Theory-Defying Exoplanet Atmospheres Force a Rethink of Theories

There's new research challenging the traditional "cosmic shoreline" boundary between planets with atmospheres and those without, proposing a third regime called the "airless valley." The study, based on JWST observations, finds that exoplanets in the airless valley have no appreciable atmospheres, while those in the cosmic shoreline have thick atmospheres. The research suggests that atmospheric loss is governed by two boundaries: a hot, outgassing-regulated "cosmic sandbar" and a cooler, escape-regulated "cosmic shoreline." This leads to three regimes for rocky planets close to stars: the cosmic sandbar regime, the cosmic shoreline regime, and the airless valley regime. The study's lead author, Barron Nguyen, notes that the findings challenge existing theories about atmospheric escape and planetary habitability.

• The study's senior author, Schaefer, emphasizes that the new model expands understanding of the boundary between airless worlds and those capable of sustaining atmospheres.
• The research highlights that exoplanets like 55 Cancri e, despite being close to their stars, have thick atmospheres, contradicting previous assumptions about atmospheric loss.
• The findings suggest that planets in the sandbar regime replenish their atmospheres through slow outgassing, while those in the airless valley lose their atmospheres more rapidly.

The research has implications for understanding planetary habitability, as the presence of atmospheres is essential for liquid surface water and, thus, potential life. The study also challenges the cosmic shoreline theory, which has been used to explain the difference in atmospheric retention between planets like Earth and those like Mercury. The findings suggest that atmospheric escape is more complex than previously thought, with planets in the sandbar regime maintaining atmospheres through outgassing, even under extreme stellar insolation.

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