Earth twin detected by scientists
A rocky planet virtually identical in size to the Earth has been discovered orbiting a distant Sun-like star.
It is the first time such an Earth twin in another solar system has been detected.
Although the planet, Kepler-20f, could have a thick water vapour atmosphere, its surface is believed to be too hot for life.
A second planet in the same system, Kepler-20e, is only slightly smaller than Earth and even hotter.
Both worlds circle their parent star closely with year-long orbital periods of just 19 and six days respectively.
Neither lie within the "habitable zone" where temperatures are just warm enough to allow liquid surface water, increasing the prospects for life.
However scientists are excited by the technical achievement of detecting Earth-sized "exoplanets" since it increases the chances of one day finding a potential life-bearing world.
The parent star, Kepler-20, is not exactly a close neighbour, being 945 light years away. The findings are reported in an early online edition of the journal Nature.
Dr Francois Fressin, one of the astronomers from the Harvard-Smithsonian Centre for Astrophysics in Cambridge, US, said: "It is the first time humanity has been able to discover an object similar to the Earth around a star, so maybe we will be able to find others.
"This could be an important milestone. I think 10 years or maybe even 100 years from now people will look back and ask when was the first Earth-sized planet found. It is very exciting."