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Proxima Centauri and Habitability

So much good material has run lately on planet-hunter Gregory Laughlin’s systemic site that Centauri Dreams feels seriously remiss in returning to it so infrequently. So there is catching up to do, but we focus today on Laughlin’s new work, with UCSC graduate student Jeremy Wertheimer, on an intriguing question about Proxima Centauri. Is the tiny star in fact gravitationally bound to Centauri A and B?

Surprisingly, much recent work has suggested otherwise, including a 1993 paper by Robert Matthews and Gerard Gilmore that set the tone for Proxima research in that decade. But Laughlin notes that the European Space Agency’s Hipparcos satellite has firmed up our knowledge of the position, distance and velocity of nearby stars, enough to demand a new look at this question. After all, Proxima is roughly 15,000 AU from the Centauri binaries, and shows only a small velocity relative to them. It would seem unlikely these stars would not be bound into a triple system, and Laughlin and Wertheimer make a strong case that they are.

Infrared image of Proxima Centauri

Image: The red dwarf star Proxima Centauri in infrared light (the brightest star below, left from center). Could Proxima’s orbit dislodge cometary materials, delivering volatiles to planets in habitable orbits around Centauri A and B? Credit: Digitized Sky Survey U.K. Schmidt Image/STScI.

But here’s where this question gets truly fascinating: we have two studies of the Centauri stars with regard to planetary formation that suggest positive things for habitable planets there. First, a 1997 study by Paul Wiegert and Matt Holman describes stable orbits for terrestrial worlds within 4 AU of either Centauri star. And a 2004 paper by Jack Lissauer and Elisa Quintana, discussed here on Centauri Dreams, shows that terrestrial planet formation within the binary system is possible. The remaining problem for habitability is that such worlds are likely to be dry, there being no stable areas for planetesimal formation beyond 4 AU from which volatiles could be delivered to the inner worlds.

But if Proxima is in a bound orbital relationship with Centauri A and B, that picture changes. From Laughlin’s paper on this work:

“One might therefore wonder about the habitability of putative terrestrial planets in the system. A possible concern with respect to habitability might arise because any planets orbiting the α-Centauri binary may be depleted in volatiles. If Proxima had been bound to the system during its formation stages, then it may have gravitationally stirred the circumbinary planetesimal disk of the α Centauri system, thereby increasing the delivery of volatile-rich material to the dry inner regions.”

The paper is Laughlin and Wertheimer, “Are Proxima and Alpha Centauri Gravitationally Bound,” as yet unpublished but submitted to The Astronomical Journal. Be sure to read Laughlin’s report on this work on the systemic site (and while you’re there, be sure to check his sly resolution of the Fermi Paradox). He and Wertheimer calculate that Proxima should orbit the Alpha Centauri stars about once every million years, with the semi-major axis of the orbit being roughly 1/6th of a light year. If Proxima is indeed stirring the Centauri planetesimal soup, dislodging comets and delivering interesting materials to the inner systems, then the odds on habitability go up. And on that score, it’s humbling and energizing to consider that Proxima, and probably the entire Centauri system, was 2 billion years old when the Sun formed.

So you can see that binding Proxima Centauri gravitationally to the Centauri A and B stars is much more than an abstract calculation. It could spell the difference between terrestrial, life-harboring worlds in that system and dry, desert planets. With current calculations showing three to five terrestrial worlds should be feasible around both stars, we may one day find that the Centauri system is an astrobiologist’s paradise. Could a two-Earth mass Centauri B “b” planet be detected with current instruments? Laughlin suggests one possibility for doing so, a reminder that even with today’s technology, we are not so far from the first verification of a terrestrial exoplanet.

Comments on this entry are closed.

  • Adam Crowl July 5, 2006, 17:53

    Hi Paul

    The 208 ten hour nights of observation would be a hard ask from any Observatory though, even to find an Earth-like planet. Need a few million for a dedicated telescope… Bill Gates, if you’re listening…

  • Administrator July 5, 2006, 18:22

    Yes, just a bit of a problem re observing time. But isn’t it amazing that it’s theoretically do-able even with our current planet-finding technology… Ah, for that big donor with an interest in the Centauri stars!

  • JD July 6, 2006, 3:11

    The concept of habitable planets around M class stars is just now at the point of being tantalizing. The questions of course are how common could they be. Older ones would probably have very low metallacity so higher life might be very problematic if it was even possible. The final one that I’ve thought upon, after reading this, are M class systems more vulnerable to stellar events (nearby nova as an example) than one centered about a larger star with it’s increased heliosphere? Would an M class centered system be more exposed to the particle emmisions from say an Eta Carinae going bang withing a few hundred LY’s?

  • Bynaus July 6, 2006, 4:09

    One problem I see is the amount of volatiles that would have to be delivered: earths oceans contain 1.4 billion cubic kilometers of water. To deliver this amount in ~6500 cycles (6.5 billion years age, 1 million year period) and neglecting losses to space and du to subduction, you need to deliver 200000 cubic kilometers of water per cycle, or 240000 cubic kilometers of ice. Thats the equivalent of 1000 8-km diameter comets! Sounds rather extreme to me…

  • ljk July 6, 2006, 10:38

    Regarding Gregory Laughlin’s “solution” to Fermi’s Paradox, this
    has also been described in SF author Robert J. Sawyer’s novel
    Calculating God: Most of the ETI in our neck of the galactic
    woods have stopped exploring and communicating to pursue
    virtual lives deep under the surfaces of their home planets.

    Some information here:


    Before there was such a thing as virtual reality, the original
    Star Trek pilot “The Cage” had a race called the Tholians
    doing something similar with their powerful minds, living
    virtual lives through their thoughts and the minds of others
    until they neglected much of their real reality.

  • Adam Crowl July 6, 2006, 18:56

    Hi Larry

    The Tholians were crystalline beings seen in a third season episode.

    The Telosians were the masters of the Cage, right from the (unaired) pilot.

    Remember that name Star Travellers – Telos IV is not a healthy place to visit.


  • Adam Crowl July 6, 2006, 18:59

    And on the comet delivery issue – most probably arrived after a single cycle as perturbation by Proxima of a Kuiper Belt would be a lot higher than the stirring of the asteroids by Jupiter.

  • ljk July 13, 2006, 0:00

    How utterly embarassing to have confused the
    Talosians with the Tholians!

    I must now turn in my phaser and communicator….

  • Merle Sue Schneiders October 24, 2006, 13:56

    Dear Sir:

    I came upon your website upon reading about Proxima Centairi in the book:And Still They Fly by Guido Moosbrugger. It was reported that two inhabitants claimed that they came from Proxima Centauri and were only here on a very short mission. If this were true, how indeed would they be able to travel such a vast distance from there to Earth?

    The Pleiadians are also mentioned primarily in this book, and according to the author, has been contacted by a young woman Semjase for many years.

    Perhaps it is all fiction, but then who can really say?

    Have a great week.

    Merle Sue Schneiders

  • Administrator October 24, 2006, 15:02

    I’m afraid I think it’s fictional indeed, but the question you pose is a valid one. The distance from Proxima Centauri is vast, about 260,000 times the distance between the Sun and the Earth. To make such a journey requires serious strides in technology which some people think will never occur. Others of us believe that we will one day be able to send at least robotic probes using solar sails, laser-drivensails or other concepts; active work goes forward on antimatter and even more exotic possibilities. The Tau Zero Foundation is being started to help focus some of the research in this field.

  • ljk March 20, 2007, 22:24

    Astrophysics, abstract

    From: Rodrigo D\’iaz Mr. [view email]

    Date: Tue, 20 Mar 2007 00:09:28 GMT (178kb)

    A possible activity cycle in Proxima Centauri

    Authors: Carolina Cincunegui, Rodrigo F. Díaz, Pablo J. D. Mauas

    Comments: 7 pages, including 8 figures and 2 tables

    Journal-ref: Astronomy & Astrophysics, Volume 461, Issue 3, January III 2007, pp.1107-1113

    Several late-type stars present activity cycles resembling the Solar one. This fact has been observed mostly in stars ranging from F to K, i.e., in stars with a radiative core and an outer convective layer. This work aims at studying whether an activity cycle can be detected in the dM5.5e star Proxima Centauri, which is supposed to be completely convective. We present periodical medium-resolution echelle observations covering the complete visual range, which were taken at the CASLEO Argentinean Observatory. These observations are distributed over 7 years. We discarded the spectra that present flare activity, and analyze the remaining activity levels using four different statistical techniques to look for a period of activity. We find strong evidence of a cyclic activity, with a period of around 442 days. We also estimate that the Ca II S index varies around 130% due to activity variations outside of flares.


  • Jupiter versus Alpha Centauri B January 6, 2010, 2:35

    Why would you need Proxima Centauri to perturb comets to enter the inner solar system of Alpha Centauri, to bring volatiles to theoretical planets? Because surely, the orbit of Alpha Centauri A and B around each other, would have a strong enough effect on perturbing comets, a far stronger effect than Jupiter, Saturn, Neptune and Uranus together does in our solar system.

  • Jupiter versus Alpha Centauri B January 6, 2010, 2:45

    More than one large planet would causes a chaotic system of resonance on the oort cloud… Stupid me.

  • Mark Oller April 12, 2010, 15:06

    Proxima Centauri is nearly in a line of sight with Alpha Centauri, so might Proxima Centauri’s gravitational lens focus light from Alpha Centauri to provide energy for a trip to Proxima Centauri or the Centauri system?