[P-PS21_29PO1] Planetary Sciences

[PPS21-P07] Evolution of a protoplanetary disk and chemical composition of planetesimals

*Hiroko NAGAHARA¹, Kazuhito OZAWA¹ (1.Dept. Earth Planet. Sci., The Univ. Tokyo)

Keywords:protoplanetary dsik, chemical evolution, dust movement

We investigate physico-chemical evolution of the proto-solar disk at the early stage by developing a new model that combines physics and chemistry with special interest to temporal and spatial evolution of the disk. Then, we discuss how the composition of planetesimals varies depending on the time and space for their formation including refractory or volatile rich ones.The basic of the model is a radial advection-diffusion equation, which includes drift and dispersion by turbulence with stochastic diffusion term calculated by the Monte Carlo method and which shows the diffusivity by the viscosity of the disk. The difference from conventional disk models is that the present method stands on the Lagrangean differentiation, and it is able to trace the movement of individ- ual particles.A considerable amount of materials in the inner regions are transported outward at the early stage (t < 10^5 yrs), which is because the surface density is much larger in the inner region at the early stage of the disk evolution. Although the outward flux is large at the early stage, there comes a larger amount of materials from the outer region even within ~10^5 yrs. The mixing ratio of materials from the inner regions to outer regions is almost unity within several AU all through the disk evolution, suggesting that thermally processed materials and unprocessed materials were mixed in the inner region of the disk. It is important that the relative abundance of materials from outer regions becomes larger with time, which implies that planetesimals formed within several AU at the early stage of the disk evolution consists partly of materials initially located at the inner regions and partly from outer regions, but those formed at the later stage contain more abundant law materials transported from the outer regions.The mixing ratio of materials from the inner and outer regions is almost unity at the early stage but the fraction of materials from the outer regions increases with time. Combining the information about the maximum temperature that the particles experienced, we can constrain that early differentiated planetesimals such as the parent body of angrites and planetesimals with refractory-rich compositions such as CV chondrites were formed at the inner region of the disk in ~10^5 yrs. On the other hand, planetesimals for other carbonaceous chondrites or ordinary chondrites that are depleted in sulfur were formed later, possibly at ~10^6 yrs.