Overview

• JWST has identified water vapor in the atmospheres of several sub‑Neptunes, with many additional targets on the observing schedule.
• Led by Artem Aguichine, the UC Santa Cruz team couples atmospheric spectra to deep‑interior evolution from formation through billions of years.
• The models incorporate extreme water states, including supercritical fluid and superionic ice, drawing on laboratory results relevant to giant‑planet interiors.
• This approach extends tools once used for icy moons to far hotter, more massive worlds roughly 10–100 times Earth’s mass.
• Authors say forthcoming JWST datasets and ESA’s PLATO mission will test and refine the predictions, and they caution that steam detections do not imply surface habitability.