James Webb maps WASP-94Ab weather 700 ly

On May 21, a team led by Sagnick Mukherjee reported in *Science* that the James Webb Space Telescope had separated morning and evening conditions on the hot Jupiter WASP-94A b, a gas giant about 690 to 700 light-years from Earth. The observations used JWST to measure the planet’s leading and trailing edges separately as it crossed in front of its star, allowing researchers to compare the two atmospheric “limbs” rather than average them together. (hub.jhu.edu) The result was a weather map in transit: cloudy mornings, clearer evenings, and evidence that mineral clouds form and disappear as air circulates around the planet. (miragenews.com) ### How did Webb separate “morning” from “evening” on a planet this far away? JWST observed WASP-94A b during a transit, when the planet passed in front of its host star, according to Johns Hopkins University and a *Nature* news report. (spacedaily.com) The team used the planet’s leading edge at the start of transit as the morning side, where air moves from night to day, and the trailing edge near the end of transit as the evening side, where air moves from day to night. WASP-94A b is tidally locked, meaning one hemisphere permanently faces its star and the other remains in darkness. That geometry makes the transition zones especially useful for studying how clouds condense and evaporate as gas moves between hotter and cooler regions. (arstechnica.com) ### What did the telescope actually find in the atmosphere? The morning limb showed clouds made of magnesium silicate, a rock-forming mineral, while the evening limb appeared comparatively clear, according to Johns Hopkins, Exeter and multiple coverage reports. Phys.org described the clouds as “sand clouds,” and Space.com said the clearer evening view gave astronomers a better read on the planet’s underlying atmospheric composition. (hub.jhu.edu) The planet’s atmosphere reaches about 2,200 degrees Fahrenheit, according to coverage summarized in Space.com’s syndicated version. At those temperatures, silicate material can exist as vapor and then condense into cloud particles under the right conditions. (arstechnica.com) ### Why are the mornings cloudy if the evenings are clear? David Sing, a Bloomberg Distinguished Professor at Johns Hopkins and a co-author, said clouds have long acted like “a foggy window” for exoplanet studies, but the new method let the team isolate where those clouds sit and what they are made of. The researchers said one possibility is that winds loft clouds on the cooler side and then drive them downward on the hotter dayside, effectively burying them from view. Another is that the process resembles fog burning off after sunrise, but at much higher temperatures. (hub.jhu.edu) Harry Baskett of the University of Exeter, a co-author cited in university and press-release coverage, said JWST had been able to isolate signatures from both the morning and evening limbs, yielding information that is “inherently 3D.” (yahoo.com) ### Why does a clearer evening side matter to astronomers? The evening-side spectrum matters because clouds can flatten or hide the chemical fingerprints astronomers are trying to measure. Space.com reported that the clearer evening limb improved the team’s view of the planet’s true composition, while Johns Hopkins said isolating the clouds allowed more accurate atmospheric measurements. The broader significance, according to the university release and related coverage, is methodological. (hub.jhu.edu) Instead of treating a transiting exoplanet atmosphere as one blended ring, researchers can now split it into distinct regions and compare them directly. ### What comes next for this line of research? The May 21 *Science* paper centers on WASP-94A b, but the technique is aimed at other cloudy exoplanets as well, according to Johns Hopkins and Exeter. (miragenews.com) Future JWST observations can apply the same limb-resolved approach to additional hot Jupiters and other transiting worlds to test whether similar cloud cycles appear elsewhere. (hub.jhu.edu) (space.com)