A model of planetary formation that predicts migrated steam exoplanets and the radius valley

The observed 'radius valley' - a dip in the distribution of exoplanet radii, which separates rocky super-Earths from larger sub-Neptunes - is at odds with current theories of planetary formation. New simulations that couple planet formation and evolution, and account for the orbital migration of planets that are largely composed of steam, are able to reproduce the valley feature.