WASP-94A b, a hot Jupiter about 700 light-years away, showed distinct morning and evening atmospheres in JWST transit data—magnesium silicate clouds at dawn and clearer skies by dusk.
JWST separated the planet’s leading and trailing edges during transit, letting researchers track air moving from night to day and back again and isolate one of the clearest atmospheric views yet for a hot Jupiter.
Temperatures above 1,000°C on the dayside may either burn off nightside clouds like extreme morning fog or drive them deep into the atmosphere through powerful winds, the team said.
Clearer evening-sky measurements also revised the planet’s chemistry to about five times Jupiter’s oxygen and carbon abundance, bringing it back in line with planet-formation models.
The method has already hinted at similar cloud cycles on WASP-39 b and WASP-17 b, offering a new tool for broader exoplanet atmosphere studies as astronomy shifts from discovery to characterization.
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JWST Unveils Daily Cloud Cycles on WASP-94A b: A Breakthrough in Exoplanet Weather and Atmospheric Science
Overview
In May 2026, astronomers made the first direct detection of daily cloud cycles on the exoplanet WASP-94A b using the James Webb Space Telescope. They observed that magnesium silicate clouds form overnight on the planet’s cooler side, creating cloudy mornings, and then dissipate under intense heat as the planet rotates, leading to clear evenings. This dramatic daily weather cycle offers an unprecedented look into exoplanet atmospheric dynamics and reshapes how scientists study alien worlds. The new methodology is crucial for more precise atmospheric characterization, paving the way to better understand a wide variety of exoplanets, from gas giants to rocky planets.