David Bowie as Thomas Jerome Newton in 'The Man Who Fell to Earth'; a Xenomorph in 'Aliens'; Scarlett Johansson as the Female in 'Under the Skin' A casual viewer might assume that if you've seen one ...

We may receive a commission on purchases made from links. Are we alone in the universe? It's a huge question with no easy answer. And, following on from that, if we aren't alone, what would beings ...