Planetesimal formation at the gas pressure bump following a migrating planet

Abstract

Context. Planetesimal formation is still mysterious. One of the ways to form planetesimals is to invoke a gas pressure bump in a protoplanetary disc. In our previous paper, we proposed a new scenario in which the piled-up dust at a gas pressure bump created by a migrating planet forms planetesimals by streaming instability in a wide region of the disc as the planet migrates inwards. Aims. In the present work, we consider the global time evolution of dust and investigate the detailed conditions and results of the planetesimal formation in our scenario. Methods. We used a 1D grid single-sized dust evolution model, which can follow the growth of the particles in terms of their mutual collision and their radial drift and diffusion. We calculated the time-evolution of the radial distribution of the peak mass and surface density of the dust in a gas disc perturbed by an embedded migrating planet and investigated whether or not the dust satisfies the condition for planetesimal formation. Results. We find that planetesimals form in a belt-like region between the snowline and the position where the planet reaches its pebble-isolation mass when the strength of turbulence is 10−4 ≤ α ≤ 10−3, which is broadly consistent with the observed value of α. Whether the mechanism of the formation is streaming instability or mutual collision depends on the timescale of the streaming instability. The total mass of planetesimals formed in this scenario also depends on α; it is about 30–100 ME if the planetary core already exists at the beginning of the simulation and grows by gas accretion, but decreases as the timing of the formation of the planetary core gets later. We also provide simple approximate expressions for the surface density and total mass of the planetesimals and find that the total planetesimal mass strongly depends on the dust mass. Conclusions. We show that planetesimals form in a belt-like region by a combination of dust pile-up at the gas pressure bump formed by a planet and its inward migration.