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Space Science

A Quarter of Sun-Like Stars Host Earth-Size Worlds 105

Posted by Soulskill
from the but-can-we-drill-for-oil-on-them? dept.
astroengine writes "Although there appears to be a mysterious dearth of exoplanets smaller than Earth, astronomers using data from NASA's Kepler space telescope have estimated that nearly a quarter of all sun-like stars in our galaxy play host to worlds 1-3 times the size of our planet. These astonishing results were discussed by Geoff Marcy, professor of astronomy at the University of California, Berkeley, during a talk the W. M. Keck Observatory 20th Anniversary Science Meeting on Thursday. '23 percent of sun-like stars have a planet within (1-2.8 Earth radii) just within Mercury's orbit,' said Marcy. 'I'll say that again, because that number really surprised me: 23 percent of sun-like stars have a nearly-Earth-sized planet orbiting in tight orbits within 0.25 AU of the host stars.'"
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A Quarter of Sun-Like Stars Host Earth-Size Worlds

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  • by Anonymous Coward

    Lots of Goldilocks and no bears.

    • Re:Great! (Score:5, Informative)

      by Greg01851 (720452) on Friday March 15, 2013 @05:21PM (#43186427)
      Actually, "within 0.25 AU" puts them too close to their star to be habitable... i.e. not in the goldilocks zone :( PS 1 A.U. is the distance of the Earth to the Sun, just in case you didn't/don't know.
      • Re: (Score:2, Funny)

        by sycodon (149926)

        PS 1 A.U. is the distance of the Earth to the Sun, just in case you didn't/don't know.

        Doesn't that make us "earthists"? It's like the Interstellar equivalent to the Imperial system.

        • Yes. And until we make first contact with any intelligent alien species, who cares?!

        • by AC-x (735297)

          It's like the Interstellar equivalent to the Imperial system

          Don't forget that the original definition of the metric meter was "one ten-millionth of the distance from the Earth's equator to the North Pole"

      • Re: (Score:3, Insightful)

        by Anonymous Coward

        It depends upon the size and temperature of the star - a planet that is 0.25 AU from a star half the size or half the "temperature" of the sun may very well be in the goldilocks zone of the star. (Remember the inverse square law!) But in this case, it looks like they are talking about earth-sized planets that are within 0.25 AU of sun-sized stars, and those are not in the goldilocks zone - but they are also a lot easier to find than earth-sized planets in the goldilocks zone are (the inverse square law stri

        • by mcgrew (92797) *

          I suspect life is rare outside this world, but I'd love to be wrong about that. We've found evidence that our closest neighbor was once hospitable to life, but yet have not found evidence of any life ever being there (we may still, most of it is unexplored). It may be that life itself is a fluke. It's also possible that we're first, or that it only happens once in a billion years in any given galaxy. Or we may find life and not recognize that it is, in fact, alive.

          We don't know a lot more than we do know.

          • by utoddl (263055)

            We've found evidence that our closest neighbor was once hospitable to life

            Mexico?

      • Re:Great! (Score:5, Insightful)

        by thomst (1640045) on Friday March 15, 2013 @10:09PM (#43188181) Homepage

        Greg01851 noted:

        Actually, "within 0.25 AU" puts them too close to their star to be habitable... i.e. not in the goldilocks zone :(PS 1 A.U. is the distance of the Earth to the Sun, just in case you didn't/don't know.

        Yep. Important datum, that.

        However ... since this announcement ONLY applies to 1-3 Earth-mass planets within .25 AU of G-type stars (because it's the result of occulation observations, and that's the limit of resolution for any current telescope), it says nothing whatsoever about Earth-ish planets that obit in the "Golidlocks zone". OTOH, I think it's not unreasonable to extrapolate that, if there're appropriately-sized worlds in too-close orbits around that high a proportion of G-type stars, there's a pretty good likelihood that there're just as many (or more) in the zone where life could evolve.

        Perhaps we'll find out when/if the James Webb telescope is launched.

        Exciting stuff, regardless.

      • by Shavano (2541114)
        But that does not preclude many more planets further out. Planets orbiting close to their stars are are easy to detect with Kepler. It has a harder time finding stars that are at Earthlike distances because such planets are much less likely to transit while Kepler is watching.
    • by gatkinso (15975)

      Plenty of bears I am sure. Hopefully we are the biggest and meanest of them.

      • by slick7 (1703596)

        Plenty of bears I am sure. Hopefully we are the biggest and meanest of them.

        It's not the bears I'm worried about but the snakes and wolves. As for the biggest, meanest and the smartest, I unfortunately doubt it.

    • So any planets outside the goldilocks zone are unbearable?

      There's no way to know for sure but I've often wondered if Earth being a binary plant and the warmer Earth core from the tidal force of the Moon affects where the goldilocks zone is. It'll certainly have made a difference on the volcanoes that broke snowball earth and the resultant explosion of complex life, and also on the intertidal zone that must have been so important when life later moved from water to land.

      There are two binary planets in ou
  • by sycodon (149926) on Friday March 15, 2013 @05:17PM (#43186385)

    As Carl said, "...billions and billions..."

    • by Greg01851 (720452)
      But Mr. Sagan didn't have any proof at the time... now there's much more evidence :)
      • by gmuslera (3436)
        Even if Earth-sized planets were not as common as this study say, just with the raw amount of galaxies in the universe you should have billons of those planets anyway.
    • by G3ckoG33k (647276)

      The submitter's "I'll say that again, because that number really surprised me: 23 percent of sun-like stars have a nearly-Earth-sized planet orbiting in tight orbits within 0.25 AU of the host stars.'" and your "As Carl said, "...billions and billions..."" don't mix well with all people.

      Many people get wound up for an aware agenda or an unaware one. Why? I have no serious idea, but I think that the lack of religion today, in general, coupled with the the non-scholar yet educated wish for sensation among sci

      • by bware (148533)

        There is no fundamental reason why one quarter of all sun-like stars shouldn't have Earth-size objects fairly close to them, according to any theory I am aware of.

        There's no reason why they should, either. Thus, observational science. To find out.

        A decade ago, we simply did not have any idea of what \eta_{earth} was. 0.01? 0.1? 1.0? No idea. Now we do. That's pretty cool.

        To me, this, along with cold dark matter and dark energy, are the quantum theory and general relativity of our time. We know that

      • by tqk (413719)

        I have no serious idea, but I think that the lack of religion today ...

        So, you're demonstrably an idiot. Understood. Carry on.

      • by gatkinso (15975)

        You mean your two cent, I think.

      • There is no fundamental reason why one quarter of all sun-like stars shouldn't have Earth-size objects fairly close to them, according to any theory I am aware of.
        Then you should make yourself more aware about solar system forming theories.

        I only know *one* the one that was taught in school or was written in science magazines in the 1970s.

        According to *that* theory rocky planets close to the star should be very common. In fact every *cloud* of *dust* with similar size and composition like the cloud our sola

  • by war4peace (1628283) on Friday March 15, 2013 @05:17PM (#43186389)

    ...that's translated as "lots of stars have planets in orbits which can in no way sustain life". Dims my hopes rather than the other way around.
    Also: would that not decrease the chance of planets in goldilocks range overall, since planet material in that system was partly used to give birth to close orbiters?

    • Re:But... (Score:4, Informative)

      by Nadaka (224565) on Friday March 15, 2013 @05:32PM (#43186507)

      2 problems with your assertion:

      1: the majority of stars are smaller and dimmer than the sun, .25 AU is not necessarily out of the "green" zone for the most common dwarf stars.

      2: earth sized planets further out from stars can not be reliable detected using current technology and processes. The fact that the earth sized planets that we can detect are plentiful does indicate that the earth sized planets we can not detect are not plentiful. Recall that the first few exo-planets were much larger than Jupiter and much closer than earth. We are constantly expanding the lower limit of mass and higher limit of distance that we can detect effectively.

      • 1: the majority of stars are smaller and dimmer than the sun, .25 AU is not necessarily out of the "green" zone for the most common dwarf stars.

        TFA uses the phrase "sun-like stars" a lot. It doesn't get more specific than that.

        It's certainly possible they're talking about "all dwarf stars", but it's not really a good way to bet.

    • Re:But... (Score:5, Interesting)

      by cnettel (836611) on Friday March 15, 2013 @05:39PM (#43186563)

      Well, we do have Mercury and Venus in our system and that hasn't hurt us, has it? (Yeah, Mercury is small, but Venus is also on the too-close side even without greenhouse gases and almost Earth-size.)

      I guess the point with Kepler is still that due to the methodology (repeated occlusions), shorter orbital periods will increase the chance of detection (more data points to establish significance), in addition to the fact that a planet closer to its host star will occlude a larger area and thus give a stronger signal. Just keeping Kepler going will increasingly shift the distribution of detected planets towards higher star-planet distances. The minimum detectable size will be more or less of a constant function of that distance, though, although again I guess repeated observations can sometimes bring out something that would otherwise be just at the noise floor.

      For reference, Kepler has just completed 4 years of operation, but actual planet detection only started on May 12 2009. If you want three confirmed events, you could per definition not yet have detected e.g. an exo-Mars. It simply hasn't passed by three times yet. If the orbital plane is different, the planet might not pass in our line of sight every time, and then working out the period and get a detection can take even longer.

      Just wait and see.

      • Re:But... (Score:4, Informative)

        by angel'o'sphere (80593) on Saturday March 16, 2013 @09:51AM (#43190331) Homepage Journal

        Most people don't understand that we can only find (with the current way how we do detection) very very few planets. Perhaps 1/300 or even less (more likely 1/900) of the systems can be observed in a way that reveals planets.

        We can only detect a planet if his orbit plane is cutting the star like this: -o-
        Ofc you can turn this now clockwise or counterclockwise, the cut does not need to be horizontal.

        However we can not detect any planet in a solar system that looks like a cut up onion to us: the star in the middle and the planets orbiting on the rings around it (because the planerts are to dim to see directly, and they never obscure the star)

    • Why does it dim your hopes? We already knew that Earth was pretty rare (1 in 8 planets in our solar system) before discovering extra solar planetary systems.

      Currently we know of 861 extra solar planets, which moves our rarity to 1 in 869. With an estimated 100 billion to 400 billion extra solar planets in the Milky Way, that becomes quite a few Earth-like planets.

      If an Earth-like planet is a million to one, then it's between 100,000 and 400,000. If it's a billion to one, then it's between 100 and 400.

      And th

      • Re:But... (Score:5, Insightful)

        by Immerman (2627577) on Friday March 15, 2013 @09:01PM (#43187855)

        Umm, what? If anything our solar system suggests Earth-like planets are very common - we have three of them here including Mars and Venus. Only Earth is firmly in the "Goldilock zone", but you can only reasonably expect one planet to fall into that zone around any given sunlike star, *maybe* two if they fall near opposite extremes.

        Given that current detection methods can't yet reliably detect a planet the size and distance of Earth the fact that we're detecting lots of larger, closer planets in no way detracts from the possible commonness of exo-Earths, it just means we're detecting lots of planets that are easy to detect, and can now say that ~1 in 4 sunlike stars has something like a Venus or Mercury - if our system is at all typically I'd expect such stars to also have a good chance of having additional Earthlike planets further out, we just can't detect them yet without being extremely lucky.

        • Re: (Score:3, Interesting)

          by Anonymous Coward

          You might want to throw Europa in there. Not a planet, and not in the Goldilocks Zone - but it's close enough to the right size, and tidal forces contribute enough heat to possibly put it in a 'Goldilocks Emeritus' category.

    • by Tablizer (95088)

      Close to the sun means that alien babes will be wearing really really skimpy bikinis.

  • As we all know, Mercury is not exactly hospitable to life. How many Earthlike planets are orbiting Sunlike stars in more Earth/Mars sized orbits?
    • by gatkinso (15975)

      I will guess 1 % of K and G type stars. Which means within 100 LY there would be about 20 such worlds.

      • by 0111 1110 (518466) on Friday March 15, 2013 @07:41PM (#43187399)

        What are you basing that guess on?

        • by gatkinso (15975)

          Based on the fact that there are approximately 512 G and 1540 K class stars within 100 LY of earth. (You can of course Google for yourself).

          512 + 1540 = 2052 *.01 = 20

          • by gatkinso (15975)

            Oh PS as far as the 1% goes... that is just a guess... straight from the bung hole. Which of course means the 20.5 figure is no better.

            Statistically speaking there is no way for us to know what the figure of merit is, so 50% would be the only appropriate guess. I just intentionally low-balled it.

  • Because the death star has been busy!
  • by gatkinso (15975) on Friday March 15, 2013 @05:53PM (#43186683)

    In 30 years we will be able to detect planetesimals smaller than the moon orbiting stars out to 300 LY. This is of course just a guess.

  • Streetlight effect? (Score:4, Interesting)

    by gmuslera (3436) on Friday March 15, 2013 @06:06PM (#43186755) Homepage Journal
    How much harder would be to find planets of those sizes if they were at a bigger distance from their sun?
    • by bjorniac (836863) on Friday March 15, 2013 @07:06PM (#43187161)

      The answer is that it's not much more difficult, but a lot more time consuming (gleaned from going to talks on the subject, not my area of expertise).

      There are two basic ways that these planets are observed: They make the stars they orbit wobble (the basic 2 body problem - each body orbits the center of mass of the pair) and they dim the light from the star when they pass in front (like an eclipse).

      The time problem comes from the fact that orbits are longer for objects more distant from the star. If we make the simplification that the orbit of the planet is basically circular, the time period for an orbit increases as radius^(3/2). (Insert semi-major axis for radius for non-circular). The standard is about three events separated by equal times to count as an observation - you have to wait to see an event at least twice to know the time period and so infer the radius of orbit, and once again to remove some flukes. Hence you're having to wait a long time looking at a star to see this happen.

      Now, on top of that you've got the possibility that there's more than one planet, that the earth-like planet isn't the dominant mass, etc etc. This can all be cleverly dealt with (multiple wobbles, multiple eclipses) but it adds time to the confirmation process.

      To give an example: Suppose you were somewhere near Proxima Centauri, and making the relevant observation looking for Earth. It would take at least three years to detect Earth, even if your telescope was amazing. Dynamics of the system would pick up the effect of Jupiter on the sun first, for the wobble detection (you wouldn't get much eclipse given the angle between the plane of the solar system and the position of PC) and it might take quite some analysis to pick up Earth at all given the effects of all the other planets.

      Anyway, I'm sure some astro people can give a much better version of all this. Suffice to say that we aren't looking for Earth like planets at Earth like radii yet, but I imagine over the next ten to twenty years there will be a lot of poor graduate students analyzing data desperately looking for Gallifrey.

      • The answer is that it's not much more difficult, but a lot more time consuming (gleaned from going to talks on the subject, not my area of expertise). Correct and not correct.

        Lets focus on the correct part first:
        We can only detect planets that transit regularly their star. That means the ecliptic is somehow perpendicular to our view.

        Try this experiment: take a pice of paper, draw a sun in the middle and a few rings around it.

        Now hold the sheet in two hands in front of you that you only can see the edge of t

  • Earth-sized planets are underrepresented because while we have the right technology, we don't have funding for spacecraft capable of detecting them.
  • Selection Bias? (Score:4, Insightful)

    by The Raven (30575) on Friday March 15, 2013 @07:27PM (#43187311) Homepage

    I am confused... can someone explain how this report is not selection biased against distant or small planets?

    To put it another way, we started by finding huge planets. As we have gotten better methods, we have found successively smaller planets. The three factors that make a planet easy to find are its diameter (occlusion of star), gravitational effect (how much the star wobbles), and distance (how likely that the planet will occlude the star from our perspective, and also factoring into the gravitational effect).

    Distant, small planets simply won't be detected from our perspective. So the report is not really saying 'Only 23% of stars have earth sized planets'. It's really saying 'We know that about 23% of stars have rocky planets that are really close. Since we have no reason to believe our solar system is extremely unique, that makes it very likely that an even greater percentage of stars have rocky planets that are farther out'.

    This is probably a huge boost to the 'how many stars have possible life sustaining planets' factor in that oft derided formula, the Drake equation.

    • by Anonymous Coward

      Kepler observes planets making transits in front of their stars. Over short times of observation, it is easy to detect large planets close to their sun (they make more frequent transits). As the timescale of the datasample increases, we will be able to detect smaller planets further out (which cause a smaller dimming of their star less frequently). Also Kepler can only detect planetary systems who's planets transit their star in our (Kepler's) line-of-sight. So as the sample time increases, more smaller pl

      • by The Raven (30575)

        This is a bit late, but I think you do not understand a simple problem with transit detection: most planetary systems do not orbit in a plane we can detect. To detect planetary transit very close to the star, the range of system planes is pretty high. But the farther out form the star, the fewer and fewer system will EVER occlude from our perspective. Our only way of detecting these systems is by measuring star wobble, and that only detects big planets.

        Se we can use this information detecting nearby occlusi

    • by EnsilZah (575600)

      Alright, I'll take a crack at explaining how it's not selection-biased against distant or small planets.

      The scientists making the observations are only making claims based on the scope of the evidence they have and their understanding of the science.
      Now to make observations without any backing evidence or understanding, reporters are employed (or clergy but not in this specific case).
      Hope that cleared things up.

  • 23 huh? There are also 23 flavors in Dr. Pepper. Is there a connection?
  • by smpoole7 (1467717) on Friday March 15, 2013 @08:47PM (#43187795) Homepage

    "Alone In The Universe: Why Our Planet Is Unique" by John Gribbin. I've just finished it. Those who've always hoped to one day chat with a Wookie or a Klingon (not to mention SETI-types) will find it thoroughly depressing, but it's filled with excellent science. There's a good review of it here:

    http://freethoughtblogs.com/bluecollaratheist/2012/05/29/alone-in-the-universe-why-our-planet-is-unique-part-1 [freethoughtblogs.com]

    Computer geeks will like it because many of its conclusions are based on cluster-run computer simulations. :) The results of the simulations are nothing short of amazing.

    Example: Earth's molten iron core is what gives us a strong magnetic field that protects our atmosphere. The only way they could get that to work out was to put a supernova(!!!) .1 light years (that's not a typo) from the solar system at a critical time while it was forming. This also helps answer why our system has an unusual mix of elements compared to other stellar systems (particularly of radioactives such as Aluminum 26 and Iron 60).

    Example: we're actually a binary planet -- Earth and Moon. The moon is thought to have formed from a planet in the Langrange point, called "Theia," that would have fractured our thick crust, making continental drift possible; the moon's gravitational effects on Earth are also critical.

    Read the book. Even if you disagree with it (and I know many here will, especially my good friends who love SETI), but it's an excellent read.

    • by a_hanso (1891616)

      The rare earth hypothesis has a lot of good points. But at the risk of being ad hominem, the author is the same guy who once supported the theory that planetary alignments could result in earthquakes: http://en.wikipedia.org/wiki/John_Gribbin#Biography [wikipedia.org]

    • by tragedy (27079)

      Hmmm. This book is by John Gribbin. Considering that he predicted that the alignment of the planets would trigger massive earthquakes worldwide and sink LA into the ocean back in the early 1980's, I'm going to take it with a grain of salt. His writing doesn't seem to be based on a lot of evidence.

      Example:

      Example: Earth's molten iron core is what gives us a strong magnetic field that protects our atmosphere. The only way they could get that to work out was to put a supernova(!!!) .1 light years (that's not a typo) from the solar system at a critical time while it was forming.

      What critical time are we talking about here? I'm guessing it's going to be a window of hundreds of millions of years if not billions of years before the actual formation of the sun. Considering that stars

      • by smpoole7 (1467717)

        > I'm guessing it's going to be a window of hundreds of millions of years if not billions of years before the actual formation of the sun.

        Read the book. (It's about a million years, and the star would first shed its outer layers -- now known to be quite common -- then explode about 100,000 years later.)

        If you don't want to buy it, fetch it from the local library or ask a friend to Lend it to you in e-form. But don't criticize it until you've read it. :)

        • by tragedy (27079)

          I read the excerpts available for it from google books. From what I could see, the author doesn't believe in footnotes/endnotes/references/etc., but rather in making authoritative-sounding speculative statements. I'm not going to go out and read an entire book, which just doesn't impress me that much, just to find out the mystery of why a supernova must occur within 1 light year of a star within a 1 million year window in order for it to have any radioactive elements at its core. We're not just talking abou

      • by smpoole7 (1467717)

        Interesting that two people here have brought up Gribbin's old (decades ago) prediction about the alignment of the planets ... which HE HIMSELF later said was bogus. His reputation has been excellent otherwise.

        I cringe when I think of some of the stuff that I used to believe and say. :)

        • by tragedy (27079)

          Well, he certainly did distance himself from it. From what I can find, there wasn't much of a mea culpa in his refutations. He seems to be more prone to say that his mistake happened because he was "too clever by far" (not an exact quote, but it was something like that), or to vaguely imply that it was never really his theory, even though he wrote the book. I mean, it's not as if he didn't write _two_ books about it. One predicting what was going to happen when the planets aligned, then another book explain

    • Example: Earth's molten iron core is what gives us a strong magnetic field that protects our atmosphere. The only way they could get that to work out was to put a supernova(!!!) .1 light years (that's not a typo) from the solar system at a critical time while it was forming. This also helps answer why our system has an unusual mix of elements compared to other stellar systems (particularly of radioactives such as Aluminum 26 and Iron 60).
      This is nonsense.
      Even if we had no strong magnetic field, still 2/3rds

    • by whodunit (2851793)

      The only way they could get that to work out was to put a supernova(!!!) .1 light years (that's not a typo) from the solar system at a critical time while it was forming

      ... what about tidal heating? It sounds like a fascinating scientific examination of how our own solar system came to be, but even if Earth IS unique, it does not follow that only planets identical or almost identical to Earth are capable of supporting life. In fact, an overly terran-centric viewpoint is harmful; from the possibility of life underneath Europa's oceans (enabled by tidal heating) and what we've learned of extremophile bacteria, life can survive and thrive in many more environments then we eve

      • by smpoole7 (1467717)

        Gribbin's point is that Earth is uniquely suited to *INTELLIGENT* life. In the very first chapter he says that, in fact, he thinks that simple single-celled life is probably common in the entire galaxy.

        Sigh.

        I recommended the book because it was a good read. READ THE BOOK. :)

  • Astronomers (and/or the reporters sending these reports) keep making comments like "... there appears to be a mysterious dearth of exoplanets smaller than Earth..."
    and then, later buried in the text:
    "...âoeThis is a guess, but theyâ(TM)re just harder to detect,â Marcy told Discovery News. âoeSmall planets dim the star less â" the dimming has to be greater than the noise to detect the planet...."

    Well, no SHIT, Sherlock. But: Observing a lack of something doesn't mean that something

One man's constant is another man's variable. -- A.J. Perlis

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