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A break in the exoplanet eccentricity distribution at 3 Earth radii and evidence of elevated eccentricities for planets in the radius valley

Presentation #301.05 in the session Formation and Demographics I.

Published onApr 03, 2024
A break in the exoplanet eccentricity distribution at 3 Earth radii and evidence of elevated eccentricities for planets in the radius valley

Planetary eccentricities and inclinations are fundamental to understanding the present dynamical state of systems and are a relic of formation history. However, previous investigations of these quantities have either been limited to small subsamples (~5%) of the exoplanet census or have marginalized over population sub-structure, obscuring rich covariances between e, i, [Fe/H], Ms, P, Rp, and other quantities. By combining photometric corrections to Kepler DR25 data and updated constraints on stellar properties from Gaia with an approximate hierarchical Bayesian formalism, we have – for the first time – produced inferences of eccentricity and inclination which “slice and dice” the Kepler census into sub-populations along multi-dimensional parameter axes. Moreover, our methods have increased the sample size of planets with confidently measured eccentricities and transit impact parameters by an order of magnitude. Our analysis has revealed some surprising early results: (1) large planets (Rp > 3 Earth radii) tend to have higher eccentricities than small planets, and (2) there is a size-dependent correlation between occurrence rates, eccentricity, and stellar metallicity. In addition, we present preliminary evidence that exoplanets in the radius valley (Rp ~ 1.8 Earth radii) exhibit elevated eccentricities compared to the bulk super-Earth/sub-Neptune population. We detect additional covariances between inclination, eccentricity, and system architecture (i.e. compactness, size similarity, and structural complexity), providing clues to the details of many planet formation processes including disk-driven migration, giant impacts, and atmospheric mass loss. These patterns suggest a common formation channel for super-Earths and sub-Neptunes and a distinct formation pathway for giant planets.

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