Linking planetary embryo formation to planetesimal formation

II. The effect of pebble accretion in the terrestrial planet zone

¹ Max Planck Institute for Astronomy, Heidelberg, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: voelkel@mpia.de
² Department of Space Studies, Southwest Research Institute, Boulder, CO 80302, USA

Received: 24 August 2020
Accepted: 23 October 2020

Abstract

Context. The accretion of pebbles onto planetary cores has been widely studied in recent years and is found to be a highly effective mechanism for planetary growth. While most studies assume planetary cores as an initial condition in their simulation, the question of the manner, location, and time at which these cores form is often neglected.

Aims. We study the effect of pebble accretion during the formation phase and subsequent evolution of planetary embryos in the early stages of circumstellar disk evolution. In doing so, we aim to quantify the timescales and local dependence of planetary embryo formation based on the solid evolution of the disk.

Methods. We connected a one-dimensional two-population model for solid evolution and pebble-flux-regulated planetesimal formation to the N-body code LIPAD. We focused on the growth of planetesimals with an initial size of 100 km in diameter by planetesimal collisions and pebble accretion for the first one million years of a viscously evolving disk. We compared 18 different N-body simulations in which we varied the total planetesimal mass after one million years, the surface density profile of the planetesimal disk, the radial pebble flux, and the possibility of pebble accretion.

Results. Pebble accretion leads to the formation of fewer but substantially more massive embryos. The area of possible embryo formation is weakly affected by the accretion of pebbles, and the innermost embryos tend to form slightly earlier than in simulations in which pebble accretion is neglected.

Conclusions. Pebble accretion strongly enhances the formation of super-Earths in the terrestrial planet region, but it does not enhance the formation of embryos at larger distances.