JWST just mapped the morning weather on a planet 690 light-years away, and the forecast of sand-like clouds exposed a 100-fold bias in how exoplanet atmospheres have been read for more than a decade

Key Points:

• The James Webb Space Telescope (JWST) used limb-resolved spectroscopy to observe the hot gas giant WASP-94A b, revealing distinct morning and evening atmospheres with cloudy mornings of vaporized rock and clear evenings due to rapid winds.
• WASP-94A b is tidally locked, causing a temperature difference of about 450 Kelvin between its morning and evening sides, resulting in vastly different atmospheric chemistry and cloud cover on each limb.
• The study corrected previous overestimations of the planet’s oxygen content, showing a more moderate enrichment consistent with planet-formation models, highlighting a bias in earlier exoplanet atmospheric analyses that averaged data across entire planets.
• Limb-resolved spectroscopy allows JWST to distinguish atmospheric properties on the morning and evening terminators during transit, providing detailed insights into atmospheric circulation, chemistry, and cloud physics that were not possible with earlier instruments.
• The findings suggest many hot Jupiter composition estimates may need revision, and JWST’s enhanced resolution is reshaping understanding of exoplanet atmospheres, with plans to apply this method to a wider range of exoplanets exhibiting diverse weather systems.