The Eccentricity Distribution of Warm Sub-Saturns in TESS

TL;DR

This study analyzes the eccentricity distribution of warm sub-Saturn exoplanets from TESS data, revealing a range of eccentricities and suggesting high-eccentricity migration influences their formation.

Contribution

It introduces a hierarchical Bayesian approach to characterize the eccentricity distribution of warm sub-Saturns using TESS transit data, highlighting the role of dynamical processes.

Findings

Majority have mean eccentricity ~0.1

Some highly eccentric planets (e ~ 0.7-0.8) identified

Highly eccentric planets found in single-transiting systems

Abstract

We present the eccentricity distribution of warm sub-Saturns (4-8 Re, 8-200 day periods) as derived from an analysis of transit light curves from NASA's Transiting Exoplanet Survey Satellite (TESS) mission. We use the "photoeccentric" effect to constrain the eccentricities of 76 planets, comprising 60 and 16 from single- and multi-transiting systems, respectively. We employ Hierarchical Bayesian Modelling to infer the eccentricity distribution of the population, testing both a Beta and Mixture Beta distribution. We identify a few highly eccentric (e ~ 0.7-0.8) warm sub-Saturns with eccentricities that appear too high to be explained by disk migration or planet-planet scattering alone, suggesting high-eccentricity migration may play a role in their formation. The majority of the population have a mean eccentricity of e = 0.103+0.047-0.045, consistent with both planet-disk and planet-planet interactions. Notably, we find that the highly eccentric sub-Saturns occur in single-transiting systems. This study presents the first evidence at the population level that the eccentricities of sub-Saturns may be sculpted by dynamical processes.