Our Galaxy May Have 50 Billion Exoplanets–and It's Still Making More

By Andrew Moseman | February 25, 2011 1:27 pm

Young. Old. Scalding hot. Icy cold. Terrestrial midgets. Gas giants. As the cavalcade of planets spotted beyond our solar system continues to grow, we get to see worlds of all sorts—and we get to speculate on the staggering number of exoplanets that might inhabit just our own galaxy.

Today’s first piece of otherworldly news involves baby exoplanets. Astronomer Christian Thalmann says his team may have spotted planets in the process of forming around three different stars, the first time scientists have spotted the process in action.

An infant star forms from a collapsing cloud of dust and gas and gathers a dense, flat disk of material that rotates with the star like a record album. The material in the disk will eventually clump up into nascent planets. Theoretical models of planet formation predicted that those protoplanets should suck up more gas and dust with their gravity, clearing a wide gap in the otherwise solid disk. [Wired]

Peering at young stars like T Chamaeleontis (T Cha) LkCa15 and AB Auriga, Thalmann and colleagues saw those telltale gaps in the dusty rings (their study is forthcoming in the Astrophysical Journal Letters). The stars are much like our own sun, so these pictures of infant solar systems could resemble what our own looked like as a baby. But though the stars are nearby in cosmic terms—T Cha lies just 350 light years away—the gaps are faint enough that it’s difficult to tell for certain if newly forming planets, and not the influence of binary stars or other objects, are creating them.

If Thalmann’s team is right, catching the birth of new worlds would be a great scientific coup. Our galaxy, however, isn’t exactly hurting for planets.

Earlier this month came the big announcement from NASA’s Kepler mission, when its scientists announced 1,200 new potential planets, including 54 found in the habitable region around their stars. Since then, project science head William Borucki has done a few back-of-the-envelope extrapolations based on Kepler’s findings, and produced some eye-popping planet tallies that he announced at last weekend’s American Association for the Advancement of Science (AAAS) annual conference in Washington: The total number of Milky Way planets could be on the order of 50 billion, with 500 million of those falling in the life-friendly Goldilocks zone.

Borucki and colleagues figured one of two stars has planets and one of 200 stars has planets in the habitable zone… And that’s a minimum because these stars can have more than one planet and Kepler has yet to get a long enough glimpse to see planets that are further out from the star, like Earth, Borucki said. For example, if Kepler were 1,000 light years from Earth and looking at our sun and noticed Venus passing by, there’s only a one-in-eight chance that Earth would also be seen, astronomers said. [AP]

Kepler—humankind’s best planet-hunter—surveys an area that accounts for just one-four-hundredth of the sky. And yet it produces a bonanza of worlds, the implications of which got extraterrestrial life enthusiasts buzzing at the same AAAS meeting. Howard Smith of the Harvard-Smithsonian Center for Astrophysics argued that the great distances and relative harshness of the universe makes humanity a de facto loner. Even if there are other civilizations, he said, we could never reach them in person or by electronic communication (at least, not without a hundred generations of humans awaiting the response). But Seth Shostak of the SETI Institute unsurprisingly saw the sunny side of a galaxy overflowing with planets.

Shostak cited an argument that says increases in computer power mean we’ll be able to analyse far more planetary data than has been possible until now. He was confident that within 24 years we would detect an alien civilisation. “There are maybe 10 21 Earth-like planets out there,” he said. “Believing there aren’t ETs is believing in miracles.” He bet the audience that we’d find ET within our lifetime or else he’d buy us a cup of Starbucks. [New Scientist]

I rarely turn down a strong cup of joe, but I hope Shostak is proved correct.

Related Content:
DISCOVER: How Long Until We Find a Second Earth?
Bad Astronomy: Motherlode of potential planets found: more than 1200 alien worlds!
Bad Astronomy: How many habitable planets are there in the galaxy?
80beats: The Estimated Number of Stars in the Universe Just Tripled
80beats: Super-Hot Super-Earth May Have an Atmosphere of Steam

Image: L. Calçada/ESO

  • Jim Johnson

    So, he’s agreed to buy you a coffee after your lifetime? Handy.

  • http://clubneko.net/ nick

    Re: Jim – well, he did say Starbucks specifically so I’m okay with getting that after I’m dead and can’t taste it anymore. 😉

    I would bet that 50 billion planets is a quite conservative estimate. Considering there are 100-400 billion stars estimated to be in the Milky Way, and stars don’t seem to form in a vacuum. There will be plenty of places where planets are less likely to form (say, the galatic core), but since we can’t see in there, we can’t actually know that, we just presume and suppose that it’s too wild and violent a place to live (much like we presumed about life in the volcanic vents at the floor of the sea). Also, stars are likely to have more than one. They don’t form in a vacuum after all (yet, they do form in a vacuum, ha ha). There’s also the fact of the recent discover that red / brown dwarves bumped up the astral population of the universe by about 3 times (which is probably where the 100-400 billion star estimate for the M-W comes in), and we have a hard time seeing those, and I imagine would have an even harder time detecting planets around them….

    But, you know scientists, they’d rather err on the side of caution, otherwise they get branded fools by the media if they’re proven wrong. But I would not be surprised in the least to hear of estimates or discoveries of hundreds of billions of planets in our home galaxy before my life is over.

  • Christopher Kandrat

    Thats pretty amazing how many exoplants exist out there. Much more research needs to be done.

  • trumpcard

    i don’t think it really takes a genius to figure this out

  • Matt

    Im glad some sensible scientist pointed out the obvious. Unless that civilsation is within 20 lightyears you can forget a meaningful conversation.

    I find it pointless looking for civilsations we cant possibly travel or investigate fully. Better to spend the money exploring our region thoroughly that we could possibly reach with probes etc in a relistic time-frame and use that data and wait for better technoplogy then spread further out each time.

    I mean anyone who says they may have found life 400 million light years away would be quite insane in saying it at the moment. It would be sceptical at 2 light years with sending a probe that can at least confirm such rediculous statements.

    So probing the cosmos and saying there are 500 million worlds in the habitable zone in our galaxy is great and means nothing.We all know life is very likley to be on some of them, so what… whens the bus going to go visit.

    Youll never change religious peoples views that Humans is gods onlyintelligent creation and we are the centre of the universe.

  • matt

    Good to see discover magazine only allowing replies on topics they know are not in current news.

    What about YOUR Health Article
    Big Picture Can Bill Gates Buy a Better World?

    Well i think his foundation is bollocks, people only help themselves if you leave them alone otherwise they rely on others and nothing gets done.

    Leave therse countries alone or solve there debt problem. Take a look at live aid in the 1980’s there to save the planet…what happened they wiped out the entire local food, clothing industries over night and the country never recovered.

    Stay the f out of other countries and let them solve it.

  • Brian Too

    The Fermi paradox is alive and well. We are finding the planets, or so it seems. So where are the intelligent aliens?

  • scribbler

    First, to believe in aliens without proof is the same as believing in God without proof. I believe there is a God because of personal proofs but I will not err by proffering that my own experience represents tactile evidence for the reader.

    Second, the more worlds we find without life, the more evidence we have that life is unique to this world. The likelihood of life on other planets shrinks with each dead world we find.

    Third, the formula quoted as “evidence” presumed that half the stars have planets. However, when you plug the other numbers in that have been observed and are not the product of Sagan’s guessing, the likelihood of life of any kind is almost nil and intelligent life almost certainly nil.

    Forth, even IF they exist, as is stated, we are so primitive that unless they contact us, we will not communicate at all. If they have the means to communicate with us, they haven’t seen fit to do so. If they are like us, we would more than likely be food to them or worse.

    Fifth, if you are going to play odds, it has been hypothesized that the odds of the chemicals for the first cell to have been in the same area at the same time is along the lines of 10 raised to the 40,000th power. Someone told me, and please, if someone knows, correct me but 10 raised to the 15,000 would be the number of electrons if you filled the known universe with electrons and made a new universe of each one and then filled those all with electrons. 10 to the 15,001 is ten times that…

    Sixth, again, correct me if I’m wrong but the known universe is a sphere about 28 billion light years across with us smack dab in the center???

    Seventh, not finding proof of God is not the same as proving there isn’t a God. While I will not attempt to prove there is a God, all science of all time has not disproven that God Exists.

    Eight (the number of new beginnings ;-), The Scarecrow that precludes any life elsewhere is certainly not propped up by the bible and knocking it down isn’t science.

    Ridiculing those who disagree isn’t the same as proving them wrong…


  • John Burton

    Scribbler, I just love you god guys!! The barbarian knows exactly the same as the scientist, the fool as the philosopher and the chimp as the Pope. Only the inspired would want to engage you in discussion. All stars form the same way and statistically it seems more probable that all would have planets. If we use a formula that says each star has no planets or they have eight as our sun, the average would be four planets on average times the 200 billion stars in our Milky Way. Only through science will it ever known; not through inspiration or scriptural quotes no matter how profoundly believed!!.

  • daniel b

    I must also agree with the guy who said that the only people who would want to, or who could be even able to handle a discussion with scribbler are the inspired. By clinging to your ‘unshakeble convictions’ regarding the possibility that other life forms exist is what is wrong with our world today. You have no business weighing in on a subject like this because the only thing you’re good for is a biased, predictable, and ignorant opinion on the subject. Do us all a favor and read your bible instead of veritable truths.

  • mike

    God is, case closed. There are no accidents, except maybe you! You cannot get something from nothing, … a physical fact!

  • amphiox

    I find it pointless looking for civilsations we cant possibly travel or investigate fully.

    What an impoverished imagination on display here. To not even try just because you don’t think we can ever know everything? With that kind of thinking we would have stayed in our caves.

    Just confirming their existence would be ground-breaking enough. It is impossible to predict what we might go on to learn by passive observation alone, but the history all human endeavor suggests the answer will be “more than we initially suspected we could”. And even if we learn nothing else, even if we could never go there, never converse, even if all we learn is information a million years old due to the distance, so be it. It is enough that we will know that they are, or were, there.

  • amphiox

    You cannot get something from nothing, … a physical fact!

    No, a physical falsehood, already demonstrated by observation.

    And a philosphical impossibility. For even God is something, so from whence came God?

  • scribbler

    How predictable. Ad hominum attacks and you didn’t even read what I wrote because you certainly attacked a view I do not hold. Scientifically speaking, open eyes gather more light than closed ones…

    I admitted the number of planets. I admitted the number in the “golden Zones”. And then I looked at the other facts and that is that so far, the more planets we add with no life, the stronger the argument is that life exists only here. I calculated the odds of life forming on its own and it takes more faith to believe it happened on its own rather than having a Cause. I admitted that IF there is anyone else out there, we know nothing of them.

    My science is solid. Other than feeling superior to those who disagree, what do you get from your flawed assertions?


  • http://discovermagazine.com Iain

    No the known universe is a sphere 84 Billion Light years across with us right in the middle!
    WHY? Because that is all we can see. For example, Go jump in a lake and submerge yourself and look around, you are in the middle of an observation bubble maybe 100 feet in radius, does that mean the lake shrunk? Same thing when lookin at the past with Hubble.
    ” not finding proof of God is not the same as proving there isn’t a God”
    not finding ET life is not proof of its nonexistence.
    Conundrums for you
    The light from the early universe had to travel approximately 42 billion light years (as a distance) to get here in the 14 billion years it has been travelling. Why?
    Photons don’t decay, that’s why we can see this ancient light! Why?
    ” the more planets we add with no life, the stronger the argument is that life exists only here” That is a specious argument, somewhat similar to me saying that the longer I go without seeing evidence of God the more probable it is that God is a fantasy.

  • Erik L.

    I would never argue with a person who does not the the difference between astronomy and philosophy.

  • Pippa

    In Da Vinci’s time it was a well known fact that man would never fly – we didn’t have the materials technology to be able to build a machine that could fly. I can’t help but also be reminded of the ‘facts’ that I was taught as child – there were no other planets out there, after all if there were we would have found them. No one bothered to tell me that we did not have the technology to find them and as a child I didn’t know to question this. I was also told that it was a fact that girls were not as bright as boys and couldn’t do math and science as well, nor could they ever play the piano as well or be composers like a man could – that group of ‘facts’ was disputed fairly early on by other’s examples, once I learnt to look. It is so easy to restrict your world by looking for comforting support of your beliefs instead of challenging them.
    Your basic science is fairly solid but your application of statistical probabilities weak, Scribbler.

  • http://discovermagazine.com Iain

    Aww scribbler won’t come back, he/she knows that his/her arguments won’t stand up to scrutiny.
    Tax religions like any other business.

  • matt

    Recently scientists created the simplest cell (they could so far..) from synthesised DNA and did this in 15 years.

    Its not surprising with a few hundred millions years simple cells were created by the Earth.

    As to the probability the figure you quote is unreal and comes from a comic book or something. You cant put a probability on something which you cannot at least test the hypothesis’ .

    Scientists are presently trying to ascertain these factors which range from 1 in 1 in the case of our planet to 1 in 50 billion (The current amount of exoplanets). The chance of life springing up can never be more than the total amount of planets in our universe in any case.

    At no point can you ever get 10 to the 40000th power as the probability unless as i said youre reading a comic book.

  • amphiox

    The chance of life springing up can never be more than the total amount of planets in our universe in any case.

    This rests on the assumption that life can only arise on planets, which may or may not turn out to be true.

  • Ema Nymton

    Scribbler, people don’t ridicule you because they disagree with you. They ridicule you because you’re a moron. There’s a difference.

  • Lazlow


    You said “…the more planets we add with no life…”. They are now finding new planets all the time but we don’t know for sure if they have life or not…so your argument is just babble. We know that many of them probably don’t have life but we are not even sure that Mars is totally dead and it’s right next door. So we are pretty sure that life does not exist on 6 planets… Mercury, Venus, Jupiter, Saturn, Uranus, Neptune. If there are 50 billion or so in the galaxy, then we have a long way to go before any statements like yours have any validity at all.

    I also hope that I am still alive when we finally do pick up signals from some other civilization. It will be fun to watch all these brain-dead anti-science people have to eat their words.

    I’m no astrophysicist and doubt some scientific theories… but I’m at least open-minded enough to read about what we are discovering and what the scientists say.

  • scribbler

    How easy your lives must be…


  • Torbjörn Larsson, OM

    I heard last week on a seminar by one of the lead Kepler scientists that accounting for geometry and noise in the raw data on exoplanets shows:
    – Smaller planets are more frequent (already predicted by the 1st Kepler data release).
    – Larger orbits are more frequent (ie rejecting earlier data on gaps ~ a few days).
    – Smaller stars are more frequent (already predicted by the 1st Kepler data release).

    That exoplanets are more frequent for larger orbits means that Earth analogs aren’t rare! The estimate was ~ 1/50 – 1/200 of stars having habitable Earth sized planets with ~ 1 year orbit.

  • Torbjörn Larsson, OM

    Fifth, if you are going to play odds, it has been hypothesized that the odds of the chemicals for the first cell to have been in the same area at the same time is along the lines of 10 raised to the 40,000th power.

    That has _never_, to my knowledge, been hypothesized in biology. It is a religious argument, that you can familiarize yourself with on Talk Origins, as creationist standard claim CB010.1: “Even the simplest, most primitive forms of life — bacteria — are incredibly complex, much too complex to have arisen by chance.”

    This claim is irrelevant to evolution, such as the evolution of cells. It is also irrelevant to abiogenesis because nobody claims that chemical to biological evolution arose purely by random chance anymore than evolution in general is purely random chance. It is also irrelevant to chemistry and physics, since using the same argument a protein could never fold into a working enzyme, the number of conformations are larger than the number of atoms in the universe and it would take too long to work through them all.

    The article is correct, we do believe for good reasons, such as the speed and ease of life arising on Earth and the overwhelming number of habitable planets (already known to be more than 50!), that we will observe inhabited planets elsewhere. Spectroscopy can reveal many indicators of life (such as oxygen on cool planets).

    How easy your lives must be…

    Easy and illuminating. Step out of your cave and discover the world with the rest of us, the light of Enlightenment (science) will in general make you happier.

  • amphiox

    How easy your lives must be…

    If you believe that, then join us. Don’t you want your life to be easier?

  • http://discovermagazine.com Iain

    How tough can it be to have faith? All one needs is ignorance and a closed mind. Two things found in abundance in Gods universe.

  • forester


    In the scientific paper (released in early February 2011) the figure for the percentage of stars with planets is listed as 34% which is closer to 1 in 3 than it is to 1 in 2. Where then is the “1 in 2 stars with a planet” estimate that Borucki mentions coming from? Is it an extrapolation to what the final numbers will be once Kepler is totally finished observing, or, more conservatively, is it what Kepler has seen up until, say, early 2011?


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