Two-Faced Weather on a Distant World Upends Exoplanet Chemistry

JWST’s limb-resolved spectroscopy of the tidally locked exoplanet WASP-94A b reveals a morning sky thick with vaporized magnesium silicate clouds (sand) and a clear evening sky, driven by strong equatorial winds that shuttle clouds from day to night. This two-hemisphere view shows that averaging light over the whole planet previously biased atmospheric readings, overestimating oxygen by ~100x; the corrected enrichment is only ~3–5x solar. The finding demonstrates that exoplanet atmospheres may be dynamic and two-faced, prompting a re-evaluation of many past measurements and encouraging limb-resolved studies on more worlds.