I saw what looked like a moon orbiting the moon of a planet in some art months ago, and I have been unable to stop thinking about it. Is that even possible and/or stable? What effects would this have on the planet's tides or orbit, if any. I know this is a little out there, but any insight to help satisfy my current obsession would be appreciated.
So what you're describing is called a "subsatellite" or more informally a "moon moon*". These are hypothetical objects where, as you describe, a moon has its own moon. We have never found one of these before, but they could exist!
They might have existed in the past around one of Saturn's moons, Iapetus. It has this weird equatorial ridge that has gone unexplained.
If Iapetus had a "moon moon" then that object's orbit could've slowly decayed until Iapetus tore it apart, forming a ring system that eventually fell down onto the moon. Who knows?
*I can't be the only one who thought of that moon moon meme? Right?
