The Dynamics of Tightly-packed Planetary Systems in the Presence of an Outer Planet: case studies using Kepler-11 and Kepler-90

TL;DR

This study investigates how an undetected outer giant planet influences the stability, dynamics, and observability of tightly-packed inner planetary systems like Kepler-11 and Kepler-90 through numerical simulations and secular theory.

Contribution

It provides new insights into the effects of outer giant planets on inner system stability, secular resonances, and potential observational signatures in Kepler-like systems.

Findings

Outer perturbers often do not affect inner system evolution except for precession.

Secular resonances can induce significant inclination changes in inner planets.

Kepler-90 can remain stable despite outer planet-induced secular interactions.

Abstract

We explore the effects of an undetected outer giant planet on the dynamics, observability, and stability of Systems with Tightly-packed Inner Planets (STIPs). We use direct numerical simulations along with secular theory and synthetic secular frequency spectra to analyze how analogues of Kepler-11 and Kepler-90 behave in the presence of a nearly co-planar, Jupiter-like outer perturber with semi-major axes between 1 and 5.2 au. Most locations of the outer perturber do not affect the evolution of the inner planetary systems, apart from altering precession frequencies. However, there are locations at which an outer planet causes system instability due to, in part, secular eccentricity resonances. In Kepler-90, there is a range of orbital distances for which the outer perturber drives planets b and c, through secular interactions, onto orbits with inclinations that are $\sim16^\circ$ away from the rest of the planets. Kepler-90 is stable in this configuration. Such secular resonances can thus affect the observed multiplicity of transiting systems. We also compare the synthetic apsidal and nodal precession frequencies with the secular theory and find some misalignment between principal frequencies, indicative of strong interactions between the planets (consistent with the system showing TTVs). First-order libration angles are calculated to identify MMRs in the systems, for which two near-MMRs are shown in Kepler-90, with a 5:4 between b and c, as well as a 3:2 between g and h.