Scientists call the satellite of a moon: moonmoons. There is a new hypothetical new class of cosmic object that you might be interested to know about. Scientists call this - Ploonets; and they are making this a thing.
It is exactly what it sounds like: a sort-of cross between a moon and a planet. And the existence of ploonets could help explain why we haven't yet conclusively found any exomoons.
A new paper submitted to the Monthly Notices of the Royal Astronomical Society, and still undergoing the peer-review process, lays it all out: Exomoons orbiting giant, Jupiter-sized exoplanets in other planetary systems could be kicked out of orbit via gravitational interactions.
From that point, they could become planetary seeds, or protoplanets. Or... ploonets.
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"This paper explores the scenario where large regular exomoons escape after tidal-interchange of angular momentum with its parent planet, becoming small planets by themselves. We name this hypothetical type of object a ploonet."
Learn more about the research on ploonets over at Science Alert.
Image: NASA/ Tim Pyle