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Cold brown dwarf seen emitting methane and generating an aurora

Astonishing new observations from the Webb Telescope (JWST) have revealed methane emissions from a cold brown dwarf — a discovery that challenges our understanding of these distant celestial bodies.

This observation suggests potential auroral activities similar to those on Earth, Jupiter, and Saturn, reshaping how we perceive the atmospheres of distant, isolated worlds.

Brown dwarfs are an enigma

Brown dwarfs are intriguing cosmic entities, larger than planets yet not massive enough to ignite like stars. They populate our galaxy in abundance, with thousands discovered within our own solar vicinity.

These objects present a fascinating blend of planetary and stellar characteristics, making them a prime focus for astronomical research.

A particularly interesting subject of study is W1935, a brown dwarf located 47 light years away.

With a chilly surface temperature of about 400° Fahrenheit, this brown dwarf is as warm as an oven used to bake chocolate chip cookies. Despite this, it exhibits conditions markedly different from those of a typical star.

Despite its poorly defined mass, estimates suggest it weighs between 6 and 35 times that of Jupiter, placing it squarely within the typical size range for brown dwarfs.

Unexpected methane glow on brown dwarf W1935

While examining W1935 among other brown dwarfs, researchers discovered a surprising phenomenon: W1935 was emitting methane.

This observation marked the first instance of methane emissions on a brown dwarf, as methane typically absorbs light rather than emitting it in such cold environments.

“Methane gas is expected in giant planets and brown dwarfs but we usually see it absorbing light, not glowing,” said Jackie Faherty, the lead author of the study. “We were confused about what we were seeing at first but ultimately that transformed into pure excitement at the discovery.”

Temperature inversions and auroras

Further investigation through computer modeling revealed another unexpected aspect: W1935’s atmosphere exhibits a temperature inversion. In this inversion, the temperature increases with altitude.

While such inversions are common in planets close to a heat source like a star, the isolated nature of W1935 makes this phenomenon particularly baffling.

“We were pleasantly shocked when the model clearly predicted a temperature inversion,” said co-author Ben Burningham from the University of Hertfordshire. “But we also had to figure out where that extra upper atmosphere heat was coming from.”

The team sought answers within our solar system by examining Jupiter and Saturn. Both planets are known for methane emissions and temperature inversions likely caused by auroras.

Consequently, auroras result from interactions between magnetic fields and high-energy particles from the sun. These interactions lead to spectacular light displays near the poles of planets.

Speculating on solar and lunar influences

Without a host star, the typical solar wind explanation for auroras does not apply to W1935. However, a tantalizing hypothesis emerged: an active moon, similar to Jupiter’s Io or Saturn’s Enceladus, might be influencing the phenomenon.

These moons, known for their dynamic geological activity, significantly impact their planets’ atmospheres.

“Every time an astronomer points JWST at an object, there’s a chance of a new mind-blowing discovery,” Faherty explained.

“Methane emission was not on my radar when we started this project but now that we know it can be there and the explanation for it so enticing I am constantly on the look-out for it. That’s part of how science moves forward,” he concluded.

This recent discovery underscores the unpredictability of space exploration and ignites curiosity. It also drives the scientific community to further unravel the secrets of the universe.

Additionally, more observations are planned to enhance our understanding of W1935 and explore the potential of an undiscovered moon fostering auroral activity on this distant brown dwarf.

The full study was published in the journal Nature.


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