NASA's Kepler mission has confirmed the first near-Earth-size planet in the "habitable zone" around a sun-like star. The newly discovered Kepler-452b is the smallest planet to date discovered orbiting in the "habitable zone"—the area around a star where liquid water could pool on the surface of an orbiting planet. (NASA Ames Research Center)

The latest update from NASA's Kepler space telescope — designed to spot distant exoplanets — adds more than 500 new possible planets to the fray. That's in addition to the 4,175 planets already found by Kepler.

And of those 500 new potential planets, scientists say, a dozen could be remarkably Earth-like. That means they're less than twice as large as Earth, are potentially rocky and are at the right distance from their host stars to harbor liquid water.

Of that dozen, one planet has been confirmed: Kepler 452b, which sits 1,400 light years away from us and orbits a star much like our own — at the same distance as Earth orbits our sun. It has a "better-than-even chance" of being a rocky planet (like Earth), according to statements from Kepler scientists. We can't know for sure what the mass of Kepler 452b is, but models suggest that it might be as much as five times as massive as Earth, with gravity twice as strong. A rocky planet that massive would likely have volcanic activity.


Artist impression of the surface of Kepler 452b. With a radius 60% larger than Earth, the planet has a better than even chance of having a rocky composition, and is likely to have a thick atmosphere and a significant amount of water. (SETI Institute/Danielle Futselaar)

Kepler 452b is a slightly closer cousin to Earth than previously discovered exoplanets. Kepler 186f, discovered last year, is considered remarkably Earth-like. But while Kepler 186f orbits a red dwarf, Kepler 452b orbits a star of the same class as our own.

[Stephen Hawking announces $100 million hunt for alien life]

But we can't know this for sure. Here's a bit about "Earth-like" planets from an earlier post on the blog:

And when we say Earth-like, we mean it in the loosest possible sense. These are planets that are the right size and distance from their sun to be rocky planets, like our own, and ones that could potentially hold liquid water. But the Kepler isn't getting a close-up view of these planets — it's measuring them based on the way they dim the light of their host stars as they pass in front of them. Some of these planets have also been confirmed through a second method on the ground that looks for wobbles (or Doppler shifts) in the starlight caused by the gravity of the orbiting objects.

So scientists can't say for sure just how much like Earth this strange new world really is. And even in the best case scenario -- where the planet holds liquid water -- that doesn't mean it holds life. But it has potential.

“Kepler 452b takes us one step closer to understanding how many habitable planets are out there,” Joseph Twicken, lead scientific programmer for the Kepler mission, said in a statement. “Continued investigation of the other candidates in this catalog and one final run of the Kepler science pipeline will help us find the smallest and coolest planets. Doing so will allow us to better gauge the prevalence of habitable worlds.”

[Most stars in the galaxy have planets in the habitable zone, according to new research]

Scientists are especially interested in studying Kepler 452b for the ways in which its star is different from our own. It's similar in size (just 4 percent more massive and 10 percent brighter) but it's at least 1.5 billion years older.

“If Kepler 452b is indeed a rocky planet, its location vis-a-vis its star could mean that it is just entering a runaway greenhouse phase of its climate history,” Doug Caldwell, a SETI Institute scientist working on the Kepler mission, said in a statement. “The increasing energy from its aging sun might be heating the surface and evaporating any oceans. The water vapor would be lost from the planet forever.”

And that means that the planet could give us a look into our distant future.

“Kepler 452b could be experiencing now what the Earth will undergo more than a billion years from now, as the sun ages and grows brighter," Caldwell said.


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