Architecture and Dynamics of Kepler's Candidate Multiple Transiting Planet Systems (1102.0543v4)

Abstract: About one-third of the ~1200 transiting planet candidates detected in the first four months of \ik data are members of multiple candidate systems. There are 115 target stars with two candidate transiting planets, 45 with three, 8 with four, and one 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.

• The paper reveals that about one-third of Kepler's transiting candidates are in multi-planet systems, highlighting stable and coplanar architectures.
• It employs numerical simulations and a power-law mass-radius relationship to assess dynamical stability and identify near-resonant configurations.
• The study indicates that low-order resonance capture is uncommon, suggesting migration-driven processes shape the final planetary system architecture.

Architecture and Dynamics of Kepler's Candidate Multiple Transiting Planet Systems

The paper authored by Lissauer et al. provides a comprehensive analysis of candidate multiple transiting planet systems observed by the Kepler Space Telescope. The paper focuses on the architecture and dynamics of planetary systems with multiple transiting planets, based on data collected during the first four months of Kepler's mission. The main findings and implications of the research on understanding planetary system formation and evolution are discussed herein.

Overview of Kepler's Multiple Planet Systems

According to the paper, approximately one-third of the 1200 transiting planet candidates identified during the initial analysis belong to systems with multiple transiting candidates. The data set consists of 115 stars with two planet candidates, 45 with three, 8 with four, one with five, and one with six candidates. The authors summarize the dynamical properties and stable configurations of these multitransiting systems.

Significantly, the researchers found that most candidate pairs were neither in nor near low-order mean motion resonances (MMRs). This distribution suggests that MMR resonance capture is not a primary mechanism governing the final architecture of many planetary systems. However, a statistically significant number of candidate pairs show a slight excess around specific resonances such as the 2:1 MMR, indicating cases of potential dynamical interaction.

Dynamic Stability and Planetary Resonances

Through numerical simulations, the paper evaluates the long-term stability of these planetary systems. Almost all candidate multi-planet systems are identified as dynamically stable. The authors employ a power-law relationship between planetary mass and radius to predict masses, aiding in stability assessments. A notable finding is the identification of systems with small deviations from resonance, potentially attributable to planet migration processes such as type-I or type-II migration within a gaseous disk.

The paper also highlights particular cases worth further investigation, where candidate planets exhibit near-resonant or multi-resonant chains, implying that at least some planets are dynamically trapped in resonance. KOI-730, for instance, features a resonant chain with period ratios 8:6:4:3, suggesting a case of resonant lock potentially maintained by convergent migration.

Multiplicity and Inclination of Planetary Orbits

An important aspect of the paper is the analysis of mutual inclinations and the occurrence rate of multiple transiting systems. By comparing the observed multiplicity and expected distribution if planets were randomly aligned, the authors propose that the majority of these systems are relatively coplanar. The multiplicity statistics suggest higher than anticipated occurrence rates for systems with multiple Earth-size and Neptune-size planets within short periods, implying favorable conditions for the formation of such systems within the same plane.

Using forward modeling techniques, the authors estimate mean multiplicities and inclination dispersions, drawing conclusions on the typical architecture of planetary systems. This statistical approach implies a low mean mutual inclination, considerably less than 10°, reinforcing the notion of a system similar in coplanarity to our solar system.

Implications and Future Directions

The implications of this research are profound for the field of exoplanetary science. These findings support models where close-in exoplanets form and migrate in a protoplanetary disk, gradually dampening eccentricities and inclinations, and become captured or nearly captured in resonant orbits. This paper contributes valuable empirical data to refine models of planetary system development and migration.

Future research may build upon these findings to investigate the compact configurations and resonant dynamics further using additional data from Kepler and other telescopes. Subsequent studies should explore results from transit timing variations, which can unveil non-transiting components in multiple systems, providing deeper insights into the masses and interactions within these dynamically rich exoplanetary systems.