Rapid Formation of Jupiter and Wide-Orbit Exoplanets in Disks with Pressure Bumps

TL;DR

This study demonstrates that pressure bumps in protoplanetary disks enable rapid formation of Jupiter-mass planets at wide orbits through pebble accretion, explaining observed exoplanets and planetary mass disparities.

Contribution

It introduces a model of planet formation in disks with pressure bumps, highlighting their role in rapid giant planet growth at wide orbits, which was not considered in previous monotonic pressure profile models.

Findings

Pebble trapping at pressure bumps facilitates rapid planet growth.

Growth sensitivity depends on initial mass and turbulence levels.

Planets can reach Jupiter mass within 0.5-3 million years at wide orbits.

Abstract

The formation of gas-giant planets within the lifetime of a protoplanetary disk is challenging especially far from a star. A promising model for the rapid formation of giant-planet cores is pebble accretion in which gas drag during encounters leads to high accretion rates. Most models of pebble accretion consider disks with a monotonic, radial pressure profile. This causes a continuous inward flux of pebbles and inefficient growth. Here we examine planet formation in a disk with multiple, intrinsic pressure bumps. In the outer disk, pebbles become trapped near these bumps allowing rapid growth under suitable conditions. In the inner disk, pebble traps may not exist because the inward gas advection velocity is too high. Pebbles here are rapidly removed. In the outer disk, growth is very sensitive to the initial planet mass and the strength of turbulence. This is because turbulent density fluctuations raise planetary eccentricities, increasing the planet-pebble relative velocity. Planetary seeds above a distance-dependent critical mass grow to a Jupiter mass in 0.5--3 million years out to at least 60 AU in a 0.03 solar-mass disk. Smaller bodies remain near their initial mass, leading to a sharp dichotomy in growth outcomes. For turbulent alpha = 1e-4, the critical masses are 1e-4 and 1e-3 Earth masses at 9 and 75 AU, respectively. Pressure bumps in disks may explain the large mass difference between the giant planets and Kuiper belt objects, and also the existence of wide-orbit planets in some systems.