Kepler-108: A Mutually Inclined Giant Planet System

TL;DR

Kepler-108 is a highly mutually inclined, eccentric giant planet system that challenges traditional disk migration models, providing evidence for planet-planet scattering effects.

Contribution

This study characterizes a highly mutually inclined giant planet system, offering new insights into planet-planet scattering and system evolution beyond coplanar configurations.

Findings

Kepler-108 has mutual inclination of 15-60 degrees.

The system's eccentricities are greater than 0.1.

The planetary configuration is inconsistent with pure disk migration.

Abstract

The vast majority of well studied giant-planet systems, including the Solar System, are nearly coplanar which implies dissipation within a primordial gas disk. however, intrinsic instability may lead to planet-planet scattering, which often produces non-coplanar, eccentric orbits. Planet scattering theories have been developed to explain observed high eccentricity systems and also hot Jupiters; thus far their predictions for mutual inclination (I) have barely been tested. Here we characterize a highly mutually-inclined (I ~ 15-60 degrees), moderately eccentric (e >~ 0.1) giant planet system: Kepler-108. This system consists of two approximately Saturn-mass planets with periods of ~49 and ~190 days around a star with a wide (~300AU) binary companion in an orbital configuration inconsistent with a purely disk migration origin.