>>12635479It's probably a generation ship searching for a new planet for an ancient race of aliens who ruined their planet due to environmental catastrophe. The final act of these aliens was to build a giant arc-ship in which their population would be put into stasis then search the galaxy for a suitable home. No doubt they passed by Earth because they didn't want to wipe out the indigenous population of Earth (unlike what humans would probably do, given our track record with discovering the Americas).
Either that, or it was just a big space rock.
