Multiplanet systems in inviscid discs can avoid forming resonant chains

Abstract

Convergent migration involving multiple planets embedded in a viscous protoplanetary disc is expected to produce a chain of planets in mean motion resonances, but the multiplanet systems observed by the Kepler spacecraft are generally not in resonance. We demonstrate that under equivalent conditions, where in a viscous disc convergent migration will form a long-term stable system of planets in a chain of mean motion resonances, migration in an inviscid disc often produces a system which is highly dynamically unstable. In particular, if planets are massive enough to significantly perturb the disc surface density and drive vortex formation, the smooth capture of planets into mean motion resonances is disrupted. As planets pile up in close orbits, not protected by resonances, close encounters increase the probability of planet-planet collisions, even while the gas disc is still present. While inviscid discs often produce unstable non-resonant systems, stable, closely packed, non-resonant systems can also be formed. Thus, when examining the expectation for planet migration to produce planetary systems in mean motion resonances, the effective turbulent viscosity of the protoplanetary disc is a key parameter.

6 pages, 3 figures, 17 page online appendix, 15 figures, MNRAS Letters accpeted

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• The Kepler-223 resonance holds information on turbulence during the gas disk phase
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• The origins of nearly coplanar, non-resonant systems of close-in super-Earths
• Migrating Low-Mass Planets in Inviscid Dusty Protoplanetary Discs
• Near Mean Motion Resonance of Terrestrial Planet Pair Induced by Giant Planet: Application to Kepler-68 System
• Architecture of planetary systems predicted from protoplanetary disks observed with ALMA II: evolution outcomes and dynamical stability
• Single Fluid vs. Multifluid: Comparison between single fluid and multifluid dust models for disc planet interactions