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New atmospheric escape models reveal the transition to metal-rich atmospheres in Super-Earths

Presentation #627.03 in the session Planetary Atmospheres - Theory.

Published onApr 03, 2024
New atmospheric escape models reveal the transition to metal-rich atmospheres in Super-Earths

Close-in, rocky exoplanets suffer intense, hydrogen-dominated mass-loss through sustained high-energy irradiation. While there are strong indications that this process can transform large Sub-Neptunes into small Super-Earths, it is unclear whether this mass-loss can terminate, and what the elemental composition of the remnant atmosphere could be. Using a new set of 1-D radiation hydrodynamics evolutionary calculations which include multi-component mass-loss and photochemistry, I show how line cooling from dragged heavy atoms and ions impacts the hydrogen-escape rates and how the relative composition of the outflow changes as the atmosphere evolves. I discuss how this results in a carbon-depleted and oxygen-rich phase of a low-mass planets life, before ultimately also this primary atmosphere is lost, consistent with recent non-detections of thick atmospheres around such worlds. Preventing the ultimate loss of the entire atmosphere is restricted only to a combination of high planet masses and low irradiation levels. Surprisingly, some high-metallicity atmospheres can retain a significant enough amount of hydrogen for it to be important as greenhouse gas and impact the further evolution of the lower atmosphere.

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