First volcanic exomoon likely discovered 635 light-years away

We've got a cosmic mystery on our hands. No one’s ever confirmed the existence of an 'exomoon,' which is a moon outside our solar system. However, a new NASA-led study might finally give us some indirect evidence for one in a system just 635 light-years away from Earth.

Astronomers have spotted a giant cloud of sodium near an exoplanet called WASP-49 b, and it might just be the clue pointing to a moon unlike any we've seen before.

Apurva Oza, a staff scientist at Caltech , has been digging into this enigma. His research suggests that this sodium cloud could be coming from a rocky, volcanic moon orbiting the gas giant planet.

Sodium discovery hints at an exomoon

Back in 2017, scientists first detected this unusual cloud of sodium around WASP-49 b. It caught Oza's attention because neither the planet -- a Saturn-sized gas giant -- nor its star have enough sodium to explain such a massive cloud.

To put it in perspective, the source seems to be producing about 220,000 pounds of sodium every second!

So, where's all this sodium coming from? That's the million-dollar question.

"We think this is a really critical piece of evidence," said Oza. "The cloud is moving in the opposite direction that physics tells us it should be going if it were part of the planet’s atmosphere."

Echoes of Jupiter's volcanic moon, Io

To make sense of this, Oza looked closer to home. In our solar system, Jupiter's moon Io is the most volcanic body we know.

It constantly spews gases like sulfur dioxide and sodium, creating vast clouds that can stretch up to 1,000 times Jupiter's radius. If a moon like Io were orbiting WASP-49 b, it could produce a similar sodium cloud.

This idea isn't just a shot in the dark. The cloud's behavior around WASP-49 b resembles the way Io's emissions create a giant gas cloud around Jupiter.

But detecting exomoons (moons outside our solar system) is no easy feat. They're often too small and faint for our current telescopes to spot directly.

Chasing exomoon clues in deep space

Oza and his team embarked on a celestial detective hunt. Since the star, planet, and cloud often overlap from our distant viewpoint, they had to watch the system over time to tease apart their movements.

Twice, they noticed the cloud suddenly growing larger when it wasn't next to the planet. That hinted at a separate body -- possibly a moon -- refueling the cloud.

Moreover, the cloud was moving faster than the planet in a way that didn't add up unless something else was in play.

It's like seeing footprints ahead of you in the sand when no one else is around -- you start to wonder who's making them.

Peering through powerful eyes

To get a better look, the team used the European Southern Observatory's Very Large Telescope (VLT) in Chile.

Julia Seidel, a research fellow at the observatory and co-author of the study, found that the cloud sits high above the planet's atmosphere, much like Io's gas cloud around Jupiter.

They also fired up a computer model to see if a moon could explain what they were seeing.

The model showed that if there were a moon orbiting the planet every eight hours, it could account for the cloud's odd movements and the way it sometimes drifted in front of the planet.

Difficulty of hunting for exomoons

While exomoons remain elusive, this research adds a tantalizing piece to the puzzle. Detecting them is tricky business.

They don't emit their own light, and they're often lost in the glare of their parent planets and stars. But clues like mysterious gas clouds give astronomers a new way to search.

"We're not just looking for tiny dots of light," Oza explained. "We're looking for the fingerprints they leave behind."

What happens next?

There's still work to be done. The team wants to observe the system longer to confirm the cloud's orbit and structure.

“The evidence is very compelling that something other than the planet and star are producing this cloud,” said Rosaly Lopes, a planetary geologist at JPL who co-authored the study with Oza.

“Detecting an exomoon would be quite extraordinary, and because of Io, we know that a volcanic exomoon is possible.”

Future telescopes and instruments could provide sharper eyes to spot these hidden moons directly.

But for now, the possibility of a volcanic exomoon orbiting WASP-49 b opens up exciting avenues. It's a reminder that the universe is full of surprises waiting to be uncovered.

The study is published in the Astrophysical Journal Letters .

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