≡ Menu

A Binary Origin for ‘Oumuamua?

The fleeting interstellar visitor we call ‘Oumuamua is back in the news, an object whose fascination burns bright given its status as a visitor from another star system. Just what kind of system is the subject of a new letter just published in Monthly Notices of the Royal Astronomical Society, in which Alan Jackson and colleagues argue that the star-crossed wanderer is most likely the offspring of a binary stellar system, these being far more likely to eject rocky objects. Our first confirmed interstellar asteroid just grows in interest.

Jackson (University of Toronto – Scarborough) is quoted in this news release from the Royal Astronomical Society as saying that the odds didn’t favor the first interstellar object detected in our system being an asteroid. Comets are more likely to be spotted, and our system is more efficient at ejecting comets than asteroids. But ‘Oumuamua is what we got, and its eccentricity of 1.2 and 30 km/sec speed pegged its orbit as hyperbolic, clearly not bound by the Sun’s gravity.

Image: Artist’s impression of ‘Oumuamua. Credit: ESO / M. Kornmesser.

How much do we know about what our Solar System can eject? For this, I turn for a moment to Greg Laughlin and Konstantin Batygin, who make this case in “On the Consequences of the Detection of an Interstellar Asteroid” (citation below):

Our own solar system has contributed many volatile-rich planetesimals to the galaxy. Specifically, within the framework of the so-called Nice model of early solar system evolution, (Tsiganis et al. 2005; Levison et al. 2008), a transient period of dynamical instability is triggered in response to interactions between the giant planets and a primordial disk comprising ∼ 30M. In numerical realizations, nearly all of this material is expelled into the interstellar medium as the instability unfolds, leaving behind today’s severely mass-depleted Kuiper belt. Given the universality of N -body evolution, one can speculate that similar sequences of events are a common feature of planetary system evolution.

Jackson and team are frank in acknowledging that with only a single interstellar object to work with, we have to assume huge uncertainties in the constraints we apply to the mass of material typically ejected from planetary systems. That point hardly needs belaboring, but we press on with the data we have to work with, keeping in mind how much play there is in our estimates.

The case for binary systems and ejected material runs like this. ‘Oumuamua shows no evident activity, making the case that it is a rocky object shorn of volatiles, and hence one that was ejected from inside its parent star’s snowline. For a star of solar mass to eject an object from within its snowline requires a companion object with a mass greater than Saturn. But our radial velocity surveys show a low occurrence rate of giant planets (~10 percent) with orbital periods of 100 to 400 days. Here the authors cite the Laughlin/Batygin paper above, which argues that ‘Oumuamua, if it is indeed rocky, implies that extrasolar asteroid belts are massive.

Giant planets inside the snowline are relatively uncommon, but binary systems are abundant, and are known to be efficient at ejecting material. The authors draw the following conclusion:

…we expect that at most 10% of Sun-like single stars will host a planet capable of efficiently ejecting material interior to the ice line. Laughlin & Batygin (2017) and Raymond et al. (2017) thus argue that if 1I/‘Oumuamua is indeed rocky, then typical extrasolar asteroid belts must be unusually massive. Similarly, recent results from micro-lensing surveys (e.g. Suzuki et al. 2016; Mroz et al. (2017) suggest that giant planets at larger separations are also not common….While giant planets are relatively uncommon, tight binary systems are abundant (Duchene & Kraus 2013), and are extremely efficient at ejecting material (Smullen et al. 2016). They may therefore represent a dominant source of interstellar small bodies.

Jackson and team conducted 2000 N-body simulations to study close encounters and ejections, finding that the fraction of rocky or devolatilised material ejected by binaries is 36 percent — the ratio of icy to rocky objects is roughly 2:1. Moreover, these simulations show that the population of icy interstellar material comes primarily from low mass stars, while the population of rocky material is dominated by intermediate mass stars.

The best guess for ‘Oumuamua: A hot, high mass binary system ejecting rocky material during the formation era of its planets. As to the ejection process itself, the paper comments:

Physically, our picture is one of planetesimals migrating inwards during the early phases of planet formation, in the presence of a protoplanetary disk. Holman & Wiegert (1999) showed that any material in circumbinary orbit migrating inward will become unstable on short timescales once it passes a stability boundary ac,out, for which they provide an empirical fit to results from N-body simulations (their equation 3). This critical distance is a function of the binary mass ratio and eccentricity and ranges from around 2 to 4 times the binary separation…

Thus we have inward planetesimal migration followed by ejection from the binary system when the object passes the stability boundary. The authors’ models show that more than 75 percent of interstellar bodies originate from binary stars, a number that is even higher for rocky objects.

Even if a typical circumbinary only ejects as much material as the Solar system we would still expect close binaries to be the source of more than three quarters of interstellar bodies due to the relatively low abundance of single star systems with giant planets like the Solar system. Whereas in the Solar system the ejected material is overwhelmingly icy, we expect that around 36% of binaries may predominantly eject material that is rocky or substantially devolatilised, leading to similar expectations for the abundance of rocky/devolatilised bodies in the interstellar population.

“The same way we use comets to better understand planet formation in our own Solar System,” says Jackson, “maybe this curious object can tell us more about how planets form in other systems.” Of course it will take more than one such object to do the job, but we’re learning that future detections of interstellar objects are likely as estimates of their occurrence rise.

The paper is Jackson et al., “Ejection of rocky and icy material from binary star systems: Implications for the origin and composition of 1I/‘Oumuamua,” Monthly Notices of the Royal Astronomical Society 19 March 2018 (abstract). The Laughlin/Batygin paper is “On the Consequences of the Detection of an Interstellar Asteroid,” submitted to Research Notes of the AAS (abstract).


Comments on this entry are closed.

  • T. Pliska March 20, 2018, 12:10

    I haven’t read any speculation on why ‘Oumuamua is so elongated. The only mechanism that comes to my mind is that it was spinning while molten, but I’d like someone who actually knows something to comment.

    • Harold Shaw March 20, 2018, 18:20

      Some speculate that it may be a contact binary, but its rapid rotation may rule that out. The explanation I see most often attributes the shape to a violent event such as the collision of two larger rocky bodies resulting in a rocky shard.

    • Harold Shaw March 20, 2018, 18:30
      • T. Pliska March 22, 2018, 15:52

        The Forbes article is interesting, but I’m not convinced, since the tumbled pebbles they site as a model are typically rounded, not spear shaped. I’d think the same mechanism would be true of an object tumbling in space.

    • Harry R Ray March 27, 2018, 9:44

      THIS JUST UP ON THE EXOPLANET.EU WEBSITE: “The Excited Spin State of 1I/2017 u1 `Oumuamua.” by Michael J. S. Belton, Oliver Hainaut, Karen J. Meech, Beatrice E. A. Mueller, Jan T. Kleyna, Harold Weaver, Marc W. Buie, Michael Drahus, Pitor Guzik. “…Two fundamental periodicities are found at frequencies(2.77+/-0.18)cycles/day and ((6.42+/-0.18)cycles/day corresponding to(8.67+/-0.34)hr and(3.74+/-0.11)hr respectively…the lightcurve…shows a double minimum at 2.77 cycles/day and a single minimum at 6.42 cycles/day…” Does this mean that `Oumuamua is NOT tumbling? ALSO: `Oumuamua is cigar shaped ONLY if it is closest to its lowest rotational energy, and “flying saucer” shaped(i.e. Humaea ON STEROIDS!) if it is closest to its highest rotational energy. REMEMBER: Karen J Meech was the person who ORIGINALLY proposed the “cigar shape” for `Oumuamua.

  • James Ph. Kotsybar March 20, 2018, 14:34

    OUMUAMUA (1I/2017U1) “Dagger Of Death”

    Oumuamua, dagger from space,
    is flung at its target end over end –
    too fast for any rocket to outpace.
    Earth, spun within the Sun’s disc, can’t defend
    against this object just recently spied
    (though it is the size of a football field) –
    a blade ten times as long as it is wide –
    packing an impact of megaton yield.
    Its name translates to messenger or scout.
    Appearing like a harbinger of doom
    from interstellar space it came about,
    missing Earth by a tiny bit of room.
    Though this did cause some brief consternation,
    It’s fading now from our observation.

  • david lewis March 20, 2018, 15:07

    If we were able to send a spacecraft to the object, I wonder what sort of things we could determine. The age perhaps? From the impact craters on the object maybe some details about interstellar space, such as the type of material and its density – which any interstellar probe we develop would face.

    Or even debri buried in those craters that could give information about other star systems aside from the one the object originiated from.

  • Andrew R Brown March 20, 2018, 16:20

    I’ve heard that Ross 614 in Monoceros is likely the originating system. A binary red dwarf system.

    • J. Jason Wentworth March 21, 2018, 1:00

      …So a unicorn kicked ‘Oumuamua our way (or slung if off his or her alicorn; perhaps the Cone Nebula in Monoceros [which is part of NGC 2264 http://www.constellation-guide.com/cone-nebula/ ] should be renamed the Alicorn Nebula), and:

      A binary star system such as Ross 614 would function as a “de-rated” Dyson Gravitational Machine (see: http://www.ifa.hawaii.edu/~barnes/ast242_s14/Dyson_Machines.pdf *and* https://www.centauri-dreams.org/2012/11/19/the-interstellar-gravitational-assist/ ). Freeman Dyson envisioned using binary white dwarf stars (or binary neutron stars, even manufactured ones!), or binary black holes as high-velocity starprobe or starship launchers. Also:

      Duncan Lunan, who in the 1970s hypothesized that an alien Bracewell probe from the double star Epsilon Boötis (also called Izar) was responsible for the radio signal Long-Delay Echoes (LDEs) of the late 1920s (he withdrew this hypothesis some years later), had also envisioned this binary star as having been used as a gravitational launcher for such probes.

      • Michael C. Fidler March 21, 2018, 23:14

        Long delayed radio echoes – 80 years with an unexplained

        Fascinating subject, I had forgotten about Epsilon Boötis and the Bracewell probe, but found an interesting pdf file on the subject:


        A Star Disturbed the Comets of the Solar System in Prehistory.

        Interesting article on Scholz’s star, their simulations suggest that Scholz’s star approached even more than the 0.6 light-years pointed out in the 2015 study as the lower limit.
        The close fly-by of this star 70,000 years ago did not disturb all the hyperbolic objects of the solar system, only those that were closest to it at that time. “For example, the radiant of the famous interstellar asteroid` Oumuamua is in the constellation of Lyra (the Harp), very far from Gemini, therefore it is not part of the detected over-density, “says De la Fuente Marcos. He is confident that new studies and observations will confirm the idea that a star passed close to us in a relatively recent period.


        • J. Jason Wentworth March 24, 2018, 2:07

          Thank you for posting that paper. Yes, LDEs definitely occurred in the late 1920s and in later years (and they still occur), but even today, we just don’t know why they happen. While the alien Bracewell probe hypothesis is, of course, the most exciting one, the other, natural-explanation-hypotheses (particularly ducting, and plasma clouds at the Earth-Moon L4 and L5 points, are also intriguing), and:

          There is a way to test the Bracewell probe hypothesis which, to my knowledge, has never been tried (perhaps due to the “giggle factor”): *responding* to the echoes by repeating ^them^ back, with silent spaces matching the delay timing so that we could hear any “second replies.” (This is the “probe acknowledgement protocol” that Ronald Bracewell suggested–he posited that a probe would likely then cease to echo [to let us know it knew that we had responded], and that if we then likewise ceased to echo, it would know that we knew it was there. This would be a language-independent way that we and the probe could acknowledge each other’s contact.)

  • Tom Mazanec March 20, 2018, 16:35

    We have detected thousands of comets over hundreds of years. None have been interstellar.

  • Robin Datta March 20, 2018, 17:05

    Our knowledge base about the details of the wider universe beyond what we physically inhabit is so sketchy that a random interstellar rock cruising by is a potential treasure-trove of inormation. The macrocosmic universe promises to hold data aplenty for the foreseeable future for generations to come.

  • Charley March 20, 2018, 18:29

    ” … and our system is more efficient at ejecting comets than asteroids.”
    Why asteroids and not comets ??


    ” But ‘Oumuamua is what we got, and its eccentricity of 1.2 … ”
    Can eccentricity > 1 ??

    • Paul Gilster March 20, 2018, 20:44

      As I understand it, an eccentricity of 1 is a parabolic escape orbit. An eccentricity of greater than 1 is hyperbolic.

      • J. Jason Wentworth March 21, 2018, 0:26

        Yup–the parabola is the perfect open, non-repeating orbit, just as the circle (an ellipse [an elliptical orbit, in this case] with an eccentricity of 0, with both foci in exactly the same place, at the center) is the perfect closed, repeating orbit, and:

        Parabolic and circular orbits don’t exist in nature, but they can be approximated very closely (even the uneven distribution of mass inside celestial bodies makes exactly circular orbits unattainable). A parabolic orbit is the path traveled by an object that has *exactly* enough velocity to escape from a celestial body–“not one micron per millennium more or less” (as Arthur C. Clarke wrote in “The Promise of Space”), so in practice all orbits are ellipses (if closed) or are hyperbolas (if open).

    • Tom Mazanec March 21, 2018, 10:55

      As I understand it, asteroids are in more stable orbits, as a general rule, than comets in our Solar System.

      • J. Jason Wentworth March 22, 2018, 8:29

        I think that was their point. Comets that would come within the “planetary zone” of a solar system were perturbed inward from their distant Oort Clouds, and even if Jovian planets further perturbed them into short-period orbits, they would (usually) be traveling in highly-eccentric orbits, from which system escape wouldn’t require a lot more energy. Also:

        Comets that weren’t perturbed into short-period orbits would have very elongated, often near-parabolic orbits (as is the case with most of the comets we see), and many Jovian planet encounters would eject comets outright, at hyperbolic velocity. Most asteroids, on the other hand, travel in more nearly circular orbits (the NEAs in eccentric orbits are usually closer to the Sun, where solar system escape couldn’t occur), and the asteroids in distant, more comet-like eccentric orbits (like Hidalgo, which swings out to Saturn’s neighborhood) are widely suspected to be extinct or inactive comet nuclei.

  • Robert March 21, 2018, 14:55

    Star Trek: The Voyage Home…. It’s looking for humpback whales.

    • ljk March 30, 2018, 16:59

      At least whales are not extinct by the early 21st Century as Star Trek 4 claimed/warned back in 1986, although the right whale may be in trouble:


  • Sean Robert Meaney March 23, 2018, 9:46

    ‘A hot, high mass binary system ejecting rocky material during the formation era of its planets.’

    A white dwarf paired with a hot high mass giant? Sirius.

  • Michael March 27, 2018, 6:11

    I wonder if we could eventually download our ‘brain’ into a miniaturised silicon sleeve, mini me’s and we live out our ‘other’ silicon lives on a small ship. When we arrive at the destination we upload our ‘brains’ into a carbon sleeve when there is enough resources available.

  • Harry R ray March 28, 2018, 11:08

    After a couple of days off-line, ArXiv seems to be back up and running! The good news: Radio emissions of NATURAL(drat)origin have been detected coming from `Oumuamua! ArXiv: 1803.10187. “Search for OH 18-cm radio emission from 1I/2017 U1 with the Green Bank telescope.” by Ryan S. Park, D. J. Pisano, J. Joseph, W. Lazio, Paul W. Chodas, Shantanu P. Naidu. “…This paper reports the first OH 18-cm line observation of…`Oumuamua…We have observed the OH lines at 1665.402 MHz, 1667,359 and 1720.53 MHz frequencies with a spectral resolution of 357 Hz…Our final results confirm the asteroidal origin of `Oumuamua…”

  • ljk March 30, 2018, 16:52

    Remember in one of the earlier Centauri Dreams articles where some folks wanted to call our interstellar visitor The Shard instead of Oumuamua?

    Well, how do you feel about The Pancake instead…


    And is it just me, or does the artist representation in the above Sky and Telescope article bear at least some resemblance to the Millennium Falcon from Star Wars?

  • ljk April 6, 2018, 10:28

    Interstellar ‘Oumuamua gives scientists new insights into formation of planetary systems

    by Laurel Kornfeld

    April 5, 2018

    Interstellar asteroid ‘Oumuamua (pronounced oh MOO-uh MOO-uh) spent only a short time traveling through the Solar System, but its passage is providing scientists with new insights into the formation processes of planetary systems.

    First seen speeding through the solar system by NASA’s Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1) on Oct. 19, 2017, the cigar-shaped asteroid was nicknamed ‘Oumuamua, which in Hawaiian means “a messenger from afar arriving first,” once it was found to have originated beyond the Solar System.

    In a new study published in the journal Monthly Notices of the Royal Astronomical Society (MNRAS), researchers at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, considered how the first-known interstellar asteroid to be detected matches current knowledge about the formation of asteroids, comets, and planets.


  • ljk June 27, 2018, 13:44

    Is the Interstellar Asteroid Really a Comet?


    ESO’s VLT Sees `Oumuamua Getting a Boost – New results indicate interstellar nomad `Oumuamua is a comet


    Cue jokes about the starship’s propulsion units turning on.

  • William Forrest June 28, 2018, 16:47

    ‘Oumuamua has an apparent shape (aspect ratio 10:1) unlike any solar system object detected to date. To claim it’s an asteroid or comet from an exo-solar system is premature. If it doesn’t walk like a duck, nor quack like a duck, it shouldn’t be identified as an exo-asteroid. The size is also quite uncertain. The commonly accepted albedo, 0.1, is appropriate for space rocks like our moon. If it’s darker, then it would be larger and vice-versa.

    Erudite speculation isn’t science.