Stability of Earth-mass Planets in the Kepler-68 System

TL;DR

This study analyzes the orbital stability of the Kepler-68 system, identifying potential stable regions for Earth-mass planets within the habitable zone through detailed dynamical simulations.

Contribution

It provides the first detailed stability analysis of Kepler-68, constraining the outer planet's inclination and identifying possible stable orbits for Earth-mass planets.

Findings

Outer planet within the habitable zone

Orbital inclination of outer planet > 5 degrees

Stable Earth-mass planet at 2:3 resonance

Abstract

A key component of characterizing multi-planet exosystems is testing the orbital stability based on the observed properties. Such characterization not only tests the validity of how observations are interpreted but can also place additional constraints upon the properties of the detected planets. The Kepler mission has identified hundreds of multi-planet systems but there are a few that have additional non-transiting planets and also have well characterized host stars. Kepler-68 is one such system for which we are able to provide a detailed study of the orbital dynamics. We use the stellar parameters to calculate the extent of the Habitable Zone for this system, showing that the outer planet lies within that region. We use N-body integrations to study the orbital stability of the system, in particular placing an orbital inclination constraint on the outer planet of i > 5 degrees. Finally, we present the results of an exhaustive stability simulation that investigates possible locations of stable orbits for an Earth-mass planet. We show that there are several islands of stability within the Habitable Zone that could harbor such a planet, most particularly at the 2:3 mean motion resonance with the outer planet.