Astronomers led by Northwestern University have uncovered an unusual feature surrounding the famous “Pink Planet”: skies stuffed with salty clouds.
For greater than a decade, the traditional world, known for its pinkish haze, has remained one among astronomy’s enduring mysteries. As one among the coldest planetary-mass companions ever directly imaged, it’s so faint that scientists have struggled to research its light from Earth. Now, observations from the James Webb Space Telescope (JWST) have revealed an environment full of exotic chemistry and clouds unlike any previously observed.
The findings provide among the first direct evidence that salt clouds can exist within the atmosphere of a chilly planetary object, confirming a prediction scientists first made greater than 15 years ago. The outcomes also highlight JWST’s ability to review extremely cold and faint worlds which can be beyond the reach of ground-based observatories.
The study was published on June 18 within the Astronomical Journal.
“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 globe performed follow-up observations to review its light, however it was too faint for ground-based instruments. That made it an ideal goal for JWST. Once we finally obtained its spectrum, it immediately looked interesting. But once we began digging deeper into the info, we realized it was not like anything we’ve analyzed before.”
Baburaj, an exoplanet researcher, is a postdoctoral associate at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). The project also involved scientists from the Space Telescope Science Institute (STScI), including Marshall Perrin, who designed the observing program for the thing. Perrin serves on the JWST Telescope Scientist Team, which helped develop the observatory and supports its ongoing operations.
A Chilly World With an Uncertain Identity
First discovered in 2013, the Pink Planet, formally generally known as GJ 504 b, orbits a Sun-like star about 57 light-years from Earth. Despite its nickname, researchers aren’t certain that it is definitely a planet.
With a mass roughly 25 times that of Jupiter, GJ 504 b lies near the boundary between giant planets and brown dwarfs. For this reason ambiguity, astronomers classify it as a “planetary-mass companion,” an object with planet-like mass that orbits a star.
Its low temperature has added to its intrigue. Most directly imaged exoplanets have temperatures starting from about 1,000 to 2,000 degrees Fahrenheit. By comparison, GJ 504 b is just about 550 degrees Fahrenheit (290 degrees Celsius), much like the temperature inside a bread-baking oven.
Based on Baburaj, the thing’s age helps explain its relative coolness. Giant planets begin their lives extremely hot and steadily cool over billions of years. The brand new research estimates that GJ 504 b is between 2.5 billion and 4 billion years old.
James Webb Reveals the Planet’s Spectrum
To research the thing, Baburaj and his colleagues used JWST to gather its faint light. They then applied advanced processing techniques to remove glare from the much brighter host star.
This approach allowed the team to acquire the companion’s spectrum, which separates light into its component colours. Because different elements and molecules leave unique signatures in a spectrum, scientists can use this information to find out the composition of an environment.
“Up to now, other astronomers observed the companion for a complete night with among the biggest telescopes on this planet to acquire a spectrum,” Baburaj said. “They usually couldn’t see the thing. With JWST, our entire statement took around two hours, and we were successful.”
Salt Clouds Solve a Longstanding Mystery
The observations revealed an environment containing water vapor, methane, carbon dioxide, ammonia and other molecules.
When researchers attempted to recreate the atmosphere using computer models, they encountered an issue. The observations could only be matched by atmospheric conditions that didn’t seem physically realistic.
The answer emerged when the team added clouds to the models. Once clouds were included, the strange inconsistencies disappeared. The outcomes suggest that salt clouds are obscuring deeper layers of the atmosphere and influencing the sunshine that ultimately reaches JWST.
“We ran simulations with clouds, and the outcomes aligned with what we learn about cold planets,” Baburaj said. “We tried three various kinds of clouds, and salt clouds fit best. Once we accounted for salt clouds, it subdued the signature of molecules hidden deeper within the companion’s atmosphere. Then, the outcomes became physically possible.”
The spectrum also indicates that GJ 504 b may contain an unusually great amount of heavy elements, often referred to by astronomers as metals. Even so, questions remain about how the thing formed. Current evidence suggests it could have originated either through processes that create planets or through processes that form small stars.
A Recent Approach to Study Cold Alien Worlds
Baburaj believes the methods developed for this study could help scientists investigate other cold and faint planetary objects.
Jupiter, for instance, comprises clouds made from ammonia ice. Although current instruments cannot yet directly study those cloud layers in the identical detail, the detection of salt clouds around GJ 504 b suggests astronomers are moving closer to that goal.
“That is the primary time we have found that salt clouds are critical to explaining the spectrum of an object,” Baburaj said. “It’s a great reminder to account for clouds in our models.”
The study, “JWST-TST High Contrast: First Direct Spectroscopy of GJ 504 b Reveals Clouds and Possible Metal Enrichment,” was supported by NASA (award number 80NSSC20K0586).