A distant object once celebrated as a rare “Pink Planet” is now challenging astronomers’ understanding of planetary formation after new observations from NASA’s James Webb Space Telescope (JWST) revealed it may be far older, larger, and more complex than previously believed.
First identified in 2013, GJ504b orbits the star GJ504 in the Virgo constellation and was initially estimated to be about four times the mass of Jupiter, with a relatively young age of roughly 160 million years. Viewed in reflected light, the object would appear magenta in color, earning it its nickname.
However, new JWST data reported by IFLScience suggests a dramatically different picture. Researchers now estimate GJ504b may be between 2.5 billion and 4 billion years old, making it far older than earlier models indicated. Its mass has also been revised upward to around 25 times that of Jupiter.
That shift places GJ504b in a scientifically ambiguous category known as a planetary-mass companion — an object too large to be a conventional planet but not clearly defined as a brown dwarf, or “failed star.” Scientists say its true origin remains uncertain.
Despite its size, the object is relatively cold compared with similar celestial bodies. Researchers estimate its temperature at about 290 degrees Celsius, which is extremely low for an object of its class but still far beyond anything survivable on Earth.
Aneesh Baburaj, a researcher at Northwestern University and lead author of the study, described GJ504b as the coldest companion object ever detected using ground-based instruments. He said its faintness made it an ideal target for JWST, which can analyze atmospheric composition in greater detail than previous observatories.
Once the telescope captured its spectrum, researchers found an unusual chemical mix in its atmosphere, including water vapor, methane, carbon dioxide, and ammonia. But when scientists attempted to model the atmosphere, the results consistently produced physically inconsistent outcomes.
To resolve the mismatch, researchers introduced cloud layers into their models, testing several scenarios. One solution stood out: the presence of salt clouds, a type of cloud never before confirmed on any astronomical object.
Baburaj said that when salt clouds were included in simulations, the models aligned closely with expected atmospheric behavior for cold planetary bodies. The clouds appeared to obscure deeper molecular signals, helping reconcile previously confusing data.
While salt clouds have been theorized in exoplanet research — including for the distant world GJ 1214b — more recent JWST studies suggest those earlier interpretations may instead be better explained by atmospheric haze rather than cloud formation.
Researchers say the findings, published in The Astronomical Journal, highlight how advanced space-based observatories are forcing scientists to reconsider long-standing assumptions about distant worlds and the boundaries between planets and brown dwarfs.
