Found: An Earthlike Planet, at Last
For the first time, astronomers using NASA's Kepler space telescope have confirmed a roughly Earth-size planet orbiting a sun-like star in the so-called "Goldilocks" zone where water can exist in liquid form on the surface and conditions may be favorable for life as it is known on Earth.

Along with the confirmed extra-solar planet, one of 28 discovered so far by Kepler, researchers today also announced the discovery of 1,094 new exoplanet candidates, pushing the spacecraft's total so far to 2,326, including 10 candidate Earth-size worlds orbiting in the habitable zones of their parent stars.

Additional observations are required to tell if a candidate is, in fact, an actual world. But astronomers say a planet known as Kepler-22b, orbiting a star, Kepler-22, some 600 light years from Earth, is the real thing.

"Today I have the privilege of announcing the discovery of Kepler's first planet in the habitable zone of a sun-like star, Kepler-22b," Bill Borucki, the Kepler principal investigator at NASA's Ames Research Center, told reporters. "It's 2.4 times the size of the Earth, it's in an orbital period (or year) of 290 days, a little bit shorter than the Earth's, it's 15 % closer.closer to its star than Earth is to the sun,

An artist's concept of Kepler-22b, a roughly Earth-size world orbiting within the habitable zone of a sun-like star 600 light years from Earth.

 
"But the star is a little bit dimmer, it's a little bit lower in temperature, a little bit smaller. That means that planet, Kepler-22b, has a rather similar temperature to that of the Earth...If the greenhouse warming were similar on this planet, its surface temperature would be something like 72 Fahrenheit, a very pleasant temperature here on Earth."

It is not yet known whether Kepler-22b is predominantly rocky, liquid, or gaseous in composition, but the finding confirms for the first time the long-held expectation that Earth-size planets do, in fact, orbit other suns in the habitable zones of their host stars.

That, in turn, greatly improves the odds for the existence of life, as it is commonly defined, beyond Earth's solar system.

Also in the hunt: The SETI Institute, or the Search for Extraterrestrial Intelligence, in Mountain View, Calif.

Jill Tarter, director of the Center for SETI Research at the institute, said a radio telescope array that was looking for signs of radio signals in the Kepler field of stars that might indicate the presence of intelligent life is back in operation after a budget-driven hiatus earlier this year.

"I'm really pleased to announce as of 6:18 this morning, as the Kepler field rose over the observatory, the ATA (Allen Telescope Array) was back on the air, continuing the search for Earth analogues."

The Allen Telescope Array, originally funded by Microsoft co-founder Paul Allen, is being used to make systematic observations of stars in the Kepler field, on the lookout for any signs of artificial signals.

Citing a 1993 paper by Carl Sagan and four colleagues that used data from NASA's Jupiter-bound Galileo spacecraft as a test for detecting life on Earth, Tarter said "one of the strongest pieces of evidence for life, indeed intelligent life on Earth, was the presence of narrow-band pulse-amplitude-modulated radio transmissions."

"While there may be some uncertainty about how to define the habitable zone, an exoplanet that could be detected through the techno-signatures of its inhabitants would surely qualify as an Earth analogue," she said.