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Mg2SiO4 particle aggregation aboard the ISS

Context. Particle aggregation in the solar nebula played a major role in the framework of planet formation; for example, primitive meteorites and their components formed by different aggregation processes. These processes are still not completely understood.
Aims. Electrostatic forces probably influenced particle aggregation in the early Solar System. We developed an experiment that was carried out under long-term microgravity conditions aboard the International Space Station (ISS) to expand the knowledge of charge-influenced particle aggregation.
Methods. Aggregation of freely floating, elongated, angular, and polycrystalline Mg2SiO4-particles was observed under long-term microgravity conditions while being exposed to electric fields as well as low- and high-energy electric discharges.
Results. Nearly all of the particles formed an aggregate, which freely floated in the sample chamber prior to the discharge experiments. The aggregate was attracted by the electrodes and partly disintegrated by low-energy electric discharges. High-energy arc discharges accelerated the particles, which reassembled in chains parallel to the field lines of the subsequent electric field between the electrodes. A strong shape-preferred orientation of the longest grain axis parallel to the field lines was observed in the Mg2SiO4-particles. With increasing strength of the electric field, the particle chains narrowed, leading to the formation of a compact aggregate.
Conclusions. In microgravity conditions, electrostatic forces influence the aggregation process in terms of aggregate growth rate, morphology, packing density, and particle orientation. These observations help us to better understand the formation and compaction mechanism of early Solar System aggregates.