Earthlike planet found in Goldilocks zone

WASHINGTON -- A newly discovered planet is eerily similar to Earth and is sitting outside our solar system in what seems to be the ideal place for life, expect for one hitch. It's a bit too big.

The planet is smack in the middle of what astronomers call the Goldilocks zone, that hard to find place that's not too hot, not too cold, where water, which is essential for life, doesn't freeze or boil. And it has a shopping mall-like surface temperature of near 72 degrees, scientists say.

The confirmation was announced yesterday by NASA, along with other discoveries by its Kepler telescope, which was launched on a planet-hunting mission in 2009.

It's the first planet confirmed in the habitable zone for Kepler, which had already found Earth-like rocky planets elsewhere. Twice before, astronomers have announced a planet found in that zone, but neither was as promising.

"This is a phenomenal discovery in the course of human history," Geoff Marcy of University of California, Berkeley, a pioneer of planet-hunting outside our solar system, said in an email. "This discovery shows that we Homo sapiens are straining our reach into the universe to find planets that remind us of home. We are almost there."

The new planet, named Kep-ler-22b, has key aspects it shares with Earth. It circles a star that could be the twin of our sun and at about the same distance. The planet's year of 290 days is even close to ours. It probably has water and rock.

The only trouble is the planet's a bit big for life to exist on the surface. It is about 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.

"It's so exciting to imagine the possibilities," said Natalie Batalha, the Kepler deputy science chief. Floating on that "world completely covered in water" could be like being on an Earth ocean and "it's not beyond the realm of possibility that life could exist in such an ocean," she said.

Kepler can't find life itself, just where the conditions might be right for it to thrive. And when astronomers look for life elsewhere they're talking about everything ranging from microbes to advanced intelligence that can be looking back at us.

So far, the Kepler telescope has spotted 2,326 candidate planets outside our solar system with 139 of them potentially habitable ones. Though Kep-ler-22b is a bit big, it is smaller than most of the other candidates. It is closer to Earth in size, temperature and star than either of the two planets previously found in the zone.

For Marcy, who is on the Kepler team, it is a smidgen too large, but "that smidgen makes all the difference."

Chief Kepler scientist William Borucki said he thinks the planet is somewhere between Earth and Neptune, but that it has a lot of rocky material. It's in a size range that scientists don't really know anything about. Measurements next summer may help to give a better idea of its makeup, he said.

The planet is 600 light years away. It would take a space shuttle about 22 million years to get there.