James Webb Telescope Discovery
The James Webb Space Telescope has detected an unusual atmospheric structure on the exoplanet WASP-94A b, located about 600 light-years from Earth. Analysis of transit spectroscopy data shows that different zones of the planet's atmosphere exhibit fundamentally different physical and chemical characteristics — effectively forming two atmospheres on one celestial body.
Characteristics of WASP-94A b
WASP-94A b is a hot Jupiter — a gas giant that orbits very close to its star and is in a state of tidal locking. This means that one side of the planet is constantly facing the star and is in conditions of extreme heating, while the opposite side remains in eternal darkness.
Atmospheric Nonuniformity
However, new observations have shown that even within the illuminated hemisphere, the atmosphere is nonuniform. Scientists have identified two regimes: on the morning hemisphere of the planet, which first passes through the star's disk during transit, the spectrum is smoothed and poor in molecular signals. This is explained by dense mineral clouds blocking the deep layers of the atmosphere.
Differences Between Hemispheres
On the evening hemisphere, on the other hand, the spectrum becomes significantly cleaner — water vapor and other chemical markers are clearly visible. To interpret the data, scientists have built three-dimensional climate models. According to them, clouds form on the colder night side, then are transferred by powerful winds to the morning side, where they partially persist.
Impact on Atmospheric Modeling
As they move towards the hotter daytime zone, they evaporate, and by the evening hemisphere, the atmosphere becomes significantly more transparent. The temperature contrast between the sides reaches about 126 °C, which is sufficient for a radical change in the phase state of cloud particles and the chemical composition of the upper layers of the atmosphere. As a result, the spectroscopic signal is not averaged, as previously assumed, but depends on the geographical location on the planet.
Conclusion
The study shows that the traditional approach to modeling exoplanetary atmospheres as homogeneous shells can significantly distort data interpretation. In the case of hot Jupiters, real atmospheric structures can be much more complex and dynamic than previously thought.