Self-consistent $N$-body simulation of Planetesimal-Driven Migration. II. The effect of PDM on planet formation from a planetesimal disk

Abstract

According to the canonical planet formation theory, planets form "in-situ" within a planetesimal disk via runaway and oligarchic growth. This theory, however, cannot naturally account for the formation timescale of ice giants or the existence of diverse exoplanetary systems. Planetary migration is a key to resolving these problems. One well-known mechanism of planetary migration is planetesimal-driven migration (PDM), which can let planets undergo significant migration through gravitational scattering of planetesimals. In our previous paper (Jinno et al. 2024, PASJ, 76, 1309), we investigated the migration of a single planet through PDM, addressing previously unexplored aspects of both the gravitational interactions among planetesimals and the interactions with disk gas. Here we perform the first high-resolution simulations of planet formation from a large-scale planetesimal disk, incorporating planet-gas disk interactions, planet-planetesimal interactions, gravitational interactions among all planetesimals, and physical collisions between planetesimals to investigate the role of PDM in the planet formation process. Our results show that protoplanets undergo dynamic inward/outward migrations during the runaway growth stage via PDM. Moreover, orbital repulsion combined with PDM tends to make two groups of protoplanets, outer ones going outward and inner ones going inward. Such dynamic migration significantly influences the early stages of planetary formation. These findings provide a viable pathway for the formation of Earth-like planets and ice giants' cores. Furthermore, they suggest that a standard protoplanetary disk model can account for the planetary migration necessary to explain diverse exoplanetary systems without the need for additional hypotheses.