Could 'Goldilocks' planet be just right for life?
AP

By SETH BORENSTEIN, AP Science Writer Seth Borenstein, Ap Science Writer – Wed Sep 29, 7:19 pm ET

WASHINGTON – Astronomers say they have for the first time spotted aplanet beyond our own in what is sometimes called the Goldilocks zonefor life: Not too hot, not too cold. Juuuust right.

Not too far from its star, not too close. So it could contain liquidwater. The planet itself is neither too big nor too small for theproper surface, gravity and atmosphere.

It's just right. Just like Earth.

"This really is the first Goldilocks planet," said co-discoverer R. Paul Butler of the Carnegie Institution of Washington.

The new planet sits smack in the middle of what astronomers refer to asthe habitable zone, unlike any of the nearly 500 other planetsastronomers have found outside our solar system. And it is in ourgalactic neighborhood, suggesting that plenty of Earth-like planetscircle other stars.

Finding a planet that could potentially support life is a major step toward answering the timeless question: Are we alone?

Scientists have jumped the gun before on proclaiming that planetsoutside our solar system were habitable only to have them turn out tobe not quite so conducive to life. But this one is so clearly in theright zone that five outside astronomers told The Associated Press itseems to be the real thing.

"This is the first one I'm truly excited about," said Penn StateUniversity's Jim Kasting. He said this planet is a "pretty primecandidate" for harboring life.

Life on other planets doesn't mean E.T. Even a simple single-cellbacteria or the equivalent of shower mold would shake perceptions aboutthe uniqueness of life on Earth.

But there are still many unanswered questions about this strangeplanet. It is about three times the mass of Earth, slightly larger inwidth and much closer to its star — 14 million miles away versus 93million. It's so close to its version of the sun that it orbits every37 days. And it doesn't rotate much, so one side is almost alwaysbright, the other dark.

Temperatures can be as hot as 160 degrees or as frigid as 25 degreesbelow zero, but in between — in the land of constant sunrise — it wouldbe "shirt-sleeve weather," said co-discoverer Steven Vogt of theUniversity of California at Santa Cruz.

It's unknown whether water actually exists on the planet, and what kindof atmosphere it has. But because conditions are ideal for liquidwater, and because there always seems to be life on Earth where thereis water, Vogt believes "that chances for life on this planet are 100percent."

The astronomers' findings are being published in Astrophysical Journaland were announced by the National Science Foundation on Wednesday.

The planet circles a star called Gliese 581. It's about 120 trillionmiles away, so it would take several generations for a spaceship to getthere. It may seem like a long distance, but in the scheme of the vastuniverse, this planet is "like right in our face, right next door tous," Vogt said in an interview.

That close proximity and the way it was found so early in astronomers'search for habitable planets hints to scientists that planets likeEarth are probably not that rare.

Vogt and Butler ran some calculations, with giant fudge factors builtin, and figured that as much as one out of five to 10 stars in theuniverse have planets that are Earth-sized and in the habitable zone.

With an estimated 200 billion stars in the universe, that means maybe40 billion planets that have the potential for life, Vogt said.However, Ohio State University's Scott Gaudi cautioned that is toospeculative about how common these planets are.

Vogt and Butler used ground-based telescopes to track the star'sprecise movements over 11 years and watch for wobbles that indicateplanets are circling it. The newly discovered planet is actually thesixth found circling Gliese 581. Two looked promising for habitabilityfor a while, another turned out to be too hot and the fifth is likelytoo cold. This sixth one bracketed right in the sweet spot in between,Vogt said.

With the star designated "a," its sixth planet is called Gliese 581g.

"It's not a very interesting name and it's a beautiful planet," Vogtsaid. Unofficially, he's named it after his wife: "I call it Zarmina'sWorld."

The star Gliese 581 is a dwarf, about one-third the strength of oursun. Because of that, it can't be seen without a telescope from Earth,although it is in the Libra constellation, Vogt said.

But if you were standing on this new planet, you could easily see our sun, Butler said.

The low-energy dwarf star will live on for billions of years, muchlonger than our sun, he said. And that just increases the likelihood oflife developing on the planet, the discoverers said.

"It's pretty hard to stop life once you give it the right conditions," Vogt said.
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