Speaker
Description
The discovery of the exoplanet radius valley—an apparent dearth of planets at radii around a few Earth radii—has transformed our understanding of close-in planetary systems and their formation pathways. Originating in theoretical work at CITA in 2012/2013, the radius valley has been interpreted as the outcome of atmospheric mass loss sculpting the underlying core population of short-period planets. In this talk, I will review the theoretical foundations of the radius valley with an emphasis, focusing on how its location, slope, and depth encode key physical information. I will discuss how models of atmospheric escape explain the characteristic radius scale of the valley and its dependence on orbital period and stellar type, and how these models connect the observed planet radius distribution to the underlying core masses, compositions, and thermal histories. I will highlight recent work that links the detailed structure of the radius valley—its precise radius range, width, and occurrence rates on either side—to fundamental aspects of planet formation, including the efficiency of envelope accretion, the distribution of core masses set by solid accretion and migration, and the role of stellar mass and high-energy irradiation. I will also discuss emerging evidence for other processes impacting the radius-valley such as collisions of multiple planet formation pathways. Finally, I will discuss how ongoing and upcoming surveys refine our picture of the radius valley across stellar types and environments, and how these observations, interpreted through the theoretical framework developed at CITA, are turning the radius valley into a powerful diagnostic of planet formation and evolution.
