Webb Telescope Solves a Decade-Old Mystery Hidden in the Pink Planet's Salty Skies

A Rosy World With a Strange Secret

For more than a decade, the ancient, rosy-hazed world kept astronomers guessing. One of the coldest known planetary-mass companions ever directly imaged, the elusive object was too faint for astronomers to dissect its light from Earth — until now. New observations from the James Webb Space Telescope reveal an atmosphere filled with exotic chemistry and salty clouds unlike anything seen before.

The so-called Pink Planet, formally known as GJ504b, was discovered in 2013 and is technically not a planet but rather a "planetary-mass companion" because it could be a giant exoplanet or a small brown dwarf orbiting a star. It possesses roughly 25 times the mass of Jupiter, placing it on the "fuzzy boundary" between a giant exoplanet and a brown dwarf — too massive to be a standard planet, but not massive enough to trigger the nuclear fusion of hydrogen into helium that defines a true star.

It orbits a sun-like star located 57 light-years from Earth and sits at around 550 degrees Fahrenheit — hot by Earth's standards, but extremely cold for a giant planet. A typical exoplanet usually registers between 1,000 and 2,000 degrees. The object is estimated to be 25 times Jupiter's mass and between 2.5 billion and 4 billion years old, which explains its lower temperature, as giant planets cool with age.

What Webb Found That No One Else Could

Multiple research teams had tried to study GJ504b from Earth but struggled to collect enough light to understand its atmosphere. Using the James Webb Space Telescope, however, researchers gathered the needed observations in just two hours. That efficiency is a testament to just how transformative Webb has become for planetary science.

The James Webb Space Telescope captures infrared images, which cannot be seen by the human eye, and spreads light out to reveal chemical fingerprints. After capturing the Pink Planet's faint light, researchers created a light "fingerprint" that revealed elements and molecules in its atmosphere, including water vapor, methane, carbon dioxide, ammonia, and other molecules.

Researchers found the observations only made sense when they included salt clouds in their model, suggesting the clouds were affecting the light detected by the telescope. The observations provide some of the first direct evidence for salt clouds in a cold object's atmosphere — a phenomenon scientists had theorized more than 15 years ago.

Why Salty Clouds Are Such a Big Deal

The findings, led by Northwestern University and published in The Astronomical Journal on June 18, could change how astronomers study the atmospheres of distant planets and planet-like objects. The discovery matters because the real breakthrough is not the planet's pink appearance, but the salt clouds themselves. Until now, existing atmospheric models could not fully explain the light coming from GJ504b. By adding salt clouds to their calculations, researchers were finally able to match what the telescope observed.

As one researcher put it, "This is the first time we've found that salt clouds are critical to explaining the spectrum of an object. It's a good reminder to account for clouds in our models." In other words, even the best theoretical frameworks can miss something as fundamental as clouds — and that humbling lesson applies across the entire field of exoplanet research.

Questions That Still Linger

Though this mystery may be solved, there are still questions surrounding GJ504b that will only be answered with further investigation. The Pink Planet seems to be unusually rich in elements heavier than hydrogen and helium, and the team still can't pin down the object's origin — did it form like a planet, or like a star?

Most exoplanets are discovered indirectly through the transit method or the radial velocity method. GJ504b is different because it was found using direct imaging, meaning astronomers captured actual photons of light coming from the object itself — an exceptionally difficult feat given the overwhelming glare of the host star. Webb's ability to cut through that challenge in just two hours signals a new era in how we study worlds at the edge of our cosmic neighborhood.

The Pink Planet may have finally given up one of its biggest secrets, but its true identity — planet or failed star — remains an open and tantalizing question. Future observations with Webb and next-generation telescopes are likely to keep this strange, rosy world at the center of astronomical debate for years to come.