[P-PS06] Planetary Sciences

[PPS06-P24] Examination of the Earth formation process based on the impact evolution and chemical evolution of protoplanets

*Haruya Maeda¹, Takanori Sasaki¹ (1.Department of Astronomy, Kyoto University)

Keywords:Earth, Planet Formation, Protoplanet, N-body simulation, Chemical equilibrium

Rocky planets such as the Earth are formed by accretion of solid materials in protoplanetary disk. Especially during the last stage, which is the giant impact stage of protoplanets, the surface environment of the protoplanets was very different from that of the present day. The surface environment of protoplanets is considered to have been in a molten state due to the release of gravitational energy associated with the accretion. The growing protoplanet captures disk gas and forms a hydrogen-rich atmosphere. In the interior of the protoplanet, gravitational separation of the molten magma ocean and the iron core occurs. Chemical reactions between these layers formed the chemical characteristics of the protoplanet. Subsequently, the surface magma cooled and solidified, and the primordial atmosphere was eventually replaced by a secondary atmosphere derived from degassing from the interior. In this study, we examine the formation process of the Earth based on the characteristics of the surface environment of protoplanets. We first calculate the process of the growth of protoplanets to planets through giant impacts using N-body simulation. In this process, the protoplanet acquires disk gas in its own gravitational sphere as its atmosphere. At the same time, the mantle of the protoplanet that has experienced a giant impact completely melts, and materials can move through the layered structure of atmosphere-mantle-core. Chemical equilibrium calculations are performed for this layers, and are integrated with the results of N-body simulations. An important observational constraint in this study is the density deficit of the core. The core density in the present-day Earth is known to be lower than that of pure iron. In this study, we compared the number of finally formed planets and the mass/core density deficit of the planet formed near the present Earth orbit with the present solar system. The results show that the multi-stage giant impacts that protoplanets experience give a different picture depending on the degree of dissipation of disk gas. Since the initial giant impacts occur in the pre-dissipated gas-rich disk, the protoplanet takes in an excess amount of hydrogen into its inner core. Subsequent giant impacts between the protoplanet with excess hydrogen and the protoplanet uncontaminated by hydrogen adjust the amount of hydrogen in the core to obtain a composition consistent with that of the present-day Earth.