For the first time, on the dimly glowing remnants of a failed star mere light-years from Earth, scientists have found evidence of water clouds beyond our solar system.
The clouds belong to a brown dwarf called WISE 0855, a celestial body five times as big as Jupiter and 7.2 light-years away. It formed the way a star does, from gas and dust that collapsed in on itself. But it lacked the mass required to set off nuclear fusion, so it became cold and mostly inert - more like a planet than a sun. On the planet-star spectrum, Jupiter sits just in the middle: big for a planet but not quite as big as a sun.
"It's very exciting to discover a new neighbor of our solar system that is so close," Kevin Luhman, an astronomer at Pennsylvania State University's Center for Exoplanets and Habitable Worlds, said in a statement from NASA when the brown dwarf was discovered two years ago. "And given its extreme temperature, it should tell us a lot about the atmospheres of planets, which often have similarly cold temperatures."
In a study accepted for publication in Astrophysical Journal Letters (and currently available online at the research sharing site arXiv), astronomers say they have achieved the first spectroscopic study of WISE 0855, allowing them insight into its chemical composition.
"Now that we have a spectrum, we can really start thinking about what's going on in this object," lead author Andrew Skemer, an astronomer at the University of California at Santa Cruz, said in a statement.
According to Skemer, WISE 0855 is the dimmest object ever detected with this method, which separates light into its component wavelengths to find the signatures of various molecules. At roughly minus-10 degrees Fahrenheit (about the same temperature as the North Pole in May), the brown dwarf is too cold and dark to be analyzed with normal spectroscopy. Instead, Skemer and his colleagues used infrared measurements from the Gemini North telescope in Hawaii to interpret WISE 0855's faint glow.
With that data, the astronomers detected water vapor in the brown dwarf's atmosphere. Skemer's team had suspected as much, based on photometric analysis he helped publish in 2014.
"We would expect an object that cold to have water clouds, and this is the best evidence that it does," Skemer said of the recent study.
WISE 0855's cold, cloudy atmosphere makes it a lot like Jupiter's, with one key difference: It doesn't have the molecule phosphine, which forms in Jupiter's hot interior and reacts with other compounds in the planet's upper atmosphere. Phosphine's absence from WISE 0855's spectrum suggests that the brown dwarf's atmosphere is less turbulent.
Comparing the two bodies could help astronomers understand the chemistry of water on celestial bodies beyond our own.
"The spectrum allows us to investigate dynamical and chemical properties that have long been studied in Jupiter's atmosphere, but this time on an extrasolar world," Skemer said.