The HR 8799 debris disk: Shaped by planetary migration and a possible fifth outermost planet

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
² Department of Physics, University of Warwick, Coventry CV4 7AL, UK
³ Instituto de Astrofísica, Pontificia Universidad Catόlica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile

^★ Corresponding author: pedro.poblete@univ-grenoble-alpes.fr

Received: 27 March 2025
Accepted: 2 July 2025

Abstract

Context. The HR 8799 system hosts four giant planets between a warm and cold debris disk and has an extended dusty tail beyond. It serves as an ideal laboratory for studying planetary formation and evolution. The debris disks have been observed at various wavelengths, and the planetary properties are well constrained. Nonetheless, there are still open questions regarding the role of the planets in shaping the debris disks.

Aims. We investigated the system evolution with the aim of understanding how planetary migration shaped its architecture in terms of planets and the disk.

Methods. We performed N-body simulations to model the HR 8799 system. We examined the orbital evolution of the known four super-Jupiter planets through the course of simple, imposed migration in a gaseous disk as they perturb an external massless planetesimal disk. We also explored the impact of introducing a fifth planet on the dynamical and morphological aspects of the disk.

Results. The planets migrate outward as a result of their imposed interactions with the gaseous disk while maintaining their resonant configuration. This outward migration excites the planetesimal disk and produces a transient scattered population. While a four-planet system partially reproduces the observed cavity between the star and the cold debris disk, the inclusion of a fifth low-mass planet appears to be crucial for better reproducing key morphological aspects of the cold debris disk.

Conclusions. This model provides a novel explanation for the architecture of HR 8799. Outward planetary migration, combined with mean-motion resonant interactions and a fifth low-mass planet, can effectively replicate the observed planetary architecture and the characteristics of the cold debris disk. Our findings underscore the potential important role of planetary migration in shaping debris disks.