Identification of the calcium, aluminum, and magnesium distribution within millimeter-sized extraterrestrial materials using nonresonant x-ray raman spectroscopy in preparation for the Hayabusa2 sample return mission

The nondestructive investigation of millimetersized meteoritic materials is often hindered by self-absorption effects. Using X-ray-based analytical methods, the information depth for many elements (Z < 30) is in the range of up to only a few hundred micrometers, and for low-Z elements (Z < 20), this is reduced even further to only a few tens of micrometers. However, the investigation of these low-Z elements, in particular calcium, aluminum, and magnesium, is of great importance to planetary geologists and cosmochemists, as these elements are regularly used to characterize and identify specific features of interest in extraterrestrial materials, especially primitive chondritic material. In this work, nonresonant inelastic X-ray scattering from core electrons was performed at beamline ID20 of the ESRF in a direct tomography approach in order to visualize these low-Z elements within the millimeter-sized meteoritic samples. The obtained 3D elemental distribution volumes were compared to results from X-ray fluorescence-CT and absorption CT experiments and were found to be in good agreement. Additionally, several regions of interest could be identified within the inelastic scattering volumes, containing information that is not available through the other presented means. As such, the proposed approach presents a valuable tool for the nondestructive investigation of low-Z elemental distributions within millimeter-sized extraterrestrial materials, such as the samples of the Hayabusa2 sample return mission

Formation of fused aggregates under long‐term microgravity conditions aboard the ISS with implications for early solar system particle aggregation

In order to gain further insights into early solar system aggregation processes, we carried out an experiment on board the International Space Station, which allowed us to study the behavior of dust particles exposed to electric arc discharges under long‐term microgravity. The experiment led to the formation of robust, elongated, fluffy aggregates, which were studied by scanning electron microscopy, electron backscatter diffraction, and synchrotron micro‐computed tomography. The morphologies of these aggregates strongly resemble the typical shapes of fractal fluffy‐type calcium‐aluminum‐rich inclusions (CAIs). We conclude that a small amount of melting could have supplied the required stability for such fractal structures to have survived transportation and aggregation to and compaction within planetesimals. Other aggregates produced in our experiment have a massy morphology and contain relict grains, likely resulting from the collision of grains with different degrees of melting, also observed in some natural CAIs. Some particles are surrounded by igneous rims, which remind in thickness and crystal orientation of Wark–Lovering rims; another aggregate shows similarities to disk‐shaped CAIs. These results imply that a (flash‐)heating event with subsequent aggregation could have been involved in the formation of different morphological CAI characteristics.BIOVIANordlicht GmbHDeutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Bundesministerium für Wirtschaft und Energie http://dx.doi.org/10.13039/501100006360NanoRacks LLCDr. Rolf M. Schwiete Stiftung http://dx.doi.org/10.13039/501100020027Deutsches Zentrum für Luft‐ und Raumfahrt http://dx.doi.org/10.13039/501100002946DreamUpCarl Zeiss Meditec AG http://dx.doi.org/10.13039/50110000280

Formation of chondrule analogs aboard the International Space Station

Chondrules are thought to play a crucial role in planet formation, but the mechanisms leading to their formation are still a matter of unresolved discussion. So far, experiments designed to understand chondrule formation conditions have been carried out only under the influence of terrestrial gravity. In order to introduce more realistic conditions, we developed a chondrule formation experiment, which was carried out at long‐term microgravity aboard the International Space Station. In this experiment, freely levitating forsterite (Mg2SiO4) dust particles were exposed to electric arc discharges, thus simulating chondrule formation via nebular lightning. The arc discharges were able to melt single dust particles completely, which then crystallized with very high cooling rates of >105 K h−1. The crystals in the spherules show a crystallographic preferred orientation of the [010] axes perpendicular to the spherule surface, similar to the preferred orientation observed in some natural chondrules. This microstructure is probably the result of crystallization under microgravity conditions. Furthermore, the spherules interacted with the surrounding gas during crystallization. We show that this type of experiment is able to form spherules, which show some similarities with the morphology of chondrules despite very short heating pulses and high cooling rates.Carl Zeiss Meditec AG http://dx.doi.org/10.13039/501100002806BIOVIA Science Ambassador programBundesministerium für Wirtschaft und Energie http://dx.doi.org/10.13039/501100006360Deutsches Zentrum für Luft‐ und Raumfahrt http://dx.doi.org/10.13039/501100002946NanoRacks LLCDreamUpDeutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Dr. Rolf M. Schwiete Stiftun

Sr distribution as proxy for Ca distribution at depth in SXRF analysis of mm‐sized carbonaceous chondrites: Implications for asteroid sample return missions

Reliable identification of chondrules, calcium-aluminum-rich inclusions (CAIs),carbonate grains, and Ca-phosphate grains at depth within untouched, unpreparedchondritic samples by a nondestructive analytical method, such as synchrotron X-rayfluorescence (SXRF) computed tomography (CT), is an essential first step before intrusiveanalytical and sample preparation methods are performed. The detection of a local Ca-enrichment could indicate the presence of such a component, all of which contain Ca asmajor element and/or Ca-bearing minerals, allowing it to be precisely located at depthwithin a sample. However, the depth limitation from which Ca-K fluorescence can travelthrough a chondrite sample (e.g., 115 μm through material of 1.5 g cm3 ) to XRFdetectors leaves many Ca-bearing components undetected at deeper depths. In comparison,Sr-K lines travel much greater distances ( 1700 μm) through the same sample density andare, thus, detected from much greater depths. Here, we demonstrate a clear, positive, andpreferential correlation between Ca and Sr and conclude that Sr-detection can be used asproxy for the presence of Ca (and, thus, Ca-bearing components) throughout mm-sizedsamples of carbonaceous chondritic material. This has valuable implications, especially forsample return missions from carbonaceous C-type asteroids, such as Ryugu or Bennu.Reliable localization, identification, and targeted analysis by SXRF of Ca-bearingchondrules, CAIs, and carbonates at depth within untouched, unprepared samples in theinitial stages of a multianalysis investigation insures the valuable information they hold ofpre- and post-accretion processes in the early solar system is neither corrupted nordestroyed in subsequent processing and analyses

Formation of fused aggregates under long‐term microgravity conditions aboard the ISS with implications for early solar system particle aggregation

In order to gain further insights into early solar system aggregation processes, we carried out an experiment on board the International Space Station, which allowed us to study the behavior of dust particles exposed to electric arc discharges under long-term microgravity. The experiment led to the formation of robust, elongated, fluffy aggregates, which were studied by scanning electron microscopy, electron backscatter diffraction, and synchrotron micro-computed tomography. The morphologies of these aggregates strongly resemble the typical shapes of fractal fluffy-type calcium-aluminum-rich inclusions (CAIs). We conclude that a small amount of melting could have supplied the required stability for such fractal structures to have survived transportation and aggregation to and compaction within planetesimals. Other aggregates produced in our experiment have a massy morphology and contain relict grains, likely resulting from the collision of grains with different degrees of melting, also observed in some natural CAIs. Some particles are surrounded by igneous rims, which remind in thickness and crystal orientation of Wark–Lovering rims; another aggregate shows similarities to disk-shaped CAIs. These results imply that a (flash-)heating event with subsequent aggregation could have been involved in the formation of different morphological CAI characteristics