For over 10 years, scientists have been decoding the mysterious atmosphere of a famous “Pink Planet.” Now, thanks to observations from the James Webb Space Telescope (JWST), astronomers  have found that the object harbors unusual salty clouds and an exotic chemistry in its atmosphere. The findings were recently published in The Astronomical Journal, and provide the first direct evidence for salt clouds in a cold object’s atmosphere.  

Discovered in 2013, GJ504b orbits a sun-like star 57 light-years away from Earth. Despite its nickname, scientists aren’t actually sure if it’s a planet. GJ504b has a mass that’s around 25 times that of Jupiter, and may in fact be a brown dwarf—a failed star that straddles the line between planet and star. That’s why astronomers refer to it as a “planetary-mass companion,” which means it’s a planet-sized object orbiting a star. 

GJ504b has a temperature of only 550 degrees Fahrenheit, making it difficult to study from Earth. “The Pink Planet is the coldest companion ever discovered using ground-based instruments,” Aneesh Baburaj, a study co-author and astronomer at Northwestern University, said in a statement. 

“Many teams all around the world performed follow-up observations to study its light, but it was too faint for ground-based instruments,” he added. “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.”

The JWST captured GJ504b’s faint light, and the researchers used advanced data-processing techniques to filter out the glare from its bright host star. The filtering  allowed them to break down the light coming from GJ504b into component colors that each represent a different element present in its atmosphere.  

“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.”

The team found that the Pink Planet’s atmosphere is home to water vapor, methane, carbon dioxide, ammonia and other molecules. But something was still missing from the equation. When they  fed the data to a computer model to reconstruct the companion star, the simulated atmosphere would only match their observations if it contained unusual, implausible features. 

Once they added clouds to their simulation, it was clear that only salty clouds could explain what they were seeing. 

“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,” Baburaj explained. 

Scientists still have more to learn about GJ504b, including how the mysterious object formed in the first place. But the authors of this study believe the findings could inform research on other cold, faint planets. 

“This is the first time we’ve found that salt clouds are critical to explaining the spectrum of an object,” Baburaj added. “It’s a good reminder to account for clouds in our models.”