Two-step nucleation process of silicate interplanetary dust particles at the vicinity of silicate melt

The condensation processes of interplanetary dust particles (IDPs) around a high temperature silicate melt droplet were investigated in situ by a newly developed flash heating technique under microgravity using a drop tube facility. Two-step nucleation process was captured in the vicinity of the MgSiO ₃ melt by a CCD camera. The first nucleation was observed at a distance of 7 mm from the vapor source at 0.3 s and the second nucleation was observed 1.4 s after the MgSiO₃ melt evaporated. The first nucleated particles were irregularly shaped amorphous silica with a diameter of 100-500 nm. The amorphous enstatite particles with a diameter of 70 nm nucleated 1.1 s later. The observed condensation sequence was silica and then enstatite. The difference of these condensations sequence with the chemical equilibrium was showed through the present experiment. The present in situ observation under microgravity was found to be a very useful technique to judge the nucleation sequence of various phases in very short duration within 3.0 s.