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

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

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$\sigma$)

A preparation sequence for multi‐analysis of µm‐sized extraterrestrial and geological samples

International audienceWith the recent and ongoing sample return missions and/or the developments of nano-to microscale 3-D and 2-D analytical techniques, it is necessary to develop sample preparation and analysis protocols that allow combination of different nanometer-to micrometer-scale resolution techniques and both maximize scientific outcome and minimize sample loss and contamination. Here, we present novel sample preparation and analytical procedures to extract a maximum of submicrometer structural, mineralogical, chemical, molecular, and isotopic information from micrometric heterogeneous samples. The sample protocol goes from a nondestructive infrared (IR) tomography of~10 to~70 µm-sized single grains, which provides the distribution and qualitative abundances of both mineral and organic phases, followed by its cutting in several slices at selected sites of interest for 2-D mineralogical analysis (e.g., transmission electron microscopy), molecular organic and mineral analysis (e.g., Raman and/or IR microspectroscopy), and isotopic/chemical analysis (e.g., NanoSIMS). We also discuss here the importance of the focused ion beam microscopy in the protocol, the problems of sample loss and contamination, and at last the possibility of combining successive different analyses in various orders on the same micrometric sample. Special care was notably taken to establish a protocol allowing correlated NanoSIMS/TEM/IR analyses with NanoSIMS performed first. Finally, we emphasize the interest of 3-D and 2-D IR analyses in studying the organics-minerals relationship in combination with more classical isotopic and mineralogical grain characterizations

Space-weathering induced changes in hydrated silicates: A multi-scale study combining visible/infrared spectroscopy and electron microscopy

International audienceInvestigating the effects of space-weathering on primitive bodies is paramount in assessing their composition and understanding their history. For this purpose, we conducted 40 keV He and Ar ion-implantation experiments on terrestrial phyllosilicates, the main components of primitive C-class asteroids: two serpentines, and one saponite. We emulated the effects of the solar wind component of space weathering on hydrated surfaces over timescales of 1E3-4 years in the inner solar system. Spectral changes (from 0.35 to 30 mu m in wavelength), surface topography variations, and elemental and morphological changes were investigated. In the visible range, we saw darkening for all samples, accompanied by reddening for the serpentine samples and blueing for the saponite. Spectroscopic features such as the silicate stretching and bending modes at 10 and 20 mu m respectively, as well as the (M)-OH bending mode at 16 mu m, exhibited a peak shift towards longer wavelength (red-shift), band area decrease, and band widening. The surface of Ar-implanted samples appeared polished, while no difference was noticeable for He-implanted samples. Morphological changes in the ion-implanted layers of our samples include abundant vesiculation and lattice amorphization. Mg and O appear to be particularly mobile upon ion implantation. In particular, dehydroxylation was observed for all samples. Changes observed for spectroscopic features do not correlate systematically with variations of the Mg/Fe ratio. They do correlate with oxygen loss via dehydroxylation and crystal lattice disordering and amorphization. Spectral changes in the visible range and for 10 and 20 mu m features appear to be mainly due to crystal amorphization. Variation of the hydration feature at 16 mu m correlates with both dehydroxylation and lattice amorphization. Compositional variations affect the hydration feature at 2.7 mu m more consistently. The effects detected upon ion implantation on the samples in this work support the identification of spectral trends from the remote-sensing data of primitive bodies Ryugu and Bennu as changes induced by space-weathering. Findings are also compatible with laboratory analysis on returned weathered grains from Ryugu

FTIR and X-ray micro-tomography on Itokawa particles and carbonaceous chondrites

International audienceWe report a combined IR and X micro-tomography analysis of five particles from asteroid Itokawa and a few selected fragments of several carbonaceous chondrites. These techniques are an efficient first-step in a multi-technique analytical sequence to be applied on small Solar System bodies samples, collected by space missions such as Hayabusa2 and OSIRIS-REx

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