Scott and the scribe have form together: Green has also been working on the Blade Runner follow-up, so it makes sense for him to segue over to one of Scott's other big sci-fi ideas. He takes over from Transcendence's Jack Paglen, who wrote the original draft.
Few details have emerged on the focus for the new movie, though The Wrap has ferretted out that it aims to up the terror, tighten the links to the familiar xenomorph and potentially feature multiple Michael Fassbenders (Fassbendi?) for those who like that sort of thing. And we know you're out there.
The new hire adds fuel to speculation that the untitled Scott project 20th Century Fox recently targeted for March 4, 2016 could well be the new Prometheus outing, though that will depend on everyone agreeing with the new script draft in time for the director to get to work.