HD 163296 and its giant planets: Creation of exo-comets, interstellar objects and transport of volatile material

Context. The birth of giant planets in protoplanetary discs is known to alter the structure and evolution of the disc environment, however most of our knowledge is focussed on its effects on the observable gas and dust. The impact on the evolution of the invisible planetesimal population remains insufficiently studied, yet mounting evidence from the Solar System shows how the appearance of its giant planets played a key role in shaping the habitability of the terrestrial planets. Aims. We investigate the dynamical and collisional transport processes of volatile elements by planetesimals in protoplanetary discs that host young giant planets using the HD 163296 system as our case study. HD 163296 is one of the best-characterised protoplanetary discs and has been proposed to host at least four giant planets on wide orbits as well as a massive planetesimal disc. The goal of this study is to assess the impact of the dynamical and collisional transport on the disc as well as on existing and forming planetary bodies. Methods. We performed high-resolution n-body simulations of the dynamical evolution of planetesimals embedded in HD 163296s protoplanetary disc across and after the formation of its giant planets, accounting for the uncertainty on both the disc and planetary masses as well as for the effects of aerodynamic drag of the disc gas and the gas gravity. To quantify the impact probabilities with existing and possible undiscovered planetary bodies, we processed the output of the n-body simulations with well-tested statistical collisional algorithms from studies of the asteroid belt. Results. In our simulations the formation of giant planets in the HD 163296 system creates a large population of dynamically excited planetesimals, the majority of which originate from beyond the CO snowline. The excited planetesimals are then transported to the inner disc regions as well as scattered outward beyond the protoplanetary disc and into interstellar space. In the inner disc, potential solid planets can be enriched in volatile elements to levels that are comparable or larger than those of the Earth, while giant planets can be enriched to the levels of Jupiter and Saturn. Conclusions. The formation of giant planets on wide orbits impacts the compositional evolution of protoplanetary discs and young planetary bodies on a global scale. The collisional enrichment of the atmospheres of giant planets can alter or mask the signatures of their formation environments; this process can also provide independent constraints on the disc mass. In our simulations protoplanetary discs with giant planets on wide orbits prove efficient factories of interstellar objects.