James Webb Reveals Salt Clouds on 25-Jupiter-Mass GJ 504b

Q: Does the 'pink planet's' unique atmosphere prove giant worlds form rapidly like stars, instead of slowly like Earth?

No. The new JWST results on GJ 504b do not prove that giant worlds form rapidly like stars. What the study does show is that GJ 504b has an unusual atmosphere containing water vapor, methane, carbon dioxide, ammonia, and mineral salt clouds that likely explain its pink appearance. That is a major advance in characterizing a very cold, faint planetary-mass object, and it gives astronomers a much better tool for studying similar worlds. But formation is still unresolved. GJ 504b sits in a gray zone at about 25 Jupiter masses, between a giant planet and a brown dwarf. Those two classes can form in different ways: giant planets are usually thought to grow in a disk around a star, while brown dwarfs form more like stars through rapid gravitational collapse. The atmosphere alone does not yet distinguish decisively between those pathways. The added context from related research is that atmospheric chemistry, heavy-element content, and especially isotope ratios may eventually help tell the difference. Some models, including disk instability, allow massive giant worlds to form quickly, and GJ 504b’s mass is consistent with that possibility. But the current paper does not claim proof of that scenario. So the finding is best seen as an important clue, not a verdict. It strengthens scientists’ ability to test competing formation theories, but it does not settle whether GJ 504b formed like a star, like a planet, or through some intermediate process.

Q: If a 'planet' can be 25 times bigger than Jupiter, where do we now draw the line between planets and stars?

A 25-Jupiter-mass object is generally not a planet in the strict physical sense; it sits in the brown dwarf category, between planets and true stars. The clearest line is not size but fusion. True stars are massive enough to sustain hydrogen fusion in their cores, which begins at roughly 75 to 80 Jupiter masses. Brown dwarfs fall below that, but above about 13 Jupiter masses they can briefly fuse deuterium, a heavier form of hydrogen. Objects below that threshold are usually classified as planets. That is why GJ 504b is described cautiously in the new study as a “planetary-mass companion.” At about 25 Jupiter masses, it is above the usual deuterium-burning limit, so many astronomers would call it a brown dwarf rather than a planet. The ambiguity reflects a real scientific debate: some researchers argue mass alone is too crude, and that formation history matters too. If an object formed in a protoplanetary disk like a planet, some would still treat it as planet-like even if it is unusually massive. JWST findings on other borderline objects, such as 29 Cygni b at about 15 Jupiter masses, are strengthening that argument by showing some high-mass companions may have formed like planets. But GJ 504b remains on the brown-dwarf side of the conventional mass boundary. One more point: “25 times bigger than Jupiter” usually means 25 times more massive, not 25 times larger in radius. Brown dwarfs are often roughly Jupiter-sized, just far denser.

3 articles · Updated · VietNamNet · Jul 2

JWST captured the first spectrum of GJ 504b, showing water vapor, methane, carbon dioxide, ammonia and an atmospheric signature best explained by salt clouds.
Those inorganic salt clouds solved the long-running mystery of the object's pink appearance by masking deeper atmospheric layers and reshaping the light JWST detected.
GJ 504b orbits a Sun-like star 57 light-years away and, at about 290°C, is the coldest planetary-mass companion ever found by ground-based telescopes.
The roughly two-hour Webb observation succeeded where all-night ground campaigns had failed, using infrared instruments and processing to remove glare from the host star.
Researchers said the result provides the first direct evidence for a 15-year-old prediction that very cold worlds can host mineral-salt clouds, while the object's origin remains unresolved.

Sources

VietNamNet2d ago

James Webb Space Telescope Reveals Salt Clouds, Atmosphere of 'Pink Planet' GJ 504b

The Brighter Side of News2d ago

JWST finds salt clouds in the atmosphere of a strange Pink Planet - The Brighter Side of News

AOL2d ago

Vibrant discovery: Unique, salty clouds found on iconic 'Pink Planet' - AOL

9 Sources

Now that salt clouds color alien worlds, what other exotic weather will the Webb telescope reveal on distant planets?

Does the 'pink planet's' unique atmosphere prove giant worlds form rapidly like stars, instead of slowly like Earth?

If a 'planet' can be 25 times bigger than Jupiter, where do we now draw the line between planets and stars?

Unveiling Salt Clouds on the Pink Planet: JWST’s Landmark Discovery on GJ 504b

Overview

The James Webb Space Telescope has made a groundbreaking discovery by directly detecting salt clouds—specifically potassium chloride and zinc sulfide—in the atmosphere of the exoplanet GJ 504b. Known as the 'Pink Planet,' GJ 504b is a planetary-mass companion about 25 times the mass of Jupiter, located 57 light-years from Earth, with a relatively cool temperature of around 550°F (290°C). This first-ever confirmation of salt clouds fills a crucial gap in our understanding of exoplanet atmospheres, showing that exotic cloud types exist on cold giant planets and opening new possibilities for studying planetary formation and atmospheric diversity across the galaxy.

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