Kepler-1656b's Extreme Eccentricity: Signature of a Gentle Giant

Abstract

Highly eccentric orbits are one of the major surprises of exoplanets relative to the Solar System and indicate rich and tumultuous dynamical histories. One system of particular interest is Kepler-1656, which hosts a sub-Jovian planet with an eccentricity of 0.8. Sufficiently eccentric orbits will shrink in semi-major axis due to tidal dissipation of orbital energy during periastron passage. Here our goal was to assess whether Kepler-1656b is currently undergoing such high-eccentricity migration, and to further understand the system's origins and architecture. We confirm a second planet in the system with $M_{\mathrm{c}}=0.40\pm 0.09M_{\mathrm{jup}}$ and P${}_{\mathrm{c}}=1919\pm 27$days. We simulated the dynamical evolution of planet b in the presence of planet c and find a variety of possible outcomes for the system, such as tidal migration and engulfment. The system is consistent with an in situ dynamical origin of planet b followed by subsequent Eccentric Kozai Lidov (EKL) perturbations that excite Kepler-1656b's eccentricity gently, i.e. without initiating tidal migration. Thus, despite its high eccentricity, we find no evidence that planet b is or has migrated through the high-eccentricity channel. Finally, we predict the outer orbit to be mutually inclined in a nearly perpendicular configuration with respect to the inner planet orbit based on the outcomes of our simulations, and make observable predictions for the inner planet's spin-orbit angle. Our methodology can be applied to other eccentric or tidally locked planets to constrain their origins, orbital configurations and properties of a potential companion.

Submitted to AJ;22 pages, 14 figures

References in corpus (39)

• The NumPy array: a structure for efficient numerical computation
• Dynamical Outcomes of Planet-Planet Scattering
• The Occurrence and Mass Distribution of Close-in Super-Earths, Neptunes, and Jupiters
• Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
• Origins of Eccentric Extrasolar Planets: Testing the Planet-Planet Scattering Model
• Stellar Activity Masquerading as Planets in the Habitable Zone of the M dwarf Gliese 581
• Make Super-Earths, Not Jupiters: Accreting Nebular Gas onto Solid Cores at 0.1 AU and Beyond
• The Kepler Follow-Up Observation Program. I. A Catalog of Companions to Kepler Stars from High-Resolution Imaging
• 197 Candidates and 104 Validated Planets in K2's First Five Fields
• Hot Jupiters in binary star systems
• Cavity opening by a giant planet in a protoplanetary disc and effects on planetary migration
• Steady-state planet migration by the Kozai-Lidov mechanism in stellar binaries
• Chaos in the Test Particle Eccentric Kozai-Lidov Mechanism
• Evidence for Planet-Planet Scattering in Upsilon Andromedae
• Large eccentricity, low mutual inclination: the three-dimensional architecture of a hierarchical system of giant planets
• Massive planet migration: Theoretical predictions and comparison with observations
• X-ray and Infrared Observations of Two Externally-Polluted White Dwarfs
• Spin-Orbit Alignment for the Eccentric Exoplanet HD 147506b
• Four Sub-Saturns with Dissimilar Densities: Windows into Planetary Cores and Envelopes
• SOPHIE velocimetry of Kepler transit candidates XII. KOI-1257 b: a highly eccentric three-month period transiting exoplanet
• Chaotic Tides in Migrating Gas Giants: Forming Hot and Transient Warm Jupiters via High-Eccentricity Migration
• The Jupiter Twin HD 154345b
• A disk-driven resonance as the origin of high inclinations of close-in planets
• Why do warm Neptunes present nonzero eccentricity?
• Tidal Inflation Reconciles Low-Density Sub-Saturns with Core Accretion
• The HARPS search for southern extra-solar planets XVII. Six long-period giant planets around BD -17 0063, HD 20868, HD 73267, HD 131664, HD 145377, HD 153950
• Secular evolution of eccentricity in protoplanetary discs with gap-opening planets
• Dynamics of Planetary Systems Within Star Clusters: Aspects of the Solar System's Early Evolution
• The Aligned Orbit of WASP-148b, the Only Known Hot Jupiter with a Nearby Warm Jupiter Companion, from NEID and HIRES
• Eccentric Companions to Kepler-448b and Kepler-693b: Clues to the Formation of Warm Jupiters
• A Highly Eccentric Warm Jupiter Orbiting TIC 237913194
• Search for Nearby Earth Analogs. III. Detection of ten new planets, three planet candidates, and confirmation of three planets around eleven nearby M dwarfs
• Dynamics of Stellar Spin Driven by Planets Undergoing Lidov-Kozai Migration: Paths to Spin-Orbit Misalignment
• The Stationary Points of the Hierarchical Three Body Problem
• Formation of Dark Matter Torii Around Supermassive Black Holes Via The Eccentric Kozai-Lidov Mechanism
• Mildly-Hierarchical triple dynamics and applications to the outer solar system
• How do External Companions Affect Spin-Orbit Misalignment of Hot Jupiters?
• The Minimum Gap-opening Planet Mass in an Irradiated Circumstellar Accretion Disk
• TOI-1296b and TOI-1298b observed with TESS and SOPHIE: Two hot Saturn-mass exoplanets with different densities around metal-rich stars

Cited by in corpus (7)

• Are WASP-107-like Systems Consistent with High-eccentricity Migration?
• Improving circumbinary planet detections by fitting their binary's apsidal precession
• Three Warm Jupiters around Solar-analog stars detected with TESS
• Evolution of the Planetary Obliquity: The Eccentric Kozai-Lidov Mechanism Coupled with Tide
• DMPP-3: confirmation of short-period S-type planet(s) in a compact eccentric binary star system, and warnings about long-period RV planet detections
• A One-Dimensional Energy Balance Model Parameterization for the Formation of CO2 Ice on the Surfaces of Eccentric Extrasolar Planets
• Short-Range Forces Can Catalyze Extreme Orbital Evolution in Hierarchical Triples