Hi Joshua, thanks for answering. Quick follow-up question: how come only “rogue” planets are mentioned in these arguments? (Well, it makes sense for studies about rogue planets, but it seems to happen even in discussions explicitly about captured planets, your comment being an example.) Can’t planets be “exchanged directly” between closely-passing stars? (I mean, without the exchanged planet spending a long time unbound to a solar system, in a sort of larger-scale analogue of close binaries exchanging envelope matter.)

I imagine close encounters are rare in general, but given the large number of binary and multiple-star systems that we seem to see everywhere, and my (admittedly vague) recollections of some rather tight clusters of stars with complicated/chaotic dynamics, it seems like it should be feasible (even common) for stars to exchange planets early (while they’re still part of a young cluster or complex multi-star system, and they interact closely) and then separate taking with them “stolen” planets (my understanding was that a significant fraction of stars in young clusters acquire high velocities and are “evaporated” away from their birth cluster, especially in “tight” clusters). Are the interaction time-frames incompatible with that kind of scenario or something?