Scientists have now detected far-away planets that may contain life, but what makes some people believe in extra-terrestrial beings, and not others? What really lies behind stories of alien abduction or alien invasion? And how much damage do alien species of plants actually cause? Bridget Kendall asks ecologist Chris Thomas, science-fiction writer Nnedi Okorafor and psychologist Richard McNally.

(Illustration: Artist impression of alien spaceship hovering over a city landscape. By Shan Pillay) Show less