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

https://www.npr.org/2022/01/13/ [login to see] /kepler-large-exomoon
The hunt for moons outside our solar system has just turned up another possible lunar world, a moon bigger than Earth that's orbiting a Jupiter-like planet.

The planet and its moon — if it really is a moon — orbit a Sun-like star that's over 5,000 light years away, according to a report in the journal Nature Astronomy.

"The moon is pretty alien compared to any moon in the solar system," says David Kipping, an astronomer at Columbia University. "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."

This isn't the first time astronomers have spotted something that might be a moon in another planetary system, which is sometimes called an exomoon.

In fact, Kipping and his colleagues announced a few years ago that they'd detected something moon-like orbiting a different planet. That discovery has yet to be confirmed with additional telescope observations, and some astronomers are skeptical that it will hold up to more scrutiny.