Astronomers using the James Webb Space Telescope have detected salt clouds in the atmosphere of GJ 504 b, a frigid exoplanet nicknamed the “Pink Planet.” This discovery provides strong evidence for a theory first proposed more than 15 years ago.

Discovered in 2013, GJ 504 b is one of the coldest celestial objects ever directly imaged. Its faintness had previously made it difficult to study from Earth. The recent observations by the James Webb Space Telescope allowed scientists to obtain a detailed spectrum of the exoplanet.

"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 had analyzed before," said Aneesh Baburaj of Northwestern University, who led the study. "This is the first time we’ve found that salt clouds are critical to explaining the spectrum of an object. It’s a good reminder to account for clouds in our models."

The analysis of GJ 504 b's atmosphere revealed a composition of water vapor, methane, carbon dioxide, and ammonia, among other molecules. When researchers attempted to simulate the planet's atmosphere, the models did not align with the observed data unless unique, salty features were included.

"We ran simulations with clouds, and the results aligned with what we know about cold planets," Baburaj explained. "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."

GJ 504 b orbits a star similar to our sun at a distance of approximately 57 light-years from Earth. NASA describes the exoplanet as having a color reminiscent of a dark cherry blossom, a dull magenta, and glowing from the heat of its formation.

Researchers note that while it is nicknamed the “Pink Planet,” its classification as a planet is not definitively confirmed. This discovery could offer new insights into the atmospheric conditions of other cold planets, such as Jupiter, which also features ammonia ice clouds.