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1 in 5 sun-like stars in our galaxy have Earth-like planets.

That's the conclusion of a study of the data amassed by NASA's Kepler Telescope, a robotic planet-finder trailing behind the Earth in its orbit around the sun. Kepler, which examines stars in a small patch of the sky, has identified 156 confirmed exoplanets, and a much larger number of candidates. An "Earth-like planet" is defined as an Earth-sized planet located at the right distance from its star to allow liquid water to exist on its surface.

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More below.

According to the authors of the study:

A major question is whether planets suitable for biochemistry are common or rare in the universe. Small rocky planets with liquid water enjoy key ingredients for biology. We used the National Aeronautics and Space Administration Kepler telescope to survey 42,000 Sun-like stars for periodic dimmings that occur when a planet crosses in front of its host star. We found 603 planets, 10 of which are Earth size and orbit in the habitable zone, where conditions permit surface liquid water. We measured the detectability of these planets by injecting synthetic planet-caused dimmings into Kepler brightness measurements. We find that 22% of Sun-like stars harbor Earth-size planets orbiting in their habitable zones. The nearest such planet may be within 12 light-years.
So that leaves just one question -- one big question: if planets capable of supporting water-based life exist in the billions in our galaxy, where is everybody?

If there are billions of chances for life to appear and evolve, either life is very improbable (and nobody can think of any reason why it should be) -- or else life is not rare, but technological civilizations are very rare.

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Comment Preferences

  •  or the FSM has a fickle appendage (9+ / 0-)
    If there are billions of chances for life to appear and evolve, either life is very improbable (and nobody can think of any reason why it should be) -- or else life is not rare, but technological civilizations are very rare.

    Warning - some snark may be above‽ (-9.50; -7.03)‽ eState4Column5©2013 "I’m not the strapping young Muslim socialist that I used to be" - Barack Obama 04/27/2013

    by annieli on Mon Nov 04, 2013 at 04:59:02 PM PST

  •  Whole lot of dirt out there. (6+ / 0-)

    Ready the wagons!!!

    Thanks, T&R

    "Every book is like a door"

    by Hammerhand on Mon Nov 04, 2013 at 05:10:41 PM PST

  •  We Don't Have the Ability to Detect Life on a (18+ / 0-)

    planet outside our solar system via telescope so we have no knowledge based on planets about the frequency of life.

    Technological life is virtually unknown on earth-- in over 4 billion years, earth's only had it to the degree a species could change its environment through planned activity for just the last 10,000 years. And earth's only had technology to make ourselves discoverable using the kind of technology we have to search now, for the last 100 years.

    We're rapidly migrating our communication onto cables and fibers and very weak transmission to satellites. It could be in 50 years there's almost no broadcast radio leaving the earth at strengths we had before this century.

    So if a remote civilization were just 200 out of 4,500,000,000 years earlier than us to invent radio, they'd have already gone dark by now. Make that 3-500 years to account for signal travel from the nearest few thousand stars.

    And if they're just a little bit slower than us we can't find them yet.

    Civilizations could be relatively common yet with these distances be invisible to each other at least with technology as advanced as we have to search for them right now.

    I don't think we have yet found an atmosphere that contains both oxygen and methane, which would indicate the kind of plant life we've had for the last maybe 2 billion years.

    Too early to be placing bets.

    We are called to speak for the weak, for the voiceless, for victims of our nation and for those it calls enemy.... --ML King "Beyond Vietnam"

    by Gooserock on Mon Nov 04, 2013 at 05:13:02 PM PST

    •  We haven't found any astroengineering projects (7+ / 0-)

      or received any loud radio signals. Nobody seems to be disturbing the universe on a grand scale in our neighborhood.

      And if technological civilizations are common, why hasn't even one of them colonized the galaxy yet? Or unleashed Von Neumann probes? Most estimates of how long it would take for a civilization to "conquer the galaxy" with sub-light-speed travel are on the order of 100 million years. They should be here by now.

    •  We can't detect life per se yet, but we are (10+ / 0-)

      beginning to detect planetary atmospheres. I can tell you flat out that if they find a planet with significant oxygen in the atmosphere, I'm saying there's life there.

      It will probably only be the equivalent of blue-green algae, but hey - they're cute too, and better conversationalists than a Tea Partier is.



      Is it true? Is it kind? Is it necessary? . . . and respect the dignity of every human being.

      by Wee Mama on Mon Nov 04, 2013 at 05:38:56 PM PST

      [ Parent ]

      •  Yes, in another generation (7+ / 0-)

        we will probably have a list of exoplanets with biosignature gasses in their atmospheres.

        If the unexpected diversity of exoplanets is any guide, I would bet that there will be also an unexpected diversity of chemical signals that are hard to explain abiotically.

      •  I am surprised no one mentioned the Drake Eq. (8+ / 0-)

        This latest finding adds one more piece to the Drake Equation.

        In 1961, astronomer Frank Drake laid out a justification for using radio telescopes to observe the cosmos in the search for extraterrestrial life. His rationale for doing so was that no matter how improbable the genesis of life on planet Earth, given the sheer number of stars in the Milky Way galaxy, intelligent species could have evolved simultaneously in significant numbers. Of course, at the time that Drake composed his now-famous equation, we had practically no idea what values to assign any of the variables he used. Thanks to major improvements in imaging technology and our improved understanding of the dynamics of planet formation, we can now be relatively certain of at least a few of the missing values.
        You can try this online, just plug in values you think make sense.  (e.g.,  number of stars = 300 Billion, add this articles current claim of 20% Earth-like, assume 1 planet per solar system actually has life, of that intelligent life happens 100% of the time and 100% of those communicate and last for 100,000 years....

        For that range of variables, I get only 600,000 planets with communicating, intelligent life... out of 300 billion stars.  That is about 2 in a million.  Using more conservative estimates (e.g. 10% of life becomes intelligent) you rarely get above 40,000 as N (the number of communicating intelligent civilizations in the galaxy). That puts the odds at about 1 in 10 million. Often, I get less.

        To put that in perspective, assume there are about 300 million people in the USA.  Using the favorable odds (2 in a million), that would be about 600 people.  If you picked 600 random people in the US, would you be surprised if you didn't know any of them?  Would you be surprised if you went your whole life without ever meeting any of those 600 people?  

        Using less favorable odds (1 in 10 million), you would drop that number down to a mere 30.  Even if those 30 were trying to find each other, would you be surprised if they never did?

        "When puzzled, it never hurts to read the primary documents—a rather simple and self-evident principle that has, nonetheless, completely disappeared from large sectors of the American experience." -- Stephen Jay Gould

        by 8ackgr0und N015e on Mon Nov 04, 2013 at 06:59:03 PM PST

        [ Parent ]

        •  I taught a seminar once on the Rare Earth (4+ / 0-)
          Recommended by:
          atana, cotterperson, Lawrence, mayim

          hypothesis. At the end we added new variables to the Drake equation based on work since he wrote it. The class split into groups and found best and worst case estimates for all the variables. When we evaluated it with all best case it predicted about a billion planets. When we used all worse case it predicted eight planets.

          Eight.

          And I'm sure there are still variables we don't appreciate yet.



          Is it true? Is it kind? Is it necessary? . . . and respect the dignity of every human being.

          by Wee Mama on Mon Nov 04, 2013 at 07:14:55 PM PST

          [ Parent ]

          •  It's clear the big drivers in that equation (2+ / 0-)
            Recommended by:
            Wee Mama, atana

            are the denominator (how many stars do you start with), and the time to exist as a detectable communicator.  

            If you take the 8 billion stars as the denominator -- assume 100% across the board and 10,000 years for communicators -- you get N = 8,000.

            Of course, you have to be communicating at the time someone is able to receive it... so that knocks things down even further.  After all, you could imagine a whole host of scenarios where increasing intelligence rapidly leads to extinction, or at least degrades the civilization to the point they are no longer generated detectable communications.

            "When puzzled, it never hurts to read the primary documents—a rather simple and self-evident principle that has, nonetheless, completely disappeared from large sectors of the American experience." -- Stephen Jay Gould

            by 8ackgr0und N015e on Mon Nov 04, 2013 at 07:24:32 PM PST

            [ Parent ]

            •  The big news here is that this is the first time (0+ / 0-)

              we have an empirical estimate of fp*ne.

              fi is still in the "educated guess" realm. Not many people would today guess it to be very,very small (a la Tippler). As Wee Mama pointed out, in a few decades we may have empirical evidence supporting some particular value for fl. It will be a big surprise if we find no biosignature gases anywhere.

              fi, fc, and fL are anybody's guess. Based on Earth, it's difficult to be optimistic about fL.

        •  You can check my numbers: (0+ / 0-)

          Take 10 Billion as the number of suns in the galaxy because that is the number with planets that support life.  We ignore the other 290 billion.

          Assume, per this article, 20% of these suns have 1 planet that supports life.

          Now generously assume that 100% of the time you get intelligent life and that life can communicate.

          Assume they are able to communicate for 10,000 years, which is about 100x what we have been able to achieve.

          That gives you a mere 2,000 candidates.  

          Up the time to communicate to 100,000 years and you get 20,000 candidates.  

          The net result?  We haven't moved the needle very far from our initial guesses.

          "When puzzled, it never hurts to read the primary documents—a rather simple and self-evident principle that has, nonetheless, completely disappeared from large sectors of the American experience." -- Stephen Jay Gould

          by 8ackgr0und N015e on Mon Nov 04, 2013 at 07:14:57 PM PST

          [ Parent ]

          •  Erratum (0+ / 0-)

            I should have said 10 billion capable of supporting life, but 20% actually support life.

            If you took the 10 billion and said everyone of them had a planet that supported intelligent life we could communicate with, and they were doing that for 10,000 years, you would only get N = 10,000.

            We really aren't moving the needle much.

            "When puzzled, it never hurts to read the primary documents—a rather simple and self-evident principle that has, nonetheless, completely disappeared from large sectors of the American experience." -- Stephen Jay Gould

            by 8ackgr0und N015e on Mon Nov 04, 2013 at 07:18:05 PM PST

            [ Parent ]

        •  I would like to know the values you used (1+ / 0-)
          Recommended by:
          Wee Mama

          for the various factors.

          I got N=0.6 the first time through, using
          N*=300 billion
          fp = 20%
          ne=1
          fl=100%
          fi=0.1%
          fc=1%
          and fl=100 years

          You might call that selection of parameters bio-optimistic and techno-pessimistic. But you can get pretty much any number you want out of the Drake equation depending on just how bio/techno optimistic/pessimistic you are.

          I think I am a little less bio-optimistic than fl=100%, but I doubt fi and fc are large.

          •  Oops, 20% of "sun-like stars", not all stars (1+ / 0-)
            Recommended by:
            Wee Mama

            I suppose "sun-like stars" are those within a spectral class or so of the Sun... K7 to G7? or so? What is that, 10% of all stars? If so, N*=30 billion, not 300, and N=0.06.

            Anyway, my point was that techno-pessimism can solve the Fermi paradox very easily. I consider bio-pessimism less well supported. And I consider all the schemes for hiding ET to be violations of Occam's Razor.

        •  Unless each of the thirty (3+ / 0-)
          Recommended by:
          atana, Wee Mama, VickiL

          was generating a VERY large signal of some sort and actively looking for signaling from the other 29, I wouldn't expect them to find each other.

          Perhaps, by random chance, two might be in the confines of New York City's space and locate each other in some simulations.  But most likely, unless they actively look and actively signal, no.

          Given that we know of one civilization, and said civilization isn't actively signaling very loudly, it's no surprise we see nothing when we look.

          (-6.38, -7.03) Moderate left, moderate libertarian

          by Lonely Liberal in PA on Mon Nov 04, 2013 at 07:43:03 PM PST

          [ Parent ]

          •  Bingo. (2+ / 0-)
            Recommended by:
            Wee Mama, Lonely Liberal in PA

            Even if they were trying something like smoke signals, you would have to be within about 20 miles of each other.  A light might travel further if you were on top of a mountain.  That gives you an effective area of about 1,250 square miles. (pi*20^2) With about 4 million square miles to the US, that only gives you something like .03% of the area.  Not strong odds to find someone.

            "When puzzled, it never hurts to read the primary documents—a rather simple and self-evident principle that has, nonetheless, completely disappeared from large sectors of the American experience." -- Stephen Jay Gould

            by 8ackgr0und N015e on Mon Nov 04, 2013 at 08:02:41 PM PST

            [ Parent ]

            •  Well, but there might be other ways a civilization (2+ / 0-)

              could make itself known -- like launching von Neumann probes.

              •  True (1+ / 0-)
                Recommended by:
                atana

                And that would result in an exceptionally large signal, akin to each of the 30 people mentioned above burning a city--and each of the 30 having satellites that can see the entire USA.

                They'd find each other easily.

                That implies that:

                1)  There's no civilization capable of creating von Neumann machines.

                or 2)  No civilization has chosen to do so.

                or 3)  Said probes are too energy-intensive to bother creating (or there's some other engineering hurdle that makes them unusable).

                There's tons of other solutions, including machine evolution, but these top three cover it pretty well with the others being lower probability and something creating races would think about.

                Given the state of things on planet Earth these days, my current bet is #1.

                (-6.38, -7.03) Moderate left, moderate libertarian

                by Lonely Liberal in PA on Mon Nov 04, 2013 at 08:37:46 PM PST

                [ Parent ]

                •  That's my bet too (1+ / 0-)
                  Recommended by:
                  Lonely Liberal in PA

                  The problem with #2 is that it only takes one civilization to do it.

                  •  Maybe (1+ / 0-)
                    Recommended by:
                    Wee Mama

                    If I were programming von Neumann machines, there would be a very wide determination of a life-bearing system and the unmistakable command to avoid them even if there's a faint question about it (or at least to explore only and avoid mining resources within those systems).

                    It just seems neighborly not to randomly consume moons or planets, create gravitational shifts, and potentially destroy the system's life.

                    Plus I wouldn't wish to draw attention to my home system just in case the life in question isn't exactly friendly.  What one species can engineer another can reverse-engineer, weaponize, and send back out.

                    (-6.38, -7.03) Moderate left, moderate libertarian

                    by Lonely Liberal in PA on Mon Nov 04, 2013 at 09:06:57 PM PST

                    [ Parent ]

                    •  The von Neumann machines would probably (2+ / 0-)
                      Recommended by:
                      Lonely Liberal in PA, Wee Mama

                      have to be adaptive -- capable of producing a diversity of offspring. They would evolve, and it might not be possible to ensure that they would always adhere to some fixed ethical code.

                      I'm just playing Devil's Advocate here. I think that the human concept of "technology" as something that conquers the universe probably says more about humans than it does about the universe.

                      The fact that the universe appears to be unconquered argues against that type of technology as a basic feature of the universe.

                      •  "Appears to be" (1+ / 0-)
                        Recommended by:
                        Wee Mama

                        being the operative phrase, here.  Any cosmo-engineering so grand as to encompass the entire visible Universe wouldn't be determinable to be engineering.  We'd just see it as the Universe.

                        That would require a technology developed early on--very early--and quickly, so I consider it unlikely.

                        My core take on von Neumann machines is, for the most part, why bother?  What they can learn or produce and bring back won't benefit me or even ten generations from now.  Perhaps not even a hundred generations.  We have, and probably always will have, far more immediate problems.

                        Their use to mine resources from Earth's oceans (for instance) can't be underestimated, however, and a use that does have a more immediate benefit.

                        (-6.38, -7.03) Moderate left, moderate libertarian

                        by Lonely Liberal in PA on Mon Nov 04, 2013 at 09:35:19 PM PST

                        [ Parent ]

                        •  Why wouldn't we see some engineered sections (2+ / 0-)
                          Recommended by:
                          Lonely Liberal in PA, Wee Mama

                          some unengineered sections? E.g. why is there not even one Kardashev Type III radio source in the Earth's radio sky? We would have noticed it.

                          •  Would we? (1+ / 0-)
                            Recommended by:
                            Wee Mama

                            Devil's Advocate, here.  As our technology matures, we're radiating less and less in the way of waste radio waves into the cosmos.  There's no need to.

                            Besides, digital cable is a lot crisper.

                            Most of our transmissions are lower powered and satellite-bounced.  There's not much waste there for somebody to see.

                            Additionally, it's really early days yet, comparatively speaking.  The Universe is still an extremely young and immature 14 billion, with still close to 100 trillion years remaining before the end of the Stelliferous Era.

                            That's a lot of time.  And a lot of space to have that time in.

                            It's entirely possible that we're...well, not the first, that would be unlikely, but very early.  The party may not start for another twenty billion years or so, and before this the Universe was more energetic (and hence more dangerous) than today.

                            The middle age will feature a lot less in the way of active galactic black holes, GRBs, and whatnot.

                            (-6.38, -7.03) Moderate left, moderate libertarian

                            by Lonely Liberal in PA on Mon Nov 04, 2013 at 10:09:16 PM PST

                            [ Parent ]

                          •  Ok, a galaxy-scale infrared source, (1+ / 0-)
                            Recommended by:
                            Wee Mama

                            every star inside a Dyson sphere. That strong an infrared source have been noticed by infrared astronomers.

                            You can't hide every advanced ET civilization with special pleading if there are huge numbers of them.

                          •  Possibly (1+ / 0-)
                            Recommended by:
                            Wee Mama

                            But I'd consider such an event rare (as we see tons of galaxies out there that are un-Dysoned).  And we haven't really looked all that closely yet.

                            I don't conjecture that there are huge numbers of ETs meandering around out there (or happily staying home in their galaxy, whatever they prefer).  If anything, I conjecture the number of ETs currently at or beyond 20th century Earth levels of technology to be comparatively small.  

                            Given our current understanding--which could be wrong--interstellar travel on a grand scale seems exceedingly difficult and energetically expensive.  Most ETs would stay in their home solar systems if that's the case.  

                            Again, the returns on investment are too low at 21st century technological levels to even consider doing it other than as a pure exercise we may do rarely, a la Voyager 2.

                            Absence of evidence isn't evidence of absence, but if a Type III were close and had dropped a Dyson around every star, it would stand out like a sore thumb.  So at the very least, they aren't close enough for us to notice an IR-only galaxy floating around out there.

                            (-6.38, -7.03) Moderate left, moderate libertarian

                            by Lonely Liberal in PA on Mon Nov 04, 2013 at 10:29:34 PM PST

                            [ Parent ]

                          •  Like most people's middle ages :-D (1+ / 0-)
                            Recommended by:
                            Lonely Liberal in PA



                            Is it true? Is it kind? Is it necessary? . . . and respect the dignity of every human being.

                            by Wee Mama on Tue Nov 05, 2013 at 05:00:53 AM PST

                            [ Parent ]

  •  Where is everybody? (4+ / 0-)
    Recommended by:
    julesrules39, cotterperson, mayim, VickiL

    Well, with over 8 billion other planets to choose from there are plenty of planets the Kewl Kids to hang out on.
    I'm afraid we're too young and dumb and full of...

    -4.38, -7.64 Voyager 1: proof that what goes up never comes down.

    by pat bunny on Mon Nov 04, 2013 at 05:18:03 PM PST

    •  Here's a good site on the Fermi Paradox (7+ / 0-)



      Is it true? Is it kind? Is it necessary? . . . and respect the dignity of every human being.

      by Wee Mama on Mon Nov 04, 2013 at 05:42:21 PM PST

      [ Parent ]

      •  Thank you for that link (2+ / 0-)
        Recommended by:
        Wee Mama, cotterperson

        I've incorporated it into the diary.

      •  Thanks, Wee Mama. (2+ / 0-)
        Recommended by:
        Wee Mama, mayim

        A snip from your fine link:

         

        The Fermi paradox is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for, or contact with, such civilizations.
        These planets have conditions suitable for water, and we're watery people on a watery planet. IOW, we're looking for life like our own. However, just because the conditions exist doesn't mean the planets have water or watery inhabitants, nor does it mean they are "like us."

        Just re-watched an old mini-series of Ray Bradbury's Martian Chronicles on archive.org. Most thought provoking, because the Martians had evolved into energy and took the form of matter when they needed to.

        Fascinating stuff. I just hope we're not too parochial ;)

        "Let each unique song be sung and the spell of differentiation be broken" - Winter Rabbit

        by cotterperson on Mon Nov 04, 2013 at 09:12:49 PM PST

        [ Parent ]

        •  We're looking for liquid water, yes. (2+ / 0-)
          Recommended by:
          Wee Mama, cotterperson

          because that's what makes our kind of biochemistry possible.

          Basically, life is swarms of nanomachines -- proteins, ribozymes, DNA, RNA -- and carbohydrates, which are more repetitive molecules. Our nanomachines depend on water to work.

          Conceivably, you could have life based on nanomachines in some liquid other than water, but it would be chemically very different from Earth life, and we wouldn't know what to look for. (But when the Huygens lander splashed down on Titan, everybody who looked at those pictures was probably hoping to see some improbably shaped object.)

          It is hard to imagine naturally evolved life based on nanomachines that don't require a liquid of any kind. Electronic devices are like that, but could complex electronic life they evolve without us more motile forms assisting them?

  •  No doubt that I have a cousin on one ... (2+ / 0-)
    Recommended by:
    Wee Mama, cotterperson

    of those planets too.


    Crossing the street is a noble endeavor. I’m on a personal mission to bring boy scouts and little old ladies together. - 16382

    by glb3 on Mon Nov 04, 2013 at 05:30:00 PM PST

  •  They're all living on the inside of Dyson Spheres (8+ / 0-)

    So of course we can't see them.

    BTW, don't forget that it's not just Earth sized planets that can support life, but all those Jupiter and super-Jupiter sized planets can have lots of moons which could support life, so there could be many more Earth type moons than planets.

    There are really only 10 kinds of people in this world; those who understand Binary, and those who don't.

    by Fordmandalay on Mon Nov 04, 2013 at 06:22:54 PM PST

    •  While it's true that gas giants in the habitable (4+ / 0-)
      Recommended by:
      atana, VeggiElaine, mayim, Turn Left

      zone are likely to have satellites, there are still some important questions about those satellites before they're likely to be friendly to life. Obviously enough water and a non-toxic atmosphere, but having those is less likely the smaller the satellite is. An additional limit is what the satellite is like in terms of its composition and so on - the Jovian satellites give us a glimpse of that variety, which results from the distance from the gas giant at the time of satellite formation.

      It's tough being green. Too early to say impossible, but a lot tougher than we thought when I was young.



      Is it true? Is it kind? Is it necessary? . . . and respect the dignity of every human being.

      by Wee Mama on Mon Nov 04, 2013 at 06:42:07 PM PST

      [ Parent ]

    •  Also, the study considered only sun-like stars (5+ / 0-)

      and stars cooler than the sun might also have planets in habitable zone -- or habitable moons of giant planets.

      So yet -- 8.8 billion is possibly an underestimate.

      But that only makes the Fermi question more puzzling.

      •  I'm toying with the idea of writing about whether (3+ / 0-)
        Recommended by:
        Lonely Liberal in PA, atana, mayim

        planets around red dwarfs are habitable, since there are so many of them. The habitable zone is much closer in and any planets in it are phase locked with the star. Planets without any atmosphere are necessarily sterile. Planets with an atmosphere and water raise complicated questions in a phase locked situation. A recent 3D model predicted that there would be extensive cloud formation at the point facing the star: this would reflect some light and heat and perhaps move the habitable zone further in. However, one consequence of a perpetual storm at the subastral point is that it would increase rock weathering which could potentially withdraw the needed carbon dioxide, and you could end up with a frozen planet anyway. It's not clear that a stable friendly solution is possible for the phase locked planets.

        Oh, and red dwarfs are much more variable than our sweet Sun so every million to ten million years you fry.



        Is it true? Is it kind? Is it necessary? . . . and respect the dignity of every human being.

        by Wee Mama on Mon Nov 04, 2013 at 07:30:30 PM PST

        [ Parent ]

        •  True, although (2+ / 0-)
          Recommended by:
          atana, Wee Mama

          current theory indicates that flare activity decreases with age.  Although we've found some older red dwarf stars that do flare as well, and late K class stars (technically orange) can flare.

          That's still not a barrier for mid-K class.

          I'm not sure what they're calling "Sun-like," since the Sun is class G2V, or pretty close to the top of the G class.

          Still, even if an M-class star flares for ten billion years of its life, they can live up to a trillion years or so.

          (-6.38, -7.03) Moderate left, moderate libertarian

          by Lonely Liberal in PA on Mon Nov 04, 2013 at 07:52:59 PM PST

          [ Parent ]

  •  A number of issues with this study (3+ / 0-)
    Recommended by:
    atana, Wee Mama, Turn Left

    Just a few things jump right out:
    1. There is no indication, in the abstract, of what constitutes a "sun-like" star. If we assume that "sun like" is anything in spectral classes F, G, and K (makes sense, considering Sol is G-I), that's about 20% of the stellar population.
    2. They're counting any planet that gets anywhere between 4x and .25x Earth's solar radiation. In other words, their "habitable zone" is effin' HUGE. Recent research indicates that Earth is actually pretty darn close to the inner edge of its habitable zone, because any closer and the planet begins to lose hydrogen. (Slowly, but over billions of years it adds up.) So right there, the "habitable zone" is twice too big on the inner side. And on the outer side, Mars gets half the solar radiation of Earth, and okay, maybe if it were larger and had a nice greenhouse it would be nicely habitable at that distance. But getting only a quarter of Earth's sunlight? Still habitable? Reeeealy? Forgive my doubts.

    So the way I see it, these guys have at least 4x too many planets called "habitable". And in fact, if you read the actual abstract instead of the PNAS press release, the authors agree: the 22% number drops to 5.7%.

    So 5.7% of sunlike stars with habitable planets, and 20% of stars are "sunlike", that gives us 1.14% of all stars which are sunlike with planets in the H-zone, or 2 billion-ish in the Milky Way.

    So lets say 1 in 4 of those have life, with the rest too hot or too cold or too unstable long term. now were down to half a billion. Let's say of the ones with life, 99% never develop past the bacteria stage. Now we're down to 5 million. Lets say that of the ones with complex life, 99.9% never develop intelligent life. Now we're down to 5000.

    And of those, how many blow themselves up, or destroy their own planet, or just don't think of radio, or spaceships, or have no interest in astronomy, because maybe their planet is permanently cloudy?

    And even if it's 5000 civilizations and they're all long-term, the average distance between them would be 2500 light years. Which means communication is essentially impossible with any current or projected technology.

    So that's my take on the Drake Equation.

    We are all in the same boat on a stormy sea, and we owe each other a terrible loyalty. -- G.K. Chesterton

    by Keith Pickering on Mon Nov 04, 2013 at 07:43:57 PM PST

    •  I would estimate the step from "bacteria" (3+ / 0-)
      Recommended by:
      Wee Mama, Turn Left, Keith Pickering

      to "eukarya" and multicellularity as a bit more likely than 1 in 100.

      It depends a lot on how much time the biosphere has. If Earth is very rare in having been able to maintain a biosphere for 4 billion years because of supernovae or something, then all bets are off. But it took perhaps 2 billion years to evolve complex symbioses (eukarya) and then about another billion years to evolve multicellular forms. The chemistry of the oceans and the atmosphere was changed from anoxic to oxygenated along the way, and the dissolved iron in the anoxic oceans had to be precipitated out before the oceans became oxygenated, which took a long time.

      Biochemistry that releases oxygen evolved in the Archean; oxygen toleration came later, probably early Proterozoic. Oxygen metabolism, perhaps middle Proterozoic. Multicellularity, late Proterozoic. It's hard to see how the process could have been a lot faster. And it weathered some very chilly episodes in the Proterozoic.

      I don't see that evolution as inherently very unlikely, given enough environmental stability along the way -- i.e. no major stellar outbursts, no nearby supernovae or unlucky beam sweeps from nearby gamma ray bursters etc.

      •  It's those kinds of stellar misadventures that led (2+ / 0-)
        Recommended by:
        Theodore J Pickle, atana

        to people describing a "habitable zone" for galaxies as well - too close to the center, odds are high you fry. Too far out, the dust is too thin to make a lot of good planets.



        Is it true? Is it kind? Is it necessary? . . . and respect the dignity of every human being.

        by Wee Mama on Tue Nov 05, 2013 at 05:06:19 AM PST

        [ Parent ]

      •  Yeah, it's the stability (2+ / 0-)
        Recommended by:
        atana, Wee Mama

        over the very long term that is really the kicker, and about that we have very little information.

        My personal suspicion is that M class stars are where we're going to find interesting things, like civilizations. There's just so many of them. But G stars, like us, I'd bet we're really unusual in the civilization game.

        We are all in the same boat on a stormy sea, and we owe each other a terrible loyalty. -- G.K. Chesterton

        by Keith Pickering on Tue Nov 05, 2013 at 12:17:20 PM PST

        [ Parent ]

  •  People talk about life arising as if it were (2+ / 0-)
    Recommended by:
    atana, mayim

    inevitable, but the more I know about it the less that seems like a necessity. To take one example, a key enzyme for fixing carbon dioxide, Rubisco, appears to have evolved exactly once. This is odd when you consider that eyes with lenses have evolved several times; it doesn't at first glance seem plausible that it would be that hard to evolve an enzyme to fix carbon dioxide. Yet not only has this function evolved only once; it's also a crappy enzyme. It appears that cells can't improve on it much, since they've had three billion years to tweak it and it's still a poor enzyme. Life is weirder than we think.



    Is it true? Is it kind? Is it necessary? . . . and respect the dignity of every human being.

    by Wee Mama on Mon Nov 04, 2013 at 08:29:49 PM PST

  •  The Main Issue is How Long Can a Tech Society Last (3+ / 0-)
    Recommended by:
    atana, Wee Mama, Turn Left

    One of the postulations I have read (and am far too lazy to look up) is that once a society hits a certain technological threshold it is almost certain that it will destroy itself within two or three centuries.  Given the vast distances involved and the age of the universe, the odda of two societies existing close enough at the same time to become aware of one another in that small a window are virtually zero.

    There is a time to think and a time to act and this gentlemen, is no time to think! Bud Boomer

    by celtic pride on Mon Nov 04, 2013 at 11:08:25 PM PST

  •  "Where is everybody?" (2+ / 0-)
    Recommended by:
    Wee Mama, VickiL

    They're probably pretty far away, at least by our standards.

    Or they could be pretty close, by galactic standards, and we just don't know it.

    Very interesting news.

    Tipped and recced.

    "A candle loses nothing by lighting another candle" - Mohammed Nabbous, R.I.P.

    by Lawrence on Tue Nov 05, 2013 at 03:12:29 AM PST

    •  Star Trek Theory - we are quarantined (1+ / 0-)
      Recommended by:
      Lawrence

      until we reach technological maturity

      •  That's quite possible, imo. (1+ / 0-)
        Recommended by:
        VickiL

        Seeing that our civilization is quite young by galactic standards, many of the other possible civilizations out there will be far more advanced than we are, so I find it doubtful that nobody out there is aware of us.  If their technological advances progressed in a similar manner to ours, their civilizations may be hard to imagine for us even if they are just a few thousand years more technologically advanced than we are.

        I wouldn't be surprised if we are on numerous lists of habitable zone planets being examined by scientists on other planets.

        "A candle loses nothing by lighting another candle" - Mohammed Nabbous, R.I.P.

        by Lawrence on Tue Nov 05, 2013 at 05:52:53 AM PST

        [ Parent ]

        •  Biological life may fall to technological life (1+ / 0-)
          Recommended by:
          Wee Mama

          Biological life is very fragile.  A supernova or gamma ray burst would easily snuff it out as it is evolving. I would think that 99% of life these warm water worlds may never get out of the bacteria stage.

          1% of those evolve into animals and an even small percentage of those become intelligent.

          Once intelligent, they quickly start building machines.

          •  It's hard to say, imo. (1+ / 0-)
            Recommended by:
            Wee Mama

            Are we really that rare here on earth or are we just average, as far as the evolution of life on earth-like planets goes?

            It seems to me that, as we gain more knowledge, it becomes clearer that we aren't that rare.

            In a pretty short time frame we've gone from thinking that we are unique to realizing that there probably are billions of planets just in our galaxy that are similar to ours, so we may be in for some surprises in regards to the hardiness and evolution of life on other planets.

            Even if there are "just" a few million planets in our galaxy that have technologically advanced civilizations on them... if merely half of those are more advanced than we are, then there are a lot of civilizations out there that are probably unimaginably advanced in comparison to us.

            "A candle loses nothing by lighting another candle" - Mohammed Nabbous, R.I.P.

            by Lawrence on Tue Nov 05, 2013 at 06:30:34 AM PST

            [ Parent ]

            •  a small window for intelligence (1+ / 0-)
              Recommended by:
              Wee Mama

              Sentient humans have been around for a few million years and have only been "technologically advanced" for the last 200 years.   A micro-blink when you consider the billion-year time frames of the universe.  

              In the next 100 years, some humans may be "cyborg" and in a thousand years humanity may be all machines.

              If space-faring aliens exist, chances are that they are all machines

  •  There had to be a lot of things to occur in this (2+ / 0-)
    Recommended by:
    Wee Mama, atana

    planet's formation for humans to develop an industrial, technological civilization. Just a few that come to mind include:

    -Abundant iron that eventually led to manufacture of steel
    -Abundant coal to fuel an ever-growing industrial capacity
    -Abundant copper to allow transmission of electricity
    -Abundant oil to propel the industrial revolution to its current heights
    - Abundant food to allow the growth of populations which created the need for advanced industry and other facets of modern civilization.
    -An environment both climatically and geologically stable enough to allow humanity's technological development without catastrophic disruption

    There are many more such things that I'm sure others can think of.

    Assuming that the kind of industrial/technological base we have created on this planet is a necessary precursor to space flight and/or searching the galaxy for life, even if intelligent life evolved on other planets, would they be able to develop an industrial capacity to do these things if they lacked even one of our necessary resources on this list?

    What if they lacked copper? or abundant fossil fuels? The processes that created fossil fuels in such enormous reserves on this planet are not necessarily a given for any other planet, IMO. Without fossil fuels to create the high temperatures needed to work with advanced metallurgy, or power a large industrial base, could they ever advance beyond the level of a wood or stone-based civilization?

    I think it likely that there is a lot of life out there, even intelligent life. I think it unlikely that there are a lot of advanced civilizations capable of any level of space flight, or communication beyond its own planet.

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