Debris disc formation induced by planetary growth

TL;DR

This paper models how planetary growth causes debris disc formation, showing that narrow planetesimal discs with 100 km-sized bodies at 30 AU best explain observed infrared excesses around G-type stars.

Contribution

It introduces a numerical model linking planetesimal coagulation and fragmentation to debris disc properties, clarifying their formation and evolution.

Findings

Narrow planetesimal discs best match observed infrared excesses.

Debris disc brightness depends on disc size, mass, and planetesimal size.

Early debris formation is driven by planet formation, followed by collisional decay.

Abstract

Several hundred stars older than 10 million years have been observed to have infrared excesses. These observations are explained by dust grains formed by the collisional fragmentation of hidden planetesimals. Such dusty planetesimal discs are known as debris discs. In a dynamically cold planetesimal disc, collisional coagulation of planetesimals produces planetary embryos which then stir the surrounding leftover planetesimals. Thus, the collisional fragmentation of planetesimals that results from planet formation forms a debris disc. We aim to determine the properties of the underlying planetesimals in debris discs by numerically modelling the coagulation and fragmentation of planetesimal populations. The brightness and temporal evolution of debris discs depend on the radial distribution of planetesimal discs, the location of their inner and outer edges, their total mass, and the size of planetesimals in the disc. We find that a radially narrow planetesimal disc is most likely to result in a debris disc that can explain the trend of observed infrared excesses of debris discs around G-type stars, for which planet formation occurs only before 100 million years. Early debris disc formation is induced by planet formation, while the later evolution is explained by the collisional decay of leftover planetesimals around planets that have already formed. Planetesimal discs with underlying planetesimals of radii $\sim 100\,$km at $\approx 30$ AU most readily explain the Spitzer Space Telescope 24 and 70$ \mu$m fluxes from debris discs around G-type stars.