Which sci-fi aliens might actually be out there waiting for us?

With Doctor Who back on our screens this weekend, fans will be looking forward to a whole range of new alien adversaries to enjoy and fear. But how many aliens imagined by science-fiction might actually exist somewhere out there in our universe?

We talked to astrobiologist Dr Lewis Dartnell – a UK Space Agency research fellow at the University of Leicester – to get the science behind alien life. If you want to read more, Dr Dartnell has also written a book, Life in the Universe: A Beginner’s Guide.