On the Evolution and Survival of Protoplanets Embedded in a Protoplanetary Disk

TL;DR

This study models the evolution of Jupiter-mass protoplanets formed by disk instability, showing they cannot collapse into planets at close distances and must remain farther out during early evolution, with gas accretion influencing their development.

Contribution

It demonstrates that giant planets formed via gravitational instability must stay at large radial distances initially, and explores how gas accretion affects their pre-collapse timescale.

Findings

Protoplanets within 5-10 AU cannot undergo dynamical collapse.

Minimum formation distances depend on planetary mass and disk properties.

Gas accretion significantly shortens the pre-collapse timescale.

Abstract

We model the evolution of a Jupiter-mass protoplanet formed by the disk instability mechanism at various radial distances accounting for the presence of the disk. Using three different disk models, it is found that a newly-formed Jupiter-mass protoplanet at radial distance of $\lesssim$ 5-10 AU cannot undergo a dynamical collapse and evolve further to become a gravitational bound planet. We therefore conclude that {\it giant planets, if formed by the gravitational instability mechanism, must form and remain at large radial distances during the first $\sim$ 10$^5-10^6$ years of their evolution}. The minimum radial distances in which protoplanets of 1 Saturn-mass, 3 and 5 Jupiter-mass protoplanets can evolve using a disk model with $\dot{M}=10^{-6} M_{Sun}/yr$ and $\alpha=10^{-2}$ are found to be 12, 9, and 7 AU, respectively. The effect of gas accretion on the planetary evolution of a Jupiter-mass protoplanet is also investigated. It is shown that gas accretion can shorten the pre-collapse timescale substantially. Our study suggests that the timescale of the pre-collapse stage does not only depend on the planetary mass, but is greatly affected by the presence of the disk and efficient gas accretion.