The weather forecast for the universe’s two nearest brown dwarfs is anything but mild. Thanks to the James Webb Space Telescope’s latest observations, astronomers have unveiled a dramatic meteorological portrait of these celestial bodies, which are larger than planets but not quite stars.
Located just six light-years from Earth—a cosmic stone’s throw—the brown dwarf pair exhibits extreme atmospheric conditions. With temperatures soaring to around 925 degrees Celsius at their cloud tops, the atmosphere is a swirling mix of hydrogen, helium, and traces of water vapor, methane, and carbon monoxide. To top it off, clouds composed of hot silicate particles—similar to a fiery Saharan dust storm—whirl through their skies.
“In this study, we created the most detailed ‘weather maps’ for any brown dwarf to date,” said Beth Biller, an astronomer at the University of Edinburgh’s Institute for Astronomy and the lead author of the study published in the Monthly Notices of the Royal Astronomical Society. “The fast rotation of both objects drives their weather patterns, and if we could directly see the cloud-top structures, we’d likely observe bands and vortices akin to Jupiter’s Great Red Spot.”
Brown dwarfs occupy a unique niche in the cosmos. They emit their own light due to their intense heat, much like glowing embers in a fire, but they lack the mass required to sustain nuclear fusion like true stars. This particular duo formed approximately 500 million years ago, with each dwarf boasting a diameter comparable to Jupiter’s but with masses 30 to 35 times greater.
The Webb telescope’s infrared capabilities allowed scientists to monitor changes in the brown dwarfs’ atmospheres over their rotation periods—seven hours for the larger and five hours for the smaller. This provided a three-dimensional view of their atmospheric layers, unveiling multiple cloud strata at varying depths.
“The atmospheres of brown dwarfs are highly complex,” noted Johanna Vos, an astronomer at Trinity College Dublin and co-author of the study. “Webb offers an unprecedented wavelength range and sensitivity, enabling us to comprehensively examine these atmospheres from deep within to the upper layers.”
The insights gained from studying these nearby brown dwarfs not only deepen our understanding of these enigmatic objects but also pave the way for future exploration of weather patterns on potentially habitable exoplanets. As brown dwarfs share characteristics with both stars and giant gas planets like Jupiter, they serve as valuable laboratories for understanding atmospheric dynamics in extreme conditions.
“In the future, similar techniques could be used to study weather on potentially habitable exoplanets,” Biller added, hinting at the broader implications of this research.
With around 1,000 brown dwarfs identified and over 5,000 exoplanets discovered, the cosmos continues to reveal its diverse array of worlds. The James Webb Space Telescope, with its advanced infrared observations, stands at the forefront of uncovering these cosmic secrets, offering a window into the complex and dynamic atmospheres of celestial bodies beyond our solar system.
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