The escape of exoplanet atmospheres and its imprints on the planet population

Thursday 5 July, 15:20

I will review our current understanding of the hydrodynamic escape of exoplanets large H/He atmospheres they acquired during formation in gas-rich protoplanetary discs, including basic models as well as the latest multi-dimensional hydrodynamic simulations. I will then discuss how escape of a planet's atmosphere effects its evolution and ultimately is observable properties after billions of years, arguing that most observed small planets with periods shorter than ~50 days have had their evolution controlled by the escape of their primordial atmosphere.  I will discuss the success of the escape driven evolution model to explain both the dearth of close-in Neptune-sized planets and the radius gap at 1.8 Earth radii reported by the California Kepler Survey. I will show that these observational features, coupled with other information such as stellar metallicity can be used to make strong inferences about the planet formation process, including the lack of ice-rich cores and prevalence of terrestrial planet formation. I will then discuss further observational tests of the escape driven evolution model and their status. Finally,  I will show that the model fails to account for the observed lack of Saturn and sub-Saturn mass planets in very short period orbits and discuss this result in the context of escape, planet formation and evolution. 

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