Scientists discover salt clouds swirling around 'pink planet'

(CN) — For more than a decade, a faint rosy world 57 light-years from Earth has kept astronomers guessing. Now, they have a picture of what is hiding in its atmosphere.

Using the James Webb Space Telescope, a team of astronomers led by Northwestern University studied the atmosphere of the “pink planet," a mysterious object that’s too cold and too faint for ground-based telescopes to examine in detail. What they found surprised them: clouds made of salt.

The findings were published Thursday in the Astronomical Journal in a study titled “JWST-TST high contrast: First direct spectroscopy of GJ504b reveals clouds and possible metal enrichment.”

The pink planet, formally known as GJ504b, was discovered in 2013. It orbits a sun-like star and sits near the boundary between a giant planet and a brown dwarf. At roughly 25 times the mass of Jupiter, astronomers call it a planetary-mass companion.

It also has an unusual temperature. Most directly imaged exoplanets range between 1,000 and 2,000 degrees Fahrenheit. The pink planet is just 550 degrees Fahrenheit. Scientists estimate it is between 2.5 billion and 4 billion years old.

Giant planets are born extremely hot and cool as they age, which explains why the object is unusually cold.

That low temperature made it difficult to study from Earth. Multiple teams tried and failed to obtain a clear spectrum.

“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,” said Aneesh Baburaj, a postdoctoral associate at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics, who led the study. “And they could not see the object. With JWST, our entire observation took around two hours, and we were successful.”

Webb captured the planet’s faint light, and researchers used processing techniques to remove glare from its much brighter host star. That revealed the object’s spectrum, which scientists use to identify the elements and molecules present in an atmosphere.

The spectrum showed a rich mix of chemicals, including water vapor, methane, carbon dioxide and ammonia. But when researchers tried to recreate the atmosphere using those ingredients alone, the results didn’t match what Webb observed.

“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.”

Scientists had theorized the existence of salt clouds in planetary atmospheres for more than 15 years, but this is the first evidence of them in the spectrum of such a cold object.

“The pink planet is the coldest companion ever discovered using ground-based instruments,” Baburaj said. “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 data also suggests that the pink planet may be unusually rich in heavy elements, though researchers say its origins remain unclear. Current data can’t determine whether it formed like a planet or more like a small star.

Astronomers believe these techniques could help unlock other cold, faint worlds that have resisted close study.

Jupiter, for example, has clouds made of ammonia ice that current instruments cannot fully characterize. The detection of salt clouds in the pink planet suggests that astronomers are getting closer.

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