Orbital Stability of Multi-Planet Systems: Behavior at High Masses

TL;DR

This paper investigates the stability of high-mass, multi-planet systems, revealing that traditional low-mass stability models overestimate stability at super-Jupiter masses and highlighting the role of mean motion resonances in system chaos.

Contribution

It demonstrates that stability predictions for massive, tightly packed planetary systems require adjustments for high mass effects and identifies the significance of second order resonances at high planet-star mass ratios.

Findings

Extrapolating low-mass stability models overestimates high-mass system stability.

Overlapping mean motion resonances induce chaos and instability.

High mass ratios increase the importance of second order resonances.

Abstract

In the coming years, high contrast imaging surveys are expected to reveal the characteristics of the population of wide-orbit, massive, exoplanets. To date, a handful of wide planetary mass companions are known, but only one such multi-planet system has been discovered: HR8799. For low mass planetary systems, multi-planet interactions play an important role in setting system architecture. In this paper, we explore the stability of these high mass, multi-planet systems. While empirical relationships exist that predict how system stability scales with planet spacing at low masses, we show that extrapolating to super-Jupiter masses can lead to up to an order of magnitude overestimate of stability for massive, tightly packed systems. We show that at both low and high planet masses, overlapping mean motion resonances trigger chaotic orbital evolution, which leads to system instability. We attribute some of the difference in behavior as a function of mass to the increasing importance of second order resonances at high planet-star mass ratios. We use our tailored high mass planet results to estimate the maximum number of planets that might reside in double component debris disk systems, whose gaps may indicate the presence of massive bodies.