New York - Scientists have found two Earth-sized planets orbiting a star outside the solar system, an encouraging sign for prospects of finding life elsewhere.
The discovery shows that such planets exist and that they can be detected, said Francois Fressin of the Harvard-Smithsonian Centre for Astrophysics.
They're the smallest planets found so far that orbit a star resembling our sun.
Scientists are seeking Earth-sized planets as potential homes for extraterrestrial life, said Fressin, who reports the new findings in a paper published online on Tuesday by the journal Nature.
One planet's diameter is only 3% larger than Earth's, while the other's diameter is about nine-tenths that of Earth. They appear to be rocky, like our planet.
Life-friendly
But they are too hot to contain life as we know it, with calculated temperatures of about 815°C and 426°C, he said.
Any life found on another plant may not be intelligent; it could be bacteria or mould or some completely unknown form.
Since it was launched in 2009, Nasa's planet-hunting Kepler telescope has found evidence of dozens of possible Earth-sized planets.
But Fressin's report is the first to provide confirmation, said Alan Boss of the Carnegie Institution for Science in Washington. He's a member of the Kepler science team but not an author of the paper.
The researchers ruled out a possible alternative explanation for the signals that initially indicated the planets were orbiting the star Kepler-20. The star is 950 light-years from Earth in the direction of the constellation Lyra.
The planets are called Kepler-20e and Kepler-20f.
Earlier this month, scientists said they had found a planet around another distant star with a life-friendly surface temperature of about 22°C. But it was too big to suggest life on its surface.
At 2.4 times the size of Earth, it could be more like the gas-and-liquid Neptune with only a rocky core and mostly ocean, scientists said.
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