JWST maps the weather on a hot gas giant 700 light-years away

WASP-94A b, a hot gas giant located approximately 690 light-years from Earth, has captured the attention of astrophysicists as researchers delve into its atmospheric conditions. This tidally locked giant orbits closely around one of the stars in a binary system, presenting a unique opportunity for study. A recent investigation, led by Sagnick Mukherjee from Johns Hopkins University, utilized the advanced capabilities of the James Webb Space Telescope to unveil the weather dynamics on this distant world. The concept of tidal locking means that WASP-94A b experiences no significant temperature variations between day and night, which raises intriguing questions about its atmospheric behavior. "Our aim was to decode the characteristics of such atmospheres," Mukherjee remarked. "Are they stable or turbulent? Do they exhibit winds or cloud formations?" The findings revealed that mornings on WASP-94A b tend to be cloudy, while evenings offer clearer skies. This revelation suggests that prior assumptions regarding the chemistry of this and similar exoplanets may have been overly simplistic. With a mass just below half that of Jupiter and a diameter over 70 percent larger, WASP-94A b presents a low-density structure, allowing its atmosphere to extend further into space. This unique feature facilitates observation and analysis. Typically, astronomers employ transmission spectroscopy to determine atmospheric composition by studying the light spectrum that filters through the planet's atmosphere as it transits its star. However, this method often averages out the light from the entire circumference of the planet, treating its atmosphere as a uniform layer of gas, which is a considerable oversimplification for tidally locked planets. On worlds like WASP-94A b, significant temperature differences between the day and night sides create variations in atmospheric density. These disparities, compounded by the planet's slow rotation and the resulting Coriolis effect, lead to equatorial super-rotation — a phenomenon where winds at the equator travel eastward faster than the planet's rotation. Circulation models accurately predict this behavior on WASP-94A b, further enhancing our understanding of atmospheric dynamics in distant worlds.