Possible "habitable zone" planetary system discovered only 20 light years away

After more than four years of observations using the most successful low-mass-exoplanet hunter in the world, the HARPS spectrograph attached to the 3.6-metre ESO telescope at La Silla, Chile, astronomers have discovered in this system the lightest exoplanet found so far: Gliese 581 e (foreground) is only about twice the mass of our Earth. The Gliese 581 planetary system now has four known planets, with masses of about 1.9 (planet e, left in the foreground), 16 (planet b, nearest to the star), 5 (planet c, centre), and 7 Earth-masses (planet d, with the bluish color). The planet furthest out, Gliese 581 d, orbits its host star in 66.8 days, while Gliese 581 e completes its orbit in 3.15 days.

IMAGE: European Southern Observatory Click for larger image of this artist rendition. After more than four years of observations using the most successful low-mass-exoplanet hunter in the world, the HARPS spectrograph attached to the 3.6-metre ESO telescope at La Silla, Chile, astronomers have discovered in this system the lightest exoplanet found so far: Gliese 581 e (foreground) is only about twice the mass of our Earth. The Gliese 581 planetary system now has four known planets, with masses of about 1.9 (planet e, left in the foreground), 16 (planet b, nearest to the star), 5 (planet c, centre), and 7 Earth-masses (planet d, with the bluish color). The planet furthest out, Gliese 581 d, orbits its host star in 66.8 days, while Gliese 581 e completes its orbit in 3.15 days.

From RedOrbit and Science News Astronomers Discover Lightest Exoplanet Yet

Astronomers claim to have discovered an exoplanet that is the most similar to Earth in terms of mass than any previously discovered.

Found in the constellation Libra, the planet known as Gliese 581 represents about twice the mass of Earth.

Astronomers have previously identified some 300 exoplanets, but most are much larger than Earth.

“This is by far the smallest planet that’s ever been detected,” said Michael Mayor, from the Geneva Observatory, Switzerland.

“This is just one more step in the search for the twin of the Earth.

“At the beginning, we discovered Jupiter-like planets several hundred times the mass of the Earth; and now we have the sensitivity with new instruments to detect very small planets very close to that of the Earth,” he told BBC News.

Mayor worked alongside an international team of scientists who made the observation using the low-mass-exoplanet hunting device known as the HARPS spectrograph, which is attached to the 3.6 meter ESO telescope at La Silla, Chile.

“The holy grail of current exoplanet research is the detection of a rocky, Earth-like planet in the ‘habitable zone’ – a region around the host star with the right conditions for water to be liquid on a planet’s surface,” Mayor said in a statement.

“With only 1.9 Earth-masses, it is the least massive exoplanet ever detected and is, very likely, a rocky planet”, said co-author Xavier Bonfils from Grenoble Observatory.

Although the planet passes too close to its star for life to be possible, scientists claim that another planet in the system may be.

Previous observations using the HARPS showed that the host star was known to harbor a system with a Neptune-sized planet and two “super-Earths”.

Gliese 581 d was discovered two years ago with a mass of about seven times that of Earth. It orbits its parent star in 66.8 days, according to astronomers.

“Gliese 581 d is probably too massive to be made only of rocky material, but we can speculate that it is an icy planet that has migrated closer to the star,” said team member Stephane Udry.

“‘d’ could even be covered by a large and deep ocean – it is the first serious ‘water world’ candidate,” she added.

Sophisticated modern technology allows astronomers to observe exoplanets by studying the tiny wobble in star motion. The discovery of low-mass red dwarf stars like Gliese 581 adds potential of finding other low-mass exoplanets in the habitable zones, scientists said.

“With similar observing conditions an Earth-like planet located in the middle of the habitable zone of a red dwarf star could be detectable,” said Bonfils. “The hunt continues.”

“It is amazing to see how far we have come since we discovered the first exoplanet around a normal star in 1995 – the one around 51 Pegasi,” says Mayor. “The mass of Gliese 581 e is 80 times less than that of 51 Pegasi b. This is tremendous progress in just 14 years.”

The international team’s findings will be published in the journal Astronomy & Astrophysics.

From Science News:

“The object, a mere 20.5 light-years away, could be as tiny as 1.9 Earths and isn’t likely to exceed twice that amount.”

This diagram shows the position of the four planets in the Gliese 581 system. The newly found, innermost body is Gliese 581 e, the smallest exoplanet yet discovered. The habitable zone (blue region), where water could exist as a liquid, clearly includes the outermost planet, Gliese 581 d.

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Hell_is_like_newark

can humans survive in an environment with twice the g’s found on earth?

AKD

Does the headline need revision?
“Although the planet passes too close to its star for life to be possible, scientists claim that another planet in the system may be.”

Darell C. Phillips

I’d say it isn’t nearly as important that we found the possibility of life at Gliese 581as it is the possibility that they have found us… 8^)

IConrad

Umm… don’t you mean Gliese 581-c?

Leon Brozyna

Now all they need do is to see if they can find intelligent life on the third planet from our nearest star.

Stef

Only 20 light years?
Well, as soon as we defeat the laws of physics and create a faster than light space shuttle, maybe we can make the round trip in a decade or two?
A mass 7 times that of Earth. A nice bit of gravity on that baby then. I bet it attracts a few more extinction level asteroids than the Earth does.

Steven Horrobin

AKD-
I also found the title rather misleading. Still, a remarkable find!

Steven Horrobin

Stef-
During which time the earth will have aged significantly more than that, relativistically. Space travel is certainly much harder than used to be generally believed. Remember “Space 1999”?

Adam from Kansas

If they start finding habitable planets harboring civilized space-faring life like crazy then how long before it goes like in Star Wars and we see a Galactic Senate, or what if the galaxy already has a president named Beeblebrox?
Even though no life is found yet, what about the water world? Would be nice to draw it through a portal to irrigate and green up the deserts on Earth (if it ever becomes possible)?

Mike Bryant

This is really exciting.
In related news… The president has asked NASA to immediately dispatch a message to any space aliens who may be living on that planet.
Hey all you great individuals on the newly discovered planet,
First, I, as the President of one of the family of nations of Planet Earth, would like to go ahead and apologize to your entire population for anything we may have done to have offended you, like perhaps reruns of Gilligan’s Island. Also I would like to let you know that if you find yourselves here in America, be assured that you are entitled to the best education that unions can supply, AND food stamps and welfare. Do not ever worry that you may be putting us out, we have plenty of money and we are currently printing it as fast as we can.
Welcome to America!!
Don’t forget to vote!!!

Mike McMillan

Is there a vertical scale to the diagram?

David L. Hagen

Mike B.,
We have nothing to worry about: click

Mark T

As long as they get to see every episode of Single Female Lawyer, we should be OK. Wait, no, can’t happen since that hasn’t been 20 years yet. Maybe they’re watching something else.
Mark
PS: a Futurama joke.

George Patch

Clearly the Habitable zone must assume a certain % of Carbon Dioxide, because as we all know, plants must have a very precise CO2 content to be habitable.

Fernando

CO2 content ??????

Bobby Lane

Ah, hope springs eternal for a race of aliens we can meet, trade with, go to war against and perhaps go to bed with too. Every scientist’s holy grail? Every science-fiction geek’s holy grail then as well.

Pops

Send Al gore. After listening to him bloviating for five minutes there’s no way the inhabitants will ever think it worthwhile to warp over here and conquer what’s left of our little pile of smouldering ash.

Mike McMillan

Looking at the diagram, earth would be in the blue zone directly above the 1.0 AU mark, high on the chart. To have a habitable zone 0.1 AU away, the star would have to be about as bright (color temperature) as a low wattage incandescent light bulb. A Gliesian in the zone would have a dimmer sun that would still feel as warm on the skin (or scales) as our sun does.
It would be a very happy place, because Christmas would come every other month.

Darell C. Phillips

Someday, an expedition from Gliese 581will come to Earth. They will find no intelligent life but they will find evidence of our existence in the ruins of our cities. After a time they will decode the various languages on the signs that outlawed CO2 and wonder how we could have ever been so stupid. They will see plant life returning and pushing up through the concrete and asphalt, breaking it up into smaller and smaller pieces. The alien scientists will enter us into their equivalent of what we knew as the “Darwin Awards” and then make plans for colonization of the planet.
Wait a minute. Al Gore, James Hansen et al are probably the first wave of a plan hatched on Gliese 581to get us all to suffocate ourselves. There still may be time… 8^)

Would a planet of 1.9 Earth masses have doubled gravity? Is gravity that linear? I would think it would depend on the composition too.

Jim

“and now we have the sensitivity with new instruments…”
This was the subject of a graduate seminar I attended in 1976. The speaker was clearly frustrated by the lack of state of the art sensing devices available to the scientist. And the lack of a comprehensive effort to create better sensors.
His comment was something on the order of ‘ If scientists today could have the sensors that should have been available (ie. state-of-the-art) at the time, the advancement of science would have been a full ten years beyond what it was currently . But since very little efforts were being made to advance sensor technology…they were currently ten years behind. ‘
I believe his comments were right on the mark. Advancement in sensor technology has worked wonders in some cases…like the extended capabilities of the Hubble telescope. But it has made life miserable for others…like pollutant control. I remember when PCB limits were controlled down to ~1ppm in the early 70’s because that was about the limit of convenient detection. By the early 90’s that limit had dropped to ~10ppb. the science at the time did not confirm that the danger levels were just as significant at a level of 100 times lower, but the new instrumentation/detection methods were that much better. Today those levels are approaching 10ppt and there is some talk about lowering the allowable limits of PPB levels even lower…
Jim

hereticfringe

“can humans survive in an environment with twice the g’s found on earth?”
Only the skinny ones…

George E. Smith

What is this nonsense about wanting to find liquid water ? Don’t they know that to be habitable, planets need solid ice, and no carbon dioxide; liquid water is the last thing you would want on a habitable planet.
Somebody should tell NASA to update the data on this planet, and bring it more into line with computer simulations of what life is like.
George

Mike McMillan

Jeff Alberts (13:11:10) :
Would a planet of 1.9 Earth masses have doubled gravity? Is gravity that linear? I would think it would depend on the composition too.

With a larger planet, you have more mass, but someone on the surface is farther away from the additional mass, so probably not doubled.
It would indeed depend on density, but here again, Earth with its iron core is a dense planet so that argues against double gravity.

MC

Before we all get to excited, these guys have to determine the CO2 content of the atmosphere so’s we can determine the global warming coeficient of 581. Then we can get this over to Hansen and Gore and turn all the developmental authority to them. They may want to roll into the new CO2 cap and trade legislation an additional fee for CO2 sequestration on this planet. God forbid we miss this chance to save this planet. So when this planet goes to hell in a handbasket 581 will be just right for humans and we can move on over there.
Damn!!! Gore and Hansen are are one awesome couple of guys HUH!!!!

Wondering Aloud

Jeff Alberts (13:11:10) :
“Would a planet of 1.9 Earth masses have doubled gravity? Is gravity that linear? I would think it would depend on the composition too.”
Assuming you were not being tongue in cheek.
No, gravity at the surface is proportional to the mass but inversely proportional to the square of the radius. If it has a mass equal to 1.9 times the earth it is likely also larger. Unless it is much denser than the Earth which seems unlikely it is unlikely to have anywhere near 2 times the surface gravity of the Earth. We would have to know radius to know the acceleration of gravity there.

timbrom

Pops
On the other hand, they may decide to come over and stick it to us good so that we don’t send any more like him!

John Galt

It’s amazing how many things had to fall in place for advanced life on earth to be possible.
Here’s but a few things:
_ A strong magnetic field – made possible by our molten metal core.
_ A large moon that helps shield the planet from comets and asteroids.
_ The correct mixture of various elements.
_ An orbit that puts the planet inside the habitable zone.
_ A relatively stable sun.
The list goes on and on. I find it fascinating that all metals on earth came from a star that went supernova billions of years ago.
The 64 dollar question remains — how typical or atypical is our planet?

Trevor

Correct there Wondering Aloud. Remember, the moon only has about 1/81 the mass of the Earth but it’s gravity is about 1/6 of the earths. A planet with 1.9 x EM would probably have a gravity at the surface of 1.2-1.6 Earth gravity but depends on the density of its composition and the radius. Probably quite ok as far as gravity goes. I would think that the 20 light years poses more of a problem than any extra gravity such a planet might have.

Chris H

Double the mass means double the gravity at the same distance. But since more mass means a larger planet, the surface will be at a greater distance, reducing the gravity. We can calculate exactly how much gravity is reduced:
Assuming the average density is unchanged, twice the mass means twice the volume. Volume of a sphere is proportional to the cube of the radius (i.e. the radius raised to the power of 3). Therefore the radius is proportional the cube root of the volume (i.e. the volume raised to the power of a 1/3). Hence 2 times the volume means the radius is multiplied by the cube root of 2 (i.e. 2 raise to the power of a 1/3). My calculator says this is about 1.26 . So the twice the volume means a radius that is 1.26 times larger.
With the surface being 1.26 times further away, and knowing that gravity is inversely proportional to the square of the distance (Newton), we can say that the gravity will be reduced by the square of 1.26 (i.e. 1.26 to the power of 2). Which my calculator says is about 1.59 .
So that doubled gravity will be reduced at the surface by 1.59 times. 2 divided by 1.59 is about 1.26 .
Finally, assuming the same density as the Earth (a big assumption, but hopefully in the right ballpark), we can say that twice the mass of the Earth means it’s surface gravity will be about 1.26 times as large as the Earth’s.
(I now await corrects for some horrendous mistake, since I have only worked this out verbally, rather than on paper.)
P.S. I think all of this maths simplifies to raising 2 to the power of 1/3 . So you can easily do it for masses other than 2 times that of the Earth.

Tina

I was also confused by the title.
Gliese 581 e is not in the habitable zone and it was the planet discovered today.
Gliese 581 d is the only planet in the system (yet discovered) that is clearly in the Habitable Zone. And it was discovered 2 years ago.
The rest of your article is accurate, so please update your title so that it can be accurate too. Thank you.

Ray

If we find a Twin-Earth, I hope there is not a Twin-Gore-Hensen-Mann on it.
There are lots of people with more than double of my weight and they can still walk and lift things. So, a subtantial increase of gravity should not be a problem once used to it. The only problem would be that we would not be able to dunk a basketball.
But a planet with a 1.9 G would certainly have a denser atmosphere at it’s surface, thus increasing the atmosphere/surface temperature significantly. Would that be cold enough to permit liquid water? Or even permit the binding/function of proteins and other living molecules? I have serious reservations on that one.

Burch Seymour

OT – but this is a new thread so as an FYI AW, in case this warrants a thread of its own. The gist is that the ozone hole is delaying the action of CO2, which is why the Antarctic ice has increased. Excuses, excuses…
http://www.rdmag.com/ShowPR.aspx?PUBCODE=014&ACCT=1400000100&ISSUE=0904&RELTYPE=PSC&PRODCODE=00000000&PRODLETT=G&CommonCount=0

Fraizer Smith

> If they start finding habitable planets harboring civilized
> space-faring life like crazy then how long before it goes
> like in Star Wars and we see a Galactic Senate, or what if
> the galaxy already has a president named Beeblebrox?
Yeah, then they’ll form the intergalactic panel on space climate change (IGPSCC), blame dark matter, say the debate is over.
They will claim that polaris is threatened because of the ever increasing amount of dark matter in the universe which is causing the universe to expand at an ever increasing rate. In fact, it is expanding faster than the models predicted.
They will declare that dark matter is a danger to the public and summarily decide to tax half the systems in the galaxy out of existance.

Ray

Bruce Hall (14:47:19) :
The main test of intelligent life is to be intelligent enough to not make tools to kill each other and/or destroy their planet. We have a long way to go to call ourselves intelligent.

Chris H

@Ray
That may also explain why we have not detected any intelligent life (and in fact explain why all habitable planets in the galaxy have not already been colonised by an intelligent alien race). i.e. Before any “intelligent” species becomes too intelligent, it wipes itself with weapons of mass-destruction (or else searching for the Higgs Boson before they colonise other planets & accidentally get their home planet consumed by a ‘micro’ black hole).

Chris H

wipes itself = wipes itself out

Chris D.

The new Kepler orbiting telescope ought to bring a host of new discoveries and ought to be fascinating to watch it all unfold. I’m getting the feeling that suns lacking at least one planet will turn out to be more of an exception than the rule.

Chris H

Follow-up to my previous post on gravity & mass:
We know the Moon has 1/6th the surface gravity of the Earth. Using my final equation (raising mass to the power of 1/3), I can reverse that to say 1/6th the gravity means the mass is (1/6) raised to the power of 3, which is about 0.0046 of the mass (or 1/216 if you prefer). Thus if the Moon has the same density as the Earth (probably not too far off given it was once part of the Earth’s mantle) then the Moon should have 216 times less mass than the Earth.
Google says the Moon is actually 83 times less mass than the Earth, so my calculation is 2.6 times out. Not TOO bad, all assumptions considered!

George E. Smith

“”” Jeff Alberts (13:11:10) :
Would a planet of 1.9 Earth masses have doubled gravity? Is gravity that linear? I would think it would depend on the composition too. “””
A uniform earthlike planet that was twice the mass, would be cube root of two times the diameter, so m/r^2 would be 2/2^2/3 = 2^1/3 = 1.26 times the surface gravity.
But if it is not uniform density throughout, then all bets are off and it would be different; my guess assuming a denser core is that it would then be bigger than cube root of 2 times, so gravity would be less.
So that waould say 1.26 is the maximum gravity a 2x mass planet would have.
George

George E. Smith

Remember the key words “earth like”; so presumably it isn’t a solid Uranium sphere, which would have higher gravity, but be smaller.

George E. Smith

“”” Ray (15:06:30) :
Bruce Hall (14:47:19) :
The main test of intelligent life is to be intelligent enough to not make tools to kill each other and/or destroy their planet. We have a long way to go to call ourselves intelligent. “”
Why would you expect to find intelligent life anywhere else.
The search for ET intelligent life is based on the false assumption that intelligence brings superior survivability.
In reality, Intelligence is just Mother Nature’s latest gimmic in the search for survival; and so far it looks like a loser.
So we’ve had maybe 1-200,000 years of “intelligent” life, but the dinosaurs survived for 140 million years just by being big and mean and ugly.
So humans send out a plaque with Pi to 27 decimal places on it to show how smart we are at geometry; but what if those intelligent aliens use Roman numerals; they wouldn’t know what to do with our hieroglyphics, and decimal number positional value system.
Remember, WE made up ALL of our mathematics out of whole cloth; so it has NO universal significance, and to assume that some other alien life form would get it, is simply not very intelligent.
Maybe one of these days we will get our first binary digit of actual observable data about intelligent life outside a thin shell of about +/- 15-20 km about mean sea level on planet earth; but until then; it’s pretty ho hum, and I don’t plan on hanging around for that one.
So we better get our s*** together, and solve OUR problems here on earth ourselves; because there isn’t anyone out there who is going to solve them for us.
George

Ray (15:06:30) :
I think tools have gotten us as far as we have.
And any tool can be used to kill – club, screwdriver, hammer, electric drill…

Chris H (14:45:35) :

Finally, assuming the same density as the Earth (a big assumption, but hopefully in the right ballpark), we can say that twice the mass of the Earth means it’s surface gravity will be about 1.26 times as large as the Earth’s.
(I now await corrects for some horrendous mistake, since I have only worked this out verbally, rather than on paper.)

I don’t have time to work this out myself, but I think you and George have the same right results. One thing I can add is that the period of a satellite orbiting close to the planet will have a period of about 90 minutes, just like Earth.
A long time ago I worked out the period of someone orbiting Deimos, and was using Earth’s density because I didn’t know of a better one. When I came up with 90 minutes, I played a bit more and discovered that density alone determines the low-body orbital period of a satellite. See http://wermenh.com/deimos.html for more details like why someone was orbiting Deimos (hint – he jumped).

George E. Smith (15:38:18) :

But if it is not uniform density throughout, then all bets are off and it would be different; my guess assuming a denser core is that it would then be bigger than cube root of 2 times, so gravity would be less.

Some non-uniformity is quite permissible. One of the few things I remember about such stuff is that a thin spherical shell of material of some density has a gravitational field outside of the shell exactly the same as an equivalent point mass at the center. (Inside the shell the field is zero.) So that means if the planet is nicely sorted, e.g. iron in the center, then silicates, then water, your first result is right.
Still pretty heavy, Mars’ 1/2 g sounds about right. A planet is a great place to evolve, a lousy place to thrive. I’m rather fond of O’Neill colonies, long spinning cylinders in Earth or Solar orbit.

Ray

Tom in Texas (15:58:49) :
Ray (15:06:30) :
I think tools have gotten us as far as we have.
And any tool can be used to kill – club, screwdriver, hammer, electric drill…
————–
But we are now building bigger clubs, bigger screwdrivers, bigger hammers, bigger electric drills… that can kill millions of people in one blow. We built bigger and better at it. So why stop there?
Like Cap. Kirk said, “All you need to do is say no to war.”

Robert Wood

Should I say “cool” or “hot stuff”!
It’s so hard to know these days.
Anyway, great!

Hmmm….
An earth-like planet with heavier gravity orbiting a red sun.
They should’ve named it “Krypton.”
Jor-El, call your office…