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

That’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 has been as promising.

“This is a phenomenal discovery in the course of human history,” Geoff Marcy of University of California, Berkeley, one of the pioneers 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 Kepler-22b – has key aspects it shares with Earth. It circles a star that could be the twin of our sun and at just about the same distance. The planet’s year of 290 days is even close to ours. It likely has water and rock.

The only trouble is the planet’s a bit big for life to exist on the surface. The planet 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,” Batalha said in a phone interview.

Kepler can’t find life itself, only where the conditions might be right for it to thrive. And when astronomers talk about life elsewhere, they’re talking about anything from microbes to advanced intelligence that could 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.

Even though the confirmed Kepler-22b is a bit big, it is still smaller than most of the other candidates. It is closest to Earth in size, temperature and star than either of the two previously announced planets in the zone.

Chief Kepler scientist William Borucki said he thinks the planet is somewhere between Earth and gas-and-liquid 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 astronomers have a better idea of its makeup, he said.

The planet is 600 light years away.