James Webb Space Telescope (JWST) observations have revealed the colorful secret of the Pink Planet, the coldest object of its type ever directly observed.
A team of astronomers led by Northwestern University has revealed their findings in a recent paper published in The Astronomical Journal, finally describing the rose-colored haze covering the planetary-mass companion GJ504b, thanks to JWST data.
For over a decade, researchers have speculated that atmospheric salt clouds may create the pink planet’s strange hue, but this is the first concrete evidence for the hypothesis.
The Pink Planet
Since its discovery in 2013, GJ504b, commonly known as “The Pink Planet,” has been a bit of an astronomical mystery. Even the object’s description is imprecise: a “planetary-mass companion,” a nebulous category teetering between the size of a large planet and a brown dwarf, at roughly 25 times Jupiter’s mass. Residing 57 light-years from Earth, the object’s host star is similar to our Sun.
Faint due to extremely cold temperatures, astronomers cannot obtain clear enough observations with ground-based telescopes to perform spectroscopic analysis. However, from its vantage point beyond our atmosphere, the JWST’s advanced instruments have finally provided the necessary data to make sense of the object’s strange pink atmosphere.
The exoplanets most clearly observed are much hotter than our world, with temperatures between 1,000 and 2,000°F, creating a brilliance which can be seen across the gulf of space and through Earth’s atmosphere.
This giant planet is a mere 550°F, still hot by Earth standards, but far cooler than is normal for its type. According to the new study, GJ504b is an ancient world, some 2.5 to 4billion years old, with a slow cooling over time accounting for its decreased temperature.
Challenging JWST Observation
In addition to providing the first evidence for The Pink Planet’s elusive salt clouds, the team’s research has broader implications for studying cold objects, laying the groundwork for future JWST observations of such faint glows, too dim for ground-based telescopes.
“The Pink Planet is the coldest companion ever discovered using ground-based instruments,” according to Aneesh Baburaj, 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.”
To accurately analyze the light, Baburaj’s team used an advanced data-processing technique to remove considerable glare from the Pink Planet’s host star, improving the quality of the JWST data. Breaking light into separate colors through spectroscopic analysis allows scientists to determine the elemental composition of exoplanet atmospheres using JWST data.
“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.”
Analyzing the JWST Data
The team discovered water vapor, methane, carbon dioxide, ammonia, and other molecules in the object’s atmosphere, but these results conflicted with existing atmospheric models, which only made sense if the object had an extremely unlikely combination of physical features. However, once the team added clouds to the model, the effect of their salty formations on the light made the JWST data much easier to explain.
“We ran simulations with clouds, and the results aligned with what we know about cold planets,” Baburaj said. “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.”
In addition to the salty clues, the researchers discovered an abundance of heavy metals. These may have something to do with The Pink Planet’s origins, as it may have originally formed as a star instead of a planet, but astronomers remain uncertain. In any case, the work process developed here will be essential to future JWST investigation of cold objects.
“This is the first time we’ve found that salt clouds are critical to explaining the spectrum of an object,” Baburaj concluded. “It’s a good reminder to account for clouds in our models.”
The paper, “JWST-TST High Contrast: First Direct Spectroscopy of GJ504b Reveals Clouds and Possible Metal Enrichment,” appeared in The Astronomical Journal on June 18, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.