The Exoplanet Eccentricity Distribution from Kepler Planet Candidates

TL;DR

This paper analyzes Kepler planet candidates to determine their eccentricity distribution, finding it aligns with radial velocity results and that smaller planets tend to have more circular orbits.

Contribution

It demonstrates that Kepler data can be used to infer eccentricity distribution and reveals a size-dependent trend in orbital eccentricities.

Findings

Eccentricity distribution matches radial velocity surveys

Smaller planets tend to have lower eccentricities

Transit duration variations can reveal eccentricity information

Abstract

The eccentricity distribution of exoplanets is known from radial velocity surveys to be divergent from circular orbits beyond 0.1 AU. This is particularly the case for large planets where the radial velocity technique is most sensitive. The eccentricity of planetary orbits can have a large effect on the transit probability and subsequently the planet yield of transit surveys. The Kepler mission is the first transit survey that probes deep enough into period-space to allow this effect to be seen via the variation in transit durations. We use the Kepler planet candidates to show that the eccentricity distribution is consistent with that found from radial velocity surveys to a high degree of confidence. We further show that the mean eccentricity of the Kepler candidates decreases with decreasing planet size indicating that smaller planets are preferentially found in low-eccentricity orbits.