Using NASA’s James Webb Space Telescope, astronomers have discovered a brown dwarf, named W1935, emitting infrared radiation from methane in its upper atmosphere. This finding is unexpected as W1935 is a cold brown dwarf without a host star, and there is no apparent source for the upper atmosphere energy. The astronomers speculate that the methane emission may be linked to aurorae processes.
The discovery challenges researchers because W1935 lacks a stellar wind, which contributes to auroral processes in our solar system, making it a mystery to explain the extra energy required for methane emission in the upper atmosphere. The team suggests that internal processes, similar to the atmospheric phenomena of Jupiter and Saturn, or external interactions with interstellar plasma or a nearby active moon, might account for the emission.
The discovery of aurorae on W1935 unfolded like a detective story. A team led by Jackie Faherty, an astronomer at the American Museum of Natural History in New York, investigated 12 cold brown dwarfs using the James Webb Space Telescope. W1935, discovered by citizen scientist Dan Caselden, stood out due to its unexpected methane emission. Computer models were used to infer possible explanations, revealing a temperature inversion in W1935’s atmosphere, where it got warmer with increasing altitude.
Comparisons were made with our solar system’s gas giant planets, where temperature inversions are common. Jupiter and Saturn exhibit such phenomena, and the causes include external heating by aurorae and internal energy transport from deeper in the atmosphere. The lack of a stellar wind and the absence of a companion star for W1935 present unique challenges in explaining the methane emission.
This discovery marks the first time an auroral candidate outside the solar system has been identified with the signature of methane emission. W1935 is also the coldest auroral candidate beyond our solar system. With an effective temperature of about 400 degrees Fahrenheit (200 degrees Celsius), it is approximately 600 degrees Fahrenheit warmer than Jupiter.
While aurorae have been used to explain brown dwarf observations before, W1935 is the first auroral candidate outside the solar system exhibiting methane emission. The James Webb Space Telescope enables astronomers to study the chemistry and processes of aurorae beyond our solar system in unprecedented detail.
This groundbreaking observation provides a unique opportunity to explore a solar system phenomenon in the absence of stellar irradiation. The findings from W1935 will contribute to a better understanding of the auroral processes and atmospheric phenomena in distant objects, enhancing our knowledge of the broader cosmos.
The James Webb Space Telescope, an international collaboration led by NASA with contributions from the ESA (European Space Agency) and the Canadian Space Agency, is instrumental in investigating mysteries within our solar system and studying distant worlds and the origins of the universe.
This discovery reinforces the capability of the James Webb Space Telescope to unravel celestial mysteries and deepen our understanding of the complexities of space beyond our solar system.