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 some 600 light years from Earth, is the real thing.
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.
(Credit: NASA) "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 a little bit closer to its star than Earth is to the sun, 15 percent closer.
"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.
"I think there are two things that are really exciting about Kepler-22b," said Natalie Batalha, the deputy science team lead at Ames. "One is that it's right in the middle of this habitable zone.
"The second thing that's really exciting is it's orbiting a star very, very similar to our own sun. This is a solar analogue, almost a solar twin, very similar to our own sun and you've got a planet 2.4 times the size of the Earth right smack in the habitable zone."
Equipped with a 95-megapixel digital camera, Kepler was launched from Cape Canaveral on March 6, 2009. The camera is aimed at a patch of sky in the constellation Cygnus that's the size of an outstretched hand that contains more than 4.5 million detectable stars.
Of that total, some 300,000 are believed to be the right age, have the right composition and the proper brightness to host Earth-like planets. More than 156,000 of those, ranging from 600 to 3,000 light years away, will be actively monitored by Kepler over the life of the mission.
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