[M-GI33] Computational sciences on the universe, galaxies, stars, planets, and their environments

[MGI33-09] Study of the Accretion Process of Rocky Planetesimals using Realistic Accretion Condition

*Takashi Shibata¹, Eiichiro Kokubo^1,2, Junichiro Makino³, Yota Ishigaki² (1.National Astronomical Observatory of Japan, 2.The University of Tokyo, 3.Kobe University)

Keywords:Formation of Planets, Planetesimal Accretion, Merging Criteria of Planetesimals

The accretion of planetesimals, which is a process of planet formation, has been investigated by N-body simulation. Planetesimals are thought to have evolved into protoplanets through runaway and oligarchic growth. In the study of the accretion process using the N-body calculation, which is the first-principles calculation, there are few studies that consider realistic behavior such as the bounce of planetesimals. Also, studies that consider bounces and debris have not always been calculated under realistic accretion conditions. In this study, the accretion condition of planetesimals was clarified by numerical collision experiments using Smoothed Particle Hydrodynamics (SPH). In addition, using the formulated accretion conditions, we investigated the realistic accretion process of rocky planetesimals by N-body simulation. Numerical collision experiments of planetesimals using SPH have revealed that the critical impact velocity, which is the threshold of the velocity at which bounce occurs, depends on the mass ratio and collision angle of the collision planetesimals. When the mass ratio is high or the collision angle is shallow, it becomes easy to bounce. On the other hand, it does not depend on the total mass of the colliding planetesimals. In this study, the critical impact velocity is formulated, and the bounce is determined from the collision velocity, mass ratio, and collision angle of the planetesimals. If the collision speed exceeds the critical impact velocity, it is determined to be a bounce, and here it is called an accretion condition. By applying the accretion condition to the N-body simulation that calculates the accretion process of rocky planetesimals and calculating the orbits and collisions of the planetesimals around the sun, we will clarify the more realistic accretion process of rocky planetesimals. While general planetesimals are hindered by rebounding, the planetesimals that have grown runaway take in the surrounding planetesimals due to gravity, and the growth progresses. As a result, a more dichotomized mass distribution of planetesimals was observed compared to the conventional study of planetesimal accretion processes that did not consider rebound. In this way, by considering the realistic collision behavior of bounce, runaway growth and oligarchic growth became more prominent. In other words, it can be understood that it is important to correctly handle the behavior at the time of the planetesimal collision in order to understand the realistic accretion process. In this talk, we will introduce the accretion conditions clarified by SPH simulation, and then discuss the result of N-body simulation of the accretion process of rocky planetesimals considering rebound.