'Goldilocks' Planet's Temperature Just Right For Life

The newly discovered GJ 581g planet

hide captionA National Science Foundation artist's drawing shows the inner four planets orbiting Gliese 581, a red dwarf star just 20 light-years from Earth. The newly discovered planet, in the foreground, has a 37-day orbit and, like Earth, is distant enough from the star for liquid water to exist.

Lynette Cook

The possibility of life on other planets has been a staple of science fiction for decades. Now that possibility has taken a step closer to reality as astronomers say they have found a planet orbiting a star a mere 20 light-years away that has the right conditions for life to exist.

The planetary orbits of the Gliese 581 system compared to those of our own solar system. i i

hide captionAll of the planets orbiting Gliese 581 are nearer to it than the Earth is to our sun.

Zina Deretsky/National Science Foundation
The planetary orbits of the Gliese 581 system compared to those of our own solar system.

All of the planets orbiting Gliese 581 are nearer to it than the Earth is to our sun.

Zina Deretsky/National Science Foundation

Scientists are calling it the first "Goldilocks" planet, as its temperature seems to be just right to harbor life.

"The planet has to be the right distance from the star so it's not too hot and not too cold that liquid water can exist," says Paul Butler of the Carnegie Institution of Washington. "And then the planet has to have the right surface gravity."

Butler spoke Wednesday afternoon at a news conference organized by the National Science Foundation, the organization that funded Butler's research. Astronomers have found hundreds of planets orbiting other stars in the past decade, but they have 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. But Butler has no direct evidence that Gliese 581-g actually has water.

"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 onto an atmosphere and to protect its liquid water on the surface," he says. "And of course, any subsequent discussion about life is purely speculative."

But then he couldn't resist speculating: "That being said, on the Earth, anywhere you find liquid water you find life in abundance."

A Solar System Like Our Own

There are six planets orbiting around star Gliese 581. And even if planet 581-g doesn't have life, Steven Vogt, a professor of astronomy and astrophysics at the University of California, Santa Cruz, says the solar system around Gliese 581 has an eerie resemblance to the one around our sun.

"It has an inner clutch of rocky, sort of terrestrial-like planets," he says. Those are planets like Mercury, Venus, Earth and Mars. "And then this sort of loner that's sitting on the outside, kind of like our Jupiter. But it's scaled down. This entire solar system would fit within our own Earth's orbit."

That's because Gliese 581 is a red dwarf — a pipsqueak of a star compared to our sun.

"If you think of the sun as a 100-watt light bulb, this is a 1-watt light bulb. It's like a Christmas tree light," says David Charbonneau, a planet hunter at the Harvard-Smithsonian Center for Astrophysics. "So to have the same temperature, a planet needs to be much closer to that star than it would be from the sun, where you'd have a temperature where you might have light and liquid water."

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.

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