Isn't the whole process pseudo-2D even in a 3D simulation? The moon initially moves on a plane around the and I guess most of it's broken pieces would stay in that plane?
I think in a 3D simulation, the initial fragments would have various trajectories in 3D space, and their orbits would intersect back in the original plane as they pass through it in different directions. (Unless you meant unrolling the center-of-the-orbit as a line, then the fragmentation expands that as a plane? Not sure on the implications of that.)
this might be true, but i don't see why it should be. if two pieces collide at a high speed and shatter explosively, why would they stay confined to a single plane?
I think the plane change would be small, since the velocity change experienced by the fragments would be small compared to the orbital speed. For empirical support of this idea, consider Saturn.
Another consideration the moon does not orbit the earths equator but Uranus, Saturn, and Jupiter's rings do. This suggest tidal forces play a major role and you would not end up with a ring in the same inclination as the Moon's orbit.
The plane change would be just as small or large as the change in orbit, the directions are the same. If a collision is not likely to produce significant plane change, it's also not likely to produce fragments that go to significantly lower orbit to hit Earth; and if a collision is sending some fragments towards earth, then it's sending as many fragments significantly sideways to a different orbit inclination.
