Are There Planets Around Alpha Centauri?

We’re holding out hope for the next generation of planet-finding observatories to locate Earth-sized planets orbiting other stars. But hold on, maybe we don’t need a super space observatory like ESA’s Darwin just yet. In fact, if our nearest neighbour Alpha Centauri has Earth-sized planets, we should be able to detect them with established techniques… right now, with the observatories we have today.

University of California researcher Javiera Guedes has developed a computer simulation that shows that Alpha Centauri B – the largest star in the nearby triple-star system – should have terrestrial planets orbiting within its habitable zone, where liquid water can exist.

They ran several simulations of the system’s first 200 million years. In each instance, despite different parameters, multiple terrestrial planets formed around the star. In every case, at least one planet turned up similar in size to the Earth, and in many cases this planet fell within the star’s habitable zone.

Guedes and co-author Gregory Laughlin think there are several reasons why Alpha Centauri B makes an excellent candidate for finding terrestrial planets. Perhaps the best reason is that Alpha Centauri is just so close, located a mere 4.3 light years away. But it’s also positioned well in the sky, giving it a long period of observability from the Southern Hemisphere.

Most of the 228 extrasolar planets discovered to date have been with the Doppler technique. This is where a planet pulls its parent star back and forth with its gravity. The star’s relative velocity in space changes the wavelength of light coming from it which astronomers can detect. Until now, only the largest planets, orbiting at extremely close distances from their parent stars have been discovered.

But with a nearby star like Alpha Centauri B, much smaller planets could be detected.

The researchers are proposing that astronomers dedicate a single 1.5-metre telescope to intensively monitor Alpha Centauri over a period of 5 years. In that time, any change in the star’s light should be detectable by this telescope.

“If they exist, we can observe them,” said Guedes.

Original Source: UCSC News Release

24 Replies to “Are There Planets Around Alpha Centauri?”

  1. One of the biggest problems with planets is how do they form around double stars. Surely there must be many serious issues in planetary formation. Ie. The destruction of any Oort like cloud by the two stars (meaning no water or ices available for Earth-like planets by comets), the significant effects of angular momentum changes in the systems formation, stability of planetary orbits.
    Also as far as I know, NO exo-planets have been found around any double star.
    I personally think that the chances of planets around 100AU apart or less double stars (as is Alpha Centauri) are very unlikely.

    Note: Those here might like to read my own detailed webpages on Alpha Centauri at;

    The true orbit;

    And especially what Alpha Centauri would be like to a planetary observer around one of the stars and the issues of describing the night’s sky.


  2. “Guedes and his co-author Gregory Laughlin…”

    Minor point, but it’s pretty likely that with the name “Javiera,” Guedes is a woman.

  3. I was wondering when w would finally get around to doing the obvious, looking at the closest star (which also happens to be a main eqencestar like ours) to see if it might have habitable planets. Hopefuly soon someone will take up this task.

  4. Interesting post. Another key point is that Alpha Centauri A and B are very similar to our Sun (A is almost identical), therefore finding a similarly sized planet in that system in the habitable zone may have a big impact since it can really hold life.


  5. Andrew,

    You are wrong about there being no planets found around double stars. Actually, even though RV searches are biased in that they preferentially look at single stars they nevertheless found planets in double and even a triple star systems.

  6. QeV and spaceman

    You bring up some interesting points. Qev example of Gamma Cephei is one that has caused much controversy. In this case, this was reported in 1988 and 1989, but was late retracted. In 2002, the observations were repeated restating the case of the existence of the companion. Yet in 2007 there still remains doubt of the results, as the current period alleged by the Hatzes et al. (2003)
    Others like Schneider (2005) and NeuhÇŽuser et al. (2007) have also been questioned, and in dynamical evolution has been challenged. Ie. Castro (2007) and Solovaya and Pittich (2007), who found the orbits of these companions as being unstable being so-called “dynamically full”.
    I think the problem is with interpreting the spectroscopic or indirect methods like radial velocities, especially the latter, as they are far more subjective in binary systems because of the quality of the observations. There is also some evidence that the red dwarf in Gamma Cephei might have been captured and not formed with the primary.
    Another important system was Iota Horologii, but this also has been since retracted.
    As a comment, the difficulties with binaries is that there are other factors when detecting the behaviour of exo-planets around stars that cannot be explained without also eliminating the effects of the companion star(s).
    I think this work on Alpha Centauri is important as the possibility of detecting planets because of its proximity.
    However, the existence of planets around binary star system are an interesting problem. No doubt in time this might be proven to be true, but at the moment confirmation of exp-planetary still is in early days.
    At present. 15 binary stars are suspected to have planets, but all suffer from the problems eliminating the effects of companions stars.
    I’ve read quite a few reports and current investigation being undertaken at the moment, but few have shown exo-plants exist. The most interesting aspect in the last year is the discovery of dust rings surrounding some binary systems, hich are unexpected – yet till now no planets have been yet confirmed within the large dust disks.

    This article was written a little less than a year ago (30 March 2007)

    Anyway, thanks so much for pointing out these examples.


  7. I reckon having a 1.5m telescope pointed at Alpha Centauri for 5 years would be a perfect task for a liquid mirror telescope! Low cost, no need to tilt it, why, I might even try making one myself!

  8. I think that the question of planets around the Alpha Centauri System would be a little more complicated because if I remember correctly this ia tripple star system. Are you guys forgetting about the effects that Proxima Centauri may have on such planets? If anyone has an idea please, let me know. Thanks.

  9. Many of questions posted so far are answered by the proposed program. The sooner it starts, the better.

    I will go out on a limb, based on obscure and unscientific philosophical grounds, and prophesy that we will find an Earthlike planet at Centaurus A with an oxygen-nitrogen atmosphere, liquid water, and in the habitable zone.

  10. Current solar system development models suggest that stable habitable zones can exist around binary stars given certain starting conditions (and not very strict ones, either). See for a blog entry on the topic or Google “Nader Haghighipour,” “terrestrial planets” and “binary stars” for a variety of links.

  11. Regarding the Proxima question, it orbits very far around the barycenter and is small enough so that it wouldnt disrupt either A or B’s system, other then throwing Oort or Kuiper type objects in

  12. I will go out on a limb, based on obscure and unscientific philosophical grounds, and prophesy that we will find an Earthlike planet at Centaurus A with an oxygen-nitrogen atmosphere, liquid water, and in the habitable zone.

    We’ll let you get away with this nonsense if you don’t come back here expecting credit if we do indeed find a Earth-like planet. Anyone can make a prediction based on whimsy and speculation (or even less, as in your case). And sometimes they will even guess right.


  13. I’ll go out on a limb and predict that by the time we visit a Cent., the number of people inclined to prophesize will have dramatically decreased.

  14. Statistically, it’s unlikely that there are planets; unlikely [x2] it would be earth sized; even more unlikely [x4] it would fall within a habitable zone; even more unlikely [x8] it would have an oxygen/nitrogen atmosphere or be of a similar composition to our own Earth.

    Metaphorically, if they find Earth [2] in orbit 4.3ly away, my bag is already packed…

  15. Well, i will make it short, have no desire to do a long story to explain but i have a Good feeling about it, that they will find some habital planets with life around Alpha Centauri A. Let me say this, it will no surprise me.

  16. i would nt be suprised at all if they find some small rocky worlds . i doubt even so when seti turns it attention to them any sign of intelligent life will be found . lets just say it would be a miracle if it is and slighly disturbing because if they were advanced enough it would nt be totally out of the bounds of possibilty that they could get here .

  17. As far as I know, Proxima Centauri is so far away from the other Alpha A and B that it might have little influence on planet formation around either A or B. Also, if I remember correctly, B is about as far from A as Neptune is from Sol. So it seems to me that its possible, albeit unlikely, that either A or B might have terrestrial planets. At any rate, it does make sense to scrutinize the Alpha Centauri system to the best of our abilities since it is so close. Living planets or not, I’m sure it will prove an interesting game of cosmic billiards.

  18. Pretty inconclusive collection of opinions, as regards why planets havent been searched for around Centaurus…What am I being asked to accept? that it’s easier to detect a planet orbiting a star in excess of a hundred light years away than around our nearest neighbour? that it would take 5 years with a dedicated 1.5 metre telescope to turn up any answers. I find that very difficulty to accept. This has puzzled me for some time. Surely the nearest star has got to be the best choice for observation, hasn’t it? And if not, why not? something’s not right here….

  19. Planets aren’t cpnsidered likely so no-ones bothered looking?

    A lot stranger things have happened….

  20. The reason they can’t detect planets around our nearest neighbor is that they can only detect gas giants around stars within a 300 ly or so radius from Earth. They cannot see the planets, they can only see the gravitational effect of a planet as it pulls on a star and causes it to “wobble”. Since Alpha Centauri A & B are so close it is probably the case that gas giants did not have room and/or matter enough to form. After all, if Jupiter had gathered more matter early on, we might be living in a binary system.

  21. Small, rocky worlds like the ones they are talking about do not have enough mass to affect the star in any observable way even if they are orbiting our nearest neighbor.

  22. Re Centaurian planets. In 1989 I authored a book
    with Brian Crowley (1938-2008) called “Return to
    Mars”. In this work we showed
    that the Icelandic Eddas (stories) said there
    were planets orbiting both alpha Centaurus A and
    B, stating that the one inhabitable world of B is
    called Fjalar. The book was republished by Black
    Rabbit Press in 2003. In the time elapsed, 14
    years, we thought that astronomy would confirm
    or deny our findings. Nobody did.
    We assume that the truth is scientifically
    unpalatable and an inhabitable world 4.3 ly away
    is too terrifying to contemplate.
    Anthony B Austin

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