Study: At least one in six stars has an Earth-sized planet

Jan 07, 2013
This artist's illustration represents the variety of planets being detected by NASA's Kepler spacecraft. A new analysis has determined the frequencies of planets of all sizes, from Earths up to gas giants. Key findings include the fact that one in six stars hosts an Earth-sized planet in an orbit of 85 days or less, and that almost all sun-like stars have a planetary system of some sort. Credit: C. Pulliam & D. Aguilar (CfA)

(Phys.org)—The quest for a twin Earth is heating up. Using NASA's Kepler spacecraft, astronomers are beginning to find Earth-sized planets orbiting distant stars. A new analysis of Kepler data shows that about 17 percent of stars have an Earth-sized planet in an orbit closer than Mercury. Since the Milky Way has about 100 billion stars, there are at least 17 billion Earth-sized worlds out there.

Francois Fressin, of the Harvard-Smithsonian Center for Astrophysics (CfA), presented the analysis today in a press conference at a meeting of the in Long Beach, Calif. A paper detailing the research has been accepted for publication in The .

detects planetary candidates using the transit method, watching for a planet to cross its star and create a mini-eclipse that dims the star slightly. The first 16 months of the survey identified about 2,400 candidates. then asked, how many of those signals are real, and how many planets did Kepler miss?

By simulating the Kepler survey, Fressin and his colleagues were able to correct both the impurity and the incompleteness of this list of candidates to recover the true occurrence of planets orbiting other , down to the size of Earth.

A new analysis examined the frequencies of planets of different sizes based on findings from NASA's Kepler spacecraft, correcting for both incompleteness and false positives. The results show that one in six stars has an Earth-sized planet in a tight orbit. About a fourth of all stars in the Milky Way have a super-Earth, and the same fraction have a mini-Neptune. Only about 3 percent of stars have a large Neptune, and only 5 percent a gas giant at the orbital distances studied. Credit: F. Fressin (CfA)

"There is a list of astrophysical configurations that can mimic planet signals, but altogether, they can only account for one-tenth of the huge number of Kepler candidates. All the other signals are bona-fide planets," says Fressin.

Most sun-like stars have planets

Altogether, the researchers found that 50 percent of stars have a planet of Earth-size or larger in a close orbit. By adding larger planets, which have been detected in wider orbits up to the orbital distance of the Earth, this number reaches 70 percent.

Extrapolating from Kepler's currently ongoing observations and results from other detection techniques, it looks like practically all Sun-like stars have planets.

The team then grouped planets into five different sizes. They found that 17 percent of stars have a planet 0.8 - 1.25 times the size of Earth in an orbit of 85 days or less. About one-fourth of stars have a super-Earth (1.25 - 2 times the size of Earth) in an orbit of 150 days or less. (Larger planets can be detected at greater distances more easily.) The same fraction of stars has a mini-Neptune (2 - 4 times Earth) in orbits up to 250 days long.

Larger planets are much less common. Only about 3 percent of stars have a large Neptune (4 - 6 times Earth), and only 5 percent of stars have a gas giant (6 - 22 times Earth) in an of 400 days or less.

Earth-size planets common in galaxy
The fraction of sun-like stars having planets of different sizes, orbiting within 1/4 of the Earth-sun distance (0.25 AU) of the host star. The graph shows that planets as small as Earth (far left) are relatively common compared to planets 8.0x the size of Earth (similar to Jupiter). For example, 7.9 percent of sun-like stars harbor a planet with a size of 1.0-1.4 times the size of Earth, orbiting inward of 1/4 the Earth-sun distance (closer than Mercury's distance from the sun). There are increasing numbers of planets from 8x the size of Earth down to 2.8x Earth. Remarkably, the number of planets smaller than 2.8x Earth is approximately constant with planet size, down to the size of our Earth. The gray indicates the planets discovered in this study, and the orange represents the correction applied to account for planets the TERRA software would miss statistically, typically about 20 percent. Credit: Erik Petigura, Andrew Howard and Geoff Marcy

Smaller planets aren't picky

The researchers also asked whether certain sizes of planets are more or less common around certain types of stars. They found that for every planet size except gas giants, the type of star doesn't matter. Neptunes are found just as frequently around red dwarfs as they are around sun-like stars. The same is true for smaller worlds. This contradicts previous findings.

"Earths and super-Earths aren't picky. We're finding them in all kinds of neighborhoods," says co-author Guillermo Torres of the CfA.

Planets closer to their stars are easier to find because they transit more frequently. As more data are gathered, planets in larger orbits will come to light. In particular, Kepler's extended mission should allow it to spot Earth-sized planets at greater distances, including Earth-like orbits in the habitable zone.

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User comments : 42

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Jeweller
1.6 / 5 (14) Jan 07, 2013
If there are billions of planets in the milky way, then why are there no aliens ?
antialias_physorg
4.5 / 5 (17) Jan 07, 2013
Who says there aren't?
dogbert
2.6 / 5 (14) Jan 07, 2013
Jeweller,
If there are billions of planets in the milky way, then why are there no aliens ?


There is currently no evidence that any solar system but this one has life. A multitude of planets does not equal a multitude of life bearing planets.
LariAnn
4.4 / 5 (14) Jan 07, 2013
If there are billions of planets in the milky way, then why are there no aliens ?


The aliens have been asking the same question!
javjav
4.6 / 5 (17) Jan 07, 2013
There is currently no evidence that any solar system but this one has life.

There is currently no evidence that a solar system without life exists.
antialias_physorg
4.7 / 5 (15) Jan 07, 2013

There is currently no evidence that any solar system but this one has life.

That's a statement that contains no information whatsoever. We don't really have the ability to detect life in any other solar system - so OF COURSE have we not found any. You're like a blind man that claims to know: "There is nothing to see. For anyone. Ever."

(we haven't even looked with anything but a very cursory glance at places in our OWN solar system, BTW.)

A multitude of planets does not equal a multitude of life bearing planets.

True. But until we have the ability to detect life there's no sense in making statements one way or the other.
dogbert
2.6 / 5 (16) Jan 07, 2013
A multitude of planets does not equal a multitude of life bearing planets.


True. But until we have the ability to detect life there's no sense in making statements one way or the other.


Which is why I pointed out that there is no reason to assume that life exists anywhere but here. A multitude of planets means noting in relation to life until/unless we discover life elsewhere.
TheGhostofOtto1923
1.7 / 5 (18) Jan 07, 2013
That's a statement that contains no information whatsoever. We don't really have the ability to detect life in any other solar system - so OF COURSE have we not found any. You're like a blind man that claims to know: "There is nothing to see. For anyone. Ever."
Sure we do. SETI has been looking for life for some time now. Just one example.
RitchieGuy01
1.8 / 5 (15) Jan 07, 2013
Wrong Otto darling. SETI has been looking for SIGNALS that might indicate life. But even signals don't always mean life just because It's a steady signal. The only way to know for sure, sweetums, is to send probes to a planet and look for the evidence of life.
That's like I have evidence of sorghum growing on my (former) land. But I don't know if it's growing 2 miles away unless I go there, my precious cockman.
RitchieGuy01
Jan 07, 2013
This comment has been removed by a moderator.
antialias_physorg
3.7 / 5 (7) Jan 07, 2013
SETI has been looking for life for some time now.

And I still think that looking for EM signals from aliens is sort of pointless.

- Sending EM signals is pointless (time lag and energy requirements makes sending communication probes much more sensible if one has even near light speed capabilities)
- If someone were so pointless as to use them for communication they'd use directed signals (so they'd pass us by)
- No one would be stupid enough to set up an omnidirectional beacon if they didn't know what was out there.
- Anything beyond a dedicated beacon would be of such low intensity that it isn't detectable at this distance
- Given the advances in communication technologies its not unreasonable to think we may be listening in on an entirely wrong medium. There may be something that is faster/more 'natural' to use (gravity waves?)

It's a nice try - but I don't think that it's particularly productive/promising in terms of finding aliens.
antialias_physorg
5 / 5 (5) Jan 07, 2013

Which is why I pointed out that there is no reason to assume that life exists anywhere but here.

There's no reason to assume anything with no datapoints.

Saying there is a lot of life out there is as unfounded as saying there is no life out there.

We DO know that life is possible. So there's at least that. But one datapoint is no foundation for any kind of prognosis.
javjav
5 / 5 (7) Jan 07, 2013
SETI has been looking for life
SETI has not been looking for "life", they have been looking for "Intelligent life", and only for nearby planets that could be sending extremely powerful radio signals in our direction over the last years... there is a difference.
The only way to know for sure, sweetums, is to send probes to a planet

If it happens anytime soon, I think the good news will probably come trough future giant telescopes rather from interstellar probes. Only the first method is close to be possible (although extremely expensive) and it could study thousands of planets, not just one star. Maybe a probe could follow much later, to study alien life in more detail. But just guessing.
Etreum
3 / 5 (10) Jan 07, 2013
I can assure you all, that this universe is full of life.
Tausch
3.9 / 5 (7) Jan 07, 2013
Fast forward the physorg commentary to thirty years from now:
"There must be a star without a planet!"

'Life' will have a new definition thirty years from now too.
seb
3.4 / 5 (5) Jan 08, 2013
We'll find other life.. because we'll look for it, it'll be there
FMM
3 / 5 (1) Jan 08, 2013
I doubt that we will ever find much out there except maybe some interesting chemistry. Still, that will prove nothing. The universe is damn big.
Kedas
1.5 / 5 (4) Jan 08, 2013
The more environments out there supporting Intelligent life and we can't find them the higher the chance that we will destroy ourselves or go black shortly (to protect).
ShotmanMaslo
3.7 / 5 (6) Jan 08, 2013
The universe is so vast that even if there are millions of planets with life, there may not be more than one in our galactic neighbourhood. I am very sure there is life out there, intelligent life, however finding it is another matter entirely, and it may not even be possible. Lets hope thats not the case.
jsdarkdestruction
2.3 / 5 (3) Jan 08, 2013
I agree, it is highly likely that intelligent life is out there but our odds of finding them for now might be beyond our reach imo, for the time being i think the only possibility(a very very very remote one but its possible still) would be them stumbling upon us. who knows though, the advances that have been made in the last 200 years are almost beyond belief, we've come a very long way, so who knows what we might be capable if in hundreds of years in the future.
TheGhostofOtto1923
1.5 / 5 (15) Jan 08, 2013
SETI has not been looking for "life", they have been looking for "Intelligent life", and only for nearby planets that could be sending extremely powerful radio signals in our direction over the last years... there is a difference.
Sorry, the distinction was not made. If SETI finds intelligent life it will have found life. Yes?
And I still think that looking for EM signals from aliens is sort of pointless.
But many others, with money to spend, do not. I wonder why?
Soylent_Grin
5 / 5 (4) Jan 08, 2013
Our first radio broadcasts happened about a hundred years ago. Now, because of newer and better digital technology, nobody broadcasts anymore. Our planet had a hundred year burst of noise, then went silent; civilisation is still intact though.
If other civilisations out there follow the same pattern, there would be a *very* narrow window to hear them. Hearing nothing does not mean they aren't there. We are still here, after all.
Soylent_Grin
4 / 5 (4) Jan 08, 2013
Perhaps also, the intelligences that are out there are waiting for us to give birth to one they would recognize. If we are just the meat cocoon for the rise of AI, why would they bother to talk to us yet?
TheGhostofOtto1923
1.3 / 5 (15) Jan 08, 2013
- Anything beyond a dedicated beacon would be of such low intensity that it isn't detectable at this distance
"In 1974, a largely symbolic attempt was made at the Arecibo Observatory to send a message to other worlds. It was sent towards the globular star cluster M13, which is 25,000 light years from Earth. The first Interstellar Radio Message (IRM), the "Arecibo Message", was transmitted in Nov, 1974 from Arecibo Radar Telescope. Further IRMs Cosmic Call, Teen Age Message, Cosmic Call 2, and A Message From Earth were transmitted in 1999, 2001, 2003 and 2008 from Evpatoria Planetary Radar.
Additional information on messages sent outward from Earth at: Communication with Extraterrestrial Intelligence, Active SETI, List of interstellar radio messages."

-Perhaps there are other wasteful dreamers out there as well who like generating PR for young students.
TheGhostofOtto1923
1.3 / 5 (15) Jan 08, 2013
Perhaps also, the intelligences that are out there are waiting for us to give birth to one they would recognize. If we are just the meat cocoon for the rise of AI, why would they bother to talk to us yet?
Perhaps AI is rare and valuable to machine life, who like to know what is going on elsewhere and need to share info. Perhaps interstellar travel and seeding is impractical. Perhaps, once machine life singularities emerge they evaporate, finding no reason to perpetuate themselves.
Torbjorn_Larsson_OM
5 / 5 (3) Jan 08, 2013
This is the lower limit of course. The average is perhaps 1-2 oom larger, considering that Kepler should see ~ 300 Earths if it looked at 100 000 Suns (or some other planet but most often one at a time due to misalignement). But statistics on the arxiv shows that Kepler's datapipeline has ~ 18 000 planets at ~ 11 000 stars @ 98 % accuracy as "candidates for candidates".

So each system may have at least one Earth sized on average.

@ Jeweller, dogbert: Fermi's question is too little constrained to be meaningful. There are radio silent pathways.

The more interesting question is if there is life elsewhere. All the necessary properties are there now, and the speed with which life arose on Earth shows that abiogenesis is so easy and/or enough frequently attempted that it will happen within a few billion years.

More recently, thermodynamics shows that RNA replicators are forced to crystallize in solution same as salt crystals in a drying salt lake. This will happen in < 30 000 years.
Koblog
2.7 / 5 (7) Jan 08, 2013
Big News. Many stars have earth-sized planets. Heck, OUR star has two earth-sized planets, but would you like to survive on Venus?

Face it, Earth is one special place.
lengould100
3 / 5 (2) Jan 08, 2013
" only 5 percent of stars have a gas giant (6 - 22 times Earth) " That may be bad news. From other sources, a large Jupiter in a fairly near outer orbit acts as a great protector for development of life, sweeping up damaging asteroids. Of course that source may have been in error, since it would seem (to me) that it would be preferrable to allow the asteroid belt to coalesce into a stable planet rather than hanging about making our system a shooting gallery.

There may be a great many more factors than even Drake imagined.
Ray Van Dune
2.8 / 5 (4) Jan 08, 2013
"If there are billions of planets in the milky way, then why are there no aliens?"

This is basically an informal restatement of the "Fermi Paradox" that: 1) rather simple math shows that if there were any intelligent life in the galaxy, it would have had ample time to colonize the whole thing 100 times over since the formation of the galaxy, and 2) yet we see no evidence of them.

A paradox consists of a PAIR of statements that are BOTH perceived to be true, but conflict with each other. The resolution of the paradox typically involves the finding that one of the "true" statements is actually NOT true.

There is a widespread assumption that only the first statement of the Fermi paradox may be untrue, while the second is taken as established fact beyond question.

That should be a red flag to any independent thinker. I think I know which Fermi statement is actually false, and it is not the one based on logic and mathematics: it is the one that is based on peer pressure and fear.
antialias_physorg
2.5 / 5 (2) Jan 09, 2013
This is basically an informal restatement of the "Fermi Paradox"

...which leaves out all kinds of issues that can skew the result.
Both statements can be false.

- If a species goes beyond its own world then it has the ability to live in environments other than the one it evolved in (because that is simpler to achieve than terraforming/gravity-forming of other planets) - at that point 'colonization' of other planets makes no sense because there's really no reason why one would ever go down to live on a planet.

- A species that can adapt itself is arguably near-immortal. Near-immortality, however, confers an entirely different level of risk aversion (physiological persistence still does not mean one is invulberable to accident/attack. So while 'natural' causes are eliminated 'unnatural' causes then make up near 100% of all fatalities).
Planets and solar systems in general are, from a very long living species' point of view, intolerably unsafe places.
antialias_physorg
1 / 5 (1) Jan 09, 2013
I can see a number of reasons why we see no evidence, too:

- Evidence can only be seen if there is waste (wasted radiation from undirected communications or 'city lights' or somesuch). If all their used energy goes where it's supposed to (i.e. doing the work it's supposed to) then none of it will escape to be detected by others. It seems reasonable to me that the more advanced a species is the less such waste it would produce.

HUMANS are already optimizing in that regard for chrissakes.

- An adaptable species (as noted in my last post) would also not require lights (or even cities or other megastructures. What do you need a roof over your head if the environment isn't a factor in your level of comfort? Would you even lug around a body beyond the bare minimum?)

- Or advanced species may take pains not to be noticed. THEY surely would know we're here.
Birdwatchers make sure the birds don't see them in order not to alter their behavior.
Mumrah
1 / 5 (1) Jan 09, 2013
"If there are billions of planets in the milky way, then why are there no aliens?"

This is basically an informal restatement of the "Fermi Paradox" that: 1) rather simple math shows that There is a widespread assumption that only the first statement of the Fermi paradox may be untrue, while the second is taken as established fact beyond question.


I'd second that. I find it telling that the possibility that the second statement is false typically isn't even considered as a potential theoretical resolution to the paradox (e.g. http://en.wikiped...etically ).

It seems to me that the proposal that 'They do exists, but evidence of such is ignored and/or suppressed' is consistent with all known facts but sadly nobody wants to go down that rabbit hole.
Tausch
1 / 5 (1) Jan 09, 2013
@AA
I believe your last two paragraphs infers that material science is not the answer (nor ever will be the solution) to examine the universe.

There is a way around this.
antialias_physorg
1 / 5 (1) Jan 09, 2013
I believe your last two paragraphs infers that material science is not the answer (nor ever will be the solution) to examine the universe.

As opposed to?

Material sciences are there to give us workeable/useful knowledge. For that it is (and will) be good.

If you're looking for ultimate 'truth' then that is not part of science. Ultimate truth is a contradiction in itself - or a tautology, depending on how you want to look at it.
In either case it is something that does not constitute information. and science only deals with what can be termed knowledge (i.e. anything that carries information)

Science will get us (the spcies) through the day (the lifetime of the universe - or at least that section of it where intelligences are viable).
Philosophy? Not so much.

There is a way around this.

You had a few hundred characters left to explain. I'm guessing you just say that without actually being able to back it up, correct? I call: "BS"
Tausch
1 / 5 (1) Jan 09, 2013
Something is wrong with our definition of life. A search that finds one data point says the search is flawed.

Call B.S. It's o.k.

I wrote you a few hundred characters in reply. The reply was erased when removing disallowed scripts for this site.

To reconstruct the reply word for word from memory takes over an hour for me. If you are still interested I will recall this word for word.
TheGhostofOtto1923
1 / 5 (13) Jan 09, 2013
science only deals with what can be termed knowledge (i.e. anything that carries information)
And, as that is all there is in the universe, then science and only science is capable of examining all of it.
Something is wrong with our definition of life.
Life includes machine life which is the inevitable successor to organic life. Life can be designed to function better than life itself.

In other words, intelligent design (by sentient beings that is) can do better than nature has done. Because sentients can examine life and make changes far faster than evolution can. Sentients can devise non-organic systems whose function and durability can far exceed what nature has produced. We are doing this already. This IS what technology IS.

And as this Process is Inevitable, we can assume that the universe is populated by post-organic machine singularities which are interested only in communicating amongst themselves. And so the universe appears silent to us.
TheGhostofOtto1923
1 / 5 (12) Jan 09, 2013
Obviously.
Modernmystic
4 / 5 (4) Jan 09, 2013
What does this have to do with anything? Earth sized doesn't mean habitable or even life bearing.

It's one miniscule blip of a variable amongst many that must be satisfied for life as we know it to develop via abiogenesis as we understand it. It's one of VERY many that must be satisfied to develop multicellular complex intelligent technological civilization as we understand that process.

It's like saying at least one in six solar systems contain water....
antialias_physorg
1 / 5 (1) Jan 09, 2013
A search that finds one data point says the search is flawed.

As opposed to what? A search that finds no datapoints? Or a search that finds many?

(Hint: A search that finds many ALWAYS starts with one - the first found - datapoint.)

The reply was erased when removing disallowed scripts for this site.

This sounds like you just haven't got anything but now are trying to 'sound smart' in retrospect (oh, my - what a laugh. You're WAY too late for that one, Hush1)

So try to recall those 1000 letters that 'took you over an hour' (you have some disability that allows you to type only one character every 4 seconds?).

Please. Do. I haven't laughed so long and hard in a loooong time.
Tausch
1 / 5 (1) Jan 09, 2013
A summary. Instead of word for word.

Material sciences are there to give us workeable/useful knowledge. For that it is (and will) be good.- AP

Information theoretical sciences give us workable/useful knowledge.

Ultimate truth is a contradiction in itself - or a tautology, depending on how you want to look at it. In either case it is something that does not constitute information. and science only deals with what can be termed knowledge (i.e. anything that carries information)-AP


I disagree. Our language is not infallible (exact). When we use labels and words leading to inconsistencies and contradictions we learn to avoid such language, vocabulary and words.

I will assert that this is something that constitutes information.

If assuming gravitation waves, for example, exist and further assuming that such are carriers of information, then asserting such can be represented by the material sciences is incorrect.

Heliocentric and geocentric approaches are not B.S.
cont.

Tausch
1 / 5 (2) Jan 09, 2013
Cont...

One is intractable. The other is "viable"
We limit ourselves to the extend our language ability allows.

There is a definition for life based on information theories.
That will always separate AI from what we insist are the indispensable elements shaping today's definition of life.

Birger
not rated yet Feb 04, 2013
For the millionth time...
"Life" is not the same as "intelligent life".
It is pefectly possible this world is the only one with a technological civilization, even if "life" (bacterial slime, lichen, mould) is very common.
Multicellular life will be less common.
Life with an analogue to myelin sheats around the nerve connection will be even less common.
Life with meaty fins that can evolve into sturdy limbs, see above.
Exoskeletal organisms will have BIG problems growing to large size living out of the sea, and so on.
And even if some species evolve to a level compareable to Erectus in terms of IQ, if the climate is stable there is no guarantee they will evolve further.
So, yes, there are technological civilisation in the Milky Way, and we are it.
lengould100
not rated yet Feb 05, 2013
I think it's too early in the search to say much either way. However I admit some surprise and significant disappointment that SETI et al haven't detected anything at all. Yet...

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