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 Center for Astrophysics. The fact that Earth-size planets have been found to exist around other stars like the sun marks the beginning of an era, he said.
They're the smallest planets found so far that orbit a star resembling our sun. The discovery also marks the next key milestone in the ultimate grail: the search for planets like Earth.
Scientists are seeking Earth-sized planets as potential homes for extraterrestrial life. The new findings are reported in a paper published online Tuesday by the journal Nature. One planet's diameter is only 3 percent larger than Earth's, while the other's diameter is about nine-tenths that of Earth. They appear to be rocky, like our planet.
But they are too hot to contain life as we know it, with calculated temperatures of about 1,400 degrees and 800 degrees Fahrenheit (815 degrees and 426 degrees Celsius), he said.
Any life found on another plant may not be intelligent; it could be bacteria or mold 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'd found a planet around another distant star with a life-friendly surface temperature of about 72 degrees (22 degrees Celsius). 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.