Well, here`s a bit of a reveal, during an interview with The Hollywood Reporter Ridley Scott presented these details.
"The new ship is quite different from Alien's, with its tall, refinery-like towers that Scott says he sketched rapidly, thinking of a floating tug. By contrast, the Prometheus is massive and resembles a Hawker Hunter jump jet, which is "pretty interesting in the way the engines tilt and fold," the director observes. As to the film's creature, it takes on at least four different forms as it grows and changes, sometimes "organically" in a way that [actress Noomi] Rapace calls "every woman's worst nightmare."
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