A chondrule formation experiment aboard the ISS: microtomography, scanning electron microscopy and Raman spectroscopy on Mg$$_2$$SiO$$_4$$ dust aggregates

Abstract

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$$_2$$ 2 SiO$$_4$$ 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$$_2$$ 2 SiO$$_4$$ 4 particles. The partial melting and fusing of Mg$$_2$$ 2 SiO$$_4$$ 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 ($$\varnothing \approx$$ ∅ ≈ 90 µm) to bigger and irregularly shaped aggregates ($$\varnothing \approx$$ ∅ ≈ 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.