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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., BIOVIA, Nordlicht GmbH, Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, Bundesministerium für Wirtschaft und Energie http://dx.doi.org/10.13039/501100006360, NanoRacks LLC, Dr. Rolf M. Schwiete Stiftung http://dx.doi.org/10.13039/501100020027, Deutsches Zentrum für Luft‐ und Raumfahrt http://dx.doi.org/10.13039/501100002946, DreamUp, Carl Zeiss Meditec AG http://dx.doi.org/10.13039/501100002806

Meteoritics & planetary science 57(4), 817 - 829 (2022). doi:10.1111/maps.13797, 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., Published by Wiley-Blackwell, Hoboken, NJ

Additional file1: Figure S1 XRF spectra corresponding to the measurements in points 1 to 4 in rock fragment C0076 (600 s/pt). XRF spectra were normalised for the Ta–Kα signal intensity to provide more straightforward comparison. Magnified inserts of two select energy ranges marked by dashed bounding boxes in light blue and red are displayed in parts B and C, respectively. Figure S2 CT slices that were obtained at SPring-8 beamline 20X (Nakamura et al. 2022b) show the positions of the points of interest indicated in Figure A1 in Ryugu rock fragment C0076. A red arrow marks the primary X-ray beam path and direction, fluorescence detector was positioned at the left of the CT image. Yellow circles indicate the Ca-rich grains (point 1) from which REE information is primarily obtained. Points 2–4 are matrix measurements and as such have no distinct Ca-rich grains. Separate grains along the beam path are indicated by their respective size along the beam path in orange, along with an estimate of the mineralogical phase for the larger grains.

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/10.13039/501100002806, BIOVIA Science Ambassador program, Bundesministerium für Wirtschaft und Energie http://dx.doi.org/10.13039/501100006360, Deutsches Zentrum für Luft‐ und Raumfahrt http://dx.doi.org/10.13039/501100002946, NanoRacks LLC, DreamUp, Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, Dr. Rolf M. Schwiete Stiftung