Astronomers claim to have found the most Earth-like planet yet - and they believe it could support life.
The planet - named Gliese 581g - is three times the mass of Earth and is only 20 light years away. It takes 37 days for it to orbit its parent star Gliese581, which it always faces so one side is permanently dark and the other light.
With favourable temperatures and a similar gravity to our own planet, Gliese 581g is thought to be potentially habitable, unlike its neighbours. Steven Vogt, professor of astronomy at the University of California, said: "We had planets on both sides - one too hot and one too cold - and now we have one in the middle that's just right.
"Our findings offer a compelling case for a potentially habitable planet. Any emerging lifeforms would have a wide range of stable climates to choose from."
He claimed their findings, published in Astrophysical Journal, suggested the planet was far from unusual. "The fact we were able to detect this one so quickly and so nearby tells us planets like this must be really common," he said.
Up to 20% of star systems are thought to have habitable planets - and there are tens of billions of stars in the Milky Way.
Paul Butler of the Carnegie Institution, which helped with the research, added: "Our ability to find potentially habitable worlds is now limited only by our telescope time."