Dust-to-gas ratio resurgence in circumstellar disks due to the formation of giant planets: the case of HD 163296

TL;DR

This study shows that giant planet formation can rejuvenate dust in circumstellar disks by inducing collisions that produce new dust, explaining high dust-to-gas ratios in mature disks like HD 163296.

Contribution

It introduces a model combining simulations and impact laws to demonstrate how planet formation can increase dust via collisional processes in disks.

Findings

Giant planet formation causes violent collisions that produce second-generation dust.

The dust distribution explains observed local dust enrichments.

Planetesimal collisions can release transient gas species and produce shock heating.

Abstract

The amount of dust present in circumstellar disks is expected to steadily decrease with age due to the growth from micron-sized particles to planetesimals and planets. Mature circumstellar disks, however, can be observed to contain significant amounts of dust and possess high dust-to-gas ratios. Using HD 163296 as our case study, we explore how the formation of giant planets in disks can create the conditions for collisionally rejuvenating the dust population, halting or reversing the expected trend. We combine N-body simulations with statistical methods and impact scaling laws to estimate the dynamical and collisional excitation of the planetesimals due to the formation of HD 163296's giant planets. We show that this process creates a violent collisional environment across the disk that can inject collisionally produced second-generation dust into it, significantly contributing to the observed dust-to-gas ratio. The spatial distribution of the dust production can explain the observed local enrichments in HD 163296's inner regions. The results obtained for HD 163296 can be extended to any disk with embedded forming giant planets and may indicate a common evolutionary stage in the life of such circumstellar disks. Furthermore, the dynamical excitation of the planetesimals could result in the release of transient, non-equilibrium gas species like H2O, CO2, NH3 and CO in the disk due to ice sublimation during impacts and, due to the excited planetesimals being supersonic with respect to the gas, could produce bow shocks in the latter that could heat it and cause a broadening of its emission lines.