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4h ago

JWST Resolves Morning Clouds and Clear Evenings on Hot Jupiter WASP-94A b

The Science paper shows winds carry magnesium‑silicate clouds from the planet’s cold nightside into a hot dayside where they evaporate, a process that changes how scientists read atmospheric chemistry.

JWST just mapped the morning weather on a planet 690 light-years away — and the forecast of vaporized rock clouds quietly broke a 100-fold error in how exoplanet atmospheres have been read for decades
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Artist's conception of a Jupiter-sized exoplanet orbiting close to a large star.

Overview

  • Researchers used JWST’s NIRISS instrument and limb‑resolved transmission spectroscopy to separate the planet’s leading (morning) and trailing (evening) transit spectra and found a stark weather contrast between the two limbs.
  • The morning limb is dominated by high‑altitude mineral clouds, primarily magnesium silicate, while the evening limb is relatively cloud‑free and shows clear water‑vapor absorption.
  • Modeling and spectra indicate a limb temperature difference of roughly 450 kelvin that drives equatorial super‑rotation winds which lift condensed minerals from the nightside into the day where they evaporate.
  • Reanalyzing the planet with limb‑resolved data reduced a previous extreme metallicity estimate of about 100× solar to roughly 3–5× solar, showing that averaging spectra around the whole limb can produce large composition biases.
  • The team detected the same morning‑cloud/evening‑clear pattern on at least two other hot Jupiters and plans broader JWST surveys and improved models to correct retrieval methods and refine planet‑formation inferences.