Giant Planet Formation with Pebble Accretion
Abstract
In the core accretion model, a giant-planet core forms from dust in a protoplanetary disk and accretes gas when the core reaches a critical mass. Both stages must occur in a few My before the disk disperses. The slowest stage may be oligarchic growth in which a core grows by sweeping up planetesimals. Here, I describe new simulations of oligarchic growth that include (i) planetesimal fragmentation due to mutual collisions, (ii) the capture of planetesimals by a core’s atmosphere, (iii) drag with the disk gas during encounters with the core (“pebble accretion”), (iv) particle velocities due to turbulence and drift caused by gas drag, and (v) a population of small “pebbles” that represent the transition between disruptive collisions between larger particles, and mergers between dust grains. Planetesimal collisions rapidly form a large population of pebbles. The rate at which a core sweeps up pebbles is controlled by pebble accretion dynamics, and depends strongly on pebble size. Large pebbles lose energy during an encounter with a core due to drag, and settle towards the core, greatly increasing the capture probability. Small pebbles are tightly coupled to the gas and most are swept past the core rather than being captured. The strength of turbulence in the gas mainly affects the scale height of pebbles in the disk, altering the rate at which they are accreted. Planetesimal size mainly determines the rate of mutual collisions and pebble production. Critical-mass cores can form at 5 AU from the Sun within 3 My if pebbles are 3 cm to 1 m in diameter, and the solid surface density is at least 8 g/cm^2 .
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #45
- Pub Date:
- October 2013
- Bibcode:
- 2013DPS....4551006C