James Webb Telescope Reveals Alien World With Two Completely Different Twilights: Fierce Winds Separate Day and Night

[Tracey99]

NASA's James Webb Space Telescope published dramatic findings this week about exoplanet WASP-121 b, a gas giant about 880 light years from Earth that is tidally locked to its star, meaning one side permanently faces its star in blistering day and the other faces permanently into space in deep cold night. Webb's infrared instruments measured the chemistry and temperature of the planet's dawn and dusk regions separately for the first time, revealing that the morning and evening terminator zones are surprisingly different from each other. The morning side shows cooler chemistry with molecules that have had time to form in the cold night hemisphere being dragged around to face the star, while the evening side shows hotter, more processed gases from the permanent dayside being swept around by winds.

The winds transporting heat around WASP-121 b blow at speeds estimated to exceed 5,000 kilometres per hour, faster than the speed of sound and far faster than any weather phenomenon on Earth. The morning terminator shows water vapour, carbon dioxide and other molecules; the evening terminator shows atomic gases and dissociated molecules that have been broken apart by heat. This difference tells astronomers that the winds are not simply averaging the temperature across the planet but are creating distinct chemical environments at each boundary.

WASP-121 b is a so-called hot Jupiter, a class of gas giant that orbits extremely close to its host star and is not believed to support life. But it is one of the most studied exoplanets because its extreme conditions make atmospheric signals particularly clear to observe. The findings were published in Nature and represent one of the most detailed characterisations of any exoplanet atmosphere ever achieved.

News - NASA Sciencescience.nasa.gov

[Cass93]

Winds faster than sound wrapping around a planet tidally locked to its star are the kind of weather system that makes Earth's atmosphere look extremely gentle. Understanding how heat moves on these planets is the foundation for eventually understanding which planets might be habitable

[Sienna89]

Two completely different terminator zones on the same planet tells you the winds are not fast enough to fully homogenise the chemistry between the day and night hemispheres. That is a constraint on the wind speed and the atmospheric dynamics that models can now be tested against

[ElectricPilgrim]

Webb consistently delivering results that require new papers in Nature to describe is the proof that the instrument's sensitivity is genuinely opening new territory in exoplanet science. This kind of twilight chemistry measurement was completely impossible before Webb

[ECWAlex98]

WASP-121 b is not going to have life but the techniques developed to characterise its atmosphere are exactly what will be used when Webb or its successors look at potentially habitable rocky planets. Each hot Jupiter teaches us something applicable to smaller worlds

[HiddenSeb75]

5,000 kilometres per hour winds. The fastest ever recorded wind speed on Jupiter is about 600 kilometres per hour and that was considered extreme. WASP-121 b's atmosphere is operating in a regime where our intuitions built on solar system weather simply do not apply

[QuietNomad]

The morning terminator being cooler with intact molecules and the evening being hotter with dissociated atoms is the kind of observational result that immediately suggests follow-up questions about what happens as those molecules cycle back around the night side and reform

[SammyZayn]

Hot Jupiters being the workhorses of exoplanet atmospheric science because their signals are so strong is the useful reminder that the strangest planets teach us the most. Understanding extremes first is how science usually builds toward the subtler cases

[Cheeky Shaun]

Stop calling it a "day" and "night" if the terminator is essentially a wall of 3,000-degree plasma. It's not a twilight, it's a firewall. The fact that iron rains as liquid beads is cool, sure, but let's not romanticize a planet that would vaporize us instantly. It's just a messy inferno.