Using data from the James Webb Space Telescope, researchers discovered a daily cloud cycle on the Hot Jupiter WASP-94A b. By isolating the clouds, the team can measure the planet's atmosphere more accurately and produce a clearer picture of its composition. The results appear in the journal Science. Coauthor David Sing said general cloudiness has long been a thorn in their side when studying exoplanets.
The researchers observed the planet during a transit and took separate spectra of the leading edge as it began to cross the star and the trailing edge as it finished. The leading edge corresponds to morning, when air flows from night to day, while the trailing edge is evening, when flow reverses. They found morning skies full of magnesium silicate clouds and clear skies in the evening.
The team proposes two explanations: strong winds could lift clouds on the night side and push them deep into the interior on the hot day side, hiding them before sunset; or clouds could form in darkness and then vaporize when they reach the day side at more than 1,000 degrees. Earlier Hubble data that averaged clouds and gas implied hundreds of times more oxygen and carbon than Jupiter, but the new JWST measurements show only five times those amounts. The researchers also found the same cycle on two other worlds, WASP-39 b and WASP-17 b, and plan larger JWST studies of cloud cycling on many exoplanets. Additional coauthors and funding come from several universities, observatories, NSF, NASA and the European Union Horizon program.
Difficult words
- spectrum — a range of light separated by wavelengthspectra
- transit — when a planet passes in front of a star
- magnesium silicate — a mineral material forming some planet clouds
- isolate — to separate one thing from othersisolating
- composition — the chemical make-up or material parts
- vaporize — to change from solid or liquid to gas
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Discussion questions
- Why is isolating clouds important for measuring a planet's atmosphere more accurately? Give one or two reasons.
- Which of the two explanations for clouds disappearing on the day side do you find more convincing: strong winds pushing clouds inward, or clouds vaporizing at high temperature? Explain briefly.
- How could studying cloud cycles on many exoplanets change what we know about planets outside our solar system?
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