[IPARCOS astro-seminar] Nov15 - A radius valley btw migrated steam worlds and evaporated rocky cores

[IPARCOS astro-seminar] 15/11/2023
Dr. Dr. Remo Burn (MPIA)
Title: A radius valley between migrated steam worlds and evaporated rocky cores
Abstract: The radius valley (or gap) in the observed distribution of exoplanet radii, which separates smaller super-Earths from larger sub-Neptunes, is a key feature that theoretical models must explain. Conventionally, it is interpreted as the result of the loss of primordial H/He envelopes atop rocky cores. However, planet formation models predict that water-rich planets migrate from cold regions outside the snowline toward the star. Assuming water to be in the form of solid ice in their interior, many of these planets would be located in the radius gap contradicting observations.
In this talk, I will present a theoretical model of planet formation and evolution, with a consistent modeling of the planets' interior, which can reproduce the observed radius valley as well as the drop of sub-Neptune occurrence, the so-called radius cliff. The key ingredients are atmospheric loss and an equation of state that allows for lower density supercritical phases at the relevant, high temperatures in close-in sub-Neptunes. The lower density of supercritical steam increases the radius of water-rich sub-Neptunes and brings them into agreement with observations. The radius valley is in this framework the transition from small, rocky super Earth to sub-Neptunes with supercritial, water-rich envelopes. Water-rich sub-Neptunes are favored dry compositions by our modeling.