Photophoresis boosts giant planet formation

TL;DR

This paper demonstrates that photophoresis effectively removes dust from protoplanetary atmospheres, thereby accelerating giant planet formation within the limited timescales observed.

Contribution

It introduces photophoresis as a key mechanism that enhances dust removal, addressing a critical bottleneck in core accretion models of giant planet formation.

Findings

Photophoresis can levitate and push dust grains outward in planetary atmospheres.

Dust removal via photophoresis accelerates gas accretion onto protoplanets.

This mechanism helps reconcile formation timescales with observational constraints.

Abstract

In the core accretion model of giant planet formation, a solid protoplanetary core begins to accrete gas directly from the nebula when its mass reaches about 5 earth masses. The protoplanet has at most a few million years to reach runaway gas accretion, as young stars lose their gas disks after 10 million years at the latest. Yet gas accretion also brings small dust grains entrained in the gas into the planetary atmosphere. Dust accretion creates an optically thick protoplanetary atmosphere that cannot efficiently radiate away the kinetic energy deposited by incoming planetesimals. A dust-rich atmosphere severely slows down atmospheric cooling, contraction, and inflow of new gas, in contradiction to the observed timescales of planet formation. Here we show that photophoresis is a strong mechanism for pushing dust out of the planetary atmosphere due to the momentum exchange between gas and dust grains. The thermal radiation from the heated inner atmosphere and core is sufficient to levitate dust grains and to push them outward. Photophoresis can significantly accelerate the formation of giant planets.