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Published December 21, 2011, 09:14 AM

Scientists confirm discovery of two Earth-sized planets

SAN JOSE, Calif. _ NASA's Kepler mission has found the first Earth-size planets orbiting a sun-like star outside our solar system. But they're too hot to support liquid water _ or life.

By: Lisa M. Krieger, Associated Press

SAN JOSE, Calif. _ NASA's Kepler mission has found the first Earth-size planets orbiting a sun-like star outside our solar system. But they're too hot to support liquid water _ or life.

This latest discovery marks a milestone that takes scientists one step closer to finding a planet like our own.

Two weeks ago, Kepler found a planet that was the perfect temperature. But this planet, Kepler-22b, is too big to have a rocky surface.

The new discoveries, Kepler-20e and Kepler-20f, are the right size. But they're close to their star, making them fiery hot worlds.

So now the hunt is on to find a "Goldilocks" planet with the best of both worlds: a hospitable place.

"In the cosmic game of hide and seek, finding planets with just the right size and just the right temperature seems only a matter of time," said Natalie Batalha, a contributing author to the new research who oversees the Kepler's scientific investigations at NASA's Ames Research Center in Mountain View's Moffett Field.

"We are on the edge of our seats knowing that Kepler's most anticipated discoveries are still to come," said Batalha, also a professor of astronomy and physics at San Jose State University.

The $600 million Kepler space telescope detects planets and planet candidates by measuring dips in brightness _ a blink, essentially _ when a planet crosses in front of a star. Additional evidence, such as a gravitational wobble, is required to confirm that the orb is a real planet.

Mountain View scientists manage Kepler's ground system development and mission operations. They're responsible for the software pipeline that analyzes the data _ identifying the best planet candidates to forward to the Kepler team.

The first planet, a Jupiter-sized giant, was found about 15 years ago.

Kepler's tally of confirmed planets is now 33. Another 2,326 are possible planets _ of which 1,000 have been found just since February.

Tuesday's news, published in the journal Nature and announced by teleconference, shows that the telescope is getting better at finding small Earth-sized places.

The new planets reside within a curious five-planet solar system. It's unlike our solar system, where small, rocky worlds circle close to the sun and large, gaseous worlds are farther away.

Instead, the planets that circle star Kepler-20 are organized in alternating sizes: large, small, large, small and large.

"The architecture of that solar system is crazy," said David Charbonneau of Harvard University. "In our solar system, the two different kinds of planets don't mingle. This is the first time we've seen anything like this."

And they're very far away _ 950 light years distant. If traveling the speed of the space shuttle, it would take millions of years to get there.

Kepler-20e and 20f are rocky places, made of silica and iron _ Earthlike, but without an atmosphere.

But the surface temperature of Kepler-20e, which orbits its sun every 6 days, is more than 1,400 degrees Fahrenheit _ hot enough to melt glass. Kepler-20f orbits every 19.6 days and is 800 degrees _ as hot as Mercury.

Researchers can't rule out the possibility that the planets had liquid water after their creation, when they might have been farther from the sun. Perhaps there was a window of time _ several billion years long _ when they were habitable.

Now, they'll just keeping looking.

"This is the first time that we've crossed the Earth-sized threshold," said Francois Fressin, an astronomer at the Harvard-Smithsonian Center for Astrophysics, who led the discovery team.

"It demonstrates for the first time that Earth-size planets exist, and that we can detect them.

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(c)2011 the San Jose Mercury News (San Jose, Calif.)

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