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First rocky, Earth-sized planet found outside our solar system

SAN JOSE, Calif. – The place is inhospitable, with molten temperatures and possibly clouds of melted silicon. But a discovery across the galaxy is giving hope to searchers of intelligent life.

A team led by NASA Ames researchers has confirmed the existence of the first rocky planet outside our solar system. Kepler-10b is closest in size to Earth of 519 extra-solar planets discovered so far. It is about 1  1/2 times the Earth’s diameter and speeding around a star similar to our sun in the constellation Cygnus, about 560 light-years away.

“It’s unquestionably a rocky world orbiting a star outside our solar system,” said Natalie Batalha, deputy science team leader for the Kepler Mission at NASA Ames. She and about 50 other scientists published their discovery Monday in the Astrophysical Journal.

Unlike the majority of the so-called exoplanets detected so far, Kepler-10b is solid and not gaseous. “It’s something you can stand on,” she said.

Its size and composition are significant because an Earth-sized, solid planet is more likely to harbor water, essential for life. Kepler-10b, which is 20 times closer to its star than Mercury is to the sun, can’t sustain life. But it still has astronomers excited.

In September, astronomers led by a University of California, Santa Cruz, professor announced they had found what was probably a rocky planet, called Gliese 581g. But other scientists discounted the discovery, pointing to an error in data analysis. So its existence is unconfirmed.

One reason controversies arise over planets outside the solar system is that even astronomers’ most powerful tools can’t see them. Instead, scientists prove the existence of exoplanets by scanning the galaxy and searching for regular but slight dimming of light from stars. That dimming can be caused by a “planet transit,” when an orbiting planet periodically blocks the star’s light, like an eclipse. A planet’s size can be calculated from how much light it blocks when passing in front of its star.

Kepler-10b’s discovery, announced Monday at a meeting of the American Astronomical Society in Seattle, is a major dividend paid by NASA Ames’ Kepler spacecraft, launched in March 2009.


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