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The possibility of life on other planets has been a staple of science fiction for decades. And now that possibility has taken a step closer to reality. Astronomers say that they've found a planet orbiting a star a mere 20 light years away and it has the right conditions for life to exist. As NPR's Joe Palca reports, the astronomers are calling this the first Goldilocks planet.
JOE PALCA: Just to review: Goldilocks was the little girl who didn't like porridge that was too hot or too cold. That's what a planet around another star would have to be like in order to harbor life.
Dr. PAUL BUTLER (Carnegie Institution of Washington): The planet has to be at the right distance from the star so that it's not too hot, not too cold, liquid water can exist. And then the planet has to have roughly the proper surface gravity.
PALCA: That's Paul Butler of the Carnegie Institution of Washington. He spoke this afternoon at a news conference organized by Butler's funder, the National Science Foundation.
Astronomers have found hundreds of planets orbiting other stars in the past decade, but they've all been so far from their suns that any water would be solid ice, or so close that liquid water would boil away. The new planet, called Gliese 581-g, is different.
Now, Butler has no direct evidence that Gliese 581-g has water.
Dr. BUTLER: What we know is that this planet exists at the right distance for liquid water, and that it has the right amount of mass to hold on to an atmosphere and to protect its liquid water on the surface. And of course, any subsequent discussion about life is purely speculative.
PALCA: But then, he couldn't resist speculating.
Dr. BUTLER: That being said, on the Earth, anywhere you find liquid water you find life in abundance.
PALCA: There are six planets around Gliese 581. Even if 581-g doesn't have life, Steven Vogt of the University of California Santa Cruz says the solar system around Giese 581 has an eerie resemblance to the one around our sun.
Dr. STEVEN VOGT (University of California Santa Cruz): It has an inner clutch of rocky, sort of terrestrial like planets.
PALCA: Like Mercury, Venus, Earth and Mars.
Dr. VOGT: And then this sort of loner that's sitting on the outside, which is kind of like our Jupiter, but it's scaled down. This entire solar system would fit within our own Earth's orbit.
PALCA: That's because Gliese 581 is a red dwarf, a pipsqueak of a star compared to our sun.
Dr. DAVID CHARBONNEAU (Harvard Smithsonian Center for Astrophysics): If you think of the sun as a 100-watt light bulb, this star is a one-watt light bulb. It's like a Christmas tree light.
PALCA: David Charbonneau is another planet hunter at the Harvard Smithsonian Center for Astrophysics.
Dr. CHARBONNEAU: So, to have the same temperature a planet needs to be much closer to that star than it would be from the sun to have a temperature where you might have life and liquid water.
PALCA: Charbonneau says the next step will be to try to analyze the atmosphere of this planet and other Goldilocks planets that are probably out there to see if they contain oxygen, another key chemical for life. Those findings are probably some years off, but Charbonneau predicts they will come.
Joe Palca, NPR News, Washington.
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