A Planet's Rotation Revealed Its Fiery Secrets express
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.