Coupling Surface-Atmosphere Feedbacks: A Scheme for Modelling Atmosphere Evolution of Rocky Exoplanets

Atmospheric escape is a fundamental process that shapes the evolution of exoplanets. Given that the majority of known exoplanets reside on short orbital periods (i.e., less than 100 days), they are subjected to prolonged and intense irradiation from their host stars. This high-energy, impinging stellar flux, especially in the X-ray and extreme ultraviolet (XUV) regimes, provides the conditions for triggering significant hydrodynamic gas outflows (i.e., atmospheric escape), which holds the key to explaining observed demographic features such as the Neptunian desert and the radius valley. 

 

For smaller rocky exoplanets, there is an important feedback between atmospheric escape (which fractionates the overall atmospheric chemistry) and interior outgassing (which controls the initial atmospheric chemistry) from the planetary surface. Specifically, as atmospheric escape proceeds, the surface pressure decreases, which in turn alters the outgassing chemistry. 

 

We present a theoretical framework that self-consistently models atmospheric dynamics, from a hydrostatic lower atmosphere to a hydrodynamic outflow, and is directly coupled to an interior outgassing model. By evolving this system in the time domain and around different stellar types, our scheme explores the longevity and transformation of hybrid and secondary atmospheres of rocky planets. This will also provide a physical basis for interpreting the "cosmic shoreline."