# James Webb Telescope Maps Twin Atmospheres of Hellish Exoplanet WASP-121 b in a First

*2026-06-15 22:02 UTC · Science · 2 min read*

> The James Webb Space Telescope has for the first time mapped distinct morning and evening atmospheres on ultra-hot exoplanet WASP-121 b, confirming theoretical predictions about tidally locked planets.

Astronomers using the James Webb Space Telescope have made the first direct observation of dramatically different atmospheric conditions between the morning and evening sides of a distant exoplanet. Led by Cyril Gapp of the Max Planck Institute for Astronomy in Heidelberg, the team studied WASP-121 b — an ultra-hot gas giant 900 light-years from Earth — and confirmed a stark atmospheric asymmetry long predicted by theory but never directly observed.

WASP-121 b is a tidally locked "hot Jupiter," meaning the same face always points toward its host star. The dayside scorches at around 2,770 Kelvin (roughly 2,500°C), while the nightside sits at about 1,000 Kelvin (725°C). Powerful eastward winds carry this heat outward, expanding the evening-side atmosphere while leaving the morning side comparatively cool and compact. JWST’s infrared sensitivity let researchers track how water vapour and carbon monoxide signals shift between these two zones during a single planetary transit.

The results, published in Nature Astronomy, mark a landmark for exoplanet science: for the first time a telescope has resolved the fine longitudinal structure of an alien atmosphere down to a scale of 30 degrees of planetary rotation. Researchers say the technique opens the door to detailed climate modelling of exoplanets, potentially including worlds closer to habitable conditions.

## Sources

- [phys.org](https://phys.org/news/2026-06-jwst-reveals-dawn-dusk-atmosphere.html)
- [sciencedaily.com](https://www.sciencedaily.com/releases/2026/06/260611024559.htm)

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TechTools News · https://techtools.cz/tools/news/article/1837-james-webb-telescope-maps-twin-atmospheres-of-hellish-exoplanet-wasp-121-b-in-a
Česká verze: https://techtools.cz/tools/news/clanek/1910-teleskop-jamese-webba-poprve-zmapoval-dve-odlisne-atmosfery-pekelne-exoplanety