The film was shot without a script, the actors were given the freedom to make up their lines as they went along. The story was created later, in post production. No one, including the directors, knew how the story would turn out until the film was shot and edited. All the visual effects/CGI were created to match the actor's improvised lines in the film.
At the end of the movie, when we see the underside of the alien ship, if you have English (SDH) subtitles on, the ominous alien voice is subtitled as saying "STUR" which means SATURN in the ancient language Chaldee. Each letter in Chaldee corresponds to a number, S=60,T=400,U=6,R=200. If you add it up, it equals 666.