Experimental Chondrule Formation I - Lightning Discharge Experiments under Microgravity Conditions at the International Space Station

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With this project we intend to study the formation mechanism of chondrules, one of the most important and most frequent solids formed within the first million years of the Solar System. Although known for almost hundred years the formation mechanism is still a matter of intense scientific debate. Just recently the discussion about the formation mechanism of chondrules get several new impulses and re-activated a few of the most favorable formation mechanism like nebular lightning discharges (e.g. Johansen and Okuzumi, 2018), nebular shock waves (e.g. Desch et al., 2012; Fedkin et al., 2012) and asteroidal collision (e.g. Sanders and Scott, 2012). In addition several new aspects of the chondrule formation process itself were published (Palme et al., 2015; Friend, 2017). Taking all this into account the lack of experimental chondrule formation at conditions relevant to the solar nebula, e.g under microgravity, is obvious.The new experimental approach presented here will be performed under microgravity conditions aboard the International Space Station during Alexander Gerst´s current space mission. The sample container will returned to Earth in December 2018 for detailed analytical laboratory studies. The experiment was accepted as one of only three experiments within the framework of the “Ueberflieger”- competition. The proposal presented here will cover the detailed analytical study of the sample material after returned to Earth and the evaluation of the full digital video coverage of the experiment.The main goals of the project are:1) Is lightning are reasonable process to produce chondrule like objects under microgravity conditions?2) Do melting of dust aggregates enhance particle growth?3) What are the structural details of the chondrule like objects formed and can they be related to specific known chondrule types expected to form at high cooling rates, like cryptocrystalline, radial olivine or barred olivine chondrules.4) What are the geochemical consequences on chondrules formed by lightning discharges?5) What is the degree of crystallinity obtained?6) Do we see phase separation and/or the formation of other phases like pyroxene, commonly found in chondrules?