E-mail updates
Follow on Twitter
Subscribe to RSS
M. Kornmesser / ESO
A cartoon view of the Milky Way shows stars bristling with planets. The planets, their orbits and the sizes of their host stars are all vastly magnified in the cartoon.
A statistical analysis based on a survey of millions of stars suggests that there's at least one planet for every star in the sky, and probably more. That would add up to 160 billion planets or so in the Milky Way.
"We conclude that stars are orbited by planets as a rule, rather than the exception," an international research team reports today in the journal Nature.
The estimate may sound amazing: Just a year ago, the world was wowed by the claim that at least half of the 100 billion or more stars in the Milky Way possessed planets, yielding a figure of 50 billion planets. The latest survey now suggests that there's an average of 1.6 planets per star system, which would work out to 160 billion. But perhaps the most amazing thing about the findings is ... astronomers don't find them amazing at all.
"I am not surprised by the numbers," Didier Queloz, a planet-hunter at the Geneva Observatory who was not involved in the survey, told me in an email. Back in 2008, Queloz was part of a different research team that concluded one-third of the stars like our sun harbored super-Earth-size planets — the kinds of planets that could support life.
Over the past couple of years, findings from a variety of planet-hunting missions — including NASA's Kepler space telescope, the European Space Agency's COROT telescope and ground-based telescope surveys — have reinforced the view that planets are plentiful.
"Results from the three main techniques of planet detection are rapidly converging to a common result: Not only are planets common in the galaxy, but there are more small planets than large ones," Caltech astronomer Stephen Kane, a member of the team behind the findings reported in Nature, said in a news release from the Space Telescope Science Institute. "This is encouraging news for investigations into habitable planets."
Six years' worth of data
The new findings draw upon six years' worth of data from two wide-field surveys known as PLANET and OGLE. These surveys use a network of telescopes around the world, scanning the night sky for very rare events in which the light from one star system is amplified by the gravitational-lensing effect of another star (and perhaps a planet) passing in front of it. This particular planet-hunting method is known as microlensing, as opposed to the transit method (which looks for telltale dips in starlight as a planet crosses its parent star's disk) or the radial-velocity method (which looks for the slight gravitational wobble in a star that has a planet in orbit).
A. Feild / STScI / NASA / ESA
This graphic explains how microlensing is used to detect planets. Click on the image for a larger version.
During their six years of searching, the microlensing researchers identified only three actual planets. But they combined those detections with seven earlier detections, plus all the data about non-detections, to arrive at an estimate of how probable it is that planets of different types would be found around a star.
They estimated that about 17 percent of the stars in the Milky Way should host planets in the Jupiter range (0.3 to 10 times as massive as Jupiter), 52 percent should have planets in the Neptune range (10 to 30 times Earth's mass), and 62 percent should have super-Earth-size planets (five to 10 times Earth's mass).
All these figures are surrounded by wide bands of uncertainty. For example, the researchers say their estimate of 1.6 planets per star system could actually be anywhere between 0.7 and 2.5. But the lead author of the Nature study told me that his team's estimate is the best guess yet.
"The average number we find is higher than estimates derived by other methods," said Arnaud Cassan, an astronomer at the Institut d'Astrophysique de Paris. That's because the microlensing method can detect planets as small as five times Earth's mass up to 10 times Jupiter's mass, in orbits ranging from 0.5 to 10 times as wide as Earth's. Other methods aren't that sensitive, Cassan said.
"If they could detect planets with a range farther out, our guess is that they would find more planets," Cassan said.
What are the chances?
The big issue would have to do with how precise the statistical analysis can be with such a small sample of actual detections. Microlensing events are so rare that coming upon even one is like winning the lottery, and that makes the numbers difficult to crunch. But after reviewing the Nature paper, Queloz told me that Cassan and his colleagues conducted "a very good statistical analysis of the microlensing surveys."
Whether the actual number of planets in the Milky Way is 70 billion or 250 billion, it's a big, big number — 10 to 30 planets for every human on Earth. And the number doesn't even count worlds that are less than five times as big as Earth (such as Mercury, Venus, Mars and our own planetary home), inside the orbit of Venus or beyond the orbit of Saturn (such as Uranus, Neptune and the icy dwarfs on the solar system's edge).
Still more revelations about planets beyond our own solar system are coming up this week, but the bottom line for all this is that there's a big cosmos out there — with plenty of opportunities for planets and even life to develop. And that'll always be amazing.
"We used to think that the Earth might be unique in our galaxy," Daniel Kubas, a colleague of Cassan's at the Institut d'Astrophysique de Paris and a co-author of the Nature paper, said in a news release from the European Southern Observatory. "But now it seems that there are literally billions of planets with masses similar to Earth orbiting stars in the Milky Way."
More about the planet quest:
- Three newfound worlds are smaller than Earth
- Flash interactive: How other worlds are found
- Two new 'Tatooine' planets with two suns
- SETI researchers check signals in exoplanet study
- Microlensing turns up rocky, low-mass world
- Cosmic Log archive on planets
In addition to Cassan, Kubas and Kane, authors of the Nature paper, "One or More Bound Planets Per Milky Way Star from Microlensing Observations," include J.-P. Beaulieu, M. Dominik, K. Horne, J. Greenhill, J. Wambsganss, J. Menzies, A. Williams, U. G. Jørgensen, A. Udalski, D.P. Bennett, M.D. Albrow, V. Batista, S. Brillant, J.A.R. Caldwell, A. Cole, Ch. Coutures, K.H. Cook, S. Dieters, D. Dominis Prester, J. Donatowicz, P. Fouqué, K. Hill, N. Kains, J.-B. Marquette, R. Martin, K.R. Pollard, K.C. Sahu, C. Vinter, D. Warren, B. Watson, M. Zub, T. Sumi, M.K. Szymanski, M. Kubiak, R. Poleski, I. Soszynski, K. Ulaczyk, G. Pietrzynski and L. Wyrzykowski.
Alan Boyle is msnbc.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. 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:
Maybe 250 billion planets just in our galaxy, what about the other galaxies. Well now Carl Sagan was right after all, there are billions and billions of stars, with more billions, and billions, and billions of planets, I wonder what that does to Frank Drake's equation. I see little green or gray men, with big eyes, all over the place. I'll feel less foolish now when I go outside in the early morning hours, when it is still dark, I look up at the stars and say good morning to everyone out there!! Wow, now I really wish I had a new ansible.
Do believe are other planets out there with civilizations/cultures-most likely much more tech/other advanced than us. Suppose why they send probes/craft(UFO's?) to earth, check us out also.
They do. We just won't accept it and instead, lump sightings of UFO's in with Bigfoot, Loch Ness Monster, etc.
Sad.
Well, since the universe is infinite, there must be an infinite number of possibilities that life just like ours or even exactly like ours does exist. You can still believe in God and believe in life on other planets. In fact, not to believe in life on other planets would be short changing the Creator. Are we so arrogant to believe we are the only ones? By the way, there could be a God for every planet and then one major God for the whole shootin match.
All I know, is there must be more to it than just the big bang because somebody or something had to pull the trigger.
There may be a GOD, but it's not the one in the Bible, Torah, or the Koran.
Perhaps "God" is the name we give to race of beings that are as incomprehensible to us as we would be to a microbe--
160 billion planets - and not one comes to visit us ...
Any civilization that has lasted long enough to developed interplanetary space travel has had to also learn the futility of war. Why would they want to come to a planet where that lesson hasn't been learned yet?
Let's see, there are more stars in the universe than there are single grains of sand on every beach on the earth. With each star having an average of two or three planets I would say there are millions and of life forms out there. As Stephen Hawkins stated, due to the shear number of planets in the universe "It is a mathematical impossibility that life exist only on earth." I would even take a step further and bet there are as many universes.
Hawking
It boggles the mind to hear there are still people out there that believe the earth is so special it is the only place in the entire universe that has life on it. Then there are those that the feel there is a good probability of planets with life on them but that only earth has intelligent life.
In time I believe both of those premises will be dis-proven beyond the shadow of a doubt. Of course the struggle will still be about getting disbelievers to accept the proof in front of them.
What is more amazing than the number of planets? The taxpayers have to come up with about $30.00 for each star in our galaxy to pay off the debt that our rulers have accumulated for us. Kind of puts the national debt in perspective.
Alot of comments on this board speak about "life as we know it" on other planets in different solar systems. Odds are we will not find the same types of life on other planets in these solar systems. The cosmic ingredients need to differ only slightly to alter life forms on planets in these other star systems "goldilock" zones. So, we will probably be looking at life forms very much alien to us. Also, many of the planets considered habitable around other stars may not be habitable to us should we go there due to radiation levels and/or atmospheric conditions. But, given the number of possible cosmic combinations in this vast universe, there many be a civilization similar to ours looking back at us. Question is how advanced they are and whether or not they even care that we are here.
Do they even care that/if we are here??? now that's a million dollar question.
I in keeping with your query; If the answer to your question happens to be yes ...I would wonder as to the why of that answer.
Who write's this stuff. 160 Billion planet's? I think all these scientist's are crazy. 160 Billion planet's. Give me a break. Did they count them one at a time?
Did you even bother to read the article, or are you just reacting to the headline?
Already we've been attacked by Mars. They've covertly taken over the governments of the developed world. You'd think we'd have learned our lesson and not get sucked into another war.
160 billion planets = too much to comprehend = brain hurts!
This stuff is so much more interesting than the Kardashians.
Please tell me I spelled their name wrong.
Wouldn't have a clue. Sorry.
I'm going to privatize my own planet----Whites Only.
I don't believe it will ever be possible to communicate with other worlds in this dimension, it doesn't add up. But I believe if mathematics says another dimension exists then one day we will go there.
There is the real possibility that the Universe is not only filled with life but intelligent life. That could explain why we have not been contacted. We are simply not very interesting. For any advanced beings capable of travel between the stars what do we have to offer? Pictures of your aunt Louise? Invade the Earth, for what purpose? Minerals, metals, water, just what? All of everything is available on 160 billion planets+. With earth size planets and moons likely 10 times that number in our single galaxy. We currently communicate by radio but how would a very advanced intersteller traveling race communicate? Radio would simply be too slow. Quite likely they have discovered another faster way to communicate over great distances. We therefore may be wasting our time trying to pick radio signals where there are none. We are now discovering that we are not the center of the Universe and not the center of anything. Life developed on this planet by chemisty and prodcused some intelligente creatures but we are not traveling to the stars in our lifetime so we are low on the totem pole. We still cannot get over our thinking that some supernatural being created us special. We will find out likely in a few hundred years that we are not special and the "God" we created is going to go the way of the dodo bird.
This is so cool. the numbers alone tell us we WILL find other life and rarely, intelligent life. It will change us forever and finally, hopefully put a nail in the coffin of our ancient and superstitious "religions" that claim we are alone.
Unfortunately, I won't be alive to see it.
neither will mankind
At least not in this incarnation. Our souls keep coming and going, in and out of time and space. Still the headstrong individuals we are we tend to repeat our mistakes. We interact with each other time after time. We will see the far futures and mull over the pasts as we spend eternity among the stars, some long gone, others yet to be.
In truth it is an existence that is beyond the tiny truths we live and die for today. It goes on and on surpassing one god after another along the way.
This is what I believe. In the beginning, God created all the heavens and earth. The entire universe and all life in it. The universe is probably teeming with life some as we know it and as we do not. However, I think that the Genesis account is most likely a metaphor. It was not meant to be a scientific text. It is a guide for man to learn about God. The bible tells us how to go to heaven. But science can tell us how the heavens go. There is no reason why science and religion must be at odds. All that we know about the universe is what we can see through telescopes, space probes and theoretical models. We still have much to learn. May God lead us on our journey of discovery.
Don't mean to be offensive, but I've always predicted that if we find life on other planets or decide we will, religious people will just modify their interpretation of the Bible and claim that aliens are all OUR God's children. It's always the "metaphor" thing. Very convenient.
It's really arrogant.
So Jesus only came to save us? Did he visit the creatures in the Zeta Reticuli system and how was he killed to pay for their sins: Cross or laser death ray?
Yeah, it gets wacky.
It blows my mind how one moment the bible is fact and literal the next it is a metaphor then it tells us how to go to heaven but it can't show us what heaven is (I guess heaven is a metaphor). Science and religion is totally at odds and will always be unless in the future you come up with a lucky guess. But that is ok feel free to change your story it has no affect on me.
He came to save sinners, not animals or plants. Humans have sin. Animals have instinct. And plants need sun and water.
Animals have instinct, some humans have intelligence and the rest go to church ... church is for sinners.
No God that created this universe would be concerned over human sin. It's ridiculous.
Just look up at the sky at night and it's pretty obvious we are about as important to the workings of the universe as a flea on the ass of a dog.
But humans are prideful and we have to tell ourselves we are in Gods image and we own the world and there is no other life in the universe and we are special and we get to kill and eat and enslave every other creature on the plant and bla bla bla.
The best thing that will happen to the planet earth and the universe is the day we go extinct.
Well avarage guy, according to God's word, it will be YOU that will become extinct. What do you think the Genesis flood was all about 4,500 years ago? God was so angry with mankind, he destroyed everyone except Noah, his 3 sons and their wives...eight people started it all over. Jesus is coming again, and he will destroy all the evil doers. Too bad, I wouldn't even waste my breath trying to teach you a little reality because you choose to be the proverbial fool. Someone who was even remotely seeking truth wouldn't say and do as you, good luck. I have a book that tells it all in great detail, with no conflicts. It's called the Holy Bible. What do you have? A Marvel comic book about flying saucers.
What the AverageGuy has wildjoe is science, far more factual and reliable than the bible.
So we came from 3 sons and their wives hey [don't tell that to National Geographic] so that may explain some of you. That is just as lame as we all came from Adam and Eve and the wives their sons married that did not exist.
Interesting for sure.
You cannot reason with a closed mind. Bible-thumpers burned people alive and have tried to control the minds of men for hundreds of years. Other religions have done the same for thousands of years. All you can do is listen to them, shake your head and walk away. They are more to be pitied than anything else. The minute they finally get dead they will realise the gullible and foolish lives they led. Then they will get another chance to be just as pig-headed that this time they will believe the next fairy tale they are raised to believe.
so the biggest problem we face is the distance....need to find a new way to travel such huge amounts of time/space...
wildjoe, I have something....it's called reasoning.
if we figure on a fair number of planets around any given star like 4 ,then there are 400 billion of them in this galaxy alone .there are billions of galaxies out there,but lets stay with the closest one, our own. if we use the same probability of life as in our own solar system and figure it as being only one percent,it should really be something like 2 percent counting planets ,moons, asteroids ,dwarf planets ,then its possible 4 billion planets in this galaxy alone could harbor some kind of life.some of that life will evolve in time like ours and after millions of years of evolution will look up to the stars and ask the same questions we are asking ourselves,are we alone? is there anyone else out there? more than probably there is ,but the distances are so great even only looking at our own galaxy. a star with a live planet thats searching like we are doing can't see us, can't hear us,they get to us and no way of knowing we are here,even with radio waves,even at the speed of light,if our messages have been traveling for 100 years and the next civilized planet is 1000 light years away,the messages haven't had the time to get there,they have to travel for 900 more years,the irony is ,by the time they get there ,maybe them or us,or both have ,for one reason or another,ceased to exist.
To date there is no real images of any planets outside of this solar system only artist "renderings". Perhaps spaced based telescopes will bring us those.
No one has stepped one foot or even orbited any planet outside of our own system.
No-one has spoken to any self-aware, sentient life from any planet outside of our own.
Science demands proof yet here we have a lot of folks that accept life as we know it existing on other planets outside this system, without one iota of proof, yet many of them openly profess their unabashed utter hatred for Judeo-based faith.
..................
Hey man I believe there are other planets, in other solar systems it makes sense, however since we are talking about science here and not faith, I'll be needing some photographs.
Now about there being life on other planets, life as we know it, I'll be needing someone to go there and send back video or it didn't happen, We are talking science here not faith.
"Science" always assumed the universe was static, but in the 1930's, Mr. Hubble discovered the universe was expanding. The Bible says in 17 places that God spreads out the universe-quotes over 2,000 years old! The Hubble telescope verified that the universe was Quantized and that our galaxy was nearly dead center. You'll have to study Einstein's gravitational time dilation to understand the impact of a quantized universe. Here's what the Hubble has confirmed, out to billions of light years: There's the Milky Way, then nothing for a million light years, then, a surrounding shell of galaxies, then, nothing for another million light years, then, another shell of galaxies surrounding that, then, nothing for a million light years....So what have you learned? This: the Earth is at the focal point of a gravitational "well". That means far distant starlight would reach us on the same day! Oh my, I've been reading all these totally ignorant babblings. Study The Bible and some real, observational science if you ever hope to rise up out of your own well of ignorance. Now watch, here comes the name calling and the Bla, bla, bla.
Boy are you ever wrong but it sounds cool and convincing, you need to go back and study what Hubble said.
Hard to understand why religious fundamentalists reject science. The creation of the heavens and the Earth described in the book of Genesis sounds a lot like the big bang theory. I don't recall the Bible stating that the Earth is flat or that it is at the center of the universe. Nor does it tell us that Earth is the exclusive habitat for all life in the universe. Also, I could never find that "truth" actually written in the Bible that claims the Earth is 5,000 years old. Perhaps there is a God who created Man and Man's insatiable desire to seek the true nature of things, but perhaps she is too busy with the universe(s) to be bothered with the Arab-Israeli conflict or who wins the Super Bowl.
Just read Isaiah Chapter 40 and one can find out what shape the earth is: "...It is he that sitteth upon the circle of the earth, and the inhabitants thereof are as grasshoppers, that stretcheth out the heavens as a curtain, and spreadeth them out as a tent to dwell in...
So 'circle' and 'sphere' have the same definition in your dictionary?
Is the word 'metaphor' in your dictionary,
or are we supposed to understand that the earth is only inhabited by creatures resembling grasshoppers?
As I said years ago the milky way is just someone elses "small lake" or a "piece of rock" on someone else's big planet and so on all the way out for ever and ever, there is no end.
--Hopefully no one is going to burn that big rock in a fire,--- if it gets used as coal or something of nuclear bomb material etc!----just saying----
Same thing downwards, have you ever looked at just one water molecule? look at the electrons on that molecule, and think of all the "creatures" living there, the only difference is your perspective of seize!---Keep thinking---if you saw what I have seen, you would start thinking that way!
I was born 75 years too early. I wanna go check them out!