JWST Reveals GJ504b Has Salt Clouds and 25-Jupiter-Mass Atmosphere 60 Light-Years Away

Q: What gives a world 25 times more massive than Jupiter its mysterious pink color?

GJ504b’s mysterious pink color appears to come from exotic salt clouds high in its atmosphere, especially clouds made of potassium chloride and zinc sulfide. James Webb Space Telescope observations showed that these clouds are not a minor detail but a key part of explaining the object’s spectrum. Researchers found that their atmospheric models produced an unrealistic thermal structure unless they included cloud cover. When they added salty clouds, the data made sense, indicating those clouds strongly shape the light astronomers receive from GJ504b. That cloud layer likely alters and filters the planet’s thermal glow, giving it the rosy or dull-magenta appearance that led to its “pink world” nickname. The atmosphere is also chemically complex, containing water, methane, carbon monoxide, ammonia, hydrogen sulfide and likely carbon dioxide, but the evidence points to the salt clouds as the main reason for its distinctive color. The finding is notable because it is the first time salt clouds have been considered essential to explaining the spectrum of such an object. In short, the pink hue is best explained not by the planet’s size or heat alone, but by how high-altitude potassium chloride and zinc sulfide clouds affect the light coming from its atmosphere.

Q: This world is 25 times heavier than Jupiter. Is it a super-planet or a failed star?

It is best described as a **brown dwarf candidate on the planet–brown dwarf boundary**, not a clear-cut “super-planet.” At about **25 times Jupiter’s mass**, GJ504b sits well above the commonly used **13-Jupiter-mass threshold** where objects can burn deuterium, the usual dividing line between giant planets and **brown dwarfs**, often called failed stars. It is still far below the roughly **75–80 Jupiter masses** needed to sustain hydrogen fusion and become a true star. That said, astronomers have not settled the case. The new JWST study refers to GJ504b as a **“planetary-mass companion”** because its origin may matter as much as its mass. Its atmosphere appears enriched in heavy elements such as **carbon, oxygen and possibly sulfur**, which can point to formation in a **protoplanetary disk**, the way Jupiter formed, rather than by direct collapse like a star. So the mass argues strongly for **brown dwarf**, while the chemistry and possible formation history leave room for calling it an **extreme giant planet**. That is why researchers frame it as an ambiguous object near the dividing line. In practical terms, if classified by **mass and internal physics**, GJ504b is more likely a **failed star**. If classified by **how it formed**, it may yet qualify as a very massive planet.

3 articles · Updated · ScienceAlert · Jun 28

JWST spectra of GJ504b — a dim pink companion less than 60 light-years away — indicate salty clouds and an atmosphere containing water, carbon monoxide, methane, ammonia and hydrogen sulfide.
290C temperatures and a puzzling thermal anomaly initially broke standard atmospheric models; simulations only became physically plausible when researchers added salt clouds, likely potassium chloride or zinc sulfide.
The new analysis also recasts GJ504b as older and heavier than some earlier estimates: about 10% smaller than Jupiter, roughly 25 times more massive, and likely 2.5 billion to 4.5 billion years old.
Those chemical fingerprints may also hint it formed in a debris disk like a planet rather than as a failed star, offering a template for studying other cold, faint planetary-mass companions with JWST.

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ScienceAlert22h ago

James Webb Space Telescope Reveals GJ504b 'Pink Planet' Has Salty Clouds, Noxious Atmosphere

threads.com22h ago

GJ 504 b, the Pink Planet, has salt clouds: JWST's first spectrum reveals a noxious gas mix and a heftier, older world that may have formed as a planet.

MSN22h ago

JWST uncovers rare salt clouds on mysterious 'Pink Planet'

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If salty clouds swirl on a distant world, what other exotic weather awaits discovery in our galaxy?

What gives a world 25 times more massive than Jupiter its mysterious pink color?

This world is 25 times heavier than Jupiter. Is it a super-planet or a failed star?

JWST Reveals GJ504b Has Salt Clouds and 25-Jupiter-Mass Atmosphere 60 Light-Years Away

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