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‘Oumuamua, Thin Films and Lightsails

The interstellar object called ‘Oumuamua continues to inspire analysis and speculation. And no wonder. We had limited time to observe it and were unable to obtain a resolved image to find out exactly what it looks like. This morning I want to go through a new paper from Shmuel Bialy and Abraham Loeb (Harvard University) considering the role radiation pressure from the Sun could play on this deep sky wanderer. Let’s also review what we do know about it, which I’ll do with reference to this paper’s introduction, where recent work is discussed. For it seems that each time we look at ‘Oumuamua anew, we find something else to talk about.

Discovered in October of 2017 by the Pan-STARRS survey (Panoramic Survey Telescope and Rapid Response System) in Hawaii, ‘Oumuamua stood out because of its hyperbolic trajectory, flagging it as an interstellar object, the first ever discovered passing through the Solar System. The object’s lightcurve indicated both that it was tumbling and had an aspect ratio of at least 5:1 and perhaps higher, an unusual shape for known asteroids and comets. I won’t provide all the references here, as they’re easily found both in the paper cited below and in other related work.

Image: The track of `Oumuamua as it passed through the inner solar system in late 2017. Credit: Brooks Bays / SOEST Publication Services / Univ. of Hawaii.

What stood out in 2018 was detection of non-gravitational acceleration in ‘Oumuamua’s motion, which could be consistent with cometary activity, although as we’ve seen in other posts on this site, no such activity has been noted by way of a cometary tail or gas emission and absorption lines. This despite a relatively close approach to the Sun of 0.25 AU. The Micheli et al. paper noting the acceleration was addressed in another 2018 paper from Rafikov et al., which pointed out that torque from any cometary outgassing should have had effects on the object’s spin, but this does not appear in our admittedly limited observations.

What Bialy and Loeb consider in today’s paper is the possibility that solar radiation pressure — imparted by the momentum of photons from the Sun — is responsible for the acceleration, expressed as an excess radial acceleration ∆a ∝ r−2, where r is the distance of ’Oumuamua from the Sun. If so, ‘Oumuamua would of necessity be a thin object with a small mass-to-area ratio — this is required in order to make the radiation pressure effective.

We can work out constraints on the object’s area through its observed magnitude. The paper proceeds to show that a thin sheet roughly 0.3 mm thick and some 20 meters in radius will allow the non-gravitational acceleration computed in the Micheli paper.

I was intrigued enough at this point to ask Dr. Loeb about those dimensions, which vary with albedo (the incident light reflected by a surface). He told me that the 20-meter figure would be the radius if the object is a perfect reflector, though the size would be larger if the value for the albedo is smaller. We do see variations in reflected light as ‘Oumuamua rotates over an eight-hour spin period. Thus, considering the object as a thin surface, we could imagine a conical or hollow cylindrical shape. “You can easily envision that by rotating a curved piece of paper and looking at its net surface area from different viewing angles,” Loeb told me.

So let’s back up a moment. We are asking what properties ‘Oumuamua would have to have if its non-gravitational acceleration is the result of solar radiation pressure. We do not know that solar radiation is the culprit, but if it is, the object would need to be a thin sheet with a width in the range of 0.3 mm. This scenario explains the acceleration but forces the question of what kind of object could have these characteristics. A major problem is that, as mentioned above, there are too many degrees of freedom in our observations to nail down what ‘Oumuamua looks like. We did not have observations sensitive enough to produce a resolved image.

Image: Oumuamua as it appeared using the William Herschel Telescope on the night of October 29. Credit: Queen’s University Belfast/William Herschel Telescope.

We do know that if ‘Oumuamua is accelerating because of solar photons, it must represent what the paper calls ‘a new class of thin interstellar material.’ The researchers note the possibility that such material is naturally produced in the interstellar medium, but go on to consider an artificial origin. Could ‘Oumuamua be debris from a technological civilization, a discarded lightsail?

A fascinating speculation indeed. From the paper:

Considering an artificial origin, one possibility is a lightsail floating in interstellar space as debris from an advanced technological equipment (Loeb 2018). Lightsails with similar dimensions have been designed and constructed by our own civilization, including the IKAROS project and the Starshot Initiative. The lightsail technology might be abundantly used for transportation of cargos between planets (Guillochon & Loeb 2015) or between stars (Lingam & Loeb 2017). In the former case, dynamical ejection from a planetary system could result in space debris of equipment that is not operational any more (Loeb 2018) and is floating at the characteristic speed of stars relative to each other in the Solar neighborhood.

We’re past the stage where we can image ‘Oumuamua with our telescopes and it’s too late to get a mission off to chase it with chemical rockets, which means that the only way we have of pressing the investigation forward is to look for other such objects in the future. But we can look at the properties of thin films to determine whether an object like a lightsail could survive interstellar travel, given encounters with dust and gas between the stars. Returning to the paper:

Collisions with dust grains at high velocities will induce crater formation by melting and evaporation of the target material. Since the typical time between dust collisions is long compared to the solidification time, any molten material will solidify before the next collision occurs, and thus will only cause a deformation of the object’s surface material, not reduction in mass. On the other hand, atoms vaporized through collisions can escape and thus cause a mass ablation.

Bialy and Loeb find that for the mass-to-area ratio they have calculated for a thin-film ‘Oumuamua, the object could travel through much of the galaxy before losing a significant fraction of its mass. Collisions with gas particles in the interstellar medium as well as the stresses of centrifugal and tidal forces are also considered. None of these present problems for the object’s survival until we reach a maximal travel distance in the range of 10 kpc (well over 32,000 light years). Earth is approximately 25,000 light years from the center of the galaxy.

Image: This is Fig. 1 from the paper. Caption: The maximum allowed travel distance through the interstellar medium (ISM), as a function of (m/A). The blue and red lines are limitations obtained by slow-down due to gas accumulation, and vaporization by dust-collisions, respectively. The plotted results are for a mean ISM proton density of (n) ∼ 1 cm−3. All lines scale as 1/(n). The dashed magenta line is our constraint on ’Oumuamua based on its excess acceleration. The Solar Galactrocentric distance is also indicated. Credit: Bialy & Loeb.

Avi Loeb has recently written about how we might find evidence for extraterrestrial civilizations long gone. From that perspective, he considered the possibility that ‘Oumuamua is just such an artifact, and told me this in an email:

With the perspective of my recent essay in Scientific American, `Oumuamua could be defunct sails floating under the influence of gravity and stellar radiation. Similar to debris from ship wrecks floating in the ocean. The alternative is to imagine that `Oumuamua was on a reconnaissance mission. The reason I contemplate the reconnaissance possibility is that the assumption that `Oumumua followed a random orbit requires the production of ~1015 such objects per star in our galaxy. This abundance is up to a hundred million times more than expected from the Solar System, based on a calculation that we did back in 2009. A surprisingly high overabundance, unless `Oumuamua is a targeted probe on a reconnaissance mission and not a member of a random population of objects.

Loeb also made a comment in his email that ties in to what Breakthrough Starshot is attempting to quantify, a series of missions to the same target — hundreds if not thousands of probes — sent swarm-like to ensure that at least one or a few come close to the world under observation. If something like this were happening with ‘Oumuamua, and given that PAN-STARRS barely detected the object at closest approach, we would not know about any of its fellow probes.

Addendum: Just as I was publishing this I learned of a paper by Eric Mamajek (University of Rochester), who notes that ‘Oumuamua appears to have originated at the Local Standard of Rest (LSR), which is the galactic frame of reference. Quoting Mamajek: “Compared to the LSR, ‘Oumuamua has negligible radial and vertical Galactic motion…” According to Dr. Loeb in a subsequent email, less than one star in 500 is at that frame of reference to the same precision. (The Mamajek paper, “Kinematics of the Interstellar Vagabond 1I/’Oumuamua (A/2017 U1),” can be found here in preprint form).

It’s an interesting point. If ‘Oumuamua turned out to be artificial, would there be an advantage in such a position? Perhaps so, for as Loeb goes on to say in his email:

I view a sail (like `Oumuamua) floating in interstellar space with stars (like the Sun) running into it as if it were a buoy floating on the ocean surface with boats colliding with it. An artificial origin would naturally place floating sails at the LSR, perhaps as relay stations.

Another item of interest:

Trilling et al., “Spitzer observations of `Oumuamua and `Oumuamua’s density and shape,” as presented at the American Astronomical Society DPS meeting #50, finds no detection of thermal emission from `Oumumua, implying that it must be very reflective or small, which is consistent with the Bialy and Loeb paper. The abstract of the Trilling paper is here.

And a final point: While catching up with ‘Oumuamua would be immensely challenging, Andreas Hein and colleagues have suggested how it might be done. For more, see Project Lyra: Sending a Spacecraft to 1I/’Oumuamua (formerly A/2017 U1), the Interstellar Asteroid.

The Bialy & Loeb paper is “Could Solar Radiation Pressure Explain ‘Oumuamua’s Peculiar Acceleration?” (preprint). The Micheli et al. paper on ‘Oumuamua’s acceleration is “Non-gravitational acceleration in the trajectory of 1I/2017 U1 (‘Oumuamua),” Nature 559 (27 June 2018), 223-226 (abstract).


{ 194 comments… add one }
  • Elad Silver October 30, 2018, 1:15

    Came here by a link posted by a friend.
    This is great stuff, the best part about it is a simple peraon who does not come from the physics background can understand every word.
    Thank you!

    • J. Jason Wentworth October 31, 2018, 1:28

      That is a great compliment to the author, which I strongly second! (There is actually very little in science and engineering that cannot be described non-mathematically, such that anyone can understand it. Arthur C. Clarke did this for astronomy and astronautics in “The Making of a Moon,” “The Exploration of Space,” “The Promise of Space,” and numerous essays, and Carl Sagan and Isaac Asimov did it in their non-fiction books.) Unfortunately, there don’t seem to be many good popularizers in action today. The only really concise one I can think of is Neil deGrasse Tyson (there are others, of course, but he has that gift of explaining much with few words).

      • ljk October 31, 2018, 10:40

        Dennis Overbye of the New York Times is an excellent translator of space science to the masses.


        • J. Jason Wentworth November 1, 2018, 15:32

          Very good–I had heard of him (his surname), but knew nothing more about him. If he hasn’t already written any books, he should (even a compilation of his New York Times articles would be well worth publishing). The late Walter Sullivan (who wrote the SETI-related book “We Are Not Alone”) was his predecessor at the New York Times.

  • Paolo October 30, 2018, 2:02

    I’ve seen claims that we just cannot deduce shape and rotation of a celestial body from its light curve, especially so far away and so small… Can someone please contradict this?

    • Alex Tolley October 30, 2018, 10:22

      I have previously asked whether 1D lightcurves can be used to deduce 3D shapes. I am convinced that this dimensionality reduction cannot be reversed for all but the simplest cases.

      • Michael C. Fidler October 31, 2018, 6:29

        But the light curves where not just one dimensional, the observations from the Spitzer Space Telescope infrared camera where taken from some 150 million miles behind earth’s orbit! So there should be some good data in the time and angle difference between earth’s view and Spitzer’s.

        • Alex Tolley October 31, 2018, 10:02

          Can you show that the loss of 1 dimension can be restored? Think of converting shadows to 3D objects. The astronomers’ version of Plato’s Cave?

        • wdk October 31, 2018, 10:55

          When it was mentioned that Spitzer was 150 million kilometers away, it got me wondering. Had assumed that it was located at one of the Earth-Moon or Earth-Sun Lagrangian points, but that was not the case:

          [Since launch in 2003]” it follows a heliocentric instead of geocentric orbit, trailing and drifting away from Earth’s orbit at approximately 0.1 astronomical units per year (a so-called “earth-trailing” orbit).”

          So by now there’s considerable angular width for views. Judging from that, about 1.5 radians or 85 degrees between Earth and Spitzer by now, about 80 degrees a year ago. So, if there were a light curve variation that varied as observed from the two sites, it would be possible to attach a geometry to the source derived from the two varying signals – unless the line of sight for the two observing telescopes were practically on top of each other. But it looks like the geometry would not stay that way long, if at all.

          Shape determination gets more difficult with a longer baseline or narrower angular separation, such as with a star. In that case, emission lines and absorption lines in stellar atmospheres help. There are distinct ways in which the lines collected are spread due to stellar rotation, expansion or contraction due to the overall contribution of light at a wavelength from a spherical surface – or perhaps any geometry. But in the case of this object, I doubt if there were sharp lines related to the surface light absorption features. For example, the sun is rich in sharp lines in its spectrum – and still appears that way reflected off the moon. This is even though the moon absorbs solar radiation unevenly. But generally, even though you can do spectral analysis of the moon, by comparison, the moon does not absorb light as nearly as sharply in narrow bandwidths. But in this case, it’s not the moon but a small and distant object like an asteroid.

          So there would appear to be some circumstances working in favor of deriving the shape and rotation of ‘Oumuamua and some making it difficult.

          • Michael C. Fidler October 31, 2018, 20:05

            Some images that may help:


            Some excelent images of Oumuamua orbit by Guy Ottewell:

            Spitzer position in space is about 1.5 AU from earth or 150 million miles. Its angle from earth’s view was about 90 degrees, by the time ʻOumuamua was spotted we were (earth) ahead of it and it was above the plan of the ecliptic. The problem is that it was not visible to Spitzer in the late November, 2017 observations, just wondering if Spitzer observed it earlier? The point I see is that at 90 degrees, if a sail of some sort it would not be visible if the broadside was facing earth! Of course Spitzer was 150 million miles further away than earth’s 30 million miles to ‘Oumuamua.

            But it makes me wonder why they stated Spitzer observation this way:
            “After thirty hours of staring – a relatively long time – the object was not detected, and subsequent orbital analyses confirmed that the camera was pointed correctly towards it. The limit to its emission, however, was so low that it enabled the team to constrain some of its physical properties. The lack of an infrared signal, for example, suggests it has no gas or dust, species that would be expected if it were a cometary-like body.”

            Please visit Guy Ottewell’s website, he is the best illustrator of cosmic perspective for our simple minds! ( And does a great yearly beautifully illustrated Astronomical Calendar )


            • ljk November 2, 2018, 9:28

              Spitzer “staring” at Oumuamua for 30 hours reminds me of the two SETI attempts made with our visitor. As with most of SETI then and now, they were largely done as tokens to say “See, we tried, but no signal, therefore, no aliens.”

              Perhaps I am being a bit harsh here, but not too much based on my knowledge of SETI and METI history. They could still be tracking Oumuamua in this way if they really wanted to.

              Yes, Guy Ottewell’s work is amazing. I posted that link a while ago in another Oumuamua so I am glad to gave it a refresher. His book on Halley’s Comet was a true work of art and science.

              • Michael C. Fidler November 2, 2018, 11:18

                One of the ways to learn is by illustrations, especially being males since our minds are more adapted to looking at the details. Drawings work much better then pictures because they they highlight the idea being presented without cluttering it with other objects and the ability of a giving xray details. I always liked the drawings done in the older Scientific American and have a copy of The Amateur Scientist by the same. This is why Ottewell’s work is so effective in explaining some very abstract thoughts and both use very similar illustration styles. Looking at the some of the AiXiv papers on exoplanets, I would think an alien would have better luck at deciphering what they mean with the math jargon and it would be nice if an artist could draw the concepts. Just some wishful thinking…

                • ljk November 2, 2018, 14:36

                  Most modern science papers make the Atacama Desert look positively soaked with moisture. And then they wonder why the public is not into science, assuming they care at all.

                  • Michael C. Fidler November 2, 2018, 19:50

                    I think the public cares, they are just put off by how intimidating big science is, Not bragging, but the star parties I put on at the Oregon state parks during the summer I usually have a 100 to 150 people coming saturday nights to listen and look thru the telescope. Most are adults and the older ones are usually very complementary.

                    • ljk November 7, 2018, 10:38

                      Most of the people running star parties are interested amateurs who love what they are doing. I am talking about Big Institute and Academia Science.

      • jake October 31, 2018, 17:02

        I believe that the problem can be framed such that algorithms used in CT can back out the shape: https://en.wikipedia.org/wiki/Radon_transform

        • Alex Tolley October 31, 2018, 22:04

          An interesting idea, but tomography uses lots of transmission data from a static object where the angles are known for each slice, rather than surface reflection data from an unknown tumbling form. I think you are suggesting that the frame of reference doesn’t matter, whereas I think tomography requires known views to compute the structure in a 2D slice (and create 3D views using lots of slices.
          If this approach worked, wouldn’t someone have applied it to create a 3D structure, rather than just approximate the shape using the lightcurves?
          As a thought experiment, assume that the object was spherical, but has some relatively high albedo spots on its surface, rather like the exposed salt areas on Ceres. The light curve would suggest an oblate object as it rotated/tumbled, rather than a sphere with bright spots. [With tomography, the transmission of the signal through the object varying due to density or shape would not have this problem assuming rotation on a single axis.]

  • AlexT October 30, 2018, 4:33

    Due to huge lack of information about dicussed object there is possible to imagine unlimited number of versions and explanation about misterious event, but in reality it is always remain the white noise that is deeply burying real facts.
    We could never check what it was in reality – Oumuamua, so Bialy & Loeb wrote another one narrative for Sci-Fi novel. Is it science?

    • Alex Tolley October 30, 2018, 10:19

      That was my thought when I read about this elsewhere. Speculation based on very limited information. The calculations certainly help to put constraints on the proposed model, which would make it the basis for a hard SF story.

      • Ralph Woodin November 3, 2018, 23:56

        Arthur C. Clarke – Rendezvous with Rama seems like a good fit for Oumuamua.

        • AlexT November 4, 2018, 13:18

          Almost every idea good fit for Oumuamua.

  • Ron S. October 30, 2018, 9:48

    Consider the two statements:
    a) Detected no outgassing.
    b) Did not detect outgassing.

    These are completely different. What was determined was ‘b’, yet there is rampant speculation based on ‘a’ being true.

    • Thomas Goodey October 30, 2018, 14:45

      Your two statements (a) and (b) are equivalent. I think you mean (c) “Detected that there was no outgassing.”

      • bjk October 30, 2018, 20:02

        I would argue that (a) and (c) are equivalent, and both different from (b).

        (a) meaning that it has been confirmed there is no outgassing
        (b) meaning it is unsure whether there it outgassing, as none has been detected

    • Hamilton1 October 30, 2018, 14:54

      Actually your two statements are identical. What you mean is:
      a) no outgassing exists.

      but the unprecedented depth of the images show activity at least a level below every other observed comet. The more than 200 comets which have exhibited non-gravitational acceleration were all easily identifiable as comets without any such deep imagery being required.

    • Ron S. October 30, 2018, 17:46

      Thomas and Hamilton1,

      I believe my grammar is correct. The first statement (a) is a positive detection of no outgassing: equal to zero, where the error bars are suitably tight with respect to the conclusive statement. The second (b) is an experimental result that is not definitive either way, whether due to error bars or signal to noise ratio. The present situation conforms to (b).

    • Robin Datta November 2, 2018, 0:07

      Detected no outgassing: there may have been outgassing that was not detected.
      Did not detect outgassing: there may have been outgassing that was not detected.

      • Adam Crowl November 4, 2018, 1:58

        A very slow probe if it was one. But maybe it was quick enough if the ETIs are local.

    • Anaxagoras November 6, 2018, 1:22

      Outgassing that can be switched off during the closest approach to the sun seems like an even neater trick than a natural solar sail.

  • Michael Fidler October 30, 2018, 9:49

    Paul, this article is great and reminds me of the open minded thoughts that the community of SETI scientist have been noted for.

    Two interesting possibilities that may support this.
    1. Why the object came in so close to the Sun, right thru the habitable zone and into the area that most multi planet systems have their Rocky planets.
    2. Where is it going from here, we read a lot of conjecture on where it came from but if it is heading to another star nearby that has planets…

    • ljk October 30, 2018, 13:31

      Yes. Astronomers are having trouble figuring out where it came from – but it should be relatively easier to figure out where it is going. That could answer a few questions right there.

      Anyone here good at celestial mechanics?

      • Michael C. Fidler October 31, 2018, 20:39

        It shows that it is heading for the square of the constellation Pegasus, fitting because Pegasus is the mythical winged divine stallion.


        I took a look with Stellarium and Sky Chart / Cartes du Ciel and found the brighter stars in that area were around 320 to 600 light years away. I did find one that was at 200 light years, HD 224508 a G5 similar to the Sun. Red dwarfs would be too dim to pick up but if someone wants to do a more indepth search here are several good FREE programs:

        • Ron S. October 31, 2018, 21:26

          “Pegasus is the mythical winged divine stallion”

          The overlapping Chinese constellation is Black Tortoise of the North. This is appropriate since Oumuamua is moving slowly.

          • ljk November 2, 2018, 9:30

            Plus tortoises live a long time and tend to win races by being slow and steady.

    • Thomas Goodey October 30, 2018, 14:50

      Nail on the head, Michael!

      (1) None of the discussions I have read have considered the blatant fact that the trajectory of Oumuamua is exactly that which would be pursued by an artificial craft doing an Oberth maneuver and diving as close to the Sun as possible without being utterly overheated.

      (2) Of course where Oumuamua is going is the real question, and that’s what the stellar dynamics experts should be working on.

      If the purpose of the sundive was to perform an Oberth maneuver, which I think is virtually obvious, then all the speculation as to where it came from is completely worthless.

      • Ron S. October 30, 2018, 17:51

        “diving as close to the Sun as possible without being utterly overheated”

        Sampling bias. Detection of objects crossing much further out or out of the plane of the solar system is less probable.

      • jonW October 31, 2018, 10:27

        If this were a craft employing the Oberth effect, we should have seen a substantial gain in velocity at its closest approach to the sun, more so than with an unpowered slingshot. We did not see such a gain in velocity, so it does not seem to have been the case.

        • Hamilton1 October 31, 2018, 13:14

          When we first saw it, it was already 22 million miles past Earth. Estimates of its velocity at perihelion are based entirely on it being a natural object, and the presence of non-gravitational acceleration has complicated those calculations.

        • Thomas Goodey November 1, 2018, 14:25

          It hadn’t even been seen at that time.

      • Reagan S October 31, 2018, 13:54

        Is it not entirely possible to use what we know about it’s trajectory to, for lack of knowing a better word, reverse-engineer it’s path to discover where it came from?
        If it is artificial, I think it’s probably worth knowing where such a creation came from, perhaps even more so than where it is going.

      • T Broadt October 31, 2018, 20:08

        Since it was not observed until well after perihelion, who’s to say that it isn’t a solar sail that was launched from our own system from a close solar orbit?

    • AlexT October 30, 2018, 15:40

      open minded…
      1. Why the object came in so close to the Sun

      Explanation very simple – very advanced ETI, that was riding on Oumuamua through our Solar system. Are eating only vegetable, so they are needed our Sun light to organize summer time on Oumuamua to grow their seeds… (may be to grow their analog of cannabis) .

      2. Where is it going from here…

      Taking in account ping-pong like bouncing around our Sun, we can suppose that for unknown period of flying in free space Oumuamua could have start point from every point of our Universe. In connection to Oumuamua destination – the same conclusion can be done, after long time of ping-pong travel, every destination is possible (similar to path that was represented in “Game-Changer: A Pluto Orbiter and Beyond” article) .
      So I suppose that every open minded individuum can choose every start/stop point he likes, all variants are equal.

      • ljk November 2, 2018, 9:34

        Better hope these ETI are not actual vegetables themselves. See the 1951 film version of The Thing from Another World. :^)

        • AlexT November 4, 2018, 3:53

          I’ve never seen this film, but will try to find :-)

  • Harry R Ray October 30, 2018, 9:59

    The main reason why Micheli et al considered `Oumuamua to be a comet was that the acceleration ceased at exactly the point in the trajectory where you would expect outgassing to cease. This poses a problem to Bialy and Loeb’s conclusions. However, I think I can kill two birds with one stone here. Although no signifigant mass loss occurs, enough may occur to render the steering mechanism inoperable at perihelion, which initiates a sequence of events leading to initiation of tumbling just prior to the initial discovery image, and completely rendering the lightsail inoperable in just a few weeks, leading to the cessation of acceleration, but NO deceleration at a point similar to the one at which a comet would stop outgassing. That would be the most elegant NATURAL solution. However we should also explore non-natural ones, too! Has anyone attempted to derive a MESSAGE from the lightcurve? Would there be a logical reason for `Oumuamua to cease acceleration WITHOUT decelerating, if it were a still functioning interstellar probe? If either author could respond to these questions, I would appreciate it, because this is so hugely important. Finally, one of the test-sequence launches of breakthrough starshot lightsails PRIOR to the Proxima b launch should be a “shrapnel” fleet covering the projected position of `Oumuamua a couple of decades from now to see if we can get an image of it!!!!!

    • Harry R Ray October 30, 2018, 13:23

      Speaking of messages: I heard recently that someone PROVED that data can be “downloaded” into gravitational waves, and that this data can somehow be “extracted” from the wave patterns. Someone ought to create a machine learning system that can DO that ASAP, and test it out on all the wave patterns detected so far! Especially the binary neutron star merger. The message I would hope to find would be something analogous to “watch the skies”, because, remember, it was just a matter of weeks between the merger and the detection of `Oumuamua. I have repeatedly brought up(in comments on this website)the whole slew of “coincidences” regarding `Oumuamua, but not this one until now. I assume that Bialy and Loeb can now BACKTRACK `Oumuamua’s putative SRP acceleration all the way to perihelion and derive the precise SECOND `Oumuamua reached perihelion, if, just by coincidence that was ALSO the precise second when the two neutron stars merged, GAME OVER!!!!!

      • ljk October 30, 2018, 14:06

        No doubt my primate brain is limiting my imagination here, but how would such two very different and very far apart cosmic events be connected/related here?

        When Voyager 1 flew through the Jupiter system on March 5, 1979, a powerful and different type of gamma ray burst (GRB) was detected. While an amazing coincidence, I do not see them as being connected.

        But willing to be enlightened here. And what were those other Oumuamua “connections”, while we are here? This blog’s text search feature is rather limited.



        • Harry R Ray November 13, 2018, 12:30

          All of my “co-incidences” were originally listed in a comment on Paul’s ORIGINAL `Oumuamua blog: An Interstellar visitor? Google Centauri Dreams/An interstellar visitor? and scroll down to read my comment in its entirety. NOW: For a NEW co-incidence which will knock your socks off! The newly discovered S1 stellar stream has just started to pass directly through our stellar neighborhood, and an associated dark matter hurricane will totally engulf our solar system before the end of the century. If `Oumuamua is a non-natural AI, it may not be interested in us whales, or anything LIVING. It may just be interested in how the dark matter will impact our solar system as a whole.

      • Alex Tolley October 30, 2018, 14:53

        Wikipedia has perihelion on 09/09/2017
        Wikipedia entries of gravity wave detections was most recently 08/17/2017.

        So you can probably rule out that linkage.

  • Norman October 30, 2018, 10:09

    It is a bubble. Is there any spectragraphic data?
    I would assume that it is graphene.
    That it acts like a Repeater (passive) antenna and can be used to scan its heading and duplex its path, that is return data to its source.

  • DCM October 30, 2018, 12:01

    Could there some day be a Distant Early Warning Line at the edge of the solar system able to launch small robot craft to study and land on intruding interstellar objects and relay information?

    • ljk October 30, 2018, 12:41

      How many do you think we might need to properly cover the Sol system? What kind of instruments would they to do the job? How about an energy source? And who would maintain/replace them?

      • DCM October 30, 2018, 17:01

        Robots could maintain them.
        Didn’t have in mind a sphere of craft. A few carriers to launch them.
        I wonder if cosmic rays could be used for energy along with visible light.

        • ljk October 30, 2018, 17:23

          And who maintains the maintainers? :^)

    • Alex Tolley October 30, 2018, 14:46

      There is no value putting these DEW line sensors in a sphere around the sun at some large AU radius. Better to put the sensors close to, or on, Earth and give them the necessary power and hence range. Unlike early warning lines in WWII and the Cold War, there is no horizon to peak over and therefore offer location advantage. We do place anti-missile facilities nearer their prospective targets for 2 reasons – the Earth’s curvature, the relatively slow speed of ABMs, and the power requirements and atmospheric absorption of newer laser weapons.

      • DCM October 31, 2018, 16:51

        If the objects are detected from Earth chances are by the time any vessel could get to that distance they’d be gone, especially if they’re really speeding.
        Unless they’re on a track to pass through the inner system, of course.

    • Harry R Ray October 30, 2018, 15:43

      Go to https://www.oklo.org and read “Intercept” by Greg Laughlin. Oh, and in a postscript: FAREWELL KEPLER! It’s now official. The mission is over.

  • wdk October 30, 2018, 12:01

    From the Oxford Dictionary of the English Language:
    1. an object made by a human being, typically an item of cultural or historical interest: “gold and silver artifacts”
    2. something observed in a scientific investigation or experiment that is not naturally present but occurs as a result of the preparative or investigative procedure: “widespread tissue infection may be a technical artifact”

    At the very least we have an object of interstellar origin.
    I take it that that is not in wide dispute.
    But from there we have issues of whether it is an artifact (1), naturally occurring in a distant nature or we are confronted with artifacts (2) of trying to study a distant, small faint object, fortuitously detected.

    Our statistics prior to its arrival indicated we were unlikely to ever see such an object unless it were tossed at us. Now what kind of “artifact” is that?

    Need to think more about the more recently uncovered clues this object left us to add further argument or conjecture. But at this point I do notice a tie in to another recent Centauri Dreams entry – and that concerns the plans for exploration of dwarf planets beyond the orbit of Pluto (Game Changer – A Pluto Orbiter and Beyond). Without checking, odds are that ‘Oumuamua’s hyperbolic exit trajectory is not in the vicinity of these targets (It’s out of the solar system orbital plane); nor is Jupiter in the right spot in the given year or month based on these studies. But the same principles of targeting could be applied to an intercept.

    ‘Oumuamua has a time of flight t to radial distance r on its exit hyperbola, and so would a coasting probe with some mid course corrections. The problem for the probe is getting the accuracy and getting it on an energetic enough exit to do the catch up.

    There are a couple of other problems too.

    For one, an ion propulsion mission requires choice of either solar or nuclear propulsion – and probably a conventional booster to give it a significant kick as well. But this case requires nuclear electric by default. That means convincing review committees and
    watchdog organizations that it is well worth the trouble to put together such a device.

    And at that sending it after this vs. other targets.

    Theories and observations of the Kuiper Belt, etc. have been discussed for decades. And some of the individual dwarf objects out there have some interesting properties too ( e.g., rates of rotation, oblateness, possibly varied chemistry). There is science to be done there.

    So it really comes down to whether ‘Oumuamua is as distinctive as we are claiming or arguing about. If it is what it appears at minimum and face value, then why does it not cause more of a stir in our scientific hierarchy? Is it considered too science fiction-like to be real? Is it just something that hasn’t had time for committee consensual momentum? Perhaps learned articles will someday be written about how we let this opportunity pass. I hesitate to say that there is a window for action – for this is much like the issue of sending an interstellar probe, but on a smaller scale. Would sure like to see this investigation be taken to the next level.

    • Robin Datta October 30, 2018, 15:46

      One good image could possibly reset the Fermi Paradox.

  • ljk October 30, 2018, 13:27

    I cannot accept that we cannot get some kind of space probe to Oumuamua, especially since the astronomers’ original prediction of discovering one to ten such interstellar visitors each year has clearly not panned out.


    Even if it takes several decades to get to it, it will be worth it. Paging Elon Musk….

    • Harry R Ray October 30, 2018, 17:12

      As posted in my above comment, laser propulsion is the only alternative. The good news is that if Breakthrough Starshot stays ON SCHEDULE for the 40 year arrival at Proxima b, they should have a PROTOTYPE laser array in operation in HALF THAT TIME that could propel a hundred or so lightsails at a signifigantly slower speed, but fast enough to reach `Oumuamua in just a few months, even though it will have overtaken Voyager 1 by that time.

      • ljk October 30, 2018, 17:25

        While I have nothing personal against this method, I would feel more confident if we used a method that we have now, or perhaps a near one with just a few reasonable tweaks. I do not want to wait for Breakthrough Starshot to happen in regards to Oumuamua.

        • Harry R Ray October 31, 2018, 9:20

          Either way, we GET there at approximately the same time, which is what’s really important. Better yet, why not do BOTH!

          • ljk October 31, 2018, 10:51

            Unless there is a ramped up effort for Breakthrough Starshot that I am unaware of, I think using a currently existing method of propulsion will be faster just by the virtue of it already being available.

            Is anyone actually working on a mission to Oumuamua, or is this all just so much talk? Whose butt do I have to kick into gear to make this happen?

  • Gary Wilson October 30, 2018, 14:36

    Wow, an enormous amount of speculation for such an extremely limited data set. Imagination is a tremendous asset but funding takes more than imagination. Unfortunately I would say this intriguing object came through our system at a time point when we are unequipped to give it the investigation it deserves.

    • ljk October 31, 2018, 10:56

      Yes, those aliens should have been more considerate and given us more time to get our 60-plus year old Space Age into a better position for such an event. :^)

      Am I the only one who is frustrated that despite some of the strides we have made with our space efforts since 1957 (or the 1940s if you want to count the V-2 in terms of rockets that have actually reached outer space), there is so much more we could have done by now. Not only having a space probe or two ready for near-immediate investigations of surprise visitors, but also for permanent colonization. Hope now rests with private industry – just like they predicted in 1950 with Destination Moon.

  • iwanttobelieve October 30, 2018, 15:01

    Suppose it accelerated by ejecting small dense cargo rather than a stream of gases? Perhaps since it’s tumbling it could just release something from whichever tip is moving backwards fastest.
    If you postulate (for Hallowe’en purposes) that this was aimed at the solar system, surely it would leave something behind, ideally cancelling the cargo’s momentum relative to the sun in the process?

    • Bryan Kelly November 9, 2018, 14:25

      Perhaps it’s mostly trapped gases absorbing and emitting photons, effectively pumping light for radiation pressure propulsion.

  • Gary Wilson October 30, 2018, 15:05

    I just want to echo the comments of Elad Silver. I return to this site every day because the subjects are fascinating, extremely well explained for lay readers, and the people who come on here care enough to comment and reply to questions from people like me who want to learn more. A job brilliantly done Paul. Long may you decide to continue this effort.

    • Paul Gilster October 30, 2018, 16:03

      Much appreciated, Gary. Glad to have you here.

  • Robin Datta October 30, 2018, 15:19

    The more it is analysed and contemplated, the curioser and curioser ‘Oumuamua gets!

    The speculations are well within the realm of SETI, yet sans biosignatures, sans habitability, sans radio emissions, sans megastructures: an example of why we must be alert for all clues, not just those that have been formally approved.

    • ljk October 30, 2018, 16:21

      The page you linked to says “Document not found.”

      Please find it for us, thank you. :^)

      • jonW October 30, 2018, 23:02

        There’s some invisible html crud at the end of the link, copy the link instead of clicking, and remove the crud before visiting, and after all that you will find… a chapter from Alice in Wonderland.

      • Robin Datta October 30, 2018, 23:57
  • jonW October 30, 2018, 17:14

    I just read that the Parker Solar Probe has now reached a velocity of over 70 km/s relative to the sun. If we can get these kinds of velocities from a slingshot, we should send a sun-hardened probe through a slingshot calculated to catch up with ‘Oumuamua and settle things once and for all.

    • hiro October 30, 2018, 19:23

      I’m not sure people at NASA are willing to take this high risk high return. If this object turns out to be an ordinary rock, someone will be grilled alive (by president Trump) big time.

      • J. Jason Wentworth October 31, 2018, 7:27

        Maybe, but maybe not… While most of his work has been kept focused on Earthly matters, in bits and pieces (in various articles and interviews that I’ve read or seen/heard), I’ve heard President Trump discuss space matters, and not just the Space Force (which has been considered and advocated for many years); he is just the latest policymaker to advocate for its establishment, and:

        Even in this area, he has mentioned the need for planetary defense against asteroids and comets. If ‘Oumuamua is a natural object, its kin–while their odds of hitting the Earth are small–would be even more dangerous than a long-period comet “with Earth’s name on it,” because of the *very* short warning time (perhaps none, if it came from the daylight sky, like the Tunguska and Chelyabinsk objects) and the higher impact velocity of an interstellar interloper moving at a speed like ‘Oumuamua’s. A group of patrol spacecraft, perhaps in solar orbits, could remedy this surveillance deficiency; also:

        He has discussed the importance of space industrialization, including asteroid mining, and the need for technology development to facilitate this. He is interested in tax incentives, enterprise zones, and–where appropriate–government anchor tenancy in order to create a favorable and stable economic environment to nurture these new industries. In addition:

        President Trump has also–like Jeff Bezos–mentioned long-range (late in this century and beyond) goals such as solar system colonization and interstellar probes (like NASA’s under-discussion 2069-launched Alpha Centauri probe [which looks likely to be solar sail powered]), and the need to begin developing the supporting technologies for these now. As well:

        Being a businessman who is used to trying new things and taking calculated risks (his buying what became the Trump Shuttle airline routes from Eastern Airlines is an example of this [his airline was also a leader in adopting new technologies, as it introduced some of the first passenger self-service check-in kiosks]), he might look at an ‘Oumuamua mission as a rather similar venture–a high-risk/high-reward mission that, even if it failed, or if ‘Oumuamua turned out to be a basically “pedestrian” object, would still serve to advance spacecraft technology and capabilities; plus:

        If a solar sail expert–we’re fortunate to have a few here!–contacted President Trump and briefed him on the near-space and deep-space applications–including commercial ones–of solar sail spacecraft and “hovering” solar sail statites (as well as of solar sail-equipped, “latitudinally-offset orbit plane” non-Keplerian satellites [which would in effect ‘create new orbital real estate,’ including north and south of the increasingly-crowded equatorial Clarke Belt]), I suspect that his response wouldn’t be, “Can we do this?”, but “^How^ can we do this, and as quickly as possible?”

      • ljk October 31, 2018, 9:52

        We should explore Oumuamua via space probe first and foremost because is it our first known interstellar visitor. Whether it is natural or otherwise is not the main reason here, though of course the possibility that it is artificial is a non-trivial factor. But I sincerely doubt that “heads would roll” if Oumuamua looked like a space rock. It would be a space rock from another star system, that is what matters!

        As for who should send it, there are other space agencies, plus we have Elon Musk and Jeff Besos.

    • J. Jason Wentworth October 31, 2018, 11:55

      I heard that on the ABC radio news yesterday, as well as the sad news of Kepler’s demise. I was pleasantly surprised that both of these unmanned missions’ milestones were mentioned during the brief (just five minutes at the beginning of each hour, and–I *think*–two minutes at each half-hour news break) radio news breaks, and not just once or twice, but for most of the day (and today as well, so far), and:

      Usually only the “more exciting” (in their view, not mine) robotic missions–such as Mars landers, outer planet flybys, etc.–get mentioned on the national radio news at all, and then only for an hour or two’s worth of news breaks…then it’s back to the political pap, celebrity gossip, and “stupid criminal tricks” (as David Letterman might call them :-) ). Also:

      In his 1978 (revised in 1979) book on unmanned space probes, called “Planetary Encounters,” Robert M. Powers–in the chapter about ultraplanetary and interstellar probes (‘The Lights in the Sky–Stars”)–describes several such “gravitational accelerator” (with rocket power) maneuvers that could be used by such probes. They are, in order of increasing solar system exit velocity:

      [1] The two-planet or four-planet Voyager trajectory (Jupiter, Saturn, [and also Uranus and Neptune, in the latter case]);

      [2] An Earth-Sun, close solar flyby trajectory, with a powered perihelion pass;

      [3] A Jupiter reverse flyby, fall toward the Sun, and powered perihelion maneuver trajectory, and:

      [4] A complicated Saturn reverse flyby with a rebound inward off Jupiter, a powered very close Jupiter flyby (perijove maneuver), and a close solar flyby, either un-powered or–for maximum velocity–powered during the perihelion pass.

  • Rob Flores October 30, 2018, 17:21

    We will find other extra solar objects;
    Such a fuss over this object, beyond just taking some readings
    and file them away to compare with the next visitor.

    I have the suspicion that if were not for the very talented
    artist firing up imaginations, it would recede in importance.
    If the artist had drawn up a flatened peanut shape with much pockmarking then it might not inspire so much.

    Instead what was presented as “rendition” looks like,
    a) a piece of some gigantic structure
    b) an unnatural slicing of a larger stellar object

    In both cases, the artistry of the image leaves room to imagine
    all sorts of origins story, (I am sure someone or TWO is writting
    a new SF novel on this encounter even though RAMA is already out there.

  • Scott Guerin October 30, 2018, 18:16

    It came closest to Earth 0.1616 AU (24,180,000 km; 15,020,000) on Oct 14, 2018. That’s half the minimum between Earth and Mars. So, it had a pretty good look at us if it wanted. Great summary!

  • Harry R Ray October 30, 2018, 18:25

    Paul Gilster: I would like to take some time off from contemolating the nature of `Oumuamua itself, and instead focus on the Bialy,Loeb ArXiv preprint itself. From our experience regarding preprints regarding Boyajian’s Star, the only preprints that made it to MAJOR JOURNALS involved either proposing(Boyajian et al)natural solutions or refuting(Schaffer)them. No non-natural solutions EVER made these journals! Did Dr Loeb happen to mention to you which journal they were going to submit this to? Nature and Science are out because of their embargo policies, but the one I hope for is The Astrophysical Journal. If it IS published there, it would be a milestone for SETI science, regardless of the validity of their hypothesis.

  • wdk October 30, 2018, 20:35

    Amidst of contemplating what kind of artifact ‘Oumuamua was, forgot an intended remark:

    Since the object on its near approach to the sun is bobbing or accelerating more than a dense object would, would that not further obscure where it came from?

    First it had to be detected and tracked. Then it had to be observed for a period accelerating due to some form of pertrubation such as light pressure or ejected matter. Bad enough if there an acceleration curve, but if it is not uniform, those backward tracks are going to get more dispersed.

  • Charley October 30, 2018, 20:51

    Has anyone given any consideration to the idea that perhaps this is nothing more than a natural ‘gravity assist’ phenomena. Rather than some kind of space alien craft and/or debris?
    There’s nothing that would preclude just out a hand that a natural body could be on a trajectory that might result in just such an acceleration due to the particular path it was just happening to be on.

    • Reagan S October 31, 2018, 14:08

      I am by no means an expert, but I think the point was that the acceleration was far closer to what you’d expect of an Oberth maneuver than of an unpowered slingshot.
      IE, lower than we’d expect for an Oberth maneuver, but a great deal higher than we could expect of an unpowered slingshot.
      I’d say that it’s a classic case of using Occam’s Razor, but this entire event has been so thoroughly improbably it’s barely worth mentioning.

    • Charley October 31, 2018, 23:48

      Paul Gilster: any consideration to the idea that perhaps this is nothing more than a natural ‘gravity assist’ phenomena?

      • Paul Gilster November 1, 2018, 8:22

        A gravity assist of an outgassing object like a comet would fit here, I think, although outgassing has not been observed. Given how tricky it has been to study ‘Oumuamua, though, we can’t rule out a natural solution by any means.

  • Hamilton1 October 30, 2018, 22:00
  • George King October 30, 2018, 23:08

    OK, my ‘Oumuamua musical reference this time is to “Standing on Shaky Ground,” . . . we’ll go with the Delbert McClinton version.

    Very intriguing possibilities, but the science is a bit tenuous with the limited information available.

    Hadn’t realized (or at least focused on) before seeing the first image in this particular article that ‘Oumuamua not only came in for a close approach but did so from almost a perpendicular orientation to the ecliptic. Not necessarily a bad orientation for an interstellar probe sent to examine a far away system via a flyby.

    By this point, it looks like ‘Oumuamua will just have to be the interstellar visitor that got away. Hopefully, we get enough lead time on the next one to maybe send out a welcoming probe of our own to examine it.

  • HSchirmer October 30, 2018, 23:26

    A size of 20 meters seems a bit small for a lightsail, perhaps it’s a small segment torn out of a much larger sail? You’d expect any interstellar sail to be large AND redundant. A huge solar sail with separate segmented “panes” seems like a practical idea, perhaps this is a small part of a much larger sail…

    • Mark S October 31, 2018, 13:58

      Size estimate was based on how much light it reflects: so it it reflected close to 100% of light hitting it it would be around 20 m. At lower percentages the area would grow proportionally.

  • J. Jason Wentworth October 31, 2018, 3:11

    The “escaped or jettisoned stellar sail or laser-pushed lightsail” hypothesis has also been touched upon in science fiction. In Robert Forward’s novel “Rocheworld” (also called “Flight of the Dragonfly”), a large shred of an Earth probe’s jettisoned aluminum lightsail, presumably from a robotic fly-through mission launched decades earlier, fluttered down into the ammonia-water ocean of Roche and dissolved into aluminum hydroxide. ClearWhiteWhistle, one of the amorphous intelligent inhabitants of the ocean, found that area of the water, at and near the surface, to be bitter due to the compound. In addition:

    I too am not sure that it’s too late to send a chemical rocket-powered probe to fly by (or even rendezvous with or “land” on [‘dock’ with, as on small asteroids and comets having negligible gravity]) ‘Oumuamua. In fact, fast–for our current technology–interstellar space probes (to explore the interstellar medium) have already been studied and found to be feasible, and their launching technique could also be utilized by a similar probe to “Oumuamua, as follows:

    A small probe, stacked atop several series-staged STAR motors (the small but high-acceleration spherical-case and elliptical-case solid propellant rocket motors that are used as satellite apogee kick motors; both spin-stabilized and movable nozzle-stabilized STAR motors are available), could be launched to Jupiter (by almost any of today’s launch vehicles) on a reverse-flyby trajectory that would rob it of its orbital velocity, making it fall in toward the Sun, and:

    It could also be flung out of the ecliptic–as the Pioneer 11 and Ulysses probes were by Jupiter–in order to get onto an intercept course to ‘Oumuamua. During its close perihelion passage, the STAR motors would be fired in quick succession, to conduct an Oberth maneuver deep in the Sun’s gravitational well that would provide the velocity necessary to catch up with ‘Oumuamua. If necessary (for a slow flyby, a rendezvous, or a “landing”), the probe could carry a small RTG-powered (gridded) ion drive or Hall effect thruster drive, a low-thrust but high-specific impulse onboard propulsion system that would facilitate matching velocities with the target. Also:

    While the admittedly (and frustratingly) limited data that were collected do not rule out the possibility that ‘Oumuamua might be artificial (its odd, un-optimized [regarding closely examining any of the Sun’s planets], “like natural” trajectory is consistent with Carl Sagan’s idea about ‘discreet survey missions’), speculating from a sparse data set can lead down a dead-end path, as “The Case of the Hollow Martian Moon” famously demonstrated:

    Based on the then-most-accurate figures for the secular acceleration of Phobos and its (indirectly-determined) size and mass, in the late 1950s I. S. Shklovsky concluded that it was likely a large, thin-walled hollow metal sphere, which of course could only be artificial. More accurate subsequent observations (and the consideration of tidal effects, which hadn’t been done previously) showed that a natural object best fitted the observations, which Mariner 9 eventually confirmed (even Mariner 7’s one, distant picture of the moon, taken in August of 1969, left a little room for doubt, as Phobos appeared oval–like descriptions of some UFOs :-) –in that shot). As well:

    Since our uncertainty about ‘Oumuamua’s nature is even greater, and because–although we *should* detect other interstellar interlopers (if they’re natural) for population statistics reasons, we can’t guarantee this (if it’s artificial, all bets are off), this “double uncertainty” alone is reason enough to send a probe to examine it much more closely.

    • ljk October 31, 2018, 9:43

      How would being oval make Phobos naturally natural? If these hypothetical Martians wanted to hide and therefore preserve their knowledge in space inside that moon, wouldn’t make it look like a big planetoid be a sensible tack?

      Of course they might also have taken a real space rock and did just enough restructuring of its interior to store their artifacts within and did not bother with the exterior due to time, resources, etc.

      Maybe Phobos was an interstellar space ark and they were just getting ready to leave orbit when some catastrophe befell them. So all of the knowledge of the Martian civilization still resides within that small “moon”, including perhaps some Martians themselves. How dense is Phobos (and Deimos), anyway?

      To those with an excessively pragmatic bent, do not panic, we are just having some fun speculation here with a nod towards how one might preserve their culture some day via space.

      • Reagan S October 31, 2018, 14:18

        A type 1 civilization, which is absolutely bare minimum to hijack a moon and use it as a space ark would be capable of protecting themselves from any natural catastrophe.
        The far more worrying possibility is that it was an artificial catastrophe they fled from, caused by the martians themselves. This would mean that somewhere between where we are, a type 0.81 civilization and a type 1 where the martians hypothetically are, exists a technology dangerous enough to be capable of causing an necessary planet-wide evacuation.
        The other possibility is that the martians attempted to flee their home into their moon, only to be stopped and vaporized in their tracks, by a hypothetical type 3 civilization. Such a civilization would surely possess technologies capable of hiding themselves from even our most sensitive equipment. However, they could do nothing against human (or whatever they are) error, like the kind that could result in, say, a solar sail floating through space.

      • J. Jason Wentworth November 1, 2018, 17:09

        That’s not what I wrote. The appearance of Phobos in that distant Mariner 7 shot, in which it looked oval, resulted in some speculation at the time that such an appearance might be expected if Phobos was artificial, rather than natural (“…Mariner 7’s one, distant picture of the moon, taken in August of 1969, left a little room for doubt [that it might ^not^ be a natural object], as Phobos appeared oval…”). Also:

        When I worked at the now-closed Miami Space Transit Planetarium, that Mariner 7 picture–and a brief mention of that speculation about Phobos’ true nature in 1969 (that it just *might* be artificial)–was included in the late Jack Horkheimer’s 1988 planetarium show “Walk on Mars,” which we console operators ran many times. The two moons also figured prominently in it, and:

        The late Ann Bishop, a local (WPLG Channel 10) television journalist who narrated that portion of the program, said–just as the Mariner 7 picture appeared on the dome–that Mariner 6 and 7 didn’t photograph Phobos, “but that Mariner 7 did photograph Phobos’ shadow. It wasn’t round, like other moons’, but elliptical–which some said might be expected if Phobos was artificial”; in addition:

        This passage in the program erred in saying that the picture was of Phobos’ shadow (we used a close-cropped, high-magnification blowup of that Mariner 7 shot so that the image of Phobos would be easily visible to the audience; JPL and The Planetary Society say that it shows the moon itself, not merely its shadow: http://www.jpl.nasa.gov/missions/mariner-7/ and http://www.planetary.org/multimedia/space-images/mars/first-spacecraft-photo-of-phobos.html ). At that very high magnification (which the show production personnel created when they made all of the 35 mm slides for the show), the image of Phobos had a blurred outline, and looked more like a shadow. As well:

        From its appearance (because charcoal-black Phobos *looks* like a shadow when seen against the much brighter, ruddy face of Mars, but looks “lunar gray” in pictures of it taken against the “even blacker blackness” of space), Jack must have presumed that the Mariner 7 picture was of Phobos’ shadow, not of the moon itself. “Walk on Mars” was among my favorite shows to run, because the older equipment that we were using required considerable skill and practice in order to run a seamless, well-polished show. (We also had, in the lobby, a small slice from a Mars meteorite cemented into a little raised platform that visitors could walk across; they then each received a commemorative card that certified that they had ‘walked on Mars’ [I’ve walked on Mars more times than Buzz Aldrin has walked on the Moon…]. :-) )

        • ljk November 2, 2018, 10:09

          Thank you for that wonderful bit of space history regarding Jack Horkheimer et al. My apologies for misinterpreting your comment on Phobos, but then we might not have been treated to your story. :^)

          Mariner 6 and 7 – two successful planetary missions that were overshadowed first by Apollo 11, which has happened just weeks earlier, and then Mariner 9 in 1971/1972, which put all previous Mars missions to shame in terms of image and data return. It also did not help that Mariner 6 and 7 managed to miss a lot of the non-crater features of Mars just like Mariner 4 – either that or the scientists of the day interpreted the distant views of Nix Olympia (later Olympus Mons) as a huge impact crater rather than the huge volcano it really is.

          I have often wondered how far we might have been in our Mars explorations if the first three Mariners had better imaged the parts of the Red Planet that wowed scientists only after NASA had given up on sending humans there.

          So they really had a slice of Martian meteorite that people stepped on? Aren’t those kinds of space rocks far too rare and valuable to be treated in that manner?

          • J. Jason Wentworth November 4, 2018, 16:59

            You’re welcome, and that’s okay. Except for Mariner 10 and Cassini (a Mariner Mark II spacecraft; the Voyagers are Mariners as well [they were originally called “Mariner Jupiter-Saturn”]), all Mariners were launched in pairs, and besides the Voyagers, only Mariner 6 & 7 accomplished a “twin mission.” Mariner 7 almost didn’t make it, as contact with it was lost soon before its Mars flyby. The DSN broke off tracking Pioneer 8 to search for it. After picking up a weak signal (from its low-gain antenna, I think) and re-establishing contact through its high-gain antenna, it was found to have changed velocity due to its battery having exploded, and:

            While Mariner 7 was re-directed to cover Mars’ southern polar region after Mariner 6’s successful flyby, it–and their predecessor, Mariner 4–all had the bad luck to miss the most spectacular features of the planet (Valles Marineris, Olympus Mons, and the three Tharsis Ridge volcanoes)! :-) (I too have wondered if the proposed Saturn V-launched manned flyby missions might have occurred, had those features been seen earlier.) In fact, the 1969 Mariners returned TV pictures of a great deal of featureless terrain. There was talk afterward about Mars being too bland to warrant more missions, but luckily the Mariner 8 & 9 orbiter missions were already too far along to be easily cancelled. Also:

            Mariner 8 never reached parking orbit (its Centaur second stage suffered a guidance system failure), but Mariner 9 made up for all of the planning that had gone into *both* missions. Not only did it reveal the wonders of Mars (and its moons) that its predecessors had missed, but its ability to wait out the dust storm drove home how lucky JPL had been with the three flyby missions. Amazingly, the Mariner 8/9 mission book didn’t mention the moons at all (even though the spacecraft’s chosen orbits passed fairly close to theirs), and that was NASA headquarters’ reason for initially refusing Carl Sagan’s request to observe them. As well:

            Yes, our piece of Mars was a uniform dark gray, and it was about 10 mm square and 2 mm – 3 mm thick. It was sliced from the Allen Hills Meteorite (found in Antarctica) that contained bubbles of trapped Martian air. Jack Horkheimer–and Art Smith, the curator of the planetarium–knew a lot of people in NASA, industry, and academe, and this enabled them to obtain things that otherwise might have been very difficult if not impossible to get.

      • J. Jason Wentworth November 2, 2018, 7:06

        As he related in his 1973 book “The Cosmic Connection,” Carl Sagan and Dr. Joseph Veverka had such an exciting “What if…?” experience late one night in the JPL Image Processing Laboratory, when they became the first people to see Phobos close-up, courtesy of Mariner 9. While it looked like how asteroids were imagined to appear, except perhaps for its craters (most artistic depictions of asteroids back then didn’t include craters [Sagan had finally secured permission from “by-the-book” NASA headquarters officials to turn the spacecraft’s scan platform toward both Martian moons by pointing out that it would be the equivalent of a free mission to the asteroid belt; the planet-obscuring dust storm raging below also helped :-) ]), for a few moments they saw what looked like evidence of intelligent life on Phobos:

        On the picture there was a bright spot in the center of the large crater which is now named Stickney (the maiden surname of Angeline Hall, the professor, mathematician, abolitionist, and suffragist wife of the astronomer Asaph Hall, who discovered both Martian moons at the U.S. Naval Observatory during the opposition of 1877: http://www.google.com/search?source=hp&ei=rx7cW47vCcHB0PEP96O7iA4&q=angeline+stickney&oq=Angelina+Stick&gs_l=psy-ab.1.0.0i22i10i30j0i22i30l9.3473.10497..14313…0.0..0.135.1890.0j15……0….1..gws-wiz…..0..0j35i39j0i131.2Aa-l4Q-XQg ). Having had no luck in finding Martian satellites, he was about to give up, but she insisted that he keep looking; thanks to her urging, he discovered Deimos, and soon afterward–while watching and waiting for it–he found Phobos (which he at first thought was two or three inner moons, since it would appear on both sides of Mars during the same night–he was very astonished to find that its orbital period was only about a third of a Martian day). Ninety-four years later:

        Sagan and Veverka gaped at the Mariner 9 image of Phobos, and particularly at the anomalous bright spot in the center of the dark, shadowed crater Stickney. It looked to Sagan as if they were seeing a star through an enormous hole through Phobos, or–even more haunting–that they were looking at an artificial light! But when they instructed the computer to remove all single-bit errors, the bright spot went away. Also:

        More recently, the Phobos Monolith (see: http://en.wikipedia.org/wiki/Phobos_monolith ) has attracted attention, and its locale is the suggested landing site of a proposed mission called PRIME (Phobos Reconnaissance and International Mars Exploration). While its suggested natural origin–that it’s a large, partially-buried fragment of crater ejecta–is most likely correct, the best-resolution pictures of it are small enough that we can’t yet be 100% sure of this, and:

        The position of the UFO “cultists” (*not* the sceptical yet open-minded scientific Ufologists, who aren’t out to confirm the ETH [extraterrestrial hypothesis] or the IDH [inter-dimensional hypothesis], but patiently collect data and follow wherever the data lead) is that “Aliens are everywhere!”, and that the Phobos Monolith can only be an alien artifact. This is an unscientific attitude, but so is its ‘photographic negative’ counterpart, the “It’s not aliens; it’s *never* aliens!” attitude that many scientists have and espouse. The proper scientific attitude lies on the gray path between these two extremes:

        “All anomalous objects and phenomena should be examined, and never ignored or laughed at just because they seem absurd (the acceptance of recovered meteorites, rocket propulsion in a vacuum, and relativistic time dilation suffered from these unflattering human reactions), and the resulting data must be followed wherever they lead, regardless of how prosaic–or fantastic–the conclusions may be.”

        • ljk November 2, 2018, 14:33

          Mind-boggling that NASA did not plan on having Mariner 9 imaging the two moons of Mars.

          I also recall comments that NASA wanted to focus the Voyager probes’ instruments on Jupiter rather than its moons, as the latter would not be as interesting. Mind baffling.

          • J. Jason Wentworth November 4, 2018, 17:18

            Carl Sagan was equally stunned, as his request only involved turning the scan platform holding the TV cameras (which was being moved to take other shots), but NASA HQ was “by-the-book”; nowhere did the flight plan mention Phobos or Deimos, so he couldn’t do it. (On the Viking missions, NASA considered deleting the orbiters’ TV cameras in order to save money, until numerous scientists protested that their superior cameras’ images would be of great geological and meteorological value [and they also proved vital for finding sufficiently safe landing sites].) Also:

            I wasn’t aware that NASA wanted the Voyagers to pay little attention (relatively speaking) to Jupiter’s moons. (That notion originated at NASA *headquarters*, I’d suspect, as the JPL planners had targeted each probe to pass close to three Galilean moons [Voyager 2 got Europa close-ups, plus the Io “volcano watch”], and both got distant looks at Amalthea).

            • ljk November 5, 2018, 10:52

              The same space agency thought the Mercury astronauts would not need windows because, hey, why would they want to look outside in Earth orbit?

              This is why I should be even less surprised at all those folks who were against the Pioneer Plaques and Voyager Records.

            • ljk November 5, 2018, 11:24

              And much more recently, they did not want to put a camera on Juno because it was not part of the main mission.

              Now we know what we all would have missed out on if Juno did not have an optical/electronic eye on Jupiter, both for science as well as space science outreach. I really hope NASA has learned its lesson here, half a century later.

  • Michael C. Fidler October 31, 2018, 7:13

    I’m just wondering if this lightsail might be a lot more technically advanced the what we are currently looking at developing.

    Let’s just look at what might be possible even in our lifetimes:

    1. We have a sheet that is somewhere around 1/2 millimeter thick, just think what could be done in our not too distant future with quantum engineering in a layer of atoms that deep.
    2. The ability for self repair, possible compared to what our skin does when cut.
    3. The whole object can change and become a huge AI or a quantum entanglement teleportation telescope.
    4. The whole structure could be like a hologram so that if a large part of it is destroyed it could rebuild itself, like a lizard regrows a tail. It may even take material it encounters to energize or add parts as needed since it was at the Local Standard of Rest (LSR).
    5. And of course for the more advanced luxury model would transport spacecraft or relay the close up 3d movies of the planets its AI brain finds interesting. So all that flashing and changing brightness could be like the reporters trying to get a good close image of the politician on his soapbox. ;-})
    6. Quantum DNA.

    • J. Jason Wentworth November 2, 2018, 8:14

      Michael, you’ve just described a more capable variant of a thin-film spacecraft (which was originally envisioned for cleaning up orbiting space junk, by wrapping itself around such discarded objects like gift-wrapping paper) that NASA, academe, and industry are working on right now–the Brane Craft (“brane” being short for “membrane,” see: http://www.google.com/search?ei=DijcW-_rC8LA0PEPt5a_kAQ&q=brane+craft&oq=brane+cra&gs_l=psy-ab.1.0.0j0i22i30l3j0i22i10i30j0i22i30l3.2406.8366..10958…1.0..0.134.1130.0j9……0….1..gws-wiz…..6..0i71j35i39j0i67j0i131j0i10.zILSDalM72k )! While the currently-envisioned Brane Craft is essentially a thin-film solar panel with distributed electrospray thrusters embedded in it, there is no reason why a solar sail (or laser-pushed lightsail) Brane Craft–with included thin-film solar cells and, optionally, variable-albedo steering panels (JAXA’s IKAROS interplanetary solar sail has both, see: http://en.wikipedia.org/wiki/IKAROS )–couldn’t be built, and:

      Another method of controlling a “BraneSail Craft” would be “bendable and twist-able corners and/or edges,” which would provide pitch, yaw, and roll torques (as do the vanes–small steering sails–that are affixed to the corners of some non-spinning square and triangular solar sail designs [some earlier square sail designs also called for reeling in the edges of the sail to provide off-center turning torques]). In addition:

      In his 1977 book, “Interstellar Travel: Past, Present and Future,” John W. Macvey described searching for abandoned (deliberately or otherwise) ships, probes, instrument packages, and exploration equipment that ancient interstellar expeditions to our Solar System might have lost, or left behind here. He listed possible objects in hyperbolic (open) orbits around the Sun, ones in closed orbits around the Sun, its planets, and/or their satellites, and artifacts left on–or below (buried or in caves)–the surfaces of solid Solar System bodies, and:

      Of these, he wrote that any alien artifacts in hyperbolic orbits around the Sun would be, not surprisingly, impossible to find (or so nearly so that the difference would be utterly negligible, because if they whipped around the Sun long ago, they would be extremely distant today). *IF* ‘Oumuamua is more than it seemed to be from afar (we simply can’t know, although its odd velocity change coupled with no observable cometary activity is interesting), then we lucked out on that score, because such single-pass flyby, hyperbolic-orbiting artifacts would be far more likely to be way out in interstellar space, hopelessly beyond our ability to detect then, unless they emitted (sufficiently strong and properly-aimed) radio or optical signals of some sort.

      • J. Jason Wentworth November 2, 2018, 8:41

        ADDENDUM: A “BraneSail Craft” intended for interstellar operation could also (in addition to thin-film solar cells for use near a star) incorporate, for providing power in the dark void between the stars, thin-film alphavoltaic or betavoltaic atomic batteries, like those being investigated for use on the Breakthrough Starshot probes’ StarChip payloads. Also:

        Since it could change shape (the “original concept” Earth-orbiting Brane Craft is intended to wrap itself around space junk objects and de-orbit them using its electrospray thrusters), an interstellar “BraneSail Craft” could form itself into a parabolic reflector (perhaps a 2D “trough”-type one), in order to support narrow-beam radio or optical communication to and/or from its distant base. While the BraneSail Craft was coasting at a constant velocity, its focal point detector(s) might be able to periodically separate from the BraneSail and “hover” there (at its focal point), via electrostatic means and/or retention wires or fibers, *OR*: The entire BraneSail might be made to function as a steerable-beam, patch-antenna flat array, which could transmit (and receive in) narrow, high-gain “pencil beams.”

    • Mephane November 5, 2018, 5:46

      > “quantum entanglement teleportation telescope.”

      Quantum entanglement does not lead to or allow teleportation, no matter, energy or information can be tranferred through it.

      What it does is let you infer some information about the other, distant particle. I.e. by measuring your half of the entangled pair, you can tell what state the other half must be in, but you cannot alter the state of the remote half (if you change the state of your local particle, the entanglement just breaks).

  • Marshall Eubanks October 31, 2018, 8:56

    First, I do not agree with the conclusions of the Mamajek paper. The difference between the 1I inbound velocity and the Gaia DR1 LSR is 13.5 km/sec, which does not appear to be unusually close to the LSR (typical star rms velocities about the LSR are about 30 km / sec, and the 1I velocity thus well within the scatter plots of the Hipparcos stars about the LSR). It’s a little small, but not strikingly so.

    Second, it’s not “too late to get a mission off to chase it with chemical rockets.” They reference Seligman & Laughlin

    but that paper does not conclude a mission to 1I is impossible. All they do is reference our paper https://arxiv.org/abs/1711.03155 (and do a good job summarizing it):

    Hein et al. (2017) reported a preliminary investigation of
    mission designs aimed at intercepting ‘Oumuamua itself. At
    present (and especially going forward) such missions are very
    challenging to mount, due to the large ∆v’s required to catch
    up with the rapidly departing object. Hein et al. (2017) considered trajectories that include direct transfers, as well as
    missions that employ a combination of Jovian gravity assist
    and Solar Oberth maneuvers (see, e.g. Bond & Allman 1996),
    and they speculated on the potential use of advanced technolo-
    gies such as solar sails, laser propulsion, and magnetospheric
    “chipsat” acceleration.

    However, it is true that I don’t see how we could do this without a major effort starting immediately, and I don’t see that starting up.

    The orbital geometries are against us – Jupiter and Saturn are in the right places to help with solar Oberth maneuvers only if we launch relatively fast (by the early 2020s), which we are not in a position to do without a really major crash effort. If it’s a reconnaissance probe, and if they were interested in our ability to respond to unexpected events, they picked their flyby time well,

  • ljk October 31, 2018, 9:44


    Have we missed an interstellar comet four years ago?

    Piotr A. Dybczyński (1), Małgorzata Królikowska (2) ((1) Astronomical Observatory Institute, Faculty of Physics, A.Mickiewicz Univ, Pozna\’n, Poland, (2) Space Research Centre, Polish Academy of Sciences, Warsaw, Poland)

    (Submitted on 30 Oct 2018)

    New orbit for C/2014 W10 PANSTARRS is obtained. High original eccentricity of e = 1.65 might suggest an interstellar origin of this comet. The probable reasons for missing this possible important event is discussed and a call for searching potential additional observations in various archives is proposed.

    Comments: Comments are welcome

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

    Cite as: arXiv:1810.12766 [astro-ph.EP]
    (or arXiv:1810.12766v1 [astro-ph.EP] for this version)

    Submission history

    From: Piotr Dybczyński [view email]

    [v1] Tue, 30 Oct 2018 14:18:15 UTC (42 KB)


    • Marshall Eubanks October 31, 2018, 11:41

      The observational evidence for the “Interstellar” comet 4 years ago is weak and the comet/asteroid orbit community is not convinced.

    • Hamilton1 November 4, 2018, 14:50

      Bill Gray is a superb contributor to the mpml. He has now ruled out this comet as interstellar.

  • Charley October 31, 2018, 12:27

    paper https://arxiv.org/abs/1711.03155 presents an analysis of straight impulse maneuvers that would allow interception of this object. In 2025, which would seem to be the most reasonable and earliest time that a launch could be performed the velocity required is already a of the order of 40 miles per second! Whether that includes the Earth’s orbital speed I’m not sure but it’s pretty doggone fast.

  • Mark S October 31, 2018, 13:47

    Hypothesis: the reddish organic crust that develops on comets can polymerize and remain after volatiles are depleted.

    So what we saw could have been a rubbery coating on a defunct comet.

    • Harry R Ray November 1, 2018, 9:22

      I seriously doubt if such a remanant coating could remain in one piece while tumbling the way `Oumuamua appears to be.

  • Geoffrey Hillend October 31, 2018, 15:30

    It should have a high albedo or the spectra should indicate a metal composition if is was part of a light sail.

  • Daniel Högberg October 31, 2018, 17:40

    I had a good feeling about this the first time I read about it, and now my gut gives me the same tingling sensation again. I do believe this is something more than just an asteroid/comet.. But I have the imagination of a child so who am I to guess about this phenomenon.. Okay, I confess, I WANT TO BELIEVE!

    • ljk November 1, 2018, 9:35

      Unless you actually worship them, aliens are not a belief system. They have a scientific plausibility for existing in reality.

      • Daniel Högberg November 1, 2018, 11:16

        I do not get what you are talking about. I want to believe that we are not alone in the galaxy, and I hope that during my life time we will find the first evidence of an extraterrestrial civilisation. What you read in between the lines will have to stand for you.

        • ljk November 1, 2018, 16:03

          People often say they either believe or do not believe in aliens, the same way they say they believe in angels, ghosts, and the Loch Ness Monster.

          The difference is that aliens are scientifically plausible, meaning they can be proven by the tenants of science.

          I just have an issue with the term belief in this context, as it implies the supernatural and the worship of such beings.

          I think there is life of all kinds in the Universe, and there is scientific evidence for its existence in the form of “smoking guns”. However, I am waiting for proof via science to know for certain.

          • AlexT November 2, 2018, 4:06

            Finally you are talking about your belief too.

            Modern science does not have proves that there is any life elsewhere outside the planet Earth… Meanwhile we have not found any evidence. So meanwhile – it is belifs only.
            Me too believe that there should be extraterrstrial life somewhere outside our planet, but in same time I am realizing very well , that there is no any facts that can prove my beliefs…

            • ljk November 5, 2018, 11:29

              I was trying to differentiate the various types of the word “belief”, which most people use arbitrarily and often without comprehending their wider and off-base meanings when it comes to science.

              If the Universe is full of complex organic molecules and there are worlds with oceans of liquid water – both of which we have scientific proof for – while that does not automatically mean there is life, it also improves the chances for its existence just the same, “belief” or not.

              But we can keep playing the semantics game if you want to.

              • AlexT November 6, 2018, 17:45

                Modern science does not have answer what is the life and what are all critical factors that turn the chemical matter to live organism. Modern science still cannot make lab experiments that can create a live organism from chemical substance (organic or nonorganic), so we do not have possibility to build and test different “life creation” models in difference environment.
                I suppose probability that Earth life is alone in whole Galaxy (or Even Universe) is same order as probability that life is wide spread.
                May be panspermia will start from our own planet – with Homo Sapience Space expansion and life in our Galaxy will became widespread, after our expansion. Finally someone has to be first, why can’t we be this one – first?

              • ljk November 7, 2018, 10:41

                Quoting from this article:


                Asked if he believed the hypothesis he put forward, Bialy told AFP:

                “I wouldn’t say I ‘believe’ it is sent by aliens, as I am a scientist, and not a believer, I rely on evidence to put forward possible physical explanation for observed phenomena.”

                There, a Harvard professor said so, too.

                • AlexT November 7, 2018, 14:26

                  Yes, this quote proves that Bialy – is believer too (despite he deny it), his belief cannot be proved by science (it is only version), but in same time it cannot be easily disproved too… In connection to the question “what Oumuamua is?” – status-quo will stay “open” forever.
                  Let imagine (open minds), it is similar to situation if main, most respectable SETI actors will finally declare that all SETI efforts got negative result and conclude – there is no any ETI in our Universe and all SETI institutes should be closed :-)
                  Do you really think that “Harward professor” – is the scientific evidence proving Oumuamua Light Sail version?
                  There (below, in this comments branch) is very detailed comment of JASON HIGLEY on the issue, I cannot explain my own position better, than this author.

                  • ljk November 7, 2018, 14:43

                    I am merely grateful that not every human is a soulless automaton with a mind that cannot get past its programming.

  • hiro October 31, 2018, 17:59

    At this moment, this object is both natural & artificial at the same time until we take a much closer observation.

    • AlexT November 1, 2018, 10:30

      Was it Shrodinger’s cat?
      If so it could be described by wave function

      • hiro November 11, 2018, 17:32

        ~ 92% natural vs 8% artificial, the normal symmetric (Gaussian) distribution doesn’t apply if one considers the rare Earth hypothesis (we’re not alone in Laniakea supercluster or the universe in general).

  • Coacervate October 31, 2018, 18:33

    Did anyone observe it with radar? I know little about the technique except it seems to provide rather good images when optical telescopes are too weak. Maybe the space monsters were testing to see if we had radar… nevermind

    • ljk November 1, 2018, 9:32

      Space monsters?

    • Marshall Eubanks November 1, 2018, 12:14

      Remember, radar goes as 1/Distance^4; this small body was never near enough to do planetary radar.

    • J. Jason Wentworth November 4, 2018, 17:26

      I was wondering that, too. Also, were any attempts made to contact ‘Oumuamua by radio (sending prime-numbers, etc.)? While the odds of receiving a reply weren’t/aren’t good (although sending such transmissions to it may still be possible), it wouldn’t have (and still might not) hurt to try to raise it.

  • Michael October 31, 2018, 19:37

    Just wondering if a positive electrostatic charge has built up on the rock by its long interstellar journey and solar photon generation that is creating an electrostatic sail effect.

    • AlexT November 1, 2018, 4:46

      I have similar suspicion :-)
      Suppose this explanation significantly closer to reality than interstellar solar sails.

      • Harry R Ray November 1, 2018, 9:33

        I have a suspicion, that; if this were the case, `Oumuamua would have spun up to the point where it would have broken apart by the same mechanism Rafikov believes if the acceleration were caused by outgassing.

        • AlexT November 1, 2018, 10:20

          I this version seams to be plausible too, even more than electric charge.
          Do to lack of reliable information about object – it is possible to propose multiple natural/physical/astronomical explanations to observed facts, without ETI involvement…

  • Alex Tolley October 31, 2018, 21:42

    Slide deck that incorporates all observations up to that point and covers the issues of what it is and where it came from. Seems to suggest a depleted comet.

  • T. R. Bosley, III October 31, 2018, 21:59

    I’m 68.
    Anything for Dr. Fermi, construed with the most meager of plausibility.
    (And sharpish, please; I’ll be 69 next month.)

    • ljk November 1, 2018, 9:41

      Do you mean the Drake Equation? Because Dr. Fermi is long gone, so he probably could not care less. :^)

      As for Fermi’s famous “Where are they?” comment, my usual first response is: There are 400 billion stars making up the Milky Way galaxy, which is over 100,000 light years across and about 10 billion years old. With Kepler showing that almost every star has a collection of planets, that is a lot of systems to explore and colonize. Plus what would make ours stand out among so many others?

      • Michael C. Fidler November 1, 2018, 10:47

        Well if anybody is looking I’m sure they must get one hell of a laugh! :-)

        I believe T.R Bosley, III is saying that proof of someone else whatever meager evidence would answer where are they!

        • ljk November 1, 2018, 16:10

          I understand. It would be nice if we had earlier warning of Oumuamua and a probe to send to it. This does not mean that our visitor would answer Fermi’s Paradox, but they would have been nice to have for space science.

  • Andreas Hein November 1, 2018, 7:31

    Dear Paul,
    Thank you very much for another great blog article! Regarding the reachability of ‘Oumuamua via a spacecraft based on currently existing technologies, we have argued that although difficult in terms of schedule, it would be possible:

    Andreas M. Hein, Nikolaos Perakis, T. Marshall Eubanks, Adam Hibberd, Adam Crowl, Kieran Hayward, Robert G. Kennedy III, Richard Osborne (2017). Project Lyra: Sending a Spacecraft to 1I/’Oumuamua (former A/2017 U1), the Interstellar Asteroid. arXiv preprint arXiv:1711.03155.

    With a launch in 2021, we could launch a spacecraft to ‘Oumuamua, using a powered Jupiter flyby and solar Oberth maneuver, existing solid rocket boosters, Parker Solar Probe heatshield technology, and a Falcon Heavy launcher.

  • ljk November 1, 2018, 9:42

    Speaking of light sails, here is a progress report on one made by humans:


    • J. Jason Wentworth November 1, 2018, 17:47

      SpaceX appears to have changed the name of the launch vehicle to “Facon Heavy” (now I’m hungry for bacon :-) ). Hopefully this time all of the Falcon Heavy’s booster cores will also “stick” their landings (although that was a spectacular view of the first FH’s center core plunging into the sea next to its drone ship at high velocity!). Also:

      If all goes well, the other solar sail spacecraft, NEA Scout, should be on its way not too long after LightSail 2. (*SIGH* Nope–its SLS vehicle’s launch date has slipped to 2020: http://en.wikipedia.org/wiki/Near-Earth_Asteroid_Scout [maybe NEA Scout’s team should have a chat with ULA, SpaceX, and/or Blue Origin…]), and:

      I just hope that astronomers (optical and possibly also radar astronomers) don’t find solar sails to be a nuisance to their observations. Time exposures, spectrograms, and radar observations (of Solar System objects) could be compromised if a solar sail was in the field of view (or perhaps even just in an observer’s sky), if the Sun-sail-observer (and/or the sail-radar telescope) angle was just right. (Something of this general nature happened in the 1960s, when radio astronomers, most notably Bernard Lovell [he wasn’t a knight yet] made a huge fuss over the USAF’s Project West Ford, the notorious “needles” experiment which involved millions of wire whisker dipoles being orbited in order to create an “artificial ionosphere” to reflect very short wavelength radio signals around the Earth.)

      • ljk November 2, 2018, 9:59

        Since we will not have a light sail starcraft for decades (am I the only one who is bothered by all the issues involved with the making of a megalaser – and not just technical ones?), that is a problem, if at all, astronomers will not have to contend with any time soon.

        For that matter, how would and might a light sail interfere with astronomical observations, if at all?

        • J. Jason Wentworth November 4, 2018, 17:36

          If humanity isn’t mature enough to peacefully handle the high-energy devices that will be required for starlight, the whole interstellar enterprise is likely something for which humanity isn’t sufficiently mature. Also:

          Even solar sails could degrade if not outright ruin astronomical observations with their optical (and even radio) reflections, at the appropriate angles. (Even asteroids annoy astronomers, when time exposures of deep sky objects are found to be “crawling with asteroid tracks” [and sometimes, even meteor trails; I’ve seen such meteor rail-riddled pictures].)

          • ljk November 5, 2018, 11:41

            Since our various superpower nations have decided to start ramping up nuclear weapons production again, I have even less confidence that a megalaser will be built purely for scientific reasons, and as the means to push a light sail even more so.

            History and current events have shown that nothing that is or can be turned into a weapon gets funded first as anything other than a means to threaten and kill others. Yet I see people in this blog and elsewhere talking about the megalaser as if it will be a done deal in the next few decades and with no consequences along the way.

            • Alex Tolley November 5, 2018, 17:03

              Wasn’t Lubin’s DE-STAR laser (larger arrays) supposed to be useful for planetary defense, but clearly also be used for national defense? Vaporizing satellites would be one obvious use. This is dual-use technology, and worth developing, but we should have our eyes open to who has the funds to make this a reality and for what purpose.

              • ljk November 6, 2018, 10:19

                Want to take out a satellite in Earth orbit but don’t have the cash or the technology for fancy weapons systems? Just disperse a bucket of pebbles circling our planet at 18,000 MPH.

            • J. Jason Wentworth November 6, 2018, 15:12

              My response is a shrug (not at you, but at the situation). I have never thought that weapons development will cease, or that dual-use technologies will only be utilized for peaceful purposes (only budgetary pressure can affect this, and it can only slow it, not stop it). As the devil (portrayed by Vincent Price) said in the 1957 film, “The Story of Mankind”: “Man’s heart is in his weapons.” Also:

              The first Soviet and U.S. satellites were orbited by modified ballistic missiles, as were the first cosmonauts and astronauts (ditto for the lunar and planetary probes of the USSR and the USA). Indeed, those military technologies (including tracking radars, radio and inertial guidance systems, computers, cryogenic chemical handling equipment, etc.) made those missions possible, and:

              The Starshot launching laser (to use the term from Larry Niven’s interstellar lightsail starship-*and* bartending-related short story, “The Fourth Profession”) is way overkill for destroying enemy satellites and spaceships, but it would be very useful for planetary defense operations against hazardous asteroids or comets. Even so, if we swear off developing such laser technology, other nations and societies will (even if on a smaller scale, for anti-satellite use). Unless we resolve to use only solar sail propulsion for interstellar spacecraft (which is a viable, but limited, option), we will have to use energies of such intensities that they could also be used in weapons; indeed, the latter may have to precede the former, judging by how ballistic missile technologies enabled the Space Age.

  • Harry R Ray November 1, 2018, 12:16

    OK Centauri Dreams readers: We no longer have this wonderful piece of speculation all to ourselves anymore! It has finally gone “public” on the internet at https://www.universetoday.com. Their article goes into much less depth than Paul’s blog, and kinda sensationalizes it a bit, it’s worth a look. I can’t immagine what will happen when the major news outlets get a hold of it!

    • ljk November 2, 2018, 8:54
    • Harry R Ray November 6, 2018, 13:36

      I was afraid this would happen. It’s gone beyond the internet. All over the TV(CNN, ABC, NBC). Fortunately, the print media seem a little bit more restrained. Nothing from the New York Times or USA today yet(don’t know about the Washington Post)and, surprisingly, The Atlantic(the super-hyper of Boyajian’s Star)has come out with an emphatic “thumbs down”

  • Harry R Ray November 1, 2018, 12:23

    The exact same article(TO THE WORD)is now ALSO up on https://www.phys.org! HERE WE GO!!!!!

  • Caravela Sideral November 2, 2018, 15:28

    The trajectory per se is intriguing. The approach above the plane of the solar system, would allow an automatic probe with millions of years of sophistication a total system coverage and a fantastic data harvest … Speculation, obviously, but extremely exciting …

    • AlexT November 4, 2018, 13:24

      Wandering, who is the end user of this “millions of years” collected data?
      Dead civilization?

  • JASON HIGLEY November 4, 2018, 13:39

    Regarding “Could Solar Radiation Pressure Explain ‘Oumuamua’s Peculiar Acceleration?”

    My personal opinion is that it would be very nice if what they were speculating were to turn out to be true, however, the following comes to mind:

    1. “Based on the survey properties and the single detection, Do et. a (2018) estimated that interstellar density…”
    In statistical analysis, we cannot imply a population or derive statistics from a sample of one. This is the same problem as in the SETI.

    2. “…if outgassing was responsible for acceleration (as originally proposed by Micheli et al. 2018), then the associated outgassing torques would have driven a rapid evolution in “Oumoumua’s spin, incompatible with observations.”

    Considering the short observation period of this object, combined with the already rapid rotation, odd shape of at least 5:1, and albedo variability indicating a complex aperiodic presentation of specific surface features, I suspect that there’s a good chance that we could not detect changes due to torque imposed vector variation due to it’s chaos-like tumbling presentation in a such a short sample (the animation and light curves of which can be seen at the wikipedia article https://en.wikipedia.org/wiki/'Oumuamua .)

    3. “This work was supported in part by a grant from the Breakthrough Prize Foundation”. This reminds me of clinical drug trials sponsored by pharmaceutical companies, smoking studies by cigarette companies, or environmental studies by petrochemical companies; there’s reason to suspect biased thinking in the paper. Breakthrough Initatives, https://en.wikipedia.org/wiki/Breakthrough_Initiatives is a multi-pronged effort, but what’s interesting here is that this paper brings together two separate areas of their investigation (SETI and Starshot) into one contemplation. Regarding the objectivity of the investigators, one has to ask, do the authors have other works in progress or that they’ve previously written that would cause them to want to validate their prior or current works? The answer IMO is yes (based on their other published works). Not that that’s necessarily a bad thing; people looking at a specific series of questions/problems will often tend to be the first to observe characteristics of objects that fit with patterns they’ve observed previously, but the human tendency to super-impose perspectives based on past experience, or fill in the dots if you will, can be a myopic experiential bias that has no basis in reality (i.e. why focus on light sails?). More specifically, they see things in terms of light sails because that’s what they do every day, not necessarily wrong, but suspect in the least. Why would E.T.’s use a form of propulsion that is consistent with the prior work of the authors? In the least it’s highly coincidental, at worst it seems self-serving IMO.

    4. “Although ‘Oumamua has a red surface color, similar to organic-rich surfaces of Solar-System comets and D-type asteroids (Meech et al. 2017) this does not contradict the artificial scenario, since irrespective of the object’s composition, as it travels through the ISM its surface will be covered by a layer of interstellar dust, which itself is composed of organic-rich materials (Draine 2003.)”
    IMO this is highly contradictory! If one follows this reference to the Draine 2003 paper, one sees that there is absolutely no indication of how long it would take for ISM dust deposition to occur in sufficient amounts to alter the presentation of a light sail to appear to be comet/asteroid like. Indeed this seems very contradictory to their argument that this could be a purposefully directed probe, as IMO a directed probe would not seek to be coated in ISM dust to impair
    the light sail performance (indeed it might actively seek to clean/remove it over time). And if E.T.’s were trying to be a camouflaged probe, I would not think it stealthful to present an asteroid with unnatural/non-keplerian motion while still within easy imaging range.

    5. If it’s technological detritus, this seems antithetical to its behaviors of being a directed probe (i.e. the close solar passage.) It seems to me that that finding (by others) that

    Kinematics of the Interstellar Vagabond 1I/’Oumuamua (A/2017 U1)
    Eric Mamajek

    “…In the Local Standard of Rest frame (circular Galactic motion), ‘Oumuamua is remarkable for showing both negligible radial (U) and vertical (W) motion, while having a slightly sub-Keplerian circular velocity (V; by ~11 km/s). These calculations strengthen the interpretation that A/2017 U1 has a distant extrasolar origin, but not among the very nearest stars. Any formation mechanism for this interstellar asteroid should account for the coincidence of ‘Oumuamua’s velocity being so close to the LSR.”

    I think this argues against the probe actively accelerating with a purpose, and is more like being drifting galactic sea foam (metaphor) that our Sun has overtaken.

    6. And last but certainly not least is
    “Since it is too late to image ‘Oumuamua with existing telescopes or chase it with chemical rockets (Seligman & Laughlin 2018), its likely origin and mechanical properties could only be
    deciphered by searching for other objects of its type in the future.”

    They might as well have said, since our paper is not scientifically provable, we can say whatever we want. Being unable to further test any of their suppositions by further observation of proposed characteristics (jet-caused torque, non-keplerian motion or other inexplicable behaviors) puts their speculation into a highly anti-scientific realm IMO (even SETI seeks repeatability/testability).

    (but I hope they are right :^)
    Jason W. Higley

    • AlexT November 4, 2018, 18:08

      Thanks a lot for the sober analysis, agree with every your point.
      It seams to me, that your comment is more scientifically grounded than discussed article.

  • Harry R Ray November 4, 2018, 15:15

    Here’s some food for thought. The authors stated that if, indeed; `Oumuamua DOES turn out to be a lightsail, that it could either be “discarded” or still be a part of an active mission. Well, why not both at the same time. Suppose it was launched in the distant past to check out a promising recently formed planet. Upon approach eons later it picks up radio transmission from said planet, and it initiates the following plan of action: ONE: Somewhere, approximately at Voyager 1’s current distance from the sun, It jettisons its lightsail with a small red(very important)camera with the means to transmit data back to the MAIN probe. This main probe then deploys a MAGSAIL to slow it down to below solar capture speed. The lightsail continues on its hyperbolic path, covered with grey intergalactic “grease”(which has recently been discovered permeating intergalactic space)until it nears perihelion where the grease boils off the red camera/transmitter combo, but is protected from boil-off by weaved fabric comprising the lightsail, which acts as an insulator. The lightsail then makes a distant flyby of Earth, photographing the planet and transmitting the data back to the main probe for AI analysis. Noting that the lioghtsail was NOT intercepted at or after closest passage to Earth, the main probe initiates a course correction, which, in the future, will allow it to be captured into lunar orbit. As soon as possible after lunar orbit insertion, it lands on the far side of the Moon, and immediately launches a microsat into lunar orbit which continually transmits data about Earth when it is hidden behind the moon, and awaiting us humans to encounter it a la Arthur C Clarke’s and Stanley Kubric’s Black Monolith. Obviously, this scenario is extremely contrived to fit the data(grey with a red “end”)but, if true, we may not need to go to `Oumuamua, because the REAL `Oumuamua will be coming to us!!!!!

  • wdk November 4, 2018, 18:09

    Where I was in school back in the 1970s, most of the faculty in the astronomy and astrophysics department were concerned with stellar structure, evolution and atmospheres. So when I asked one of these distinguished professors in a more general astrophysics course which that day discusing meteoritics whether she was familiar with any interstellar meteorite samples, she explained that the odds of any arriving in the solar system were prohibitively high – and hence none had been discovered – nor asteroids of comets with such orbital elements.

    As ‘Oumuamua trails off into the high celestial sphere and this topic for comment eventually closes, I still have to wonder about the odds of it arriving and another object similar to it being detected.
    For people who have followed things like orbital decay of satellites, you sense that the predictions about what day it is going to drop into the atmosphere seems to converge – on the event. Skylab was a good example.

    Similarly, now that we have actually detected an object with high eccentricity or the excess energy to leave the solar system without getting a boost from Jupiter or Saturn, there are claims that this is a regular event that – until recently – was going on just under our ability to sense it with ground or space telescopes.

    But amid all this there was also a significant change in our sense of how the galaxy was constructed. Kepler results, for example, were a fundamental illustration of this. Before Kepler, we knew for a few decades that there were some planets around other stars, but the low hanging fruit detected by doppler studies did not give us nearly the population density we assume now. And before the doppler detections of hot Jupiters, etc. around main sequence stars, the most tangible evidence for planets was the formation of accretion disks around newly formed stars. Astronomers were not sure that accretion disks would routinely turn out solar systems before they destabilized or dispersed.

    Yet prior to October last year there were orders of magnitude more people warning of asteroid collisions than astronomers warning that we might miss an interstellar visitor. natural or an artifact.

    With that background – and the fact that many astronomy and astrophysics departments were more concerned with structure and evolution of stars, plus that stellar formation theory seeming to suggest that collapsing clouds needed enough mass to collapse into self-luminous objects like stars – or maybe brown dwarfs, planets in other star systems were not given much credence prior to the 1980s. They were dismissed as something more like systematic errors in long tedious exercises of astrometry. That was the perspective from astronomy departments of the 1970s tracing the evidence, no matter what one might have been reading in science fiction stories, including the instructors, for all I knew.

    So, putting myself in my instructors’ shoes, I would say one reason they did not think there were many interstellar asteroids or arriving meteorites was that circum-stellar disks did not last long enough to produce planets and the planets were not there to hurl objects out of these solar systems.

    So then we have faith now that circum-stellar disks can coalesce into all type of planets and some of the debris can be hurled out on interstellar trajectories – and even all manner of moons, dwarf planets and planets such as Neptune. And between the 1990s days of planets discovered by doppler studies and the Kepler sampling of a small segment of the sky, we have become planet rich and now the interstellar medium supposedly has significantly more than colliding Oort clouds or dust exploded stars.

    But in 2017 there were orders of magnitude more people warning of asteroid collisions than astronomers warning that we might miss an interstellar visitor. natural or an artifact.

    This is log scale stuff. It’s easy to miss-estimate.

    I’ve seen versions of the Drake equation to address the likelihood of planets, life, and intelligent life. I am not familiar with an equivalent that
    predicts the likelihood of interstellar objects tossed our way naturally
    or artificially. But at the very least, I can see how how our estimates of likelihood would change with our perception of stellar systems over the past forty years.

  • wdk November 5, 2018, 11:48

    There was another matter that I had intended to include in the summary above. Beside recommending fresh assessments of the likelihood of interstellar asteroid and cometary transits ( no doubt underway), I meant to suggest that impact debris fields on Earth and other bodies should be examined as well for evidence of collisions with “precursors” to ‘Oumuamua. Whatever statistics of transits result, they should have some substantiation with impact histories.

    The annual Lunar and Planetary Science Conference held since the lunar landings devote a large portion of their papers to the equivalent of lunar rock assessments for other bodies and objects recovered from areas on earth where meteorites are easy to locate and identify: the ice packs of Antarctica, Greenland, the Sahara Desert… And consequently, beside the obvious culprits in the asteroid belt or comet trails, we have been able to identify secondary effects of planetary or satellite (the Moon) impacts. The oval or football shaped craters are indicators of glancing blow impacts which could have ejected rocks back into space – rocks from the surface of Mars, the Moon, Vesta, Ceres…

    The point is that although these collisions are rare based on the craters identified, and so would the rocks ejected and eventually colliding with the Earth, there should be something akin at work with the earlier ‘Oumuamuas – if they exist, consistent with our increased assessment of planetary debris escape mechanisms form other stellar systems.

    Granted, impacts would be higher energy than the debris associated with Near Earth Asteroids, but not necessarily much higher than solar system
    comets from the Oort cloud. The criterion is eccentricity perceptibly above 1.00.
    Identification of cometary debris in terrestrial geology, I suppose someone else will have to address. But if anything were to survive, what would we look for in an interstellar meteorite hit?

    Going back to the Lunar and Planetary Science conferences, radionuclides with decay half lives on the order of the Earth’s age. If a vein of ore remained intact, even if re-heated, the content of the original and decay products would indicate when the object formed originally:

    Half life measures Decay End Products
    thorium- Lead (Pb)-208
    uranium-238 4.5 billion years, Lead (Pb)-206
    uranium-235 700 million years, Lead( Pb) -207

    While the table above looks straight-forward, the isolation of rare elements and isotopes is complex and the balancing of evidence from the various transformation histories is too. But nonetheless, there might be rocks on earth with U-238 concentrations amid lead products suggesting ages exceeding that of the Earth (e.g., 6 billion years) – or younger – but not necessarily on account of terrestrial history. This could be the case if the infall of rocks from the stars is on order of that from Mars or the Moon and
    we were lucky enough not to have them burn to vapor.

    Anyway, does their absence indicate that ‘Oumuamua is a fluke? Does it mean that the impact conditions are too difficult? Or does it mean that our previous scientific objectivity threw out such data as spurious?

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