Shock-Wave Heating Model for Chondrule Formation: Thermal Evolution of Precursor Dust Particles and Hydrodynamics of Molten Droplets

Chondrules are millimeter-sized, once-molten, spherical shaped grains universally contained in chondritic meteorites, which command a majority of meteorites falling onto the Earth. They are considered to have formed from chondrule precursor dust particles in the solar nebula; they were heated and melted through flash heating events in the solar nebula and cooled again to solidify in a short period of time. A shock-wave heating model is one of the most plausible models for chondrule formation. In this thesis, we investigate two themes about the shock-wave heating model for chondrule formation. The former theme is about the dust thermal histories when they meet shock waves generated in the protoplanetary disk. The latter theme is about the hydrodynamics of molten dust particles exposed to the high-velocity rarefied gas flow. First, we notice the heating rate of the precursor dust particles before they melt in the gas flow. It is known that the precursor dust particles should be heated rapidly enough (> ∼ 10 Khr−1) at a temperature range of 1273− 1473K in order to prevent the isotopic fractionation of sulfur contained in chondrules. In the shockwave heating model, the gas frictional heating can heat the dust particles rapidly enough in the post-shock region. However, the dust particles can be heated in the pre-shock region by the radiation mainly emitted from the post-shock gas and dust particles. It has not been investigated how the radiation field affects the heating rates of the precursor dust particles. We study the conditions for the rapid heating constraint by numerical simulating the shock-wave heating model taking into account the radiation transfer, and obtain the heating rates of the precursor dust particles for various conditions. We find that the heating rates decreases drastically