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

A chondrule formation experiment aboard the ISS: microtomography, scanning electron microscopy and Raman spectroscopy on Mg2_2SiO4_4 dust aggregates

We performed an experiment under long-term microgravity conditions aboard the International Space Station (ISS) to obtain information on the energetics and experimental constraints required for the formation of chondrules in the solar nebula by ’nebular lightning’. As a simplified model system, we exposed porous forsterite (Mg$_2$SiO$_4$) dust particles to high-energetic arc discharges. The characterization of the samples after their return by synchrotron microtomography and scanning electron microscopy revealed that aggregates had formed, consisting of several fused Mg$_2$SiO$_4$ particles. The partial melting and fusing of Mg$_2$SiO$_4$ dust particles under microgravity conditions leads to a strong reduction of their porosity. The experimental outcomes vary strongly in their appearance from small spherical melt-droplets (∅≈ 90 µm) to bigger and irregularly shaped aggregates (∅≈ 350 µm). Our results provided new constraints with respect to energetic aspects of chondrule formation and a roadmap for future and more complex experiments on Earth and in microgravity conditions

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