Art by H. R. Giger
"I know I'm not the only person on the UK blogging and film writing scene to have heard these rumours, and we almost certainly heard them from the same or associated sources, but I've gone on to speak with another party. Despite this individual having to be rather careful about what they were saying, they certainly didn't quash the story.
So. Let's go with it. How does Ridley Scott's Prometheus fit into universe of the Alien films?
Quite simply: it has the Alien aliens in it. The catch, though, is that you might not recognise them – at least, not at first.
Remember how the alien took on canine qualities after gestating in a dog? You may even suppose that the first film's alien was so recognisably humanoid because it had grown in a human. The same applies here: generation by generation, the creature mutates. As Prometheus begins, the xenomorph is not too recognisable. Sure, it has that alien DNA that Scott and Fassbender teasingly referred to, but it's missing... well, it's missing human DNA. Or dog DNA.
All you have to do is imagine how it might look if it were to mix DNA with another alien species... and I think we're starting to work it all out.
I learned that the film's setting is, in part, a planet that has been terraformed to create the perfect environment in which a particular bioweapon would prosper. Terraformed deliberately to farm the weapon? I got no clear answer. Is this bioweapon the alien? I got no clear answer. While there was a lot of wheezing and coughing on my end of the phone, there was a good deal of quiet smirking on the other, it seems.
I did ask if the film is really going to be called Prometheus. The answer? "Maybe not. Though they are calling it that for a reason."
Sadly, I was not able to confirm the rumoured use of an 8-foot animatronic Space Jockey, but the way I was told "there's nothing we're calling a space jockey here" just led me to believe, perhaps erroneously, that it would be the same character, or at least species, but with a new name. On past information, that name would seem to be "The Engineer", but I may be getting ahead of myself to join those particular dots so readily when their sources aren't the same.
Anyway. The only thing I'm completely sure of here is that Prometheus does indeed take place in the same universe as Alien, and in this universe there's a big terraforming operation going on, somehow related to the classic Giger xenomorph."
Original Source is here