Planetesimal Growth in Evolving Protoplanetary Disks: Constraints from the Pebble Supply

Abstract

In the core accretion model, planetesimals grow by mutual collisions and engulfing millimeter-to-centimeter particles, i.e., pebbles. Pebble accretion can significantly increase the accretion efficiency and help explain the presence of planets on wide orbits. However, the pebble supply is typically parameterized as a coherent pebble mass flux, sometimes being constant in space and time. Here we solve the dust advection and diffusion within viciously evolving protoplanetary disks to determine the pebble supply self-consistently. The pebbles are then accreted by planetesimals interacting with the gas disk via gas drag and gravitational torque. The pebble supply is variable with space and decays with time quickly, with a pebble flux below 10 M _⊕ Myr ^−1 after 1 Myr in our models. As a result, only when massive planetesimals (>0.01 M _⊕ ) are luckily produced by the streaming instability or the disk has low viscosity ( α ∼ 0.0001) can the herd of planetesimals grow over a Mars mass within 2 Myr. By then, planetesimals only capture pebbles about 50 times their mass and as little as 10 times beyond 20 au due to limited pebble supply. Further studies considering multiple dust species in various disk conditions are warranted to fully assess the realistic pebble supply and its influence on planetesimal growth.

Keywords

• Planetesimals
• Protoplanetary disks
• Circumstellar dust
• Planet formation