Discovered in 2013, the Pink Planet orbits a sun-like star located 57 light-years from Earth. At roughly 25 times the mass of Jupiter, it sits near the fuzzy boundary between giant planets and brown dwarfs. So, astronomers refer to it as a “planetary-mass companion,” meaning that it’s a planet-sized object orbiting a star.
Illustration Credit: NASA/Goddard Space Flight Center
Scientific Frontline: Extended "At a Glance" Summary: The "Pink Planet" (GJ504b)
The Core Concept: The "Pink Planet" (GJ504b) is an extremely cold planetary-mass companion located 57 light-years from Earth that possesses an atmosphere enveloped in salt clouds. Roughly 25 times the mass of Jupiter, the object sits near the boundary between giant exoplanets and brown dwarfs.
Key Distinction/Mechanism: Due to its advanced age and low temperature of 550 degrees Fahrenheit, the object is too faint to analyze using standard ground-based telescopes. Using the James Webb Space Telescope (JWST), astronomers captured the companion's light and stripped away the host star's glare to analyze its spectrum, revealing that salt clouds are actively masking the deeper molecular signatures in its atmosphere.
Origin/History: Discovered in 2013, the Pink Planet eluded precise atmospheric analysis for over a decade. In June 2026, researchers at Northwestern University published groundbreaking JWST observations, providing the first direct evidence for salt clouds in a cold celestial object—a phenomenon scientists had theorized over 15 years ago.
Major Frameworks/Components:
Spectroscopy: Breaking down the object's dispersed light into component colors to detect exotic chemistry, including water vapor, methane, carbon dioxide, and ammonia.
Astrophysical Modeling: Reconstructing the atmosphere via simulation, which demonstrated that accounting for salt clouds was mathematically and physically necessary to match the JWST data.
Stellar Glare Reduction: Advanced data-processing techniques employed to separate the exceedingly faint thermal emissions of the companion from the intense light of its sun-like host star.
Branch of Science: Astrophysics, Planetary Science, and Exoplanetology.
Future Application: The data-processing techniques and atmospheric models pioneered in this study will be heavily utilized to analyze other cold, faint celestial objects. This methodology sets a precedent for discovering even colder cloud formations, such as ammonia ice, in distant planetary systems.
Why It Matters: This marks the first time salt clouds have proven critical to explaining a celestial object's spectrum, fundamentally altering how astrophysicists must account for cloud cover in future atmospheric models. Furthermore, the high metallicity of the atmosphere provides crucial new clues for understanding whether the object formed as a traditional planet or a failed small star.
Discovered in 2013, the Pink Planet orbits a sunlike star located 57 light-years from Earth. At roughly 25 times the mass of Jupiter, it sits near the fuzzy boundary between giant planets and brown dwarfs. So, astronomers refer to it as a “planetary-mass companion,” meaning that it’s a planet-sized object orbiting a star. Illustration courtesy of NASA/Goddard Space Flight Center.
Northwestern University–led astronomers have discovered salty skies surrounding the universe’s famous “Pink Planet.”
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 is too faint for astronomers to dissect its light from Earth. But new observations from the James Webb Space Telescope (JWST) reveal an atmosphere filled with exotic chemistry—and salty clouds unlike anything seen before.
The observations provide some of the first direct evidence for salt clouds in a cold object’s atmosphere, a phenomenon scientists theorized more than 15 years ago. The discovery also marks an important step toward studying increasingly cold objects, which are too dim to examine with ground-based telescopes.
“The Pink Planet is the coldest companion ever discovered using ground-based instruments,” said Northwestern’s Aneesh Baburaj, who led the study. “Many teams all around the world performed follow-up observations to study its light, but it was too faint for ground-based instruments. That made it a perfect target for JWST. When we finally obtained its spectrum, it immediately looked interesting. But once we started digging deeper into the data, we realized it was not like anything we have analyzed before.”
An expert on exoplanets, Baburaj is a postdoctoral associate at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). This work was conducted in collaboration with scientists at the Space Telescope Science Institute (STScI), including Marshall Perrin, who devised the observing program for this object. Perrin is a member of the JWST Telescope Scientist Team, which contributed to the telescope’s design and is responsible for its current day-to-day operations.
Old and Cold
Discovered in 2013, the Pink Planet (dubbed GJ504b) orbits a sunlike star located 57 light-years from Earth. Despite its nickname, astronomers are unsure if it’s a planet at all. At roughly 25 times the mass of Jupiter, GJ504b sits near the fuzzy boundary between giant planets and brown dwarfs. So, astronomers refer to it as a “planetary-mass companion,” meaning that it’s a planet-sized object orbiting a star.
Further complicating the mystery, repeated attempts to study it with ground-based telescopes have fallen short. While most directly imaged exoplanets are closer to 1,000 to 2,000 degrees Fahrenheit, GJ504b is just 550 degrees Fahrenheit (290 degrees Celsius)—roughly the temperature of a bread-baking oven.
The companion’s age is responsible for its chilly temperature, Baburaj said. Although they are born blistering hot, giant planets cool as they age. And the new study estimates GJ504b is between 2.5 billion and 4 billion years old.
Using the JWST, Baburaj and his team captured GJ504b’s faint light. Then, they used advanced data-processing techniques to strip away glare from its much brighter host star. This combination finally revealed the companion’s spectrum, a graph that breaks down dispersed light into component colors. Each color represents a different element. So, by analyzing an object’s spectrum, scientists can uncover the presence of specific elements and molecules.
“In the past, other astronomers observed the companion for an entire night with some of the biggest telescopes in the world to obtain a spectrum,” Baburaj said. “And they could not see the object. With JWST, our entire observation took around two hours, and we were successful.”
Famous World Comes into Focus
The data revealed a rich mix of chemicals, including water vapor, methane, carbon dioxide, ammonia, and other molecules. To reconstruct the companion, the researchers fed these data into an astrophysical model. But something didn’t add up. The companion’s simulated atmosphere only matched the observations if it contained unusual, physically implausible features. When the researchers added clouds to the model, the unusual characteristics vanished. Salt clouds likely veiled the atmosphere’s deeper layers, shaping the light that reached JWST.
“We ran simulations with clouds, and the results aligned with what we know about cold planets,” Baburaj said. “We tried three different types of clouds, and salt clouds fit best. When we accounted for salt clouds, it subdued the signature of molecules hidden deeper in the companion’s atmosphere. Then, the results became physically possible.”
The spectrum also suggested that GJ504b is unusually rich in heavy elements, or metals. However, the mystery of the object’s formation persists, with current data suggesting it could have formed either like a planet or a small star.
Baburaj says the techniques used in the study could help unravel other mysteries surrounding cold, faint planets. Jupiter, for example, hosts clouds made of ammonia ice. While those cloud types remain beyond the reach of current observations, the detection of GJ504b’s salt clouds suggests astronomers are getting closer.
“This is the first time we’ve found that salt clouds are critical to explaining the spectrum of an object,” Baburaj said. “It’s a good reminder to account for clouds in our models.”
Funding: The study was supported by NASA.
Published in journal: Astronomical Journal
Authors: Aneesh Baburaj, Jean-Baptiste Ruffio, Marshall Perrin, Jerry W. Xuan, William O. Balmer, Yayaati Chachan, Quinn M. Konopacky, Travis S. Barman, Mathilde Mâlin, Kielan K. W. Hoch, Emily Rickman, Kimberly Ward-Duong, Laurent Pueyo, Julien H. Girard, Isabel Rebollido, Alexis Bidot, Christine Chen, Kadin Worthen, Cicero Lu, Jens Kammerer, Roeland P. van der Marel, Nikole K. Lewis, Jeff Valenti, Sara Seager, Chris Stark, Rémi Soummer, Jay Anderson, Charles-Philippe Lajoie, Mark Clampin, and C. Matt Mountain
Source/Credit: Northwestern University | Amanda Morris
Edited by: Scientific Frontline
Reference Number: asph061826_01
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