Resonant sub-Neptunes are puffier

Vol. 687
1. Letter-to-the-Editor

Resonant sub-Neptunes are puffier

Exoplanets whose masses have been measured through transit timing variations (TTVs) have systematically lower densities than those whose masses have been measured with radial velocities (RVs). This discrepancy was initially feared to reflect shortcomings in the TTV mass measurement methods. It was later attributed to either a measurement bias, from RVs struggling to measure masses as low as TTVs can for planetary systems close to a dynamical resonance, or to a true difference in the properties of resonant and nonresonant planets. Leleu et al establish through a careful statistical analysis that the latter is true: that resonant planets, including those measured only through RVs, do have lower densities, and that the density of a planet increases with its distance from a resonance. They show that these observational trends have counterparts in synthetic planet populations, in which the nonresonant planets went through giant collisions that both increased their densities and expanded their orbits.