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An Origin for a Far Traveling Asteroid

I used to think the Kuiper Belt object Quaoar was hard to pronounce (“Kwawar”), and even muffed it despite having plenty of time to practice before the recent Tennessee Valley Interstellar Workshop. Pontus Brandt (JHU/APL) had mentioned Quaoar in his talk in Huntsville as a target that lined up in useful ways with a proposed interstellar precursor mission he was presenting, one designed to examine dust distribution from within the system by looking back at our heliosphere at distances up to 1000 AU, seeing it as we see other stars’ dust environments.

So I summarized Brandt’s ideas in my wrap-up talk and couldn’t get Quaoar pronounced properly without multiple tries. But even Quaoar pales into the realm of everyday lingo when compared to 1I/’Oumuamua. Please tell me how to do this. The word is a Hawaiian term for ‘scout,’ and the Ulukau: Hawaiian Electronic Library’s online dictionary tells me it’s pronounced this way: ō’u-mu’-a-mu’-ă. I could work with that and maybe get it right in a talk, with extra practice. At least until I look at it — all those vowels defeat me.

The object originally tagged A/2017 U1, then, is now tagged as interstellar in the combined 1I/’Oumuamua, the 1 indicating it is the first such object to be observed, the I indicating interstellar. It is fitting that 1I/’Oumuamua was the name chosen by the Pan-STARRS team in Hawaii that first brought this object to our attention.

Image: The trajectory of 1I/ ‘Oumuamua, which made its closest approach to Earth on October 14, coming within 24,000,000 km, or about 60 times the distance to the moon. Credit: NASA/JPL-Caltech.

As far as the sheer number of objects making long interstellar journeys, consider what New Horizons PI Alan Stern recently told Astronomy Magazine (see The First Known Interstellar Interloper):

According to Stern, Jupiter, Saturn, Uranus, and Neptune combined probably ejected 1013 to 1014 objects larger than 1 km early in our solar system’s history, when it was still cluttered with debris left over from the planet-formation process. Multiply that by the 1011 stars in the Milky Way, and one comes up with numbers like 1024 to 1025 objects larger than a kilometer. Smaller objects like 1I/‘Oumuamua must be orders of magnitude more plentiful.

We’ve just seen, in the work of members of the Initiative for Interstellar Studies, how reaching such an object might be attempted. Now the question becomes, where did it come from? On that score, we have quick work indeed from Eric Gaidos (University of Hawaii at Manoa), working with Jonathan Williams at the same institution and Adam Kraus (University of Texas at Austin). The trio believes it has traced 1I/‘Oumuamua’s origins and presents its case in a paper submitted to Research Notes of the American Astronomical Society.

Gaidos and team traced the path of 1I/’Oumuamua backwards along its route and took into account the numerous variables along the way in so extended a journey. The likelihood, the researchers believe, is that the object originated in a nearby young stellar cluster. They point to the Carina and Columba Associations, the word ‘association’ referring to stellar associations, which are loosely bound star clusters whose stars share a common origin. They still move together through space but are at this point gravitationally unbound. The estimated distances to the Carina and Columba Associations range from 50 to 85 parsecs (163 to 277 light years); the age of stars within these groups is on the order of 45 million years. An object ejected at 1-2 kilometers per second soon after star formation would thus have had time to reach the Sun.

From the paper:

We suggest that A/2017 U1 formed in a protoplanetary disk in the Carina/Columba associations and was ejected by a planet ≈40 Myr ago. The absence of ice indicates an origin inside the “ice line” of the disk plus an ejection velocity of 1-2 km sec−1 (assuming the cluster was already unbound), constrain the mass mP and semi-major axis aP of the planet.

What kind of planet could have ejected this object? The paper examines the issue both for solar mass stars as well as M-dwarfs:

Permitted values (grey zone) center around a 20-30M⊕ planet forming by a few Myr within a few AU, reminiscent of the core accretion scenario for giant planet formation. In contrast, a “super-Earth” at ∼1 AU could eject ice-free planetesimals from a lower-mass M dwarf.

Image: This is half of the paper’s Figure 1, showing only the projection from a protoplanetary disk around a solar mass star. The paper’s second chart, not shown here, gives equivalent information for an M-dwarf. The caption continues: “Below the red line planets accrete rather than scatter planetesimals. Above the green line planets eject planetesimals at > 1 km sec−1. Below the purple line planetesimals are captured into clouds by the cluster tide. Below the black line planetesimals require > 10 Myr to escape. To the right of the blue lines planetesimals contain ices.” Credit: Gaidos, Williams & Kraus.

As the paper notes, future interstellar interlopers may well have radiants similar to 1I/’Oumuamua. Practicing our skills on this celestial wanderer may thus tune us up for another.

The paper is Gaidos, Williams and Kraus, “Origin of Interstellar Object A/2017 U1 in a Nearby Young Stellar Association?” submitted to Research Notes of the American Astronomical Society (abstract). Our interstellar wanderer seems to be spawning a growth industry in these early days following its detection. See also Zwart et al., “The origin of interstellar asteroidal objects like 1I/2017 U1,” submitted to Monthly Notices of the Royal Astronomical Society (preprint). I haven’t read this one yet and thus won’t comment.

Comments on this entry are closed.

  • andy November 14, 2017, 13:20

    Regarding the name and spelling, Wikipedia gives the following:

    The common name ʻOumuamua was chosen by the Pan-STARRS team. The name is Hawaiian in origin (ʻou means reach out for, and mua, with the second mua placing emphasis, means first, in advance of), and reflects the nature of the object as a “scout” or “messenger” from the past. The first character is not an apostrophe, but a Hawaiian ʻokina.

    I’m also trying to figure out the pronunciation, going by this page, it starts with a glottal stop, and it seems like the “ou” is somewhat like the word “owe” (but without the “w” sound at the end which you usually have in English) – I have seen some conflicting information about that so it would be good to hear someone who actually speaks the language pronounce it!

  • ljk November 15, 2017, 10:45

    Update on `Oumuamua, Our First Interstellar Object

    By: Kelly Beatty | November 10, 2017

    The arrival of an object from beyond the solar system caught astronomers by surprise — but that doesn’t mean that they were unprepared to study it.


    To quote:

    But asteroids are not catalogued by name alone, and this is the first of an entirely new class of object. So, at the suggestion of MPC associate director Gareth Williams, the IAU adopted the identifier “I”, for interstellar. “All parties involved in the discussion agreed that the proposal was suitable,” he says. “Took less than a day to sort out, announcement followed the day after.” As noted in the announcement on MPEC 2017-V17, “Correct forms for referring to this object are therefore: 1I; 1I/2017 U1; 1I/`Oumuamua; and 1I/2017 U1 (`Oumuamua).”

    Those who work the comet and asteroid trade aren’t enamored with the use of “I” — after all, the IAU has gone out of its way to avoid using “I” and “O” in designations because they look too much like the numerals “1” and “0”. Several have suggested substituting “E” (for extrasolar) instead, but Williams defends the IAU’s decision, noting that “E” could be interpreted as “extraterrestrial,” with the implication of intelligence behind the object, and “G” (for “galactic”) is too limiting.

    A Moving Target

    The first characteristic that marks `Oumuamua as being from outside our solar system is its orbital eccentricity, 1.19. If you ever took geometry, you might recall that the eccentricity of an ellipse can’t exceed 1.0. In fact, dynamicist Bill Gray (Project Pluto) regrets that he didn’t pick up on 1I’s interstellar nature a few days sooner — his orbit-calculation software kept rejecting the eventual solution as being impossible.

  • Michael Fidler November 16, 2017, 10:28

    APO Time Resolved Color Photometry of Highly-Elongated Interstellar Object 1I/’Oumuamua.

    “We report on g, r and i band observations of the Interstellar Object ‘Oumuamua (1I) taken on 2017 October 29 from 04:28 to 08:40 UTC by the Apache Point Observatory (APO) 3.5m telescope’s ARCTIC camera. We find that 1I’s colors are g−r=0.41±0.24 and r−i=0.23±0.25, consistent with the visible spectra of Masiero 2017, Ye et al. 2017 and Fitzsimmons et al. 2017, and most comparable to the population of Solar System C/D asteroids, Trojans, or comets. We find no evidence of any cometary activity at a heliocentric distance of 1.46 au, approximately 1.5 months after 1I’s closest approach distance to the Sun. Significant brightness variability was seen in the r observations, with the object becoming notably brighter towards the end of the run. By combining our APO photometric time series data with the Discovery Channel Telescope (DCT) data of Knight et al. 2017, taken 20 h later on 2017 October 30, we construct an almost complete light curve with a most probable lightcurve period of P≃4 h, and reveal the most useful locations during 1I’s rotation phase for additional data to improve constraints on its lightcurve. Our results imply a double peaked rotation period of 8.1 ± 0.02 h, with a peak-to-peak amplitude of 1.5 – 2.1 mags. Assuming that 1I’s shape can be approximated by an ellipsoid, the amplitude constraint implies that 1I has an axial ratio of 4.1 to 6.9, which is strikingly elongated. Assuming that 1I is rotating below its critical break up limit, our results are compatible with 1I having a density > 1.0 g cm−3, or having modest cohesive strength. Astrometry useful for constraining 1I’s orbit was also obtained and published in Weaver et al. 2017.”


    • Michael Fidler November 20, 2017, 10:19

      On the dynamical history of the recently discovered interstellar object
      A/2017 U1 – where does it come from?

      Another where did it come from, is that four or five? Anyway this time something a little more interesting, seems one of are neighbors may be throwing rocks at us!

      “A/2017 U1 is the first interstellar object recorded inside the Solar System. We try to answer the obtrusive question: where does it
      come from? After a careful search in the close vicinity of the Sun we looked a bit further. Finally, we have checked over 200 thousand
      stars and found just a handful of candidates. If we limit our investigation to the Sun surroundings within about 30 pc, the most probable candidate for the A/2017 U1 parent stellar habitat is a star UCAC4 535-065571 but GJ 876 cannot be completely ruled out. However, the origin of A/2017 U1 from a more distant source is still an open question.”



  • Harry R Ray November 20, 2017, 10:33

    There is an OUTSIDE CHANCE that Oumuamua originated in the Gliese 876 system. “On the dynamical history of recently discovered interstellar object A/2017 U1 – where does it come from?” by Pitor A Dybczynski, Malgorzata Krolikowska.

  • ljk November 20, 2017, 12:56

    20 November 2017 — ESO Science Release eso1737

    ESO Observations Show First Interstellar Asteroid is Like Nothing Seen Before— VLT reveals dark, reddish and highly-elongated object

    For the first time ever astronomers have studied an asteroid that has entered the Solar System from interstellar space. Observations from ESO’s Very Large Telescope in Chile and other observatories around the world show that this unique object was traveling through space for millions of years before its chance encounter with our star system.

    It appears to be a dark, reddish, highly-elongated rocky or high-metal-content object. The new results appear in the journal Nature on 20 November 2017.

    The release, images and videos are available on:


  • ljk November 20, 2017, 13:01

    First Known Interstellar Visitor is an “Oddball”

    November 20, 2017

    Gemini Observatory Press Release

    For release at 16:00 UT (6:00 a.m. HST), Monday November 20th

    Gemini Observatory provided key observations in characterizing an object visiting from outside our solar system, ‘Oumuamua. After the object was discovered by Pan-STARRS1 on Haleakala, both Gemini telescopes dropped everything to observe ‘Oumuamua for three nights as it quickly dimmed from view.

    Researchers found that despite its interstellar origin, the object is similar in composition to some objects in our Solar System but its shape is unlike anything found around our Sun.


    To quote:

    Since its discovery ‘Oumuamua has faded from view. The object’s rapidly increasing distance from the Earth and Sun now makes it too faint to be studied by even the largest telescopes.

    “Needless to say, we dropped everything so we could quickly point the Gemini telescopes at this object immediately after its discovery,” said Gemini Director Laura Ferrarese who coordinated the Gemini South observations for Meech’s group.

    “What we found was a rapidly rotating object, at least the size of a football field, that changed in brightness quite dramatically,” according to Meech. “This change in brightness hints that ‘Oumuamua could be more than 10 times longer than it is wide – something which has never been seen in our own Solar System,” according to Meech.

    ‘Oumuamua shares similarities with small objects in the outer Solar System, especially the distant worlds of the Kuiper Belt – a region of rocky, frigid worlds far beyond Neptune. “While study of ‘Oumuamua’s colors shows that this body shares characteristics with both Kuiper Belt objects and organic-rich comets and trojan asteroids,” says Meech, “its orbital shape says it comes from far beyond.”

    The research led by Meech is published in the November 20th online issue of the journal Nature.

  • ljk November 20, 2017, 13:07

    Earth’s First Known Interstellar Visitor Unmasked


    20 November 2017


    To quote:

    The team gathered data from telescopes around the world, including the Canada-France-Hawaii Telescope (CFHT), the United Kingdom Infrared Telescope (UKIRT) and the Keck Telescope on Maunakea, the Gemini South telescope, and the European Southern Observatory (ESO) Very Large Telescope (VLT) in Chile. Marshalling all of these resources yielded a wealth of data that revealed `Oumuamua’s unusual nature.

    “We had to act quickly,” explains team member Olivier Hainaut from ESO in Garching, Germany. “`Oumuamua had already passed its closest point to the Sun and was heading back into interstellar space. This felt very much like the beginning of the famous science fiction story, Rendezvous with Rama.”

    “Needless to say, we dropped everything so we could quickly point the Gemini telescopes at this object immediately after its discovery,” said Gemini Director Laura Ferrarese, who coordinated the Gemini South observations for Meech’s group.

    “The CFHT data was absolutely critical for understanding the light curve, for our initial understanding of the orbit, and determining that this object was more like an asteroid and not a comet,” noted IfA’s Richard Wainscoat.

    “What we found was a rapidly rotating object, at least the size of a football field, that changed in brightness quite dramatically,” according to Meech. “This change in brightness hints that `Oumuamua could be more than 10 times longer than it is wide – something which has never been seen in our own Solar System,” according to Meech.

    “An axis ratio like that is truly extraordinary – we have never seen anything in the solar system that is this elongated”, says Lance Benner, a specialist in radar imaging of near-Earth and main-belt asteroids at the Jet Propulsion Laboratory in California.

    `Oumuamua does have some similarities to small objects in the outer Solar System, especially the distant worlds of the Kuiper Belt – a region of rocky, frigid worlds far beyond Neptune. “While study of `Oumuamua’s colors shows that this body shares characteristics with both Kuiper Belt objects and organic-rich comets and trojan asteroids,” said Meech, “its hyperbolic orbit says it comes from far beyond.”

    “We are continuing to observe this unique object,” added Hainaut, “and we hope to more accurately pin down where it came from and where it is going next on its tour of the galaxy. And now that we have found the first interstellar rock, we are getting ready for the next ones!”

    Astronomers estimate that an interstellar asteroid similar to `Oumuamua passes inside the orbit of Earth several times year, but they are faint and hard to spot, so they have been missed up until now. It is only recently that survey telescopes, such as Pan-STARRS, are powerful enough to have a chance to discover them. “Our successful follow-up observations are a model for the future – especially when the next major survey telescope, LSST, comes on line,” added Meech.

    This research is presented in a paper entitled “A brief visit from a red and extremely elongated interstellar asteroid”, by K. Meech et al., appears in the journal Nature on November 20, 2017.

  • DJ Kaplan November 20, 2017, 15:16

    What’s the chance that a rock with this shape could have survived its trip without being broken up by collisions with other bodies?

    I’m not saying that it’s an alien craft, but…

    (Of course, the “reconstruction” art gives the impression that we are confident that it’s a rock.)

    • Harry R Ray November 20, 2017, 18:56

      The object is at least the size of a football field, but MOST LIKELY 800 meters by 80 meters by 80 meters, if its ALBEDO turns out to be the EXPECTED value of 0.04(HST and SST should be able to CONFIRM this). The KEY here is its MASS!!!! NO NATURAL OBJECT OF THESE DIMENSIONS can either be hollow or a rubble pile and do a FULL ROTATION once every 7.34 hours without FLYING APART!!!! If its mass is determined to be considerably LESS than 1g/cm3, BINGO!!!!!!!!!

      • Harry R Ray November 20, 2017, 19:13

        What are the odds of the FIRST macroscopic interstellar object having a radius ratio THREE TIMES LARGER than ANY of the MILLIONS of solar system macroscopic objects ALREADY DISCOVERED, and; passing JUST 15 million miles from Earth and NOWHERE AS CLOSE TO ANY OTHER PLANET IN OUR SOLAR SYSTEM? Astronomical on steroids, I bet!!! ALSO, if this object is composed of mainly ice, its close passage to the should have caused some of that ice to VAPORIZE due to its low albedo meaning that most of the sunlight during that passage being absorbed and CONVERTED to heat. Since we saw NO coma, this vaporization would have had to have occurred INTERNALLY, ALSO causing the object to break into pieces! Due to this, in my opinion, Oumuamua is NOT composed of ice! Looking MORE AND MORE like something NOT NATURAL!!!!!!!!

  • Harry R Ray November 20, 2017, 19:15

    OOPS! I meant “…during its closest passage to the SUN…”