Experimental study of condensation process of minerals in the primodial solar nebula.

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Condensation of mineral grains from gas at high temperatures took place in the primodial solar nebula, and solid planets and meteorites were formed by accretion of these grains. In the present research project, the following experiments on condensation were carried out to understand the primodial solar nebula; (1) condensation experiments of forsterite, (2) reaction experiments between olivine and Si-rich gas, and (3) coarsening experiments of olivine.(1) A new vacuum furnace, in which silicates are volatilized by heating and condensation takes place from the gas, was specially designed. By using this furnace, experiments were carried out in the system Mg_2SiO_4-H_2, which mimics the solar composition. Conditions for the condensation were determined, and it was concluded that the condensation is mainly controlled by temperature and forsterite whiskers can grow by the VLS mechanism. Condensates in the system MgSIO_3-H_2 produced at Carnegie Institution, U.S.A. were also examined. It was concluded that heterogeneous nucleation would play an important role in the condensation process.(2) Reaction between condensates and residual gas is another important process during the condensation. Preliminary experiments on reaction between olivine and Si-rich gas indicate that the reaction hardly took place for olivine crystals larger than the order of 1 um.(3) The crystal size is one of the most important factor not only for the reaction kinetics but also for solid-gas fractionation. Preliminary experiments using forsterite crystals indicate that coarsening due to Ostwald ripening was not effective even in slowly cooled nebula.