JWST phase curve reveals strong atmospheric drag and nightside clouds on 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 with extreme atmospheric conditions, including high temperatures, strong winds, and dramatic differences between its day and night sides. Using the James Webb Space Telescope, scientists measured how the planet's infrared emission changes as it orbits its star, creating a spectroscopic phase curve. Comparing these observations to advanced 3-D atmospheric models, they found that the models predict about 12% more emission than what is observed, highlighting ongoing challenges in understanding hot Jupiter atmospheres.

The data show clear evidence for strong atmospheric drag, which slows down winds and affects how heat is distributed around the planet. The nightside of WASP-121 b emits less light and lacks strong absorption features, likely due to the presence of clouds. One puzzling result is a trend where the brightest spot on the planet shifts eastward at shorter wavelengths, a feature not explained by current models or by removing known atmospheric opacity sources.

These findings demonstrate the complexity of ultra-hot Jupiter atmospheres and the need for improved models to fully interpret JWST data. The study also emphasizes the importance of accurately measuring the planet's radius when comparing observations to models.

Key findings
- WASP-121 b shows strong atmospheric drag and nightside clouds
- 3-D models overpredict the planet's emission by about 12%
- Nightside spectrum lacks strong absorption features
- Eastward phase offset at short wavelengths is unexplained
- Results highlight the complexity of ultra-hot Jupiter atmospheres

Scientific study

The Days Drag On on WASP-121 b: Interpreting its NIRISS Spectroscopic Phase Curve with General Circulation Models (external link)