2:39 pm
Mon December 5, 2011

Found: Earth-Like Planet That Might Be Right For Life

Credit NASA/Ames/JPL-Caltech
This artist's conception illustrates Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star. It is the first planet that NASA's Kepler mission has confirmed to orbit in a star's habitable zone — the region around a star where liquid water, a requirement for life on Earth, could persist.



The planet is about two and a half times the size of the Earth. It orbits a little closer to its star than our planet does to our sun, and goes around once every 290 days compared to our 365. But its star is a bit cooler than our sun, says William Borucki of NASA Ames Research Center, who heads NASA's Kepler Space Telescope mission, which detected this planet.

"That means that that planet, Kepler-22b, has a rather similar temperature to that of the Earth," Borucki says. "Its surface temperature would be something like 72 Fahrenheit."

It's not yet clear what kind of surface the planet might have — researchers don't know if the planet is made mostly of rock or water or something else. And don't expect astronauts to climb on a rocket and go there any time soon.

"The star is some 600 light years away," says Borucki, "so it's not terribly far away but not terribly close either."

More 'Viable Candidates' Likely

Kepler-22b marks a significant first for NASA's Kepler Space Telescope, which launched in 2009 on a mission to find other Earths outside our solar system. The telescope has been staring at over a 150,000 stars in one patch of sky, watching and waiting for a slight dimming. That telltale dimming happens when an orbiting planet passes in front of a star, partly obscuring its light.

So far, Kepler has seen signs of 2,326 planets, ranging in size from Earth-size to Jupiter-size. The vast majority of these possible planets still need to be confirmed through more observations.

At least five of those candidates appear to be small planets in the habitable zones of their stars, suggesting that Kepler-22b is just the first of more to come. "We believe that we've got some very, very viable candidates here that are Earth-sized, near-Earth-sized, and in the habitable zones," says Natalie Batalha of San Jose State University in California, who is on the Kepler team.

Over the last decade or so, scientists have confirmed the presence of hundreds of planets around distant stars, but they're mostly gas giants. Small worlds that could potentially have a rocky surface and maybe even alien life crawling around have been much harder to find.


"I think it may be time to discard the 'habitable zone,' " says Kuchner. "I think maybe what this discovery is telling us is that it is time to move past it and start asking the next question, which is, 'Is the planet moist and juicy, like our own planet Earth?' "


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