James Webb Telescope unmasks diverse weather and hidden water on distant exoplanets

Astronomers using the James Webb Space Telescope (JWST) have mapped the twilight zones of the ultra‑hot gas giant WASP‑121 b, revealing stark contrasts between its evening and morning terminators. The evening side shows stronger carbon‑monoxide absorption, hotter temperatures that dissociate water, and vigorous eastward winds, while the morning side appears cooler, likely due to mineral‑cloud formation that blocks infrared radiation.

A separate JWST‑based study of the mini‑Neptune TOI‑270 d suggests that water on such common planets may be sequestered deep beneath their hydrogen‑rich atmospheres, rendering it invisible to current observations. Computer simulations indicate that heavy water can sink below the observable layers, implying that many sub‑Neptune worlds could harbor far more water than their spectra reveal. These findings refine models of exoplanet atmospheres, improve estimates of planetary composition, and guide future searches for truly habitable worlds.