This Famously Weird 'Pink Planet' May Have Salty Clouds, Study Finds
NEWS | 28 June 2026
Outlandishly alien worlds spark our collective cosmic imagination like nothing else. This never-ending variety includes super-Earths smack dab in their star's habitable zone, frigid Hoth-like locales, and creepy worlds that may resemble giant celestial eyeballs. However, some worlds are difficult to classify because they're so cold and dark that they're nearly invisible to ground-based observatories. If only humanity had some sort of incredibly sensitive infrared space telescope at our disposal, such a facility could more effectively detect the scant spectral signals emanating from these elusively dim bodies. Fortunately, we have exactly that. The James Webb Space Telescope, which has helped examine an object like no other: a giant pink world with salty clouds and a swirling atmosphere containing some of the chemicals found under your kitchen sink, a new study reveals. "The Pink Planet is the coldest companion ever discovered using ground-based instruments," explains Aneesh Baburaj, a postdoctoral associate who studies exoplanetary evolution at Northwestern University, and the study's lead author. "Many teams all around the world performed follow-up observations to study its light, but it was too faint for ground-based instruments. "That made it a perfect target for JWST. When we finally obtained its spectrum, it immediately looked interesting. But once we started digging deeper into the data, we realized it was not like anything we have analyzed before." Astronomers initially discovered this intriguing object, designated GJ504b, in 2013. It's located less than 60 light-years away, orbiting a Sun-like star at an immense distance; more than 40 times farther than Earth sits from the Sun – farther out even than Pluto. Scientists can't fully agree on what GJ504b actually is. It may be a massive planet or a brown dwarf, a mysterious class of objects more akin to failed stars than planets. Accordingly, the researchers dub GJ504b a "planetary-mass companion". The newly published assessment based on simulations and JWST spectral data – which serves as a chemical 'fingerprint' to reveal a body's chemical constituents – also yielded updated mass and age estimates that suggest GJ504b is much heftier and older than some previously believed. Bafflingly, GJ504b appears to be around 10 percent smaller than Jupiter but 25 times more massive. It's also relatively cold. Giant bodies are born blisteringly hot, but this object is several times cooler than its thousand-degree counterparts: only around 290 degrees Celsius (550 degrees Fahrenheit), hinting that it may be 2.5 billion to 4.5 billion years old – potentially around the age of our Solar System. More mysteriously, when the researchers tried to experimentally reconstruct its characteristics by feeding JWST data into their astrophysical models, a weird thermal anomaly popped up, as if they were missing a source of opacity in GJ504b's atmosphere. They could only make this physically implausible "isothermal region" go away when they simulated cloud cover – salty cloud cover. "We ran simulations with clouds, and the results aligned with what we know about cold planets," Baburaj says. "We tried three different types of clouds, and salt clouds fit best. When we accounted for salt clouds, it subdued the signature of molecules hidden deeper in the companion's atmosphere. Then, the results became physically possible." Though their exact nature is still uncertain, such salty clouds may be made of potassium chloride or zinc sulfide. Additionally, the researchers found evidence for a noxious atmospheric mix that may contain water, carbon monoxide, methane, ammonia, and hydrogen sulfide swirling within the pink-hued haze. Analyzing the spectral data from other planetary-mass companions, as per this work, could illuminate the dim, murky histories of other baffling bodies throughout the cosmos. Related: Strange Stars Look Suspiciously Like They've Been Eating Planets For example, GJ504b's heavy element profile (in astronomy this includes everything beyond helium) appears to be enriched with carbon, oxygen, and possibly sulfur, compared to its star; in our own solar backyard, Jupiter seems to be similarly enriched. This tentatively suggests that GJ504b may have formed as a planet, from a protostellar disk full of debris, rather than as a failed star. Given these revelations, this study marks a milestone for using JWST and modeling techniques to unveil chilly, indistinct objects. "This is the first time we've found that salt clouds are critical to explaining the spectrum of an object," Baburaj concludes. "It's a good reminder to account for clouds in our models." This research was published in The Astrophysical Journal.
Author: Ivan Farkas.
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