A Tidal Origin for a 3-body Resonance in Kepler-221

Abstract

Over the course of the last two decades, traditional models of planet formation have been repeatedly challenged by the emerging census of extrasolar planets. Key among them is the orbital architecture problem: while standard models of orbital migration predict resonant orbits for short-period objects, most planets do not appear to lie in orbital resonances. Here we show that the four-planet system Kepler-221, not previously recognized to have active orbital resonances, has a three-body commensurability relation unique within the Kepler sample. Using a suite of numerical experiments as well as a perturbative analysis, we demonstrate that this system likely began as a resonant chain and proceeded to undergo large-scale divergence away from resonance, under the action of tidal dissipation. Our results further indicate that obliquity tides, driven by a secular spin-orbit resonance and mutual inclination, are an excellent candidate for driving this orbital divergence, and that the high tidal luminosity may also explain the anomalous size of planet b, which lies within the Fulton radius gap.

15 pages, 9 figures, accepted for publication in AJ

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• Architectures of Compact Super-Earth Systems Shaped by Instabilities
• The dynamics of the TRAPPIST-1 system in the context of its formation
• Dynamics and Origins of the Near-Resonant Kepler Planets
• The Origin of Universality in the Inner Edges of Planetary Systems
• Dissipative Capture of Planets Into First-Order Mean-Motion Resonances
• Is the orbital distribution of multiplanet systems influenced by pure three-planet resonances?
• Tidal interactions shape period ratios in planetary systems with three-body resonant chains
• Kepler-80 Revisited: Assessing the Participation of a Newly Discovered Planet in the Resonant Chain
• Three-Body Resonances in the Saturnian System
• Tidally Heated Sub-Neptunes, Refined Planetary Compositions, and Confirmation of a Third Planet in the TOI-1266 System
• Close-in compact super-Earth systems emerging from resonant chains: slow destabilization by unseen remnants of formation
• The Dynamical History of the Kepler-221 Planet System