Tyler Fairnington

A Formation Dichotomy Revealed in the Eccentricity Distribution of TESS Warm Sub-Saturns

We present the eccentricity distribution of warm sub-Saturns (4-8 Re) in TESS, to reveal their formation pathways. Using the photoeccentric effect, we inferred eccentricities and the underlying population distributions of sub-Saturns with periods 8-200 days with Hierarchical Bayesian Modelling. Our models include both single and mixed distributions, reflecting potentially diverse formation pathways. Our resulting distribution suggests a mixed history: approximately 85% of warm sub-Saturns are on circular orbits, suggesting in-situ or disk formation, while the remaining 15% have high eccentricities (e>0.5), requiring formation via dynamical interactions and/or high eccentricity migration. We also find a lower fraction of eccentric sub-Saturns compared to Jovians. This suggests that larger planets form, and potentially interact with comparably massive planets.