James Webb Space Telescope reveals one of the most mysterious worlds in the universe might have a volcanic moon

• Astronomers using the James Webb Space Telescope discovered evidence of an aurora on a brown dwarf.
• Typically, a key ingredient to produce aurora is high-energy particles from a star.

NEW ORLEANS — When astronomer Jackie Faherty peered into space using information from the James Webb Space Telescope, there was something she couldn't take her eyes off of.

Brown dwarf W1935, a world larger than Jupiter drifting alone in open space about 47 light-years from Earth, was letting off a methane signature unlike anything ever seen before.

Brown dwarfs are some of the most unusual and mysterious objects in space. They form like stars but don't grow massive enough to generate their own energy via nuclear fusion in their cores. For this reason, experts sometimes call them "failed stars."

The astronomers expected to see methane gas in the atmospheres of the brown dwarfs they were studying, but they didn't expect that any of the objects would actually emit methane.

The methane emission in the data "was like a pebble in a shoe. I couldn't get rid of it. I could only focus on this one feature," Faherty, who works at the American Museum of Natural History, said in a presentation at the 243rd meeting of the American Astronomical Society.

It's the first time such a methane fingerprint has appeared on a brown dwarf, Faherty said.

"For your typical brown dwarf just traversing the galaxy in solitude, your brown dwarf is very mysterious. It does not want to give away any of its secrets," said Austin Rothermich, a graduate student at the City University of New York, who presented other research on brown dwarfs at the conference.

But that methane hint may have given away one of this brown dwarf's biggest secrets: a volcanically active moon in its orbit.

Jupiter and Saturn offer clues

It turns out methane emissions, similar to those observed on W1935, are also found on Jupiter and Saturn.

On those two planets, the methane emissions are linked to aurora — the dancing lights that appear when charged particles from the sun interact with the planets' magnetic fields and atmospheres.

On Earth, the aurora is also called the northern lights.

Faherty and her team concluded that this unusual brown dwarf likely hosts aurora, too.

But the mystery didn't end there.

Typically, to produce an aurora you need a nearby star. But there is no nearby star to W1935. So what was supplying the high-energy particles to power its aurora?

Faherty and her team suspected a different kind of companion could be at work: an active moon.

Both Jupiter and Saturn have active moons that regularly eject material into space. Jupiter's moon Io erupts lava material into space while Saturn's Enceladus ejects geysers. Both types of material contribute to the two planets' auroras, and that's what could be happening with W1935, too.

"That does not mean that we're declaring that we have found an active moon, but it's one of the explanations," Faherty said.

Other possible solutions the team is exploring include free-floating matter in space, called interstellar plasma.

Whatever the reason may be, it takes very sensitive tools to detect brown dwarfs in the first place. So arriving at these conclusions would not have been possible without Webb, Faherty said.

"I don't think I emphasized this enough, these are so stinking faint. So faint. JWST was an absolute requirement to measure this," Faherty said.