The Pink Planet has a secret. Its skies are filled with salt clouds, a feature never before directly confirmed on any cold planetary object. Astronomers using the James Webb Space Telescope finally cracked the mystery of GJ 504 b, a faint pink world 57 light years from Earth that has puzzled scientists for more than a decade.
A cold world with a colorful haze
GJ 504 b was first spotted in 2013 orbiting a Sun like star. It is one of the coldest planetary mass companions ever directly imaged. With a mass about 25 times that of Jupiter, it sits near the fuzzy boundary between giant planets and brown dwarfs. Astronomers call it a planetary mass companion because they are not certain it is actually a planet. Its low temperature, between 2.5 billion and 4 billion years old, gives it a distinctive pinkish hue that earned it the nickname Pink Planet.
Salty skies and exotic chemistry
Northwestern University postdoctoral associate Aneesh Baburaj led the study published June 18 in the Astronomical Journal. Using JWST, his team detected water vapor, methane, carbon dioxide, ammonia, and something unexpected: salty clouds. This is the first direct evidence that salt clouds can exist in the atmosphere of a cold planetary object, confirming a prediction scientists made more than 15 years ago. The object was so faint that ground based telescopes could not analyze its light. JWST was the perfect tool to finally get a clear spectrum.
Local astronomers at Northwestern and the Space Telescope Science Institute, including Marshall Perrin who designed the observing program, were deeply invested. The Pink Planet had drawn follow up observations from teams around the world, but none could crack its secrets until now. The findings highlight JWST's ability to study extremely cold and faint worlds beyond the reach of ground based observatories.
This discovery does not just solve a decade old puzzle. It opens a new window into the chemistry of cold worlds and shows that salt clouds, once only theoretical, are real.
