A veil of salty clouds has been discovered on a puffy “pink planet” that has evaded imaging for more than a decade because it’s so cold, astronomers say.
If you were to travel the 57 light-years to “see” the object, called GJ504b, you would view a world still glowing from the heat of its formation. The color, astronomers say, is akin to a dark, cherry-blossom hue.
Despite its moniker, GJ504b might not actually be a planet at all; it’s about 25 times the mass of Jupiter, according to the new research. This mass straddles the line between that of gas giants and brown dwarf stars, leading astronomers to call the object a planetary-mass companion.
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Astronomers haven’t been able to learn much about the “pink planet” from direct imaging with ground-based telescopes because the light from the sunlike star that it orbits (at about the same distance between Pluto and our sun) overwhelms its relatively faint glow. Most directly imaged exoplanets are much hotter, at around 1,000 to 2,000 degrees Fahrenheit. Meanwhile temperatures on GJ504b reach just 550 degrees F.
In the new study, Aneesh Baburaj, a postdoctoral associate at Northwestern University, and his colleagues used the James Webb Space Telescope (JWST) to capture the dim light emanating from the object. After accounting for the light from GJ504b’s bright host star, the team could look at data on the wavelengths, or colors, of light coming only from the companion object. Each color in the resulting spectrum is tied to a specific element. The atmosphere, the researchers found, is full of the heavy elements carbon, oxygen, nitrogen and sulfur, Baburaj says. (Astronomers refer to any chemical element that’s heavier than hydrogen and helium as a heavy element.)
The detected elements were likely part of compounds such as water vapor, methane, carbon dioxide, ammonia and others. But after feeding the information into a computer model, the team was puzzled.
“Atmospheres of giant companions generally show a decrease in temperature as one goes higher up in the atmosphere. In the absence of clouds, our models indicated the presence of a small region of the atmosphere where the temperature is constant,” or isothermal, Baburaj says. “The presence of the isothermal region is physically implausible.”
After adding salty clouds to the model, “the isothermal region in our model disappeared, making the results plausible,” Baburaj says. The researchers think the clouds are full of chloride salts, such as potassium chloride, and/or sulfide salts, such as manganese sulfide.
They also discovered that GJ504b is very old: the object likely formed between four billion and 2.5 billion years ago, which would explain its chilly temperatures.
Mysteries still surround this pink puffball. “We are curious about what kind of salt clouds might be present in its atmosphere, but we probably need additional JWST time to answer this question,” Baburaj says.
The team also hopes to resolve the companion’s actual nature, whether it’s a giant planet or a brown dwarf star. “There are other ongoing JWST studies on this object that might be able to answer [that] question,” Baburaj says.
The study, a collaboration between researchers at Northwestern and scientists at the Space Telescope Science Institute, was published today in the Astrophysical Journal.