Tidal Inflation is Stronger for Misaligned Neptune-Sized Planets Than Aligned Ones

Abstract

Recent observations have revealed an intriguing abundance of polar-orbiting Neptune-sized planets, many of which exhibit unusually inflated radii. While such misaligned orbits point to a complex dynamical history, the connection between their orbital orientations and planetary structures remains poorly understood. In this study, we analyze a sample of 12 misaligned and 12 aligned planets using structure models that incorporate tidal heating. We use various statistical tests to demonstrate with at least $90\%$ confidence that misaligned planets experience more tidally-induced radius inflation compared to aligned planets. This inflation likely stems from their dynamically active histories, which often place them in close-in, eccentric, and highly inclined orbits. We further present a case study of WASP-107~b, an exceptionally inflated polar Neptune, and model its history using a simple coupled orbital and radius evolution approach. Our results place constraints on the planet's tidal quality factor that agree with recent JWST observations.