Presentation #208.05 in the session Atmospheres 2.
The preponderance for stars to host close-in planets means atmospheric escape, driven by these extreme irradiation levels plays a vital role in controlling an atmosphere’s evolution. The broad-brush picture of the loss of hydrogen from sub-neptunes, creating super-earths and carving the radius-gap is now firmly established with theoretical models. However, far more exciting questions abound: does escaping hydrogen take other, heavy elements with them (observations of metals in exospheres seems to suggest yes)? Does atmospheric escape change the chemical inventory of a planetary atmosphere? What sets atmospheric chemistry of terrestrial planets stripped of their large natal hydrogen dominated atmosphere, escape, outgassing or some combination? Using a new generation of multi-species escape models that include the drag, settling and chemical interactions of multiple species, I will discuss answers to the above. I will focus on a couple of critical questions relevant to forthcoming atmospheric spectroscopy measurements: does the C/O ratio of hydrogen dominated sub-neptunes evolve from their primordial values, and does any hydrogen survive the transition from sub-neptune to super-earth?