Using new observations from the James Webb Space Telescope (JWST), astronomers have discovered methane emission from a brown dwarf, an unexpected finding for such a cold and isolated world. The results were published in the journal Naturesuggests that this brown dwarf may produce auroras similar to those seen on Jupiter and Saturn, as well as on our planet.

Larger than planets but lighter than stars, brown dwarfs are ubiquitous in our solar neighborhood, and thousands have been identified. Last year, Jackie Faherty, senior scientist and senior director of education at the American Museum of Natural History, led a team of researchers given time at JWST to study 12 brown dwarfs.

Among them was CWISEP J193518.59–154620.3 (or W1935 for short), a cool brown dwarf 47 light-years away that was jointly discovered by Backyard Worlds: Planet 9, community science volunteer Dan Casselden, and the NASA CatWISE team. W1935 is a cool brown dwarf with a surface temperature of about 400°F. The mass of W1935 is not well known, but it likely ranges from six to 35 times the mass of Jupiter.

After looking at several brown dwarfs observed with JWST, Faherty’s team realized that W1935 looked similar, but with one striking exception: It was emitting methane, something not seen before in brown dwarfs.

“Methane gas is expected to be present on giant planets and brown dwarfs, but we generally see it absorbing light rather than glowing,” said Faherty, the study’s lead author. “At first we were confused by what we saw, but eventually it turned into pure excitement of discovery.”

Computer simulations revealed another surprise: The brown dwarf likely has a temperature inversion; This is a phenomenon in which the atmosphere warms as altitude increases. Temperature changes can easily occur on planets orbiting stars, but W1935 is isolated and has no apparent external heat source.

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

To investigate, researchers turned to our own solar system. They looked specifically at studies of Jupiter and Saturn that showed methane emissions and temperature changes. Auroras are the likely cause of this feature in giants in the solar system, so the research team suggested that they detected the same phenomenon in W1935.

Planetary scientists know that one of the main causes of auroras on Jupiter and Saturn is high-energy particles from the Sun that interact with the planets’ magnetic fields and atmospheres, heating the upper layers. It is also the cause of the aurora borealis we see on Earth, often called the Northern Lights or Southern Lights because they are so unusual near the poles. However, due to the absence of a host star for W1935, the solar wind cannot contribute to the explanation.

There is another attractive reason for the aurora in our solar system. Both Jupiter and Saturn have active moons that occasionally eject matter into space, interacting with planets and enhancing the aurorae on those worlds. Jupiter’s moon Io is the most volcanically active world in the Solar System, spewing lava tens of kilometers into the air, while Saturn’s moon Enceladus spews water vapor that both freezes and boils as it enters space from its geysers.

More observations are needed, but the researchers suggest that one explanation for the aurora in W1935 could be an active moon that has not yet been discovered.

“When an astronomer points JWST at an object, the potential for a striking new discovery opens up,” Faherty said. “Methane emissions weren’t my focus when we started this project, but now we know they might be there, and the explanations for it are so intriguing that I’m constantly on the lookout for them. It’s part of the advancement of science.”