Self-gravity of debris discs can strongly change the outcomes of interactions with inclined planets

TL;DR

This study investigates how the self-gravity of debris discs influences the orbital evolution of inclined planets, revealing that self-gravity tends to align the system and significantly alters disc morphology compared to non-self-gravitating models.

Contribution

The paper demonstrates through N-body simulations that debris disc self-gravity affects planetary inclination and eccentricity evolution, challenging previous assumptions based on massless disc models.

Findings

Self-gravity causes systems to become quasi-coplanar except in polar cases.

Disc morphology becomes similar in radial and vertical directions due to self-gravity.

Massless disc models overestimate vertical dispersion for inclined planets.

Abstract

Drastic changes in protoplanets' orbits could occur in the early stages of planetary systems through interactions with other planets and their surrounding protoplanetary or debris discs. The resulting planetary system could exhibit orbits with moderate to high eccentricities and/or inclinations, causing planets to perturb one another as well as the disc significantly. The present work studies the evolution of systems composed of an initially inclined planet and a debris disc. We perform N-body simulations of a narrow, self-gravitating debris disc and a single interior Neptune-like planet. We simulate systems with various initial planetary inclinations, from coplanar to polar configurations considering different separations between the planet and the disc. We find that except when the planet is initially on a polar orbit, the planet-disc system tends to reach a quasi-coplanar configuration with low vertical dispersion in the disc. When present, the Zeipel--Kozai--Lidov oscillations induced by the disc pump the planet's eccentricity and, in turn, affect the disc structure. We also find that the resulting disc morphology in most of the simulations looks very similar in both radial and vertical directions once the simulations are converged. This contrasts strongly with massless disc simulations, where vertical disc dispersion is set by the initial disc-planet inclination and can be high for initially highly inclined planets. The results suggest caution in interpreting an unseen planet's dynamical history based only on the disc's appearance.