EXOA15

James Webb Space Telescope observations are tentatively revealing a pattern of airless or thinly blanketed worlds around low-mass stars, evidenced in part by a lack of “dayside cooling.” This raises a fundamental question—following the escape of primordial hydrogen, when will ionising irradiation also evaporate the high-molecular-weight atmospheres supplied by volcanism on a rocky planet? The 500-hour Rocky Worlds DDT program will probe this question, guided by the hypothesis that atmospheric escape sculpts a Cosmic Shoreline. However, before the puzzle can take shape, its pivotal pieces require further exploration and debate:
* What are the strongest atmospheric constraints we can infer from transmission and emission observations?
* What are the optimal observing strategies to detect atmospheric features?
* Under what conditions can a bare rock revive an atmosphere?
* How well do we understand M-dwarf evolution, particularly X-ray flare activity over time?
* What level of ionising irradiation can drive hydrodynamic escape of metal-rich atmospheres, and how does this process depend on planetary mass?
* How will the launch of ELT, PLATO and ARIEL boost atmospheric characterisation?
We invite contributions that explore observations (both real and simulated) and models of star-planet evolution (including interior, atmospheric, and escape processes). If some of the rocky planets in the habitable zones of the galaxy’s most common stars can retain their atmospheres, the universe could be teeming with life—and astronomers just might be able to observe its signatures in the near future.