ARCHITECTURE AND DYNAMICS OF <i>KEPLER</i> 'S CANDIDATE MULTIPLE TRANSITING PLANET SYSTEMS

TLDR

About one-third of the ~1200 Kepler transiting planet candidates are in multiple systems, with 115 stars hosting two, 45 hosting three, 8 hosting four, and one each hosting five or six candidates. The authors characterize the dynamical properties of these candidate multi‑planet systems. They performed numerical integrations assuming a nominal mass–radius relationship to test stability and used observed multiplicity frequencies to constrain the true multiplicity and mutual inclination distribution. The period‑ratio distribution shows most candidate pairs are neither in nor near low‑order resonances, with only modest excesses near 2:1; numerical integrations confirm that virtually all systems are stable, supporting that most are true planets, yet a single population model underpredicts singly transiting systems, implying a population of multi‑planet systems with super‑Earth and Neptune sizes and low to moderate mutual inclinations.

Abstract

About one-third of the ∼1200 transiting planet candidates detected in the first four months of Kepler data are members of multiple candidate systems. There are 115 target stars with two candidate transiting planets, 45 with three, 8 with four, and 1 each with five and six. We characterize the dynamical properties of these candidate multi-planet systems. The distribution of observed period ratios shows that the vast majority of candidate pairs are neither in nor near low-order mean-motion resonances. Nonetheless, there are small but statistically significant excesses of candidate pairs both in resonance and spaced slightly too far apart to be in resonance, particularly near the 2:1 resonance. We find that virtually all candidate systems are stable, as tested by numerical integrations that assume a nominal mass–radius relationship. Several considerations strongly suggest that the vast majority of these multi-candidate systems are true planetary systems. Using the observed multiplicity frequencies, we find that a single population of planetary systems that matches the higher multiplicities underpredicts the number of singly transiting systems. We provide constraints on the true multiplicity and mutual inclination distribution of the multi-candidate systems, revealing a population of systems with multiple super-Earth-size and Neptune-size planets with low to moderate mutual inclinations.