For more than a decade, one of the universe's most mysterious worlds has puzzled astronomers. Known as the “Pink Planet”, this distant object has remained largely hidden from scientific investigation because it is incredibly faint and difficult to observe. Now, thanks to the powerful James Webb Space Telescope (JWST), scientists have finally uncovered its secrets—and what they found is astonishing.
Researchers led by Northwestern University have discovered that the Pink Planet, officially known as GJ504b, is surrounded by unusual salt clouds and contains a rich mix of exotic chemicals. This marks the first strong evidence that salt clouds exist in the atmosphere of such a cold planetary object, confirming theories that scientists proposed more than 15 years ago.
The discovery opens a new window into understanding some of the coldest and faintest worlds in the universe.
A Strange and Mysterious World
GJ504b was first discovered in 2013. It orbits a star similar to our Sun located about 57 light-years from Earth. Although it is often called the Pink Planet because of its rosy appearance, scientists are still debating whether it should even be classified as a planet.
The object is about 25 times more massive than Jupiter, placing it in a gray area between giant planets and brown dwarfs. Brown dwarfs are often described as "failed stars" because they are too small to sustain the nuclear fusion that powers stars.
Because of this uncertainty, astronomers prefer to call GJ504b a planetary-mass companion—an object with a planet-like mass that orbits a star.
Too Faint to Study
Since its discovery, scientists have tried repeatedly to study GJ504b using some of the world's largest ground-based telescopes. However, they faced a major challenge.
The object is extremely faint and lies close to a much brighter host star. The star's glare makes it difficult to isolate the light coming from GJ504b itself.
According to lead researcher Aneesh Baburaj, many research teams spent entire nights observing the object but still failed to obtain a detailed spectrum, which is the key tool astronomers use to understand an object's atmosphere.
This is where the James Webb Space Telescope made all the difference.
With its advanced infrared instruments and location far above Earth's atmosphere, JWST was able to collect the faint light from GJ504b in only about two hours.
After carefully removing the overwhelming glare from the nearby star, researchers finally obtained the object's spectrum, revealing details that had never been seen before.
One of the Coldest Worlds Ever Imaged
Most directly imaged exoplanets are extremely hot, often reaching temperatures between 1,000 and 2,000 degrees Fahrenheit.
GJ504b is very different.
Its temperature is only about 550 degrees Fahrenheit (290 degrees Celsius), roughly comparable to the inside of a household baking oven.
While that may sound hot by Earth standards, it is remarkably cold compared with most giant planets that astronomers have directly photographed.
Scientists believe the object is between 2.5 and 4 billion years old. Giant planets gradually cool over time, and its advanced age likely explains why it has become so cold.
Because of its low temperature, GJ504b offers a rare opportunity to study atmospheric conditions that are more similar to those found on cooler planets.
A Chemical Treasure Trove
The James Webb observations revealed a surprisingly rich atmosphere.
Researchers detected signs of:
Water vapor
Methane
Carbon dioxide
Ammonia
Other complex molecules
Each of these chemicals leaves a unique signature in the spectrum of light coming from the object.
By examining these signatures, scientists can determine the composition of an atmosphere even when the object is trillions of kilometers away.
However, when researchers attempted to recreate the atmosphere using computer models, they encountered a major problem.
The models produced strange and physically unrealistic results.
Something important was missing.
The Secret Ingredient: Salt Clouds
The breakthrough came when researchers introduced clouds into their atmospheric simulations.
They tested several cloud types and discovered that salt clouds provided the best match to the observations.
Once salt clouds were included, the mysterious inconsistencies disappeared.
Scientists believe these clouds act like a veil, blocking light from deeper layers of the atmosphere. This changes the way molecules appear in the spectrum and explains why earlier models produced impossible results.
The discovery is significant because it provides the strongest evidence yet that salt clouds can form in the atmospheres of cold planetary objects.
For years, astronomers predicted such clouds should exist, but until now they had never been clearly identified.
The finding demonstrates how important clouds are when interpreting observations of distant worlds.
Without accounting for them, scientists can easily misinterpret what they are seeing.
Rich in Heavy Elements
The observations revealed another surprise.
GJ504b appears to contain an unusually large amount of heavy elements, which astronomers often refer to as "metals."
In astronomy, metals include everything heavier than hydrogen and helium.
A high concentration of these elements could provide clues about how the object formed billions of years ago.
However, the evidence remains inconclusive.
The object may have formed like a giant planet, gradually building up material inside a disk surrounding its star. Alternatively, it might have formed more like a small star through the collapse of a cloud of gas.
At present, both possibilities remain open.
Why This Discovery Matters
The discovery of salt clouds is about much more than a single distant world.
It represents a major step toward studying colder and fainter objects across the galaxy.
Many planets and planetary companions remain beyond the reach of current ground-based observatories. The James Webb Space Telescope is now showing that these hidden worlds can finally be explored in detail.
The techniques used in this study could also help scientists investigate objects closer to home.
For example, Jupiter contains clouds made of ammonia ice. While current instruments cannot directly observe all such cloud layers on distant planets, discoveries like GJ504b suggest astronomers are moving closer to that goal.
Every new observation helps improve atmospheric models and deepens our understanding of how planets evolve.
A New Era of Planet Exploration
The Pink Planet has spent years as one of astronomy's greatest mysteries. Now, thanks to the James Webb Space Telescope, scientists have uncovered a world filled with methane, water vapor, ammonia, carbon dioxide, and extraordinary salt clouds.
What once appeared as a faint pink dot has become one of the most fascinating planetary objects ever studied.
More importantly, the discovery proves that JWST can reveal details about cold and distant worlds that were previously impossible to observe.
As astronomers continue exploring the universe with this revolutionary telescope, GJ504b may be just the beginning. Countless hidden worlds are waiting to be discovered, and some may prove even stranger than a planet with skies made of salt clouds.
Reference: JWST-TST high contrast: First direct spectroscopy of GJ504b reveals clouds and possible metal enrichment, The Astronomical Journal (2026). https://iopscience.iop.org/article/10.3847/1538-3881/ae6919
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