Scientists Finally Peered Inside The Mysterious Pink Planet

What They Found Could Rewrite How Giant Worlds Are Born

For more than a decade, a rosy, ancient world lurking 57 light-years from Earth kept astronomers guessing. Now, for the first time, scientists assessed its atmosphere and found something nobody expected: skies full of salt.

Known as the Pink Planet, or GJ 504 b, this cold, faintly glowing world orbits a sun-like star and has long frustrated researchers. While most directly imaged exoplanets run between 1,000 and 2,000 degrees Fahrenheit, the Pink Planet clocks in at just around 550 degrees Fahrenheit, roughly the temperature of a bread-baking oven. Ground-based telescopes couldn’t gather enough of its faint light to make sense of what it was made of. That changed when NASA’s James Webb Space Telescope locked onto it and pulled off a chemical reading that had never been achieved for this kind of object before.

A Northwestern University-led team has now published those findings in The Astronomical Journal, revealing an atmosphere packed with exotic chemistry and, most strikingly, salt clouds unlike anything seen in a planetary atmosphere before. “When we finally obtained its spectrum, it immediately looked interesting,” said lead researcher Aneesh Baburaj, a postdoctoral associate at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics. “But once we started digging deeper into the data, we realized it was not like anything we have analyzed before.”

Why the Pink Planet Has Stumped Scientists for Years

Discovered in 2013, the Pink Planet sits near an awkward boundary in astronomy. At roughly 25 times the mass of Jupiter, it occupies the fuzzy zone between a giant planet and a brown dwarf, what astronomers call a failed star. Scientists couldn’t even agree on how old it is, with estimates ranging widely depending on the method used. Without a precise mass or detailed chemical data, that debate couldn’t move forward.

Making matters harder, teams around the world spent years trying to study it with the biggest ground-based telescopes available and came up empty. “In the past, other astronomers observed the companion for an entire night with some of the biggest telescopes in the world to obtain a spectrum,” Baburaj said. “And they could not see the object. With JWST, our entire observation took around two hours, and we were successful.”

Salt Clouds Are the Pink Planet’s Defining Feature

Webb observed the system twice in February 2024, stripping away the glare of the host star using advanced image-processing techniques to isolate the planet’s faint signal. What came back was a rich chemical mix: water vapor, methane, carbon dioxide, ammonia, hydrogen sulfide, and more.

But the data didn’t add up at first. When researchers tried to model the atmosphere without clouds, the results looked physically impossible. Adding salt clouds, specifically compounds like potassium chloride and zinc sulfide, made everything click. “We ran simulations with clouds, and the results aligned with what we know about cold planets,” Baburaj said. “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.”

Salt clouds in a planetary atmosphere had been theorized for more than 15 years, but this marks some of the first direct observational evidence for them in a cold object. Scientists had long suspected that at low enough temperatures, certain salts would condense out of a planet’s atmosphere the way water condenses into clouds on Earth. Seeing it confirmed in real data is a significant step. Jupiter, by comparison, has clouds made of ammonia ice, a type still beyond the reach of current technology to detect directly. Finding salt clouds in the Pink Planet suggests astronomers are closing that gap.

Age and Chemistry Point to a Planet That Built Itself Piece by Piece

Its chilly cosmic temperature is a product of age: giant planets are born blistering hot and cool over billions of years. New estimates put the Pink Planet at between 2.5 and 4 billion years old.

When the team compared its chemical makeup to its host star, the Pink Planet appeared enriched in heavy elements, a pattern that would lean toward a world that built itself up slowly from solid, rocky material rather than collapsing out of gas like a smaller star. That process, known as core accretion, is the same one thought to have built Jupiter and the other giant planets in our solar system. The authors stress, however, that the current data do not fully rule out a more star-like origin, and the question of how it formed has not been settled.

Before Webb, cold and faint worlds like this one were essentially off-limits for this kind of detailed chemical analysis. Now, with salt clouds confirmed and a full chemical portrait finally in hand, the Pink Planet has gone from a pretty mystery to a genuine window into how giant worlds across the galaxy get built.

---