There could be at least a billion 'Earths' out there, say scientists

The chances of an Earth-like planet circling a distant star are far higher than previously thought, astronomers say.

They have calculated in a study of physical conditions needed for extra-terrestrial life to thrive that more than one billion habitable planets could exist in our own galaxy, each with a sufficiently stable orbit around a nearby sun to support the evolution of life.

A computer study of a solar system similar to ours has found small, rocky planets similar to Earth are likely to survive the gravitational disturbances of larger planets that could potentially throw small planets into deep space.

Astronomers have detected more than 70 "exoplanets" in orbit around other stars but all of them are thought to be hot "giants" too close to their own suns to support life.

Two astronomers from the Open University have estimated the chances of an Earth-like planet existing in the critical habitable region from a star where the temperatures are neither too hot nor too cold. This "Goldilocks zone" is critical to ensure that water exists in liquid form – believed to be one of the prerequisites for life. Barrie Jones and Nick Sleep concentrated on a nearby star, 47 Ursae Majoris, which is known to have two giant planets in orbit and is most similar to our solar system.

Professor Jones said: "Although we do not yet have the capability to detect 'tiddlers' like the Earth, we can establish theoretically which of the exoplanetary systems are most likely to have an 'Earth'.

Professor Jones, who presents the findings today to the National Astronomy Meeting in Bristol, said there was great potential for life in space. "There could be at least a billion 'Earths' in the Milky Way and lots more if we find systems like ours," he said.