Atmospheric temperature and chemical patterns measured in the ultra-hot Jupiter WASP-121 b

Star system: WASP 121 | Distance from the Sun: 858 light years

WASP-121 b is an ultra-hot Jupiter, a gas giant planet orbiting extremely close to its host star. Because it is tidally locked, meaning the same side always faces its star, the planet experiences extreme temperature differences across its surface. New observations show that the planet's rotation creates detectable changes in the light it absorbs as it passes in front of its star, revealing uneven temperature and chemical distributions.

Data from the James Webb Space Telescope show that as the planet rotates during its transit, the amount of carbon monoxide absorption increases while water vapor absorption slightly decreases. These shifts indicate that the eastern side of the planet's dayside is significantly hotter than the western side, leading to the thermal breakdown of water molecules in the warmer regions.

The findings confirm that temperature and chemical composition are not uniform across the atmosphere of WASP-121 b. By analyzing how these spectral signatures change as the planet rotates, researchers can now map atmospheric differences in greater detail than previously possible, extending beyond simple comparisons between the morning and evening edges of the planet.

Key findings
- Asymmetric light curves during transit are caused by the rotation of the planet.
- Increasing carbon monoxide and decreasing water vapor signals indicate varying atmospheric conditions during rotation.
- Higher temperatures on the eastern half of the dayside cause thermal dissociation of water vapor.
- Rotational transit observations provide a new method to map atmospheric heterogeneity on exoplanets.

Scientific study

Atmospheric asymmetries in WASP-121 b revealed by rotational transits detected with JWST (external link)