Orbital Migration of Protoplanets in a Marginally Gravitationally Unstable Disk

TL;DR

This study uses advanced 3D hydrodynamics models to explore how protoplanets migrate within massive, marginally gravitationally unstable disks, revealing complex orbital behaviors and potential stability of giant planets during such phases.

Contribution

It introduces detailed 3D gravitational radiation hydrodynamics simulations of protoplanets in MGU disks, including gas accretion and interactions, to study migration and stability.

Findings

Protoplanets of 0.01 to 10 Earth masses can remain stable for ~1000 years.

Giant planet systems similar to Solar System can be stable over 1000+ years.

Monotonic inward or outward migration does not occur in these massive, unstable disks.

Abstract

Core accretion and disk instability require giant protoplanets to form in the presence of disk gas. Protoplanet migration models generally assume disk masses low enough that the disk's self-gravity can be neglected. However, disk instability requires a disk massive enough to be marginally gravitationally unstable (MGU). Even for core accretion, a FU Orionis outburst may require a brief MGU disk phase. We present a new set of three dimensional, gravitational radiation hydrodynamics models of MGU disks with multiple protoplanets, which interact gravitationally with the disk and with each other, including disk gas mass accretion. Initial protoplanet masses are 0.01 to 10 $M_\oplus$ for core accretion models, and 0.1 to 3 $M_{Jup}$ for Nice scenario models, starting on circular orbits with radii of 6, 8, 10, or 12 AU, inside a 0.091 $M_\odot$ disk extending from 4 to 20 AU around a $1 M_\odot$ protostar. Evolutions are followed for up to $\sim$ 4000 yr and involve phases of relative stability ($e \sim$ 0.1) interspersed with chaotic phases ($e \sim$ 0.4) of orbital interchanges. The 0.01 to 10 $M_\oplus$ cores can orbit stably for $\sim$ 1000 yr: monotonic inward or outward orbital migration of the type seen in low mass disks does not occur. A system with giant planet masses similar to our Solar System (1.0, 0.33, 0.1, 0.1 $M_{Jup}$) was stable for over 1000 yr, and a Jupiter-Saturn-like system was stable for over 3800 yr, implying that our giant planets might well survive a MGU disk phase.