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NASA / JPL-Caltech / T. Pyle
An artist's rendering shows a typical close-in Earth-size planet, Kepler-20e, which is about 0.87 times as wide as our planet but orbits its parent star more closely than Mercury orbits our sun.
A simulation based on data from NASA's planet-hunting Kepler mission has determined that about one out of every six stars has an Earth-sized planet, which would translate to at least 17 billion such worlds in our Milky Way galaxy. And that's not even counting the alien Earths we'd want to live on.
These 17 billion planets would be circling their parent stars more closely than Mercury orbits our own sun — which means that, in many cases, the planets would be too hot for liquid water to exist. A few such worlds already have been found, including a "lava planet" known as Alpha Centauri Bb that's just 4.3 light-years away from us.
Someday, the type of simulation that astronomers used to estimate the number of hot Earths can be used to estimate how many habitable Earths could provide a home for life as we know it in the Milky Way. But not just yet.
"For an estimate of Earth-sized planets in the habitable zone, it's simply too early to call," said Francois Fressin of the Harvard-Smithsonian Center for Astrophysics, or CfA.
Fressin and his colleagues lay out their estimates for Earth-sized planets, as well as bigger worlds, in a paper that's been accepted for publication in the Astrophysical Journal. Their research is being discussed today at the American Astronomical Society's winter meeting in Long Beach, Calif.
The estimates are based on a list of 2,400 planet candidates that have been detected by the Kepler probe since its launch in 2009. Kepler looks for planets in a patch of sky overlapping the constellations Cygnus and Lyra, by checking for the faint dimming of a star as an alien world passes across its disk. One of the challenges is to make sure the dimming is really caused by a planet, rather than some other phenomenon such as an eclipsing binary star. Another challenge is that Kepler is sure to miss some planets, because those planets are not in a position to block the light of its parent star, as seen from Earth.
Now that the Kepler mission has been churning out detections for more than three years, there's enough of a database to arrive at some statistical conclusions about the total number of planets in the Milky Way — at least 100 billion. There's also enough data to determine what the breakdown of detections should be, and even how many of those detections will be wrong.
"We have a knowledge of false positives that's good enough that we can do a study from scratch," Fressin said.
The simulation suggests that the false-positive rate should vary depending on the size of the planet candidates, from a low of 6.7 percent for small Neptune-scale planets to a high of 17.7 percent for Jupiter-type giants. The false-positive rate for close-in planets between 0.8 and 1.25 times as wide as Earth is 12.3 percent. When all these factors were added to the calculations, the astronomers arrived at a breakdown for five types of planets currently detectable by Kepler:
- 17 percent for Earths with orbital periods up to 85 days.
- 26 percent for super-Earths (1.25 to 2 times as wide as Earth) with orbits up to 145 days.
- 26 percent for small Neptunes (2 to 4 times Earth's width) with orbits up to 245 days.
- 3 percent for large Neptunes (4 to 6 times Earth's width) with orbits up to 418 days.
- 5 percent for giants (6 to 22 times Earth's width) with orbits up to 418 days.
The results indicate that for every size of planet except for gas giants, the type of star doesn't matter. Earth-sized planets should be just as likely to form around red dwarfs as around sunlike stars. That runs counter to what was previously thought.
"Earths and super-Earths aren't picky. We're finding them in all kinds of neighborhoods," the CfA's Guillermo Torres, a co-author of the study, said in a news release.
The researchers emphasized that these are just minimum estimates — and that as Kepler provides more planet candidates at smaller scales and wider orbits, the numbers could increase. Eventually, such simulations could spit out a long-sought number: the tally of Earth-sized planets in the Milky Way expected to have conditions capable of supporting life.
"This result is a significant step towards the determination of eta-earth, the occurrence of Earthlike planets in the habitable zone of their parent stars," they wrote in their research paper.
More about the planet search:
- Kepler mission adds 461 potential planets to list
- 'Exocomets' are common across the Milky Way
- 2013 might be the year for first 'alien Earth'
- Alien planets face danger from binary stars
- Cosmic Log archive on the planet search
In addition to Fressin and Torres, the authors of "The False Positive Rate of Kepler nd the Occurrence of Planets" include David Charbonneau, Stephen Bryson, Jessie Christiansen, Courtney Dressing, Jon Jenkins, Lucianne Walkowicz and Natalie Batalha.
Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.
Leave a Comment:
You all cause me to laugh. Really you all "tickle " me.
Do we "amuse you"?
We are all made of "Star Stuff"...the elements made in Super Nova dying stars. Seeded across the universe. In a sense, we could all be called "Star guy". http://www.youtube.com/watch?v=zSgiXGELjbc&feature=player_embedded
"Hot enough for ya?"
The most overused pick-up line in bars on those planets.
What about our sun with at least 3 earth sized planets?
Two are Earth size...Venus and the Earth. Mars is 1/3 earth size but may have had life at one time and even a planet with up to twice the mass of earth could hold liquid water and support life under extreme pressures if you understand the "Bottom of earth oceans: type of life. Intelligent, self aware life may be rare on the cosmic scheme of things but there still may be others out there right now trying to see if " they are alone" in the universe.
Let's take care of the one we have first.
17 BILLION cases of "global warming"?
Quick, we need to strap Al Gore onto the first rocket going anywhere. Talk about jiob security!
Cheaper still, why not put Solar Panels in your yard and go totally Energy Neutral and save the planet. If we can control our destiny, why not start now? You will also save a lot of money over the next 25 years in Energy Costs from those money hungry utilities. Would it not be nice to thumb your nose at at least one monopoly that currently controls your life?
Eddy: how, exactly, does putting up solar panels (or anything else) here on Earth actually affect any one of the 17 billion extrasolar worlds?
Tell me, oh tell me.
So sorry to be dropping the "logic bomb" on you.
So we can have our species last long enough to develop the technology to finaly go out there and see for ourselves the vast universe. If we do not take care of this plant, we will not survive to visit others. http://www.youtube.com/watch?v=zSgiXGELjbc&feature=player_embedded
starguy, your original comment was juvenile and nonsensical, so the fact that Edward's was unrelated is hardly a "win" for you.
I'm going to open up a tanning salon on Kepler 20-e. lol
Soooo... what this article is saying... is we don't have any idea what's REALLY out there, we don't know FOR SURE what we'd look for anyway... and we've NO IDEA how to get there if we did...
So... stay tuned...
"To Boldly Go where no man has gone Before!"
...The Dream is alive and well, thank you....
We don't know what most of the probabilities are, so people can say pretty much anything they want to, including you.
So we should not expect some vastly superior race to came and save us from ourselves. We need to save our planet and ourselves from extinction.
you are working on the assumption that all life will follow the rules we have on Earth. that is not the case.
there are organisms on earth that live in highly toxic, superheated, or extreme pressure areas that would kill humans in minutes
There is something the Drake Equation missed, how many earth type planets have total solar eclipses and a civilizations that can comprehend the implications! It only occurs in a rare coincidence (as the natural philosophers like to say [the original name for a scientist])and over a very short time period , that the planet, moon and there sun are at the right distances and algnment from each other to have it occur. I think the aliens pity us because we are so slow----w, there are billions and billions of more advanced civilizations in this galaxy. Read the book "The Naked Ape" and you get some idea how they look at us.
Best wishes, and keep your eyes to the sky!
Michael C. Fidler
jock59801
"We don't know what most of the probabilities are..."
Actually we have a very good idea of what they are. The Rand Corp. did a study back in the 1960s to calculate the variables for the Drake Equation. So I'm not the one who's "saying anything I want to". You are.
gbreault85
"You are working on the assumption that all life will follow the rules we have on Earth."
No, I'm not. I'm well aware of extremophiles. But the possibility that any life form that evolved under hot, frigid, or toxic conditions could develop intellect & civilization is so remote as to be absurd. Extremophiles are by definition solitary, very rare organisms. The evolution of higher forms of life is dependent on an interrelationship between thousands to millions of different life forms.
Mike C. Fidler
"There is something the Drake Equation missed, how many earth type planets have total solar eclipses..."
That is completely irrelevant.
"...there are billions and billions of more advanced civilizations in this galaxy."
No, there almost certainly are not.
"Read the book 'The Naked Ape' and you get some idea how they look at us."
I've read Desmond Morris' 'The Naked Ape' several times, which you obviously have not, since it makes no reference to how aliens might regard us. Morris was merely speculating about human evolution based on the fact that humans are relatively hairless while other primates are not.
Unfortunately, we will never physically get to any of them----sorry Star Trek fans---they are just too far away.
If you think internal combustion engines are polluting, what about rockets lifting space ships beyond the atmosphere? Electric won't work...
There will never be enough energy or other raw materials so support "regular" space travel for proletariat. So get over NASA.
rockets are fueled by liquid oxygen or liquid nitrogen, two of the most abundant elements on the planet.
they dont pollute like a car. a car is burning a carbon based fuel, rockets dont. A rocket plloutes as much as a hydrogen car would
what if, after time, we find that yes many planets support life but ours is the only one with "intelligent" life. would that blow future peoples minds or what?
but good point Independent Image, imagine all the possible civilizations that have been blown away by their star when we see a star go pop. i never thought about that before, what a way to go.
The good news is that IF those 17,000,000,000 planets each take on equal shares of the Obama-driven debt, that's less tha $1,000 per planet!
by the time obama and the current congress is gone it will be over 20,000,000,000.
we need to find at least 3 trillion more inhabited planets.
luckily with taxes going up across the board and the riches they'll be making off the "affordable care act" they should be able to throw a little money to nasa and see what they find.
oh wait, they dropped nasa...we're all doomed to work into our 80's...just get used to the idea of having to work all your life
When they ID a planet that can be inhabited by humans I'll get my nuts in a bundle. Until then, I'll just watch Star Trek. Of course it won't matter. We (humans) are too worried about our paychecks to get back to the moon ... screw going to Mars or large spaceships. Leave solar system? Not with this group of people.
Regardless, I don't see myself moving anytime soon.
Well, this is fascinating, for sure. But is this apparent abundance of life-friendly planets an argument for or against the likelihood of ET life? We should keep listening, and there is technology, yet to be made practical that should someday allow optical resolution of distant planets. We could determine, then, if there is civilization from night lighting. But so far, on the search for ET life, the results are null. I say in 200 years we'll know with a high degree of certainty, one way or the other.
I would think that the only possible answer to your question is, the greater the abundance of life-friendly planets, the greater the likelihood of life. Either that, or I'm very obtuse.
I think he is talking about ET intelligent life, specifically about civilization, and to answer that question, just as we don't know the probability of life really well, we also don't know enough about intelligent life to make a guess on probability of civilized intelligent life in our galaxy.
It might be you could make a good idea of civilized intelligence out there given x quantity of life bearing worlds, but we need a better idea what that number would be first, it might be really rare, it might be really common.
And I hope your optimism on that score Karl pans out.
This only increases my own concern that there are potentially a number of significant hurdles or pitfalls which advancing civilizations need to negotiate if they are to successfully emerge as future full fledged denizens of the cosmos. Among those potential hurdles or pitfalls could be nuclear weapons, genetic engineering, and even global warming. But personally, I would also have to include high energy physics experiments as well. Maybe it is high time that we begin to hold international conferences on these potentially grave concerns, especially since our own "doomesday clock" has been so close to midnight for so long. (The sooner the better?) - Rick Carter
(I really should have included the danger of over population up front as well, although to some degree that was indirectly implied in the case of (runaway) global warming.) - RC
We should concentrate really hard on all star systems within 20 Ly, particularly those withing 5!!...noting when the stars bob closer and further to us as we plan to leap frog throughout the entire galaxy. All the naysayers can keep it up, for now. I for one propose a large observational network just a tad bit further than where the voyagers our right now, in distance that is. or put another way, just outside the actual solar system. Every time we reach beyond out grasp, we learn to stretch a little bit more. LIke others, I am certain that keppler missed a lot of planets. The detection scheme is briliant (ok, cheap pun), but, sadly far from efficient. We could get a better start on all this with a MOONBASE. I was wondering today, why not just plan on putting the UFP flag on the moon already and be done with it, what do we have to lose? The moon will more or less fall under the United Nations, Someone call em up and let em know ray is planning on putting a big ole United planetary federation Flag right above tycho crater.......
It is very doubtful that we are going to be able to run from one another, so please, "can we all get along" on this tiny planet which we call Mother Earth? - RC
I wonder then if we can hypothesis that there are live galaxies and dead ones too, and that our galaxy, the Milky Way, would obviously be classified as live one?
Should we rethink what dark matter is? If every star is really a solar system, then could the billions of solar systems dynamics account for the "missing" mass? Does dark energy then just goes away as a terrible extrapolation of the orbital mechanics?
Do we really know what the hell we are doing? ;-)
fire everyone at nasa--and shut them down----man never landed on the moon
fire fire them all
haha you had me going there for a second, I thought you were a space alien
Maybe we can find more global warming in other solar systems! and more progressives.
Does more life mean there is a GOD? or ONLY life on earth prove there is a GOD?
the thing is these are only earth size planets. this search is on the assumption that all life will be carbon based like us and share similar requirements for survival (i.e. oxygen, water, temperature ranges, pressure ranges, etc).
Life can take on any shape or form well beyond the restrictions we see on our own planet.
It could, it could not, life might take any shape we could imagine, life could also just be our type of life, all humanoidy and carbony everywhere, but in any case starting with our type of life is a reasonable beginning for detection, we know how to detect such life, we know its parameters for how it exists.
Myself I go for a chemosynthetic life, but I acknowledge it would be somewhat harder to detect then photosynthetic life, right now what we could potentially detect falls within the range of life we know. We need to know more about other types of life in order to search for them.
So lets start with our type, than as our knowledge of our own and other life evolves, move on to other potential types.
no doubt gbreault85. Time after time we put ourselves in the center of it all. Then nature comes along and proves our folly, everytime. In the grandeour scheme, it would seem that life needs energy and that perhaps closer in to a star there is more energy, more "food" for life. As well, we already know that life is very hardy and adaptable, thus ruling out bigger, hotter, or colder should well be noted as only ruling out the possibility for life "as we know it". Any astrobiologist worth their salt is surely making the as we know it point now.
How do we tax them? Maybe we could issue a bond, tax them in advance(some day we will be able to get there)and have the FED issue current accounts to the bond holder.
Exactly like we do with currently unreachable unborn generations.
I dare anyone to laugh at that as ludicrous.
Geezzzzzzzzzzzzzzzzzzz, genius, did you figure that all out on your TI computer?
Did they find any the size of youranus?