Journal of a Cosmic Anthropologist

Dr Boss has estimated that each Sun-like star has on average one “Earth-like” planet.

This simple calculation means there would be huge numbers capable of supporting life.

“Not only are they probably habitable but they probably are also going to be inhabited,” Dr Boss told BBC News. “But I think that most likely the nearby ‘Earths’ are going to be inhabited with things which are perhaps more common to what Earth was like three or four billion years ago.” That means bacterial lifeforms.

Dr Boss estimates that Nasa’s Kepler mission, due for launch in March, should begin finding some of these Earth-like planets within the next few years.

Recent work at Edinburgh University tried to quantify how many intelligent civilisations might be out there. The research suggested there could be thousands of them.