The James Webb Space Telescope has given astronomers a front-row seat to a celestial spectacle: the evolution of twilight on a distant, scorching exoplanet. WASP-121 b, a gas giant orbiting its star at an astonishingly close distance, offers a unique glimpse into the extremes of planetary weather. With a year lasting just 30 hours, one side of the planet is perpetually bathed in searing heat, while the other side remains in the frigid embrace of space. This extreme contrast in temperatures and conditions has allowed scientists to study the planet's twilight zones in unprecedented detail.
The research, led by PhD student Cyril Gapp, focused on the morning and evening terminators, the boundaries between day and night. By tracking the filtering of starlight through the planet's atmosphere during its transit, the team could map out how conditions shift across the planet's surface. The results revealed two distinct twilight zones, with the evening terminator showing a noticeable increase in starlight absorption and a rise in carbon monoxide levels due to the fierce winds sweeping heat eastward from the dayside.
The most fascinating discovery, however, was the dramatic difference in water content between the two terminators. In the scorching evening atmosphere, temperatures reached the point of tearing water molecules apart, resulting in noticeably less water remaining compared to the cooler morning side. This finding highlights the extreme conditions on WASP-121 b and the potential for complex atmospheric dynamics.
When comparing their results with computer models, the team encountered a puzzle. The real signal was stronger than predicted, suggesting the presence of clouds composed of vaporized minerals like silicates. These clouds, though difficult to model accurately, offer a clue to the limitations of current atmospheric models. The technique used in this study marks a significant advancement, allowing astronomers to trace atmospheric conditions longitude by longitude on exoplanets, opening up a new era of detailed exoplanet weather mapping.
