Finding structural analogues to the solar system debris disc

Abstract

Many debris discs reveal a two-component structure, with a cold outer and a warm inner component. While the former is often similar to the Kuiper Belt, the origin of the latter is still a matter of debate. In the first part of this work, we investigate whether the warm dust may be a signature of asteroid belt analogues. In the scenario tested the current two-belt architecture stems from an extended protoplanetary disc separating due to a gap opening into two collisionally evolving populations. This idea is explored with an analytic collisional evolution model for a sample likely two-component debris discs from a Spitzer/IRS catalogue. We fnd that the vast majority of systems (98%) are compatible with this scenario. Short-period comets and even inward transport from the outer belts may still be viable, not mutually exclusive, alternatives to the asteroid belt scenario. The remaining five discs (2%) harbour inner components that appear inconsistent with dust production in an asteroid belt. Warm dust in these systems must require additional mechanisms to be explained. In the second part, we perform an in depth analysis of a Kuiper Belt analogue and try to reconstruct its architecture. HR8799 is a young star with four directly imaged giant planets and a two-component debris disc. Having an architecture similar to that of our solar system, but also revealing differences such as high masses of planets and the extent and mass of the outer debris belt, HR8799 is considered to be a benchmark to test models of planetary formation and evolution. We demonstrate that models of the outer disc, proposed to reproduce Herschel observations, are inconsistent with the ALMA data, and vice versa. We propose a two-population model, comprising a Kuiper-Beltlike structure of a low-eccentricity planetesimal population and a high-eccentricity population of comets.We argue that such a structure could be explained with planet migration scenarios analogous to those proposed for the Kuiper Belt.