Using the NASA/ESA/CSA James Webb Space Telescope, astronomers have detected a brown dwarf with infrared emission from methane, likely due to energy in its upper atmosphere. The upper-atmosphere heating that powers this emission is linked to aurorae. Named W1935, this brown dwarf resides at a distance of 47 light-years.
On Earth, aurorae are created when energetic particles blown into space from the Sun are captured by Earth’s magnetic field.
They cascade down into our atmosphere along magnetic field lines near Earth’s poles, colliding with gas molecules and creating eerie, dancing curtains of light.
Jupiter and Saturn have similar auroral processes that involve interacting with the solar wind, but they also get auroral contributions from nearby active moons like Io (for Jupiter) and Enceladus (for Saturn).
“For isolated brown dwarfs like W1935, the absence of a stellar wind to contribute to the auroral process and explain the extra energy in the upper atmosphere required for the methane emission is a mystery,” said Dr. Jackie Faherty, an astronomer at the American Museum of Natural History, and colleagues.
Dr. Faherty and colleagues used Webb to observe a sample of 12 cold brown dwarfs.
Among those were W1935, an object that was discovered by citizen scientist Dan Caselden, who worked with the Backyard Worlds Zooniverse project, and W2220, an object that was discovered using NASA’s Wide Field Infrared Survey Explorer.
Webb revealed in exquisite detail that W1935 and W2220 appeared to be near clones of each other in composition.
They also shared similar brightness, temperatures, and spectral features of water, ammonia, carbon monoxide, and carbon dioxide.
The striking exception was that W1935 showed emission from methane, as opposed to the anticipated absorption feature that was observed toward W2220. This was seen at a distinct infrared wavelength to which Webb is uniquely sensitive.
“We expected to see methane because methane is all over these…
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