A point about planetary habitability

[Torco]

So, the fermi equation idea is kind of silly if we apply it to "space empires" like popsci youtubers tend to do, right? even if the galaxy was brimming with life, there's very little reason to think that that life will necessarily -or even likely- do any such thing as making starwars: but more abstractly, life does tend to expand and there's been an awful lot of time and an awful lot of stars, so why so few (none) biosignatures? it could of course be because we don't have good enough telescopes or whatever, but I think an often overlooked factor is eccentricity and what it tells us about star systems. these guys find that the peak of the probability distribution that best fits a bunch of exoplanets the eccentricity of which we can ascertain depends strongly on whether the system looks like it has a single planet, or if it looks like it has a bunch of them: namely, bunch-of-planet systems tend to have very low eccentricities, whereas single planet systems tend to have very high eccentricities. interestingly, there's no added eccentricity associated with close binaries, and a lot of stars have those, so that's good news for habitability, but on the other hand in a frictionless table kind of deal a protoplanetary disk, I understand -could be wrong- would tend to make a bunch of planets in nice regular orbits, cause the disk itself would have very tendency to be very elliptical, right? all those particles and little clouds of gases and whatever all clashing and exchanging momentum in a cloud would end up nice and circular, so those single-system high-eccentricity systems all look like they've been disturbed by some other massive thingie -another star, for example, but also sub-stellar big chonky boys, rogue jupiter-sized bodies and whatnot, of which there's very likely a lot more than what we can see, since they don't glow much, and we can see a fair few of them.

stars messing each other's systems up, or whole star systems getting scattered up by close approaches with interstellar objects could be, then, an important contributor to stellar inhabitability: i read about this stuff from time to time but I'm a total amateur, does anyone have a notion of how common it is for stars *not* come close to other stars (close as in, say, 100 AU instead of 60k, which is a lightyear) for a the whole *four billion years* the sun's been around nice and undisturbed for earth to grow mold and us?

also how cool is that for a post-apocalyptic movie?

[zompist]

It looks like stellar collisions and flybys are very, very rare:

https://en.wikipedia.org/wiki/Stellar_collision#Stellar_collisions_and_the_Solar_System

They would be more common in globular clusters or near the center of the galaxy.

[Torco]

stellar yes, but they keep finding more and more chonky substellar objects. hitting even a saturn looks like it could really mess a system up. maybe we've been lucky!