Resonant Excitation of Planetary Eccentricity due to a Dispersing Eccentric Protoplanetary Disk: A New Mechanism of Generating Large Planetary Eccentricities

TL;DR

This paper introduces a new mechanism where a dispersing eccentric protoplanetary disk can secularly excite large planetary eccentricities through resonance, even with small disk eccentricities, expanding understanding of planetary orbit evolution.

Contribution

The study demonstrates that a dispersing eccentric disk can induce significant planetary eccentricities via secular resonance, a process not previously characterized in this context.

Findings

Planets can reach eccentricities of 0.1 to 0.6 due to disk interactions.

Small disk eccentricities (~0.05) can still produce large planetary eccentricities.

Mode conversion explains the eccentricity excitation mechanism.

Abstract

We present a new mechanism of generating large planetary eccentricities. This mechanism applies to planets within the inner cavities of their companion protoplanetary disks. A massive disk with an inner truncation may become eccentric due to non-adiabatic effects associated with gas cooling, and can retain its eccentricity in long-lived coherently-precessing eccentric modes; as the disk disperses, the inner planet will encounter a secular resonance with the eccentric disk when the planet and the disk have the same apsidal precession rates; the eccentricity of the planet is then excited to a large value as the system goes through the resonance. In this work, we solve the eccentric modes of a model disk for a wide range of masses. We then adopt an approximate secular dynamics model to calculate the long-term evolution of the "planet + dispersing disk" system. The planet attains a large eccentricity (between 0.1 and 0.6) in our calculations, even though the disk eccentricity is quite small ($\lesssim0.05$). This eccentricity excitation can be understood in terms of the mode conversion (``avoided crossing'') phenomenon associated with the evolution of the "planet + disk" eccentricity eigenstates.