🪐 The Pink Planet is... salty

The Pink Planet is... salty: its clouds contain salt, a first for an object of this kind.

Discovered in 2013, GJ504b, nicknamed the "Pink Planet," orbits a Sun-like star 57 light-years from Earth. With a mass 25 times that of Jupiter and a temperature of 554°F (290°C), it sits at the boundary between giant planet and brown dwarf. Its atmosphere has finally revealed its composition thanks to the JWST.


GJ504b never reached the mass necessary to shine like a star. Despite its relative coolness (still hot enough to bake bread), it remains too faint for ground-based telescopes. In just two hours, the JWST succeeded where nighttime observations had failed, obtaining a complete spectrum of this object.

The spectrum revealed a varied chemical cocktail: water, carbon dioxide, methane, and ammonia. Yet these molecules alone were not enough to explain the data. Existing models were incompatible until the team incorporated a totally unexpected element: salt clouds in the depths of GJ504b's atmosphere.

These salt clouds, invisible until now, modify the planet's light signature by masking deeper molecules. "This is the first time salt clouds have been essential to interpret a spectrum," says Aneesh Baburaj. The results then became physically consistent.

The discovery of salt clouds opens new perspectives for studying cool atmospheres. Such clouds could be more common than previously thought, influencing our understanding of the chemistry and meteorology of these distant worlds.

However, GJ504b's origin remains in question: is it a giant planet or a failed star?

Its richness in heavy elements (metals) puzzles researchers, but that is not enough to conclude. For now, GJ504b remains an enigmatic "Pink Planet," and may one day be called a "Pink Dwarf." The detailed study was published in The Astronomical Journal on June 18.