We know that comets need to come from somewhere. We know, due to their trajectories, that they are not interstellar objects. At all, in fact.
The rest, as far as I understand it, is the good old story of two astronomers having the same idea independent of each other – and both (probably) being right.
Oh, and speaking of trajectories, there’s quite the awesome paradox involved in this: The trajectories are unstable “over the course of the Solar System’s existence”…
Chew on that sentence for a while, then I’ll continue.
What that means is that the comets can’t be like the planets and do the same thing into all eternity, going round the Sun, I mean – well, the planets don’t either, but that’s because at one point the Sun won’t be there for them anymore to go round. No, the comets have a different problem: They disintegrate just a little bit every time they come to the inner solar system and close to our star and their trajectory changes slightly with the mass they lose.
Strangely, this means that there must be a repository of comets out there somewhere on principally stable orbits, “from whence” all of them come: The Öpik-Oort Cloud.
Think about it. They simply can’t have come to be like the planets did.
Stupid thing is that we can’t prove the repository is there, even though we know it must be.