 Exoplanet habitability

Exoplanet habitability asks whether a world's physical conditions could support life, commonly using sustained liquid water as an operational target. This requires more information than mass, radius or orbital distance alone. Atmospheric escape, the volatile inventory, the greenhouse effect and heat transport can make bodies receiving similar stellar power very different.

A circumstellar habitable zone is a useful model-dependent filter for possible surface liquid water. Calculations must specify atmospheric composition and climate assumptions; incident stellar power alone is not a detection of an ocean.^[ref] An exoplanet biosignature asks a separate observational question about evidence for biology, and must be interpreted in this planetary context.