Breaking mean-motion resonances during Type I planet migration

• Published in: Monthly notices of the Royal Astronomical Society Vol. 474; no. 3; pp. 3998 - 4009
• Main Authors: Hands, T O, Alexander, R D
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 01-03-2018
• Subjects: Breaking; Damping; Eccentricity; Migration; Orbital resonances (celestial mechanics); Planetary evolution; Planetary systems; Planets; Resonance; planet-disc interactions; hydrodynamics; planetary systems; methods: numerical; planets and satellites: formation; planets and satellites: dynamical evolution and stability
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stx2711

Abstract
We present 2D hydrodynamical simulations of pairs of planets migrating simultaneously in the Type I regime in a protoplanetary disc. Convergent migration naturally leads to the trapping of these planets in mean-motion resonances. Once in resonance the planets’ eccentricity grows rapidly, and disc-planet torques cause the planets to escape resonance on a time-scale of a few hundred orbits. The effect is more pronounced in highly viscous discs, but operates efficiently even in inviscid discs. We attribute this resonance-breaking to overstable librations driven by moderate eccentricity damping, but find that this mechanism operates differently in hydrodynamic simulations than in previous analytic calculations. Planets escaping resonance in this manner can potentially explain the observed paucity of resonances in Kepler multitransiting systems, and we suggest that simultaneous disc-driven migration remains the most plausible means of assembling tightly packed planetary systems.