Atmosphere retention of rocky planets around M dwarfs

Ascertain whether small, rocky exoplanets orbiting mid-to-late M dwarfs can retain atmospheres, for example by evaluating their positions relative to the M-dwarf "cosmic shoreline" and conducting targeted observations to determine atmospheric presence and loss, in order to guide the feasibility of JWST atmospheric characterization for such planets.

Background

The paper reports the discovery and validation of two temperate planets around fully convective M dwarfs, including the Earth-sized TOI-6716 b and the Neptune-sized TOI-7384 b. It discusses prospects for atmospheric characterization with JWST and introduces the transmission spectroscopy metric (TSM) as a measure of expected signal strength.

The authors note that a key uncertainty affecting target selection is whether small, rocky planets around M dwarfs can retain their atmospheres, referencing the M-dwarf cosmic shoreline framework that relates atmospheric retention to cumulative XUV irradiation and escape velocity. Resolving this uncertainty is important for prioritizing observational resources and interpreting potential atmospheric detections or non-detections.

References

An ongoing question, however, is whether small, rocky planets around M dwarfs can retain their atmospheres; studies into the M dwarf cosmic shoreline aim to inform this debate, allowing for more targeted follow-up with, e.g., JWST \citep[see e.g.,][]{xue2025}.

— Two temperate Earth- and Neptune-sized planets orbiting fully convective M dwarfs  (2601.05799 - Scott et al., 9 Jan 2026) in Section 6.2.2, Planetary mass and atmospheric prospects