The James Webb Space Telescope has picked up fast-changing water clouds on WISE 0855, the coldest brown dwarf identified to date, according to astronomers. The object lies about 7.5 light-years from Earth and is roughly the size of Jupiter.
A team led by Brittany Miles at the University of Arizona’s Steward Observatory tracked the object for 11 hours, taking light measurements every 15 minutes. The researchers said this confirmed that water clouds on another world can thicken and thin over time. Their findings have been shared on the arXiv preprint server and cleared to appear in The Astrophysical Journal.
Moving clouds and rising gases drive the atmosphere
The study identified two forces behind the shifting atmosphere. High-altitude water clouds drift across the object as it rotates, while heat from its interior carries gases such as carbon monoxide and phosphine upward through convection, similar to liquid churning in a heated pot.
Earlier telescopes lacked the sensitivity needed to separate these overlapping signals. Webb’s advanced spectrograph, however, allowed scientists to follow small temperature variations and chemical changes as they happened.
Why brown dwarfs help explain gas giant weather
Brown dwarfs are far larger than planets yet too small to ignite as stars. At minus 8 degrees Celsius, WISE 0855 leaves astronomers unsure whether it behaves more like a star or a planet.
Miles said the active weather shows that the physical laws shaping gas giants such as Jupiter also apply to these isolated, drifting worlds. The report adds that such observations help astronomers understand gas giant planets throughout the galaxy, and that active weather appears to be widespread, even around our nearest cosmic neighbours.
