James Webb Telescope Finds Daily Cloud Cycle on Hot Jupiter Exoplanet

Astronomers using the James Webb Space Telescope observed a repeating weather pattern on the exoplanet WASP-94A b. Mineral clouds form on the cooler nightside and dissipate when carried to the hotter dayside by atmospheric winds. The planet orbits its star every four days and is tidally locked, creating a temperature difference of roughly 350 degrees Fahrenheit between its permanent day and night hemispheres.

Researchers used the telescope's Near Infrared Imager and Slitless Spectrograph to measure the atmosphere as the planet passed in front of its star.

The morning side showed thick magnesium silicate clouds while the evening side appeared relatively clear with stronger water vapor signals. The clouds evaporate once temperatures exceed 1,832 degrees Fahrenheit. David Sing, a Bloomberg Distinguished Professor at Johns Hopkins University and co-author of the study, said the observations allow scientists to determine what the clouds are made of and how they condense and evaporate.

Telescope data had indicated the planet contained hundreds of times more oxygen and carbon than Jupiter. The new JWST measurements show only about five times as much, aligning more closely with current planetary formation models. Sagnick Mukherjee, lead author and now a postdoctoral fellow at Arizona State University, said the ability to separate morning and evening regions helped reveal the cloud cycle.

The team also identified similar cycles on WASP-39b and WASP-17b. WASP-94A b was first discovered in 2014 and has a mass half that of Jupiter. Its host star belongs to a binary system in the constellation Microscopium.