the theory

Consider this: what if where Shaw and David are headed (the Engineer homeworld) is LV-426? Say that before they take off, like many of you have mentioned, the deacon slips on board. Personally, I doubt Ridley Scott would even bother showing us the deacon if he intend on using it, I hope. They reach the homeworld of the Engineers where Shaw and David are confronted with the reasons why they want to destory the human race which clearly has something to do with the creation of xenomorphs. Somewhere in the middle of the film, the deacon slips off the ship and does what it does best (killing things, harvesting others, etc). This is where Shaw and David find out from the Engineers that they must self destruction the planet. The planet is destroyed, Shaw and David escape, but not before one Engineer sends warning beacon to all who approach the planet's atmosphere to stay away except in the Engineer dialogue. This is the beacon that the Nostromo is sent to investigate. Remember, this is just a theory so feel free to comment, agree, disagree, you get the point :)