Scientists hunting alien moons think maybe they've found one bigger than Earth Scientists have found many planets orbiting distant stars, but so far no proof that any have moons. Now, researchers have detected signs of a large exomoon orbiting a Jupiter-like world.

Scientists think they've found a big, weird moon in a far-off star system

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As astronomers have found more and more planets outside of our solar system, they've wondered if any of them have moons. NPR's Nell Greenfieldboyce reports on the latest advance in the hunt for distant moons.

NELL GREENFIELDBOYCE, BYLINE: Thousands of planets have been detected in recent years, and a lot of astronomers are focused on trying to find ones that might support life. But David Kipping says, what about moons? He's with Columbia University, and he says in science fiction, a moon is often a great place to live.

DAVID KIPPING: If you've seen "Avatar" or "Star Wars," you're probably familiar with this idea that moons in of themselves could be habitable.

GREENFIELDBOYCE: And he says in our real-life solar system, some of the places that look the most intriguing in terms of having key life-supporting features like liquid water are moons. A few years ago, Kipping saw signs of what might be a moon in another planetary system. And now he's found a second possible moon. It's going around a Jupiter-like planet that orbits a sun-like star. They're really, really far away - over 5,000 light years.

KIPPING: The moon is pretty alien compared to any moon in the solar system.

GREENFIELDBOYCE: For one thing, it's weirdly bigger than Earth - like, 2 1/2 times the size.

KIPPING: We're not sure if it's rocky. We're not sure if it's gaseous. It's kind of in between the size of Neptune, which is gaseous, and the Earth, which is rocky.

GREENFIELDBOYCE: That is, if it's really there. Scientists like Kipping can't actually see this moon or even its planet. All they can do is detect a dimming in the star as the moon and planet pass in front of it and block some of the star light. Trying to tease out the subtle signal of a moon - sometimes called an exomoon - is pushing the limits.

MARY ANNE LIMBACH: You know, finding these exomoons is extremely challenging.

GREENFIELDBOYCE: Mary Anne Limbach is a researcher at Texas A&M University who also hunts for moons. She says this new possible one, which is described in the journal Nature Astronomy, does look interesting, but it needs to be confirmed.

LIMBACH: Certainly, you know, I think the object, the event does warrant further follow-up with space-based observatories.

GREENFIELDBOYCE: She says there should be a lot of moons out there to find. After all, in our own solar system, moons outnumber planets. And new telescopes, like the recently launched James Webb Space Telescope, will be much more capable of finding and confirming the presence of moons - even small ones.

Nell Greenfieldboyce, NPR News.

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