Planet-Planet Scattering and ZLK Migration -- The Dynamical History of HAT-P-11

TL;DR

This paper proposes a two-step dynamical history involving planet-planet scattering and ZLK cycles to explain the eccentricities and misalignments of HAT-P-11's planets, consistent with observations and system age.

Contribution

It introduces a combined scattering and high-eccentricity migration model to explain HAT-P-11's orbital features, incorporating tidal effects and radius inflation.

Findings

The scenario matches observed orbital parameters and system age.

Tidal radius inflation is crucial for the migration process.

N-body simulations support the proposed evolutionary pathway.

Abstract

The two planets of the HAT-P-11 system represent fascinating dynamical puzzles due to their significant eccentricities and orbital misalignments. In particular, HAT-P-11 b is on a close-in orbit that tides should have circularized well within the age of the system. Here we propose a two-step dynamical process that can reproduce all intriguing aspects of the system. We first invoke planet-planet scattering to generate significant eccentricities and mutual inclinations between the planets. We then propose that this misalignment initiated von-Zeipel-Lidov-Kozai cycles and high-eccentricity migration that ultimately brought HAT-P-11 b to its present-day orbit. We find that this scenario is fully consistent only when significant tidally-driven radius inflation is accounted for during the tidal migration. We present a suite of N-body simulations exploring each phase of evolution and show that this scenario is consistent with all observational posteriors and the reported age of the system.