Water ice clouds (exoplanet atmospheres)
Cirrus-like H₂O-ice clouds forming high in cold gas-giant atmospheres. Their direct observation on epsilon-indi-ab in 2026 (src-jwst-ice-clouds-exoplanet-2026-04) is one of the first concrete cases where cloud opacity demonstrably reshapes jwst retrievals.
Why they matter
- Atmosphere models: Most current exoplanet-atmosphere-models are cloud-free or use parameterized grey clouds because microphysics is hard to simulate; observed water-ice clouds force the field to add real cloud physics.
- Composition retrievals: Patchy H₂O-ice cover suppresses observed ammonia abundance, which can be misread as a low-NH₃ atmosphere if clouds are not modeled.
- Reflected light: Water-ice clouds are highly reflective, making them a primary target for the nancy-grace-roman-space-telescope coronagraph.