原始惑星系円盤における物質進化

抄録

  A protoplanetary disk is a dynamic system where physical and chemical processes interplay in complex manners, and it is the place where planetesimals were formed that further collided to form planets. The chemical difference among planets and planetesimals along with volatility-controlled composition of chondrites deviated from CI chondrite clearly indicate condensation and accompanying chemical differentiation are crucial. In order to gain fundamental understanding of the origin of planets, which requires integration of physics and chemistry, we have carried out evaporation and condensation experiments that enable us to describe principle behaviors of gas-solid reaction kinetics involving multiple condensed phases. Those parameters are dependent on cooling time scale and total pressure of the disk, which evolve with time and space. It is shown that phases that are not expected in equilibrium condensation appear in a dynamically cooling system, that the phases and their grain sizes are strongly dependent on the cooling time scale, and that the grains become as large as mm in size only with the chemical process, which is much larger than that usually assumed in standard models. The condensed grains with iron mantle make coagulation easier resulting in effective growth of dusts to form planetesimals.