James Webb Maps WASP-121b’s 30-Degree Atmospheric Split During 1 Transit

3 articles · Updated · spacedaily.com · Jul 10

Webb tracked WASP-121b longitude by longitude during a single transit, finding the evening limb hotter and more expanded while the morning limb appears cooler.
About 30 degrees of planetary rotation during the transit let changing atmospheric regions move into view, and stronger late-transit absorption showed the evening side was blocking more starlight.
Water signatures weakened on the hotter evening side because extreme heat can dissociate water molecules, while the stronger-than-expected morning contrast is consistent with possible silicate clouds.
Dayside temperatures near 2,770 Kelvin and nightside temperatures around 1,000 Kelvin underscore how extreme the tidally locked planet is as it orbits its star every 1.3 days.
The result marks the first detection of this rotational-transit effect and suggests exoplanet transmission spectra can no longer be treated as a single averaged atmospheric column.

Sources

spacedaily.com17h ago

James Webb Telescope Reveals Extreme Atmospheric Asymmetry on Exoplanet WASP-121b

en.clickpetroleoegas.com.br17h ago

The James Webb telescope spotted a planet 700 light-years from Earth with mornings full of sand clouds and nights with clear skies, the temperature difference between the two hemispheres reaches an impressive

The Universe. Space. Tech17h ago

Hot world WASP-121 b, where water breaks down

How does a planet's spin allow the Webb telescope to create the first alien weather map?

Will mapping this ultra-hot world's weather rewrite our theories on how planets form?

JWST’s 2026 Discovery: Mapping a 30-Degree Atmospheric Split on WASP-121b

Overview

In June 2026, the James Webb Space Telescope made a groundbreaking direct observation of the ultra-hot Jupiter WASP-121b, revealing a dramatic 30-degree atmospheric split between its dawn and dusk regions. This was achieved using the innovative Rotational Transit Technique, which allowed astronomers to map the planet’s atmosphere in detail during a single transit and precisely probe the boundary between day and night. These detailed observations mark a new era in exoplanet research, paving the way for future studies of other ultra-hot gas planets and helping scientists better understand the complex atmospheric dynamics of these extreme worlds.

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