Characterizing Keplers Multi-planet Systems

Abstract: The Kepler mission”s census of transiting exoplanets has shown that sub-Neptune size planets with short orbital periods are extremely common. Given their small sizes, the properties of these planets can be difficult or impossible to constrain via radial velocity observations. Mutual gravitational interactions in multi-planet systems cause variations in the arrival times of planets” transits. These variations are a valuable probe for measuring planets” masses and eccentricities, thereby constraining their compositions and formation histories. I will discuss the results of our analysis of the transit timing variations (TTVs) of 145 Kepler planets from 55 multi-planet systems. Numerical studies of stability in multi-planet systems suggest that, given the typical masses and eccentricities inferred via TTVs, many high-multiplicity Kepler systems are on the verge of dynamical instability. This suggests that many members of the present-day planetary system population may have started out with similarly high multiplicities but suffered instabilities on somewhat shorter timescales, leaving behind a range of lower-multiplicity outcomes. A better theoretical understanding of dynamical stability in such systems can help relate the present-day distribution of planetary system architectures to those produced by the planet formation process. I will describe a new analytic criterion for predicting the dynamical stability of two-planet systems. This stability criterion, based on the idea of resonance overlap, provides important insights into how a complex web of resonances mediates the dynamical stability of higher- multiplicity systems like those observed by Kepler.

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