# Earth-like exoplanet discovered a mere 20 light years away



## Proteus (Mar 5, 2010)

SPACE.com -- Odds of Life on Newfound Earth-Size Planet '100 Percent,' Astronomer Says

Odds of Life on Newfound Earth-Size Planet '100 Percent,' Astronomer Says
By Jeanna Bryner
LiveScience Managing Editor
posted: 29 September 2010
05:03 pm ET

This story was updated at 8:58 p.m. ET.

An Earth-size planet has been spotted orbiting a nearby star at a distance that would makes it not too hot and not too cold — comfortable enough for life to exist, researchers announced today (Sept. 29).

If confirmed, the exoplanet, named Gliese 581g, would be the first Earth-like world found residing in a star's habitable zone — a region where a planet's temperature could sustain liquid water on its surface. [Illustration of planet Gliese 581g.]

And the planet's discoverers are optimistic about the prospects for finding life there.

"Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say, my own personal feeling is that the chances of life on this planet are 100 percent," said Steven Vogt, a professor of astronomy and astrophysics at the University of California, Santa Cruz, during a press briefing today. "I have almost no doubt about it."

His colleague, Paul Butler of the Carnegie Institution of Washington, in Washington, D.C., wasn't willing to put a number on the odds of life, though he admitted he's optimistic.

"It's both an incremental and monumental discovery," Sara Seager, an astrophysicist at the Massachusetts Institute of Technology, told SPACE.com. Incremental because the method used to find Gliese 581g already has found several planets most of the known planets, both super-Earths, more massive than our own world outside their stars' habitable zone, along with non-Earth-like planets within the habitable zone.

"It really is monumental if you accept this as the first Earth-like planet ever found in the star's habitable zone," said Seager, who was not directly involved in the discovery.

Vogt, Butler and their colleagues will detail the planet finding in the Astrophysical Journal.

The newfound planet joins more than 400 other alien worlds known to date. Most are huge gas giants, though several are just a few times the mass of Earth.

Stellar tugs

Gliese 581g is one of two new worlds the team discovered orbiting the red dwarf star Gliese 581, bumping that nearby star's family of planets to six. The other newfound planet, Gliese 581f, is outside the habitable zone, researchers said.

The star is located 20 light-years from Earth in the constellation Libra. One light-year is about 6 trillion miles (10 trillion km).

Red dwarf stars are about 50 times dimmer than our sun. Since these stars are so much cooler, their planets can orbit much closer to them and still remain in the habitable zone.

Estimates suggest Gliese 581g is 0.15 astronomical units from its star, close enough to its star to be able to complete an orbit in just under 37 days. One astronomical unit is the average distance between the Earth and sun, which is approximately 93 million miles (150 million km).

The Gliese 581 planet system now vaguely resembles our own, with six worlds orbiting their star in nearly circular paths.

With support from the National Science Foundation and NASA, the scientists — members of the Lick-Carnegie Exoplanet Survey — collected 11 years of radial velocity data on the star. This method looks at a star's tiny movements due to the gravitational tug from orbiting bodies.

The subtle tugs let researchers estimate the planet's mass and orbital period, how long it takes to circle its star.

Gliese 581g has a mass three to four times Earth's, the researchers estimated. From the mass and estimated size, they said the world is probably a rocky planet with enough gravity to hold onto an atmosphere.

The planet is tidally locked to its star, so that one side basks in perpetual daylight, while the other side remains in darkness. This locked configuration helps to stabilize the planet's surface climate, Vogt said.

"Any emerging life forms would have a wide range of stable climates to choose from and to evolve around, depending on their longitude," Vogt said, suggesting that life forms that like it hot would just scoot toward the light side of that line while forms with polar-bear-like preferences would move toward the dark side.

Between blazing heat on the star-facing side and freezing cold on the dark side, the average surface temperature may range from 24 degrees below zero to 10 degrees Fahrenheit (minus 31 to minus 12 degrees Celsius), the researchers said.

Are you sure?

Supposedly habitable worlds have been found and later discredited, so what makes this one such a breakthrough?

There's still a chance that further observations will dismiss this planet, also. But over the years, the radial velocity method has become more precise, the researchers point out in their journal article.

In addition, the researchers didn't make some of the unrealistic assumptions made in the past, Seager said.

For instance, another planet orbiting Gliese 581 (the planet Gliese 581c) also had been considered to have temperatures suitable for life, but in making those calculations, the researchers had come up with an "unrealistic" estimate for the amount of energy the planet reflected, Seager pointed out. That type of estimate wasn't made for this discovery.

"We're looking at this one as basically the tip of the iceberg, and we're expecting more to be found," Seager said.

One way to make this a reality, according to study researchers, would be "to build dedicated 6- to 8-meter-class Automated Planet Finder telescopes, one in each hemisphere," they wrote.

The telescopes — or "light buckets" as Seager referred to them — would be dedicated to spying on the nearby stars thought to potentially host Earth-like planets in their habitable zones. The result would be inexpensive and probably would reveal many other nearby potentially habitable planets, the researchers wrote.

Beyond the roughly 100 nearest stars to Earth, there are billions upon billions of stars in the Milky Way, and with that in mind, the researchers suggest tens of billions of potentially habitable planets may exist, waiting to be found.

Planets like Gliese 581g that are tidally locked and orbit the habitable zone of red dwarfs have a high probability of harboring life, the researchers suggest.

Earth once supported harsh conditions, the researchers point out. And since red dwarfs are relatively "immortal" living hundreds of billions of years (many times the current age of the universe), combined with the fact that conditions stay so stable on a tidally locked planet, there's a good chance that if life were to get a toe-hold it would be able to adapt to those conditions and possibly take off, Butler said.
Editor's Note: This story has been updated to correct an error in the paragraph stating that Mercury is tidally locked to the sun. While astronomers once thought that was the case, they no longer do.


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## xezene (Aug 7, 2010)

Big, big news right here.


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## timeless (Mar 20, 2010)

They really should refrain from these kind of claims. It makes it look really bad when supposedly "earth-like" planets turn out to be nothing, which has happened plenty of times in the past. They don't even know if this planet could retain an atmosphere, so it's unreasonable to say there's a 100% probability that it could sustain life. These kinds of build ups and let downs increase people's skepticism in space programs, so it hurts way more in the long run.


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## susurration (Oct 22, 2009)

timeless said:


> They really should refrain from these kind of claims. It makes it look really bad when supposedly "earth-like" planets turn out to be nothing, which has happened plenty of times in the past. They don't even know if this planet could retain an atmosphere, so it's unreasonable to say there's a 100% probability that it could sustain life. These kinds of build ups and let downs increase people's skepticism in space programs, so it hurts way more in the long run.


The whole mechanism of science is degrees of probability. No scientist should (and they usually don't even though they don't directly say it; it's implied) ever claim anything they found was 100% certain. The closest we come to that is "highly likely to be evident". 

It's not really a let down to the scientific community if something hypothesised doesn't turn out to be quite true. You can learn just as much from being wrong, as you can from being confirmed. The public may be skeptical, but it's not up to the scientist to give the general public "what they want". The general public usually don't understand questions of certainty and probability. Cosmology in particular is a highly theoretical field. You have to be able to have a lot of understanding and appreciation of maths and probability to accept exploration in this field.


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## TreeBob (Oct 11, 2008)

If anything I think near misses and almost are what drive science. The closer they are the more they probably research. Everyone wants to be "the one" who finds it for certainty. It drives research and technology faster in my opinion.


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## timeless (Mar 20, 2010)

Nova said:


> The public may be skeptical, but it's not up to the scientist to give the general public "what they want". The general public usually don't understand questions of certainty and probability. Cosmology in particular is a highly theoretical field. You have to be able to have a lot of understanding and appreciation of maths and probability to accept exploration in this field.


Apparently Mr. 100% doesn't understand questions of certainty or probability either. Scientists choose to speak to journalists under their own free will, and if they consistently build up excitement and it drops out, then they might find themselves with a bit less funding next budget year.


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## xezene (Aug 7, 2010)

timeless said:


> Apparently Mr. 100% doesn't understand questions of certainty or probability either. Scientists choose to speak to journalists under their own free will, and if they consistently build up excitement and it drops out, then they might find themselves with a bit less funding next budget year.


He did make a bit of a misstep, but as this is an exciting discovery, we should try and remember that even scientists are human!


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## Lucem (Dec 2, 2009)

xezene said:


> He did make a bit of a misstep, but as this is an exciting discovery, we should try and remember that even *scientists are human!*


**gasp** _Who told you?!_


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## susurration (Oct 22, 2009)

timeless said:


> Apparently Mr. 100% doesn't understand questions of certainty or probability either. Scientists choose to speak to journalists under their own free will, and if they consistently build up excitement and it drops out, then they might find themselves with a bit less funding next budget year.


Well obtaining funding is a bit more of a complex process... . When I talk about certainty, I talk of certainty of actual findings, rather than certainty in a prediction hypothesised.

scientist + ego = :dry:



xezene said:


> He did make a bit of a misstep, but as this is an exciting discovery, we should try and remember that even scientists are human!


No way, everybody knows they are aliens plotting to take over the universe!!!!! evils all of dem! *boo* *hiss* etc etc


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## Promethea (Aug 24, 2009)

Exciting find, prot. Thx for posting. roud:


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## Red Panda (Aug 18, 2010)

timeless said:


> Apparently Mr. 100% doesn't understand questions of certainty or probability either. Scientists choose to speak to journalists under their own free will, and if they consistently build up excitement and it drops out, then they might find themselves with a bit less funding next budget year.


He did say "I have _almost_ no doubt about it."

The whole point is that this planet is the first exoplanet they found in the habitable zone of the system, just like earth is the only one in ours and it has life.


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## sarek (May 20, 2010)

This has been a while in coming. Of course, it is more of a confirmation. The odds in favour of such planets existing in large numbers are simply so overwhelming that if they were not there something in the theories must be badly wrong.

As for this particular planet. I have heard a lot of astronomers about this. But I would like to hear the opinion of an exobiologist on the matter. 

Do I understand correctly that there is little or no axial rotation? So the same side of the planet is always towards its sun. That might have an impact on atmospheric dynamics and weather systems.

Perhaps the magnetic field of the planet is also affected, depriving it of protection against radiation from the sun.

And are there major planets elsewhere in the system? If there are not, this poor planet may be suffering regular bombardments by meteors.


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## LostInMyOwnMind (May 5, 2010)

Interesting find indeed.

I guess this would answer the speculation about how much the tidal effect of the moon and our 24 hour day played in the development of life, assuming there is life there. Seems like a pretty big leap of faith.

Point your tin foil hats toward Libra boys and girls.


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## 3053 (Oct 14, 2009)

Was that not discovered last year?


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## Black Rabbit (Apr 15, 2010)

If/when they confirm life on this plant, I would be interested to see how the religious community will react. Probably a la Insane Clown Posse.

Fucking magic.


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## MachinegunDojo (Dec 27, 2009)

BellamysSocket said:


> Was that not discovered last year?


Not this, Gleise 581 simply gets a lot of press as several planets have been found in it's system.


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## 3053 (Oct 14, 2009)

MachinegunDojo said:


> Not this, Gleise 581 simply gets a lot of press as several planets have been found in it's system.


Ohhh right I must be thinking of 581c


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## DarklyValentine (Mar 4, 2010)

in a known universe scattered with 10^24 star thingies
(latest estimate)unlike long begotten times...well not too far back as all em olde civilisation spoke of it - usually in tongues
Planet urtths will9are common place)

If they are peering me at now I am soo not picking my nose ( continuity my ) followers)

I think thats 1 in 500 for earth like planets - dosnt neceesay mean of those 500 they have looked at

Wiicked you need to max this window and correct typos


But I believe in a vast known universe you are saying you expect this to be common place


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## Alaya (Nov 11, 2009)

Can't wait for the time to come and make war with whomever lives in such a planet.:dry:


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