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The cosmos may be awash in wandering, lonesome former moons, ejected from their respective planetary systems long ago.
Nobody has ever conclusively seen a moon orbiting a planet in another stellar system, partly because their small size and great distance makes them difficult to find with modern detection methods. But it’s also possible that there just aren’t very many of them.
Yu-Cian Hong at Cornell University in Ithaca, New York, Sean Raymond at the French National Centre for Scientific Research in Paris and their colleagues used simulations of the formation of planetary systems to figure out what happens to moons as their planets are still forming.
Planets are born in the chaos of early stellar systems, where they can be jostled out of position relatively easily by neighbouring worlds. They frequently brush by each other in the scramble