Overview
- The Science paper published Thursday reports that JWST’s NIRISS instrument captured different transmission spectra for WASP‑94A b’s leading (morning) and trailing (evening) limbs, revealing a persistent cloud cycle.
- Data and 3D circulation models show mineral condensate clouds (magnesium silicates, iron and sulfides) form on the cold nightside, are carried to the morning limb by equatorial winds, and then evaporate on the hot dayside because of ~450 K temperature contrasts.
- When the team analyzed the clear evening limb separately they found much lower heavy‑element abundances than earlier Hubble‑era, limb‑averaged results, revising oxygen and carbon levels to about five times Jupiter’s instead of hundreds of times.
- The authors report similar cloud‑cycling signatures on two other hot Jupiters, WASP‑39 b and WASP‑17 b, and say larger JWST programs and updated models are now underway to test how common this biasing weather is across exoplanets.
- The finding shows that treating tidally locked exoplanet atmospheres as uniform can distort chemical and formation inferences, and it gives astronomers a practical method—limb‑resolved transit spectroscopy—to reduce that bias for low‑density gas giants.