When astronomers first spotted GJ 504b back in 2013, it immediately went viral. Sitting 57 light-years away in the constellation Virgo, this giant world earned the nickname the “Pink Planet” thanks to its striking, deep-magenta hue.
But a fresh look by the James Webb Space Telescope (JWST) just proved that its color isn’t the only bizarre thing about it. According to a new study published in The Astronomical Journal, the Pink Planet is wrapped in an atmosphere filled with clouds made of vaporized salt.
The Planet That Defied Ground Telescopes
For over a decade, studying GJ 504b from Earth was an absolute nightmare for scientists. Ground-based teams would book entire nights on the world’s largest observatories, point them toward the Pink Planet, and come away with essentially nothing.
The problem? It’s incredibly faint and unusually cold.
While most gas giants we directly photograph in deep space sizzle between 1,000°F and 2,000°F, GJ 504b is a relatively chilly 550°F (290°C). That’s about the temperature of a standard kitchen oven. It’s so cold because it’s old—somewhere between 2.5 billion and 4 billion years old—and gas giants naturally cool down as they age.
Where ground telescopes failed after hours of staring, the space-bound Webb telescope cracked the case in just two hours.
How Researchers Found the Salt
Led by Aneesh Baburaj, a postdoctoral researcher at Northwestern University, astronomers used Webb’s infrared instruments to capture the planet’s unique chemical “fingerprint” (a spectrum).
The data revealed a chaotic atmospheric stew, detecting things you might expect on a giant gas world:
* Water vapor
* Methane
* Carbon dioxide
* Ammonia
However, when the team plugged these ingredients into standard atmospheric computer models, the simulations broke. The physics simply didn’t make sense.
The breakthrough came when they added clouds to block out the deeper layers of the atmosphere. They tested three different cloud compositions, and vaporized metal salts fit the data perfectly.
> “This is the first time we’ve found that salt clouds are critical to explaining the spectrum of an object,” Baburaj noted. “It’s a good reminder to account for clouds in our models.”
> Cosmic Weather: Liquid Glass vs. Table Salt
This discovery gives us a fascinating look at how planetary weather changes based entirely on temperature. Think of it as a three-tier cosmic thermostat:
Because GJ 504b sits in that golden “intermediate” temperature zone, it is too hot for water to freeze into clouds, but too cool for rocks to melt into glass rain. Instead, salt vaporizes, rises, and condenses into crystalline alien skies.
## Is It Even a Planet?
The JWST data didn’t just find salt; it also weighed the planet. Webb’s tracking suggests GJ 504b is actually much chunkier than originally thought—roughly 25 times the mass of Jupiter.
This puts the Pink Planet in a bit of an identity crisis. At 25 Jupiter masses, it straddles the blurry line between a massive gas exoplanet and a “brown dwarf” (a failed star that never grew big enough to ignite). Because of this, astronomers are officially calling it a “planetary-mass companion.”
Whether it’s a super-sized planet or a pint-sized failed star, the unique environment of GJ 504b proves that the universe has plenty of surprises left up its sleeve—and they taste a little salty.
