I would wager that it is a base outpost for them. And there are most likey a few more out their somewhere with egg silos, pyramids and more. I think the Prometheus just got luckily enough to catch this group of space jockey scientists at home base and not on spavaction! wow we have guests from earth, here why dont we mutate you give you xeno-like face with teeth tongues, (you know the kind your ex girlfriend used to have) and generally mess with all your DNA structures, that will be loads I'd fun, maybe you could take something with you as a parting gift maybe a chestbuster or a cool looking urn or egg! Have fun, come see us next year, to the future and beyond!