4.5 ± 0.5 vol%. We show that chondrules have a porosity of 6.3 ± 1 vol%. This larger porosity could be inherited due to various processes such as temperature variation during the chondrule formation and shocks or dissolution during aqueous alteration. Finally, we observed a correlation between 3D distributions of organic matter and mineral at micrometric scales, revealing a link between the abundance of organic matter and the presence of hydrated minerals. This supports the idea that aqueous alteration in AZ’s parent body played a major role in the evolution of the organic matter

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

Effects of atmospheric entry heating on the noble gas and nitrogen content of micrometeorites

International audienceFragments of the carbonaceous chondrite Orgueil were subjected to pulse-heating sequences in order to simulate the heating conditions experienced by micrometeorites (MMs) upon entry into Earthʼs atmosphere. By increasing the experimental run times from 2 to 120 s at a fixed temperature of 1350 °C, the different textures of natural MMs (from non-vesicular fine-grained particles to melted cosmic spherules) were reproduced, and the noble gas (He, Ne, Ar) and nitrogen abundances and isotope ratios of the MM analogues were subsequently determined by CO2 laser extraction-static mass spectrometry analysis. The starting material shows a heterogeneous He–Ne–Ar–N signature, consistent with the mineralogical heterogeneity of CI chondrites and the inhomogeneous distribution of various noble gas and nitrogen components among meteoritic minerals. Nonetheless, our experiments demonstrate that moderately to strongly heated Orgueil fragments retain only a few percent of their initial noble gas and nitrogen inventories, indicating that atmospheric entry heating results in extensive degassing of meteoritic dust particles. The evolution of the noble gas and nitrogen isotope ratios may, in part, be explained by equilibration with the atmosphere; however, the decreasing δ15N values may also indicate preferential degradation of a 15N-rich component by thermal processing of chondritic matter. Furthermore, the efficient loss of helium and cosmogenic neon during heating will lead to an underestimate of the 3He and 21Ne exposure ages of MMs, as well as to large uncertainties for cosmic dust accretion rates derived from extraterrestrial 3He abundances in deep-sea sediments or polar ice cores. While the relative proportions of infalling cometary and asteroidal dust on Earth are unknown, the contribution of noble gases, nitrogen, and water from cosmic dust to the terrestrial volatile inventory appears negligible

Vis–NIR Reflectance Microspectroscopy of IDPs

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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$\sigma$)

Three‐dimensional multiscale assembly of phyllosilicates, organics, and carbonates in small Ryugu fragments

International audienceWe report μm‐scale nondestructive infrared (IR) hyperspectral results (IR computed tomography, IR‐CT) in 3‐D and IR surface imaging, IR‐S) in 2‐D, at SOLEIL) combined with X‐ray nano‐computed tomography analyses (at SPring‐8) performed on eight small Ryugu fragments extracted from mm‐sized grains coming both from touchdown first and second sites. We describe the multiscale assembly of phyllosilicates, carbonates, sulfides, oxides, and organics. Two types of silicates, as well as diverse kinds of organic matter, were detected inside Ryugu material. Their spatial correlations are described to discuss the role of the mineralogical microenvironments in the formation/evolution of organic matter. In particular, we have shown that there is a redistribution of the organic matter diffuse component during aqueous alteration on the parent body, with a preferential circulation among fine‐grained phyllosilicates

Small grains from Ryugu: handling and analysis pipeline for infrared synchrotron microspectroscopy

Abstract Sample-return missions allow the study of materials collected directly from celestial bodies, unbiased by atmospheric entry effects and/or terrestrial alteration and contamination phenomena, using state-of-the-art techniques which are available only in a laboratory environment—but only if the collected material stays pristine. The scarcity of outer-space unaltered material recovered until now makes this material extremely precious for the potential scientific insight it can bring. To maximize the scientific output of current and future sample-return missions, the scientific community needs to plan for ways of storing, handling, and measuring this precious material while preserving their pristine state for as long as the ‘invasiveness’ of measurements allows. In July 2021, as part of the Hayabusa2 (JAXA) “Stone” preliminary examination team, we received several microscopic particles from the asteroid Ryugu, with the goal of performing IR hyper-spectral imaging and IR micro-tomography studies. Here, we describe the sample transfer, handling methods and analytical pipeline we implemented to study this very precious material while minimizing and surveilling their alteration history on Earth. Graphical Abstrac

Small grains from Ryugu: handling and analysis pipeline for Infrared Synchrotron Microspectroscopy

Sample-return missions allow the study of materials collected directly from celestial bodies, unbiased by atmospheric entry effects and/or Earth alteration and contamination phenomena, using state-of-the-art techniques - but only if the collected material stays pristine. The scarcity of outer-space unaltered material recovered until now makes this material extremely precious. To maximize the scientific output of current and future sample-return missions, the scientific community needs to plan for ways of storing, handling, and measuring this precious material while preserving their pristine state for as long as the ‘invasiveness’ of measurements allows. In July 2021, as part of the Hayabusa2 (JAXA) “Stone” preliminary examination team, we received several microscopic particles from the asteroid Ryugu, with the goal of performing IR hyper-spectral imaging and IR micro-tomography studies. Here we describe the sample transfer, handling methods and analytical pipeline we implemented to study this very precious material while minimizing and surveilling their alteration history on Earth