1/ I stand corrected. 2/ However, my point was that, in order to have long enough for the construction work on the planet, we'd need to intercept it around the orbit of Neptune, so we'd need to detect it some considerable time before that. 3/ OP was talking about several hundred years in transit, not several tens of thousands of years. But your point about, why would they want to change, is valid, even within this shorter time -frame.
I would think by that point, we would be able to detect it way further out. Scientists want to and know how to, we just don't have the technology yet. At the edge of the solar system there are billions of comets and astronomers really want to see them. Their distribution will answer a lot of questions about or solar system, so once we have the technology, the scientific community will likely fund these missions. If we create the IR telescopes capable of seeing those, we'll easily be able to detect a small asteroid out almost a light year. Asteroids, even small ones, have not had enough time to cool enough to blend into the background radiation.
Having massive cultural differences is intended, but I'm really not looking to overanalyze things like timescale or why the humans decided to colonize the planet instead of living in an asteroid for eternity. Mind you, the vessel is still settled, and people still live there, it's just in orbit around the new homeworld instead of roaming around space. I do realize with the computer thing that I have yet another problem. If the DNA codes were saved in a computer index long BEFORE the humans left, and the humans were sterilized during the journey, then the DNA codes stored on the computer would be unaffected by HSC, and would circumvent my entire purpose. So now I have to find a way to sterilize the physical AND the digital DNA!
I think perhaps the easiest way to resolve that is to have the digital DNA come from the inhabitants of the asteroid. They were originally some sort of purist group who wanted to cut genetic ties to Earth. They originally cloned living humans, but soon learned the hard way of replicative fading and decide to store the remaining healthy humans digitally and use that from then on. You can have an evolution of technology and culture on the asteroid.
I think I'll sit on it for a while and try to come up with some kind of reason for it that makes sense...or actually, maybe that could have been part of the "attack" on humanity? It could just be part of the cover-up, saying that the data was corrupted somehow and not questioning it. It could raise a red-flag for those who don't already get a red-flag from the fact that the humans were sterilized in the first place. As far as I know it never really goes into detail on this yet, and this hasn't been raised as a plot point...does that sound sufficient?
1) There is always the possibility for creating colonies/factories/closed off areas with artificial oxygen. Something to understand about the Dwarf planet that she said above is that it is drifting through the Sol System so it is not likely to have ANY life no matter the atmosphere due to having long stretches of pitch blackness due to the lack of a sun.