Habitable conditions on K2-18 b remain unresolved

Ascertain whether K2-18 b can sustain habitable conditions, specifically a surface or near-surface environment with liquid water under its hydrogen-rich atmosphere, by integrating constraints from atmospheric composition, temperature structure, and radiative properties (e.g., albedo and cloud/haze coverage).

Background

K2-18 b is a sub-Neptune orbiting an M dwarf in the habitable zone and has atmospheric detections of CH4 and CO2 consistent with predictions for Hycean worlds with H2-rich atmospheres. However, habitability for such planets depends critically on whether their surface or ocean environments can maintain liquid water, which is influenced by atmospheric radiative properties such as dayside albedo and the presence of clouds or hazes.

The authors emphasize that, despite promising atmospheric composition indicators, the overall environmental context needed to confirm habitability is not yet established. Clarifying this requires targeted observations and modeling to constrain key parameters that control energy balance and surface/ocean conditions.