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Centauri Planets: Year-End Thoughts

The title of yesterday’s post — ‘The Odds on Centauri’ — would fit well with today’s musings. Alpha Centauri makes us ponder the odds not just in terms of interstellar bets and future space probes, but also in terms of the likelihood of life around these stars. And after all, 2008 saw significant work on this question, including the contributions of Philippe Thébault (Stockholm Observatory) and colleagues, whose studies of Centauri A and B show that while stable planetary orbits exist there, the odds on those planets forming in the first place are long.


Greg Laughlin (UC-Santa Cruz) isn’t necessarily daunted by this work (he explains why here), but the planet-hunter extraordinaire is realistic about life-bearing planets in this environment, and even more judicious about the possibility of a technological society making its home in the system. The question rises naturally out of recent publicity given the 20th Century Fox film The Day the Earth Stood Still, in which it was announced that the entire movie had been beamed in the direction of Alpha Centauri as a publicity stunt.

Image: Centauri A and B hanging over the horizon of Saturn. This Cassini image was captured captured from about 66 degrees above the ringplane and faces southward on Saturn. Ring shadows mask the planet’s northern latitudes at bottom. Credit: NASA/JPL/Space Science Institute.

The question: If somehow this transmission made it to Centauri, would there be anyone there to watch it? We’ll leave aside the issues that plague the original transmission, factors such as the fact that Alpha Centauri is barely above the horizon in Florida, and at the time of the transmission, according to Laughlin, “Alpha Cen (RA 14h:39m, DEC -60deg:50min) was below the horizon as viewed from 28 35 06N, 80 39 04W.” Forget that for a moment. Let’s just ask whether there might be, around one of the Centauri stars, a planet that could house a technological civilization.

Here’s what Laughlin came up with in a recent systemic post:

fp = Chance of a habitable planet orbiting Alpha Cen B = 0.6

fl = Chance that life evolved on that planet = 0.01

fi = Chance that life developed intelligence = 0.1

fr = Chance that intelligence understood Maxwell’s Equations = 0.01

fn = Chance that Maxwell’s Equations are currently understood on Alpha Cen Bb = 64,000 / 3×109 = 0.0000213.

This gives (fp)x(fl)x(fi)x(fr)x(fn) = one in eight billion, with Alpha Cen Ab kicking in an additional one in a trillion chance.

Of course, we’re plugging in most of these parameters without being able to do more than guess at their true value. Laughlin asked students in his classes, for example, to choose a value for fn based on their own estimate of how long a society will build radios. We also have to approximate values like fr, re an intelligent being’s capacity to understand Maxwell’s equations, and so on. There is not, in other words, a reason to abandon interest if you are one of those who hope for great things around Centauri, but it’s sobering to see that as things stand now, one in eight billion is a reasonable figure.

The exciting thing about our era of exoplanet discovery is that we learn game-changing things on a frequent basis. I, for one, would be delighted with the discovery of a small, rocky world around either of the major Centauri stars, one from which future study might extract spectroscopic evidence of life of whatever kind. But I’ll also be delighted at whatever we learn about planetary formation in the close binary environment, because that will help us understand how likely habitable planets may be around many stars. And if it turns out there is no one to watch The Day the Earth Stood Still wherever its stray signal may turn up, I can’t say that our hypothetical extraterrestrials will have missed much.

Addendum: Anyone who enjoyed the 1951 original of The Day the Earth Stood Still will want to read Brett Holman’s comments on the film in his superb Airminded blog. I particularly like his last line: “I do wonder just how credible a threat is a fleet of flying saucers flown by robots who can be pacified simply by speaking the words ‘Klaatu barada nikto‘?”

Comments on this entry are closed.

  • James M. Essig December 31, 2008, 21:36

    If there is even a remote chance that nearby worlds could have ETI civilizations on them, perhaps even hydrocarbon based DNA life forms, I think that we humans should definately send probes to such systems, followed by manned exploratory missions.

    The potentially wide variety of ETI bodily forms and psychodynamic makeups intreagues me to no end. Our colleagues who work in the still theoretical fields of exobiology, exopsychology, exosociology, and exopolitics would just love the future discovery of any forms of ETI civilizations.



  • Adam January 1, 2009, 2:47

    Ohhh… that’s a bit harsh! I thought it was a good film – but then I like anything with Jennifer Connelly or Keanu Reeves in it. I did like all the effort for accuracy, even the chalked equations were correct. The “nano-bugs” looked like CGI borrows from “Red Planet”, but I can’t fault the fluid dynamics number crunching that went into the “Grey Swarm”.

    One quibble… with all the effort for accuracy, then why the inexplicable “space-drive” that brought Klaatu’s fleet to a screeching halt from 0.1 c?

  • Enzo January 1, 2009, 23:02


    Would you mind posting a link to a higher res image of the Centauri
    system from Cassini ?
    I assume you got a better res image from the Cassini site.

    Thank you.

  • Didac January 2, 2009, 7:38

    A problem exists on sending probes to Alpha Centauri as suggested by Essig. If a 21st century program is developed in this sense, a idea will arise: it is not better to wait to 22nd century technlogy? If you do not wait, your 21st century probe will be easily surpassed by more moderns 22nd century probes. But, if you wait, it is very probable that your 22nd century grandchildren will do the same thinking on 23rd century technology. You know, 0.01 c is better than 0.001 c, but 0.1 c is better than 0.01 c, and so on…

  • Administrator January 2, 2009, 9:16

    Enzo, try this for a higher resolution image:


  • Administrator January 2, 2009, 9:17

    Didac, your question takes us back to the ‘wait equation,’ an interesting issue indeed:


    And we’re a long way from being finished with the debate on this one!

  • ljk January 2, 2009, 21:09

    A poster on another Web site brought up a very interesting point
    in regards to the motives of the aliens in the reimaged TDTESS:

    How did these technologically advanced ETI reach their level of
    development without restructuring or causing some kind of loss
    or harm to their native environment?

    Even if they got everything from someone else, then where did
    those beings get their knowledge and technologies from?

    Somebody had to break a few eggs to make their omelettes,
    so why was it okay for them to dig up a planet or two (or maybe
    even a whole solar system or two) and no doubt disrupt an
    ecosystem in the process, yet we humans are punished for
    attempting the same thing on our way to hopefully making
    our own interstellar society? Which the aliens conveniently
    took care of by destroying all our technology in the new film.

    So who decides who gets to fly about the galaxy passing
    judgement on other societies?

    Of course the real culprit here is Hollywood with what they
    consider to be a well-meaning but ultimately misguided
    message about Earth’s environment and how humanity is
    wrecking everything for everybody else. Getting rid of
    humans is not an ultimate solution, because as we have
    seen nature itself has wiped out many, many species over
    the last 4 billion years before we ever came on the scene.

    So why didn’t the film aliens banish or pulverize all planetoids
    and comets, since they have killed many creatures on this
    planet for eons. As I said, a misguided message that supports
    throwing out the baby with the bathwater.

    At least in the far superior 1951 film, the ETI just came to
    warn us not to soil their galactic country club with our
    barbaric manners or else. Otherwise we could do as we
    please with our world.

  • Enzo January 2, 2009, 23:37

    Thanks Paul.
    Thanks to your link I also managed to find the original PIA here :

  • Ronald January 3, 2009, 19:40

    What I find particularly interesting is the big difference between Laughlin’s first two variables:

    fp = Chance of a habitable planet orbiting Alpha Cen B = 0.6

    fl = Chance that life evolved on that planet = 0.01

    This implies, in other words, that there is a very great chance of an inhabitable planet near Alpha Cen B, but only a small chance of indigenous life there.

    Precisely this would make Alpha Cen Bb a prime target for (terraforming and) colonization.

  • ljk April 16, 2009, 10:23

    April 8, 2009

    IYA Live Telescope Today – Alpha Centauri and Eta Carinae

    Written by Tammy Plotner

    On April 8, 2009 the IYA Live Telescope was busy broadcasting from the Southern Galactic Telescope Hosting facility and fulfilling your “100 Hours of Astronomy” requests.

    Are you ready to take a look at the video that came from the adventure and to add it to our library? Then come along as we view Alpha Centauri for Astrochick and Eta Carinae for Vino…

    The following factual information is a cut and paste from Wikipedia:

    Alpha Centauri – Constellation: CENTAURUS

    Alpha Centauri, also known as Rigil Kentaurus, Rigil Kent, or Toliman, is the brightest star in the southern constellation of Centaurus and an established binary star system, Alpha Centauri AB. To the unaided eye it appears as a single star, whose total visual magnitude identifies it as the third brightest star in the night sky.


  • ravikant August 23, 2009, 22:34

    this is a nearest star system from the sun so it is a great news to ideantified a planet earth like near our star it is a realy a great hope because ti will be become reacheable in future.