Very interesting, thanks Civ! If such a Nemesis star or planet exists, it will obviously have to be destroyed. We’ll build our own Nemesis, and name it The Death Star!!
It’s possible that it exists, but it’s supposedly been ruled out at least three times, by various means. Still crops up in conversation, simply due to the (obviously non-periodic, merely occasional) violent mass extinction events.
There’s sometimes a whacky contingent of Sitchin followers and wannabees, who claim there’s a Nibiru that’s been on the same comet-like orbit for millions of years, and despite its Brigadoon-like life, somehow developed an advanced civilization first, and then turned a bunch of Earth monkeys and a bunch of petri dishes into a slave species we like to call, uh, us.
That school (such as it is) seizes on every little flicker in its psych meds to proclaim that, no, really, this time we mean it, Nibiru (or whatever moniker each uses) is on its way, and (guess what) NASA, the Trilateral Commission, the Bildebergers, the Skull ‘n’ Bones, and even the crew of Apollo 20 which filmed alien cities on the back side of the Moon are in cahoots to keep this covered up.
Ahem.
But anyway, my guess is, there’s no Oort Cloud per se, there’s probably not a Kuiper Belt per se, either, and if there are any decent-sized planets beyond Pluto, they probably move in retrograde because they were captured by the Sun, with or without the help of Jupiter and the other known planets.
Oh yeah, but regarding destroying an interloper of this kind, it’s small enough, a nuke might work, nudge it into a different trajectory; bigger, and it would require our pushing a pushable, smaller, but heavy enough other rock into the interloper rock, and give it a big knock. With this in mind, it would be a good idea to compile a thorough list of objects in retrograde orbits around the Sun. That is a double benefit, because those critters are also a bit more risky to have floating by. :’)