Near-circular orbits for planets with Earth-like sizes and instellations around M and K dwarf stars

Abstract

Recent advances have enabled the discovery of a population of potentially Earth-like planets; however, their orbital eccentricity, which governs their climate and provides clues about their origin and dynamical history, is still largely unconstrained. Here we identify a sample of 17 transiting exoplanets around late-type stars with similar radii and irradiation to that of Earth and use the ‘photoeccentric effect’—which exploits transit durations—to infer their eccentricity distribution using hierarchical Bayesian modelling. Our analysis establishes that these worlds further resemble Earth in that their eccentricities are nearly circular (mean eccentricity \(0.06{0}_{-0.028}^{+0.040}\) and ≤0.15), with the exception of one outlier of moderate eccentricity. This outlier hints at a subset population of dynamically warmer Earths, but this requires a larger sample to statistically confirm. The planets in our sample are thus largely subject to minimal eccentricity-induced seasonal variability and are consistent with emerging via smooth disk migration rather than violent planet–planet scattering.