The James Webb Space Telescope (JWST) has observed a distant exoplanet where clouds made of rocky minerals form every morning and dissipate by evening. This phenomenon occurs on WASP-94A b, a gas giant located nearly 700 light-years from Earth in the constellation Microscopium. This discovery marks one of the first direct observations of cloud cycling on a "Hot Jupiter" exoplanet.
Astronomers used the JWST to study WASP-94A b as it transited its host star. This allowed them to examine the planet's leading (morning) and trailing (evening) edges separately. The morning side showed abundant clouds of magnesium silicate, a common Earth rock mineral. The evening side, however, appeared largely cloud-free.
Researchers propose two explanations for the disappearing clouds. Strong winds may push the clouds deep into the planet's atmosphere on the day side, hiding them from view. Alternatively, the clouds could evaporate as they encounter temperatures exceeding 1,000 degrees Celsius. This is similar to fog burning off on Earth, but under much more extreme conditions.
The clear evening skies provided an unprecedented opportunity to study the planet's atmosphere directly. Earlier measurements had suggested WASP-94A b contained hundreds of times more oxygen and carbon than Jupiter. New observations indicate the planet has only about five times more oxygen and carbon than Jupiter, aligning it more closely with our solar system's gas giant.
Hot Jupiters are gas planets that orbit very close to their stars, experiencing intense heat and radiation. These conditions make them natural laboratories for studying atmospheric chemistry and cloud behavior. The research team has since identified similar cloud cycling on two other Hot Jupiters: WASP-39 b and WASP-17 b.
Scientists plan to expand their research using a larger JWST program. This program will investigate cloud cycles across many different exoplanets. It includes a gas giant that travels through the habitable zone on an eccentric orbit.
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