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H. Miura, T. Nakamoto, H. Susa (Center for Computational Physics, University of Tsukuba), A. Iida (Cray Japan, Inc.)
Chondrules are mm-sized, once-molten, spherical-shaped grains composed of silicate material in chondritic meteorites. It is considered that dust particles, which are chondrule precursors, were heated and melted, and cooled again to solidify in a short period of time, and formed chondrules, although the heating mechanism responsible for the chondrule formation has not been clearly understood yet. Shock-wave heating model is one of the popular models for the heating process. In the model, dust grains are heated due to the drag heating in the post shock flow. Conditions of the shock flow in which dust particles can be heated up to the melting point have been revealed in previous work. However, the heating condition is not enough to form the chondrules.
We examined, in a framework of the shock-wave heating model, if the shock flow can keep the heated dust particles molten stably. We numerically simulated the heating process in the flow taking into account the evaporation from the dust surface and the ram pressure from the flow onto the particle. We found that the complete vaporization condition does not change significantly, though the evaporation and the latent heat cooling take place during the heating process. We also found that the total gas pressure acting on the particle, which is a summation of the static pressure and the ram pressure, exceeds the vapor pressure of the molten dust particle. Therefore, it is possible to form chondrules, which are once-molten dust particles, in the shock-wave heating model if the dust temperature increases up to the melting point.