BBC Horizon - We Are The Aliens?

First broadcast on 14 November 2006

Clouds of alien life forms are sweeping through outer space and infecting planets with life – it may not be as far-fetched as it sounds.

The idea that life on Earth came from another planet has been around as a modern scientific theory since the 1960s when it was proposed by Fred Hoyle and Chandra Wickramasinghe. At the time they were ridiculed for their idea – known as panspermia. But now, with growing evidence, it's back in vogue and even being studied by NASA.