The chances of alien life existing on a newly-discovered Earth-like planet are 100 per cent, an astronomer has claimed.

Gliese 581g was discovered orbiting a nearby star at a distance that places it squarely in the “habitable zone” where liquid could exist on its surface. Of around 500 planets that astronomers have found outside Earth’s solar system, this is the first to be considered habitable.

The planet is a similar size to Earth and its mass indicates that it is probably rocky with a definite surface and has enough gravity to hold an atmosphere, according to Prof Steven Vogt, who led the team that discovered it.

It is as yet unknown whether water does exist on the planet or what kind of atmosphere it has. But because conditions are ideal for liquid, which is always a precursor for life on Earth, Prof Vogt believes that life will undoubtedly have begun there.

“Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say, my own personal feeling is that the chances of life on this planet are 100 percent,” he said during a press briefing. “I have almost no doubt about it.”

The findings are based on 11 years of observations by ground-based telescopes at the W. M. Keck Observatory in Hawaii.

The close proximity of Gliese 581g and the fact that it was found relatively early in the astronomers’ search suggests that there may be billions of other habitable planets like Earth in the universe.

Prof Vogt estimates that as many as one in five to 10 stars in the universe have planets that are Earth-sized and in the habitable zone.

With an estimated 200 billion stars in the galaxy, that means that around 40 billion planets could have the potential for life, he said.

The new findings by Prof Vogt and Paul Butler, of the Carnegie Institution in Washington, will be published in the Astrophysical Journal.

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