Scientists have published an unusual weather report for the giant exoplanet WASP-94A b, located 700 light-years away, revealing clouds made of molten rock and powerful winds.
The James Webb Space Telescope (JWST) has examined the atmosphere of WASP-94A b, a hot gas giant approximately 700 light-years from Earth, in unprecedented detail. The data revealed that dense clouds dominate the planet's morning terminator, while the evening terminator's sky is completely clear. According to researchers, this discovery suggests that atmospheric analyses of many exoplanets studied to date might have been misinterpreted.
Tidally Locked, Alien, and a Giant World
WASP-94A b, the subject of the research, is slightly less than half the mass of Jupiter but has a diameter approximately 70 percent larger. This gives the planet a low-density and very extensive atmosphere. For scientists, such atmospheres offer significant advantages for observation.
WASP-94A b is classified as a giant gas planet belonging to the "hot Jupiter" class. The planet completes one orbit around its star in just four days. Scientists first discovered this planet about a decade ago, but thanks to JWST, a detailed "weather report" could be prepared for the first time.
The planet is "tidally locked" due to its close proximity to its star. This means one side constantly faces its star, while the other side remains in perpetual darkness. Consequently, extreme temperature differences arise between the day and night sides. A team led by astrophysicist Sagnick Mukherjee from Johns Hopkins University sought to understand whether the atmospheres of such planets are static or dynamic, how their wind systems operate, and how cloud formations occur.
Two Sides Examined Separately
Exoplanet atmospheres are typically studied using a method called "transit spectroscopy." In this method, the chemical composition of the atmosphere is determined by analyzing the starlight filtered through the planet's atmosphere as it passes in front of its star. However, most studies conducted to date treated the planetary atmosphere as a uniform and homogeneous structure.
This time, researchers used a different approach. With the help of JWST's NIRISS (Near Infrared Imager and Slitless Spectrograph), the light changes occurring during the planet's stellar transit were meticulously separated. This allowed for separate atmospheric spectra to be obtained for the planet's "morning limb" and "evening limb."
The results showed significant differences between the two regions.
Observations revealed dense and thick cloud layers on the morning side. On the evening side, the atmosphere was largely clear. Moreover, these clouds are noted not to resemble Earth's water vapor clouds. Researchers believe the clouds are composed of substances like magnesium silicate, iron, and magnesium sulfide. In other words, evaporated rock particles circulate in the planet's atmosphere.
Powerful Winds Constantly Change the Atmosphere
Sagnick Mukherjee, lead author of the study and a postdoctoral researcher at Arizona State University, stated that the difference between the planet's two halves was much greater than expected.
According to scientists, the extreme temperature difference between the day and night sides creates extremely powerful wind systems across the planet. These winds cause clouds to form in the cooler regions of the night side. The clouds are then carried to the morning side, where they break apart and dissipate due to the intense heat from the star.
Researchers liken this process to morning fog on Earth. Just as fog formed during the night disappears as the sun rises, the mineral clouds on WASP-94A b vanish under the extreme heat of the day side.
The research reveals that exoplanet atmospheres may be much more complex than previously thought. Scientists believe that analyzing the atmospheres of many planets to date by assuming them to be uniform and homogeneous may have led to significant errors.
According to experts, studying only a single region of a planet can lead to incorrect conclusions about its atmospheric structure, formation process, and chemical composition. It is now clearer, in particular, that clouds are not evenly distributed across the planet.
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