JWST Detects 11,000-mph Winds on WASP-121b as Dawn and Dusk Atmospheres Diverge

Q: Do 11,000 mph winds and metal clouds signal the final days of this football-shaped exoplanet?

No. The 11,000 mph winds and mineral clouds on WASP-121b point to an extraordinarily violent atmosphere, not clear evidence that the planet is in its final days. What JWST has shown is that WASP-121b is an ultra-hot Jupiter with extreme day-night contrasts. Eastward winds appear to move heat from the dayside to the nightside, making the dusk side hotter than the dawn side. On the hotter side, water molecules are broken apart; on the cooler side, silicate mineral clouds may form. Those are signs of intense atmospheric physics on a tidally locked world orbiting very close to its star every 30.5 hours. There is evidence that WASP-121b is losing some atmosphere. Earlier observations have found escaping elements such as magnesium and iron, and researchers say the planet likely undergoes hydrodynamic escape, in which intense stellar radiation drives gas off the upper atmosphere. But that does not mean imminent destruction. For a gas giant, atmospheric escape can persist over long timescales without signaling a near-term end. The “football-shaped” description reflects strong tidal distortion from the star’s gravity, another marker of how extreme the system is. It suggests the planet is under severe stress, but not necessarily on the verge of breaking apart. So the best reading of the new data is that WASP-121b is a laboratory for extreme exoplanet weather and long-term atmospheric erosion. It may be slowly losing mass, but the new JWST results do not show that its end is near.

3 articles · Updated · Space.com · Jun 16

JWST observations of WASP-121b found its evening terminator hotter than its morning side, giving astronomers their clearest evidence yet of sharp atmospheric contrasts across the ultra-hot Jupiter.
Starlight absorbed during the planet’s transit changed as different longitudes rotated into view, indicating powerful winds are carrying heat from the permanent dayside toward the cooler nightside.
Water vapor and carbon monoxide signals shifted across the atmosphere; researchers say the hotter evening side may break apart water molecules, while the cooler morning side could be partly veiled by silicate clouds.
WASP-121b completes an orbit in 30.5 hours and is so close to its star that it is tidally locked and stretched into a football-like shape, conditions that help drive its extreme weather.
The Nature Astronomy study builds on earlier findings of violent jet streams and atmospheric escape on WASP-121b and could help JWST compare weather patterns on other ultra-hot exoplanets.

Sources

Space.com7h ago

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Beyond metal clouds, what extreme alien weather will JWST's new 3D mapping technique reveal?

What drives a planet-wide, supersonic weather system with cloudy mornings but perfectly clear evenings?

Do 11,000 mph winds and metal clouds signal the final days of this football-shaped exoplanet?

Unveiling WASP-121b: 3D Atmospheric Mapping, Extreme Weather, and Chemical Mysteries on an Ultrahot Jupiter

Overview

WASP-121b is an ultrahot Jupiter exoplanet that orbits its star in just 1.3 days, at a distance so close—only 2.6% of the Earth-Sun gap—that it is nearly torn apart by tidal forces, which have already changed its shape. This extreme proximity leads to dramatic atmospheric asymmetry and chaotic weather. As WASP-121b transits its star, its slight rotation allows astronomers to observe different regions of its atmosphere, revealing a world shaped by intense stellar forces and rapid orbital motion. These unique conditions make WASP-121b a key target for studying extreme planetary environments.

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