"Exploring the Formation of Warm Sub-Saturns Through Interior Structure Modelling"

Abstract

Sub-Saturns, which are planets with radii between 4 and 8 Earth radii, are key to understanding the transition from ice giants to gas giants. Their distribution is shaped by the Neptunian desert (a scarcity of Neptune-sized planets on short orbits), the Neptunian ridge (an overdensity at orbital periods of 3–6 days), and the Neptunian savanna (a slight underdensity at longer periods). These features reflect the complex interplay of atmospheric escape, migration, and formation. In this talk, I will present our recent study using the GASTLI interior structure model to derive the envelope mass fractions (fenv) of 26 warm sub-Saturns. By comparing our results to a formation model, we find that sub-Saturns require significantly metal-enriched atmospheres to match the synthetic planets. Additionally, we find a bimodal distribution of fenv, with a notable gap that aligns with theoretical predictions for the onset of runaway gas accretion.