A Planet's Rotation Revealed Its Fiery Secrets ⚡ экспресс
Observations of two transits of the ultra-hot Jupiter WASP-121 b, made with the NIRSpec and NIRISS instruments on the James Webb Space Telescope, revealed an asymmetry in transit light curves caused by the planet's rotation. The transmission spectrum shows an increase in CO absorption and a weak decline in H2O absorption as the planet rotates, indicating a stronger longitudinal temperature gradient on the evening terminator than on the morning one. This aligns with a higher temperature on the eastern half of the dayside compared to the western half. The observed changes in atmospheric composition correspond to thermal dissociation of H2O at high temperatures, while CO remains stable. The detection of longitudinal gradients in temperature and chemical composition due to the planet's rotation during transit opens a new method for probing atmospheric inhomogeneity on exoplanets with JWST, complementing studies of morning-evening terminator asymmetry.
The planet WASP-121 b is a gas giant, heated to 2500°C. It always faces its star with one side, like a globe frozen under a lamp. But as it passes in front of the star's disk, its rotation reveals different facets to us — as if that globe were slowly turned, letting us peer into every corner.
Using the James Webb Space Telescope, scientists applied the splitting of light into colors and noticed something odd: during transit, the light absorbed by water vapor weakens, while that by carbon monoxide strengthens. The secret is that the planet's eastern side is heated more fiercely and literally tears water molecules apart. Carbon monoxide, on the other hand, endures this inferno.
This approach turns a transit into a thermal scanner: previously, we only saw the day-night boundary, but now — temperature swings across the entire surface. This is a new way to read weather on distant worlds.
🎯 Strong winds carry heat from the hottest point eastward, so the eastern side is always hotter than the western — as if the planet is constantly blow-dried by a giant hairdryer.