There were three named women in this movie, two of whom were major characters.
Elizabeth Shaw took center stage throughout, but mostly surrounded by men. As a result, they were the other half in most of her conversations. Meredith Vickers was nominally in charge of the ship, but her crew was also mostly male.
Then there was the ship's medic, Ford. She was the one who actually saved the day, insofar as passing the Bechdel Test was concerned.
These three simple questions are designed to assess the portrayal of women in Hollywood films. Even in such seemingly safe hands as Ridley Scott - who has a reputation for depicting strong, female leads - the test shows how the casting and the plot can divert us with sleight of hand tactics.
In fact, Prometheus had a lot of overtly and subtly sexist language. For example, Dr Elizabeth Shaw, for all of her extreme intellect and pragmatic genius, was dismissed in the script as 'the scientist's girlfriend'. Meanwhile Vickers was persuaded to have sex by a man accusing her of being a robot and an Ice Maiden.
(Note to Vickers: the correct response to to laugh in the face of the patronizing gentleman.)
Are there two or more named female characters in the film? Yes. Do they have a conversation? Yes! In fact, there are two or three different scenes in which these women share words.
Is that conversation about anything other than a man? Ah. That's when everything narrows down to one single, solitary scene: Shaw and Ford discussing DNA over an autopsy. Shaw does talk to Vickers about philosophy and the origin of life on Earth; but Vickers just brings the conversation back to men.
Without that scene, Prometheus would not have passed the Bechdel Test.