Planetesimal Interactions Can Explain the Mysterious Period Ratios of Small NearResonant Planets
Abstract
An intriguing trend among Kepler’s multiplanet systems is an overabundance of planet pairs with period ratios just wide of a mean motion resonance (MMR) and a dearth of systems just narrow of them. Traditional planet formation models are at odds with these observations. They are also in contrast with the period ratios of radialvelocitydiscovered multiplanet systems which tend to pile up at 2:1 MMR. We propose that gasdisk migration traps planets in an MMR. After gas dispersal, orbits of these trapped planets are altered through interaction with a residual planetesimal disk. We study the effects of planetesimal disk interactions on planet pairs trapped in 2:1 MMR using planets of mass typical of the Kepler planet candidates and explore large ranges for the mass, and density profile of the planetesimal disk. We find that planetplanetesimal disk interactions naturally create the observed asymmetry in periodratio distribution for large ranges of planetesimal disk and planet properties. If the planetesimal disk mass is above a threshold of ≈0.2× the planet mass, these interactions typically disrupt MMR. Afterwards, the planets migrate in such a way that the final periodratio is slightly higher than the integer ratio corresponding to the initial MMR. Below this threshold these interactions typically cannot disrupt the resonance and the period ratio stays close to the integer ratio. The threshold explains why the more massive planet pairs found by RV surveys are still in resonance. We encourage future research to explore how significantly the associated accretion would change the planets’ atmospheric and surface properties.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 2015
 DOI:
 10.1088/0004637X/803/1/33
 arXiv:
 arXiv:1406.0521
 Bibcode:
 2015ApJ...803...33C
 Keywords:

 methods: numerical;
 methods: statistical;
 planets and satellites: dynamical evolution and stability;
 planets and satellites: formation;
 planets and satellites: general;
 planet─disk interactions;
 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 10 pages in ApJ format, 9 figures, Accepted to ApJ