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Study Sees ‘Oumuamua as a Natural Object

A paper called “The Natural History of ‘Oumuamua,” just out in Nature Astronomy, puts the emphasis on the word ‘natural.’ We know how much of a stir in the media the interstellar visitor has made given its peculiarities, and the hypothesis put forward by Harvard’s Avi Loeb that it could be a technological object. Now we have a group of 14 astronomers, European as well as American, who have assessed the available data from all angles.

This is a worthwhile effort, assembling a team at the International Space Science Institute (ISSI) in Bern, Switzerland that intends to meet once again later in the year. It considers the question of whether the extraterrestrial spacecraft hypothesis is supported by examination of all the peer-reviewed work that has thus far appeared. Matthew Knight (University of Maryland), working with Alan Fitzsimmons (Queen’s University Belfast) assembled the team. Knight believes that natural phenomena can explain ‘Oumuamua:

“We put together a strong team of experts in various different areas of work on ʻOumuamua. This cross-pollination led to the first comprehensive analysis and the best big-picture summary to date of what we know about the object. We tend to assume that the physical processes we observe here, close to home, are universal. And we haven’t yet seen anything like ʻOumuamua in our solar system. This thing is weird and admittedly hard to explain, but that doesn’t exclude other natural phenomena that could explain it.”

Image: This artist’s impression shows the first interstellar object discovered in the Solar System, ʻOumuamua. Observations made with the NASA/ESA Hubble Space Telescope, CFHT, and others, show that the object is moving faster than predicted while leaving the Solar System. The inset shows a color composite produced by combining 192 images obtained through three visible and two near-infrared filters totaling 1.6 hours of integration on October 27, 2017, at the Gemini South telescope. Credit: ESA/Hubble, NASA, ESO/M. Kornmesser, Gemini Observatory/AURA/NSF.

As we have no new observations of ‘Oumuamua, the paper produced by this team is an analysis of existing data, including a December 2017 paper on the object’s shape and spin co-authored by Knight. When the scientist calls the object ‘weird,’ he’s at least partially referring to its apparent acceleration along its trajectory, which suggests a comet even if astronomers could find no evidence of the kind of gaseous outflow that would propel even a small acceleration. We see no coma of ice, dust and gas, no evidence for gas jets, no cometary ‘tail.’

Karen Meech (University of Hawaii), who was lead author on the research paper that reported the discovery of ‘Oumuamua not long after it was identified at the Pan-STARRS observatory, had noted the object’s red color and elongated shape, apparent in changes in its reflectivity as it rotated. But on the matter of cometary behavior, Meech sees no need for anything beyond natural processes at work, saying “…while it is disappointing that we could not confirm the cometary activity with telescopic observations it is consistent with the fact that ʻOumuamua’s acceleration is very small and must therefore be due to the ejection of just a small amount of gas and dust.”

To see full text of the paper, see this link (thanks Alex Tolley for an alternate link!) On the specific question of alien technologies, the paper has this to say:

The key argument against the solar-sail hypothesis is ‘Oumuamua’s light-curve amplitude. For a solar sail to cause the observed non-gravitational acceleration, it needs to remain properly oriented towards the Sun. However, to yield the observed brightness variations, its orientation would need to be varying as viewed from Earth. Furthermore, since the actual dimensions of the solar sail would be >10:1, the orientation as viewed from Earth would need to be very nearly edge on, and remain so throughout the observations despite viewing geometry changes. It has not been shown that an orientation exists that can achieve all of these constraints imposed by the observational data. Furthermore, as discussed earlier, the shape of ‘Oumuamua’s light curve, with broad maxima and narrow minima, is consistent with an elongated ellipsoid.

We also find this on albedo:

The claim that ‘Oumuamua must be at least ten times ‘shinier’ than all Solar System asteroids to make the Spitzer Space Telescope data consistent with the ground-based observations is incorrect. The Spitzer observations are consistent with geometric albedos 0.01 ≤ pv ≤ 0.5…, with a most likely albedo of pv ~ 0.1. Comets have geometric albedos of pv = 0.02–0.07, carbonaceous and silicate asteroids have pv = 0.05–0.21, and the most reflective asteroids have pv ~ 0.5… Thus ‘Oumuamua’s measured reflectivity of about 0.1 is entirely consistent with normal Solar System small bodies.

And on the argument that the kinematics of the object are unusual:

While provocative, this argument is baseless. First, ‘Oumuamua’s trajectory is consistent with predictions for detectable inactive interstellar objects. Second, the measured number density cannot be claimed to be at odds with expectations because of our ignorance of the size distribution of interstellar objects.

‘Oumuamua is destined to remain enigmatic, for our dataset represents all that could be collected before the interstellar visitor had traveled beyond the view of our telescopes. With only a few weeks in play to observe the object, the ISSI astronomers acknowledge its rarity (“We have never seen anything like ʻOumuamua in our solar system,” says Knight) while finding its movement explicable through natural means. All report anticipating results from the Large Synoptic Survey Satellite (LSST), which comes online in 2022 and may give us more interstellar objects of the same kind, allowing a deeper and perhaps less controversial analysis.

“In the next 10 years, we expect to begin seeing more objects like ‘Oumuamua. The LSST will be leaps and bounds beyond any other survey we have in terms of capability to find small interstellar visitors,” says Knight. “We may start seeing a new object every year. That’s when we’ll start to know whether ‘Oumuamua is weird, or common. If we find 10-20 of these things and ‘Oumuamua still looks unusual, we’ll have to reexamine our explanations.”

The paper is Bannister et al. (The ‘Oumuamua ISSI Team), “The Natural History of ‘Oumuamua,” Nature Astronomy 19 July 1, 2019 (abstract). Knight’s 2017 paper is “On the Rotation Period and Shape of the Hyperbolic Asteroid 1I/’Oumuamua (2017 U1) from Its Lightcurve,” Astrophysical Journal Letters Vol. 851, No. 2 (12 December 2017). Abstract.

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{ 33 comments… add one }
  • Robert July 2, 2019, 13:17

    It could be a fully natural object appropriated as intersteller art by an advanced alien artist designed with just enough ambiguity to tease less advanced societies.

  • Michael July 2, 2019, 14:09

    My money is on an electric charge build up allowing the solar wind to accelerate it.

  • DCM July 2, 2019, 14:17

    Of course it’s a natural object.
    People are more likely to find any artificial items if they proceed assuming that everything detected is natural. We certainly haven’t found anything artificial by constantly perceiving everything as alien craft or messages.

  • Robin Datta July 2, 2019, 14:20

    The subtitle to Greg Laughlin’s post “On ‘Oumuamua “on his blog “systemic” is subtitled “‘Oumuamua slipped our grasp.” Both the speculation and the regret that followed its discovery could use that subtitle.

  • Thomas Goodey July 2, 2019, 14:27

    Is this summary all the objective material that the paper contains? If so, I do not give it very much weight. The authors seem to think that the acceleration was due to outgassing rather than to radiation pressure, but no outgassing was seen, which weakens the argument. Moreover, since OUM was tumbling, one supposes that outgassing would disturb the tumbling motion; but it didn’t. The statement that the team “believes that natural phenomena can explain OUM”, without any suggestion of any concrete possibility, is simply not helpful.

  • Harry R Ray July 2, 2019, 14:49

    “`Oumuamua’s acceleration is very small and must therefore be due to the ejection of just a small amount of gas and dust”. Paul Gilster: I tried to access the entire article online, but I hit paywall. Can you or another Centauri Dreams reader access the exact passage in the article that deals with Roman Rafikof’s counter-argument that such outgassing will inevitably spin-up a tumbling object to the point where it fragments. I know it is in the paper, because his paper was mentioned as one of the references at the bottom of the abstract. If you CAN access it, please insert it here as a reply to this comment. Thanks!

    • Paul Gilster July 2, 2019, 16:19

      Harry, Alex has now provided the link.

  • Alex Tolley July 2, 2019, 14:56

    From the paper regarding it as alien technology:

    Alien technology?
    The idea of ‘Oumuamua as alien technology has been advocated in a series of papers. The authors argue that the dimensions needed to explain the observed solar radiation pres-sure are consistent with a ‘solar sail’. While this fits some aspects of the observations — the basic idea of ‘Oumuamua having a highly flattened shape was previously considered — it appears unable to explain other key aspects of the observations, and some arguments in favour of this hypothesis are simply wrong.The key argument against the solar-sail hypothesis is ‘Oumuamua’s light-curve amplitude. For a solar sail to cause the observed non-gravitational acceleration, it needs to remain properly oriented towards the Sun. However, to yield the observed brightness variations, its orientation would need to be varying as viewed from Earth. Furthermore, since the actual dimensions of the solar sail would be >10:1, the orientation as viewed from Earth would need to be very nearly edge on, and remain so throughout the observations despite viewing geometry changes. It has not been shown that an orientation exists that can achieve all of these constraints imposed by the observational data. Furthermore, as discussed earlier, the shape of ‘Oumuamua’s light curve, with broad maxima and narrow minima, is consistent with an elongated ellipsoid.The claim that ‘Oumuamua must be at least ten times ‘shinier’ than all Solar System asteroids to make the Spitzer Space Telescope data consistent with the ground-based observations is incorrect. The Spitzer observations are consistent with geometric albedos 0.01 ≤ pv ≤ 0.5 (ref. 3), with a most likely albedo of pv ~ 0.1. Comets have geometric albedos of pv = 0.02–0.07, carbonaceous and silicate asteroids have pv = 0.05–0.21, and the most reflective asteroids have pv ~ 0.5 (refs. 75,76). Thus ‘Oumuamua’s measured reflectivity of about 0.1 is entirely consistent with normal Solar System small bodies.Finally, it was argued that ‘Oumuamua was deliberately sent towards Earth based on its ‘unusual’ kinematics and presumed scarcity. While provocative, this argument is baseless. First, ‘Oumuamua’s trajectory is consistent with predictions21 for detect-able inactive interstellar objects. Second, the measured number density cannot be claimed to be at odds with expectations because of our ignorance of the size distribution of interstellar objects.Thus, we find no compelling evidence to favour an alien explana-tion for ‘Oumuamua.

    • Harry R Ray July 3, 2019, 10:12

      WILD SPECULATION ALERT: Has anyone but me even CONSIDERED the possibility that `Oumuamua may NOT be tumbling AT ALL, but instead is a FULLY FUNCTIONAL lightsail that was, at the time of its discovery, perfectly aligned with the sun to produce the observed non-gravitational acceleration? For this to be true, one would have to invoke a “Deux Ex Machina” ON STEROIDS scenario, but, what the heck, here goes! The weird variations in the lightcurve would be totally explainable if `Oumuamua were an expandable-retractable lightsail(these things already exist, you know. google “retractable lightsail”)consisting of several independent segments. Continuous expansion(for some segments)and retraction(for others)at DIFFERENT RATES would completely explain the ENTIRE LIGHTCURVE! I know: “how convenient!”. This is EXACTLY why this will not even come up as a subject of discussion in the scientific community unless ALL OTHER EXPLANATIONS have gone COMPLETELY OUT THE WINDOW! How sad, because this idea is COMPLETELY TESTABLE using the current data. Changes in the total area of such a lightsail would lead to changes in the RATE of acceleration which should be detectable in the data by creating a machine learning algorithm focused on acceleration rate variability. Such an algorithm will almost certainly NOT be created because of obvious lament of the scientific community, which will be “Why bother!” What would be the point of such a complex system over a more simple one with a less chance of a breakdown over a timespan of billions of years? To that, I respond: THE ABILITY TO SEND A MESSAGE! OK. Why would you create this elaborate MECHANICALLY OPERATED message sending mechanism when a simple radio transmitter will do just as well. How about billions of years of exposure to interstellar radiation DEGRADING the transmitter to the point of GARBLING the radio transmission to the point where the message is IRRETREVABLY LOST! The only way to find out for sure is to run an analysis on the lightcurve to see if there IS any message in there. Seems easy enough to do. ANY TAKERS?

      • Alex Tolley July 3, 2019, 13:56

        @Harry. You would need to explain:

        1. The purpose of the expansion and retraction cycle of the sail.
        2. Why the object is not very shiny – the authors claim is has the albedo of other natural bodies. A sail would be very reflective, yet it is not.

        Occam’s razor applies here. The simplest explanation that covers all the observations is the one to pick, rather than more complex and exotic ones.

  • Paul Gilster July 2, 2019, 16:37

    Thanks for that link, Alex, as well as the quote from the paper. I’ve stripped the quote down slightly and inserted it into the text, which I tried to do without success this morning, for reasons I don’t understand but were clearly software related.

    • Ron S. July 2, 2019, 17:47

      Unfortunately this comment thread is unreadable with Firefox because the link expands the window and won’t wrap the text to its home frame.

      Long links ought to be done with tags rather than in plain text.

  • Antonio July 2, 2019, 16:49

    Text is missaligned again.

    • Paul Gilster July 2, 2019, 17:01

      Antonio, I see no misalignment in Chrome or Firefox. What browser are you using, and where is the misalignment?

      • Antonio July 2, 2019, 17:17

        I’m using Firefox 66.0.3. It’s not missaligned in the home page, but when I enter the article, text extends to the right unbounded.

        • Paul Gilster July 2, 2019, 17:27

          How odd. I can’t account for it. Has anyone else had any problems? I did have some software issues earlier today, but I’m not seeing any problems with the actual post.

          • Antonio July 2, 2019, 17:30

            Maybe the problem is with Alex long link? The Venus and Firefly posts are OK.

            • Paul Gilster July 2, 2019, 21:18

              Yes, I think it’s the long link. Let me pull that and re-insert it into the main text, and we’ll see what happens. I’ll just set up a link without quoting the URL.

              • Antonio July 3, 2019, 2:24

                Now it is OK. Thanks!

                • Paul Gilster July 3, 2019, 8:45

                  Sure, and thanks for your help, Antonio, and all of you who chimed in.

          • Andrew Palfreyman July 2, 2019, 19:32

            Yup, same old Firefox’d up as last time.

          • J. Michael July 2, 2019, 20:55

            Yes: the home page looks okay but the text of this post isn’t wrapping at screen width, instead continuing on to the right for quite a distance. Firefox ESR 52.9.0 with * various add-ons & such. (The “*” is where the text wrapped for me just now.)

            • Paul Gilster July 2, 2019, 21:17

              Thanks for the info. I’m stumped. Last night it was easy to figure out the problem, but this one makes no sense. Will work on it.

              • Alex Tolley July 3, 2019, 0:10

                Firefox Quantum 67.0.4 (64-bit) on my Windows 10 box seems fine to me.
                Is anyone with problems running FF on another OS? If you switch to another browser, Chrome, Opera, etc, is the problem still evident?

  • Neil Stahl July 2, 2019, 21:31

    I’m certainly not claiming this is the case, but if “they” wanted to maintain deniability they could use solar sail material that can change its color (and thus albedo) as needed to confound us.

  • wdk July 3, 2019, 11:00

    Alien artifact arguments should be dissected. Some of them are claims that the object is space flotsam from an alien life form. That’s one extreme. The other end of the spectrum is the idea that this object is an intended investigation of the solar system. There are hypotheses in between.

    But when we start talking about an alien “space probe” examining the solar system, we have to take into account that this thing has been in transit for over 100,000 years. Maybe millions. Human civilization originated in transit. At a very recent phase.

    So, if the visit is not about us, you have to wonder why there would be a visit of the solar system out of plane and so quick of a transit after 100 K years or more.

    By consensus on evidence the object is interstellar, but it does not fit into any pigeon hole very well so far. Maybe we need to know a lot more about circum stellar disks and asteroid belts.

    • Alex Tolley July 3, 2019, 14:02

      The idea that the probe is investigating our civilization seems remarkably human self-centered. If we send a probe to another solar system, we may just hope to explore the world. If it just happened to arrive when another civilization was emerging, they might think the same thing, even though that was not our intention. Similarly, if a von Neumann replicator was found in our solar system, there would be no reason to assume its presence was a deliberate attempt to investigate our civilization rather than a coincidence.

    • Hamilton1 July 3, 2019, 20:16

      “But when we start talking about an alien “space probe” examining the solar system, we have to take into account that this thing has been in transit for over 100,000 years. Maybe millions.”

      We can’t be sure of that. Just because it was traveling through our System at a certain rate, doesn’t prove it was moving at an equally slow speed through interstellar space. Or similarly if it was a reconnaissance craft dispatched from a much faster mother ship.

  • Curious July 5, 2019, 1:10

    Why assume it was functional? IF it was artificial it seems more likely to have been a nonfunctional remnant/castoff rather than something functioning. When we launch probes, they and their rocket upper stages are typically also expelled on outbound trajectories. https://en.wikipedia.org/wiki/List_of_artificial_objects_leaving_the_Solar_System
    Imagine where those will end up in a million years and what they might look like after collisions tiny particles along the way. If you consider that Oumuamua was millions of years old then its even more believable if it were a nonfunctioning unintentionally sent remnant as opposed to a purpose-sent machine capable of functioning for millenia to probe for intelligent life.

    A variation is that it was just the delivery mechanism for a probe that seems would be much much smaller – consider the largest microbe https://en.wikipedia.org/wiki/Thiomargarita_namibiensis at 0.75mm. If a tiny probe had been delivered by a solar sail it seems that sail might be turned to decelerate the probe and that maybe collapses the sail. The odds that we could then locate such a microprobe and identify it as such seem fantastically small.

    While its fun to speculate about that I agree that the most likely answer is some natural object that has been shaped by an as yet unknown process.

    • Law September 15, 2019, 0:48

      I agree completely. A crumpled-up out-of-control lightsail, some spent upper stage of some alien civilization… all are plausible hypotheses for the unusual shape.

      But as usual, Occan’s razor applies. Natural objects probably outnumber artificial ones by a billion to one or more (even if somebody went really crazy with the multiple-flyby star-probes).

    • Law Wong September 15, 2019, 0:51

      Oh… another problem. It’s too slow. You’d expect any reasonable probe to have much more relative motion compared to the galaxy at large.

  • Anton M. July 15, 2019, 10:10

    A mind perverse enough can identify a city as a completely natural object.

    On the other hand, what are the chances of the first and only sample of the interstellar object to be artificial? Is the galaxy full of alien derelicts? If so, why is not Earth/Moon constantly bombarded by the artifacts?

  • ljk September 3, 2019, 10:53

    At the risk of sounding like someone on this blog, THIS PAPER NEEDS TO BE READ!

    https://arxiv.org/abs/1906.03696

    Modeling the light curve of `Oumuamua: evidence for torque and disc-like shape

    Sergey Mashchenko

    (Submitted on 9 Jun 2019 (v1), last revised 30 Aug 2019 (this version, v2))

    We present the first attempt to fit the light curve of the interstellar visitor `Oumuamua using a physical model which includes optional torque. We consider both conventional (Lommel-Seeliger triaxial ellipsoid) and alternative (“black-and-white ball”, “solar sail”) brightness models.

    With all the brightness models, some torque is required to explain the timings of the most conspicuous features — deep minima — of the asteroid’s light curve.

    Our best-fitting models are a thin disc (aspect ratio 1:6) and a thin cigar (aspect ratio 1:8) which are very close to being axially symmetric. Both models are tumbling and require some torque which has the same amplitude in relation to `Oumuamua’s linear non-gravitational acceleration as in Solar System comets which dynamics is affected by outgassing.

    Assuming random orientation of the angular momentum vector, we compute probabilities for our best-fitting models. We show that cigar-shaped models suffer from a fine-tuning problem and have only 16 per cent probability to produce light curve minima as deep as the ones present in `Oumuamua’s light curve. Disc-shaped models, on the other hand, are very likely (at 91 per cent) to produce minima of the required depth.

    From our analysis, the most likely model for `Oumuamua is a thin disc (slab) experiencing moderate torque from outgassing.

    Comments: 21 pages, 11 figures, accepted by MNRAS. Added confidence intervals calculations for model parameters (Table 2). Results unchanged

    Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

    DOI: 10.1093/mnras/stz2380

    Cite as: arXiv:1906.03696 [astro-ph.EP]
    (or arXiv:1906.03696v2 [astro-ph.EP] for this version)

    Submission history

    From: Sergey Mashchenko [view email]

    [v1] Sun, 9 Jun 2019 19:27:32 UTC (448 KB)

    [v2] Fri, 30 Aug 2019 14:23:00 UTC (449 KB)

    https://arxiv.org/pdf/1906.03696.pdf

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