Did We Just Get Buzzed By Alien Space Junk?

Perhaps you heard about Oumuamua (don’t ask us how to pronounce that). The cigar-shaped object is the first item found by astronomers that is known to have come from outside the solar system and is continuing to pass through, not being captured by the sun’s gravitational field. A recent paper from [Shmuel Bialy] and [Abraham Loeb] from Harvard suggests that the thing could be a discarded light sail from an alien spacecraft.

Of course, it is fun to speculate that anything in space we don’t understand could be alien. However, the paper is doing more than just speculating. The rotation rate of the object suggests it is fairly flat (pancake-like, was the exact phrase used). In addition, it appears to experience “non-gravitational” acceleration — that is, it is accelerating due to some force other than gravity.

Others have suggested that the acceleration is due to material boiling off as the sun warms it. However, there’s no indication of that happening and activity like that ought to also change the spin rate which does not appear to be happening. Solar wind pressure could explain the changes, though. You might think that proves nothing since the solar wind pushes on everything. However, it is just like the wind in the atmosphere — sure it pushes on your car, your house, and a sailboat, but only the sailboat moves appreciably from it.

The paper argues that to produce the observed acceleration, the object would have to be very thin — on the order of 300 to 900 microns. Could such a thin structure survive a trip through interstellar space? The paper says yes, although it has to make some assumptions about the material involved. It doesn’t help that we are unable to get an actual image of the object as it whizzes by.

In all fairness, the paper doesn’t prove that the object is a solar sail. It simply proves that it could be. The reasoning is it could be a purposeful probe or just space debris. The purposeful probe seems unlikely because there were no radio emissions detected — at least down to the level of a common cell phone. Of course, that could be like primitive people seeing an airplane fly over and concluding it must be cold because there’s no smoke coming from a fire. However, space debris could be more likely. According to the paper:

Considering an artificial origin, one possibility is that ‘Oumuamua is a lightsail, floating in interstellar space as a debris from an advanced technological equipment. 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 or between stars. In the former case, dynamical ejection from a planetary System could result in space debris of equipment that is not operational anymore, and is floating at the characteristic speed of stars relative to each other in the Solar neighborhood. This would account for the various anomalies of ‘Oumuamua, such as the unusual geometry inferred from its lightcurve, its low thermal emission, suggesting high reflectivity, and its deviation from a Keplerian orbit without any sign of a cometary tail or spin-up torques.

Unfortunately, according to the paper, it is too late to get an image with any existing telescope (the pictures you see are artist’s conceptions) or to chase it down with chemical rockets. However, the paper’s conclusion calls for a search for similar objects, including some that were unlucky enough to get caught around Jupiter or the Sun. We could have an indication of an alien culture orbiting right next door and have simply failed to notice. (We’re not holding our breath.)

The solar wind played a part in keeping the Kepler telescope running — its solar panels acted as sails to prevent a failure from ending the mission. We don’t know if it was a solar sail passing through or not but we have to wonder, just like we wonder about FRBs.

125 thoughts on “Did We Just Get Buzzed By Alien Space Junk?

    1. Of course it’s never aliens. If there are aliens, and they are advanced enough to be producing space junk of this magnitude and spreading it outside their own solar system(s), we really don’t want to have to think about what that implies.

        1. Is it?

          We have a pretty good idea how life on Earth developed into the species we are today but mostly just speculation regarding the first specie’s origin.

          What if we (as in every living thing on Earth) are all the descendants of some alien fecal bacteria left by a passing UFO billions of years ago? Obviously we have no evidence for that although I’m not sure we have any against it either. I enjoy that thought because it really doesn’t change anything about who/what we are today. If anything it gives us something to be proud of.. having come so far. And at the same time, those people who just don’t get it and think it’s insulting to be shown that we are all related to other apes… It would really piss in their Cherios wouldn’t it! Hah! Imagine all those heads exploding!

          So, anyway.. what if we developed interstellar travel some day? What if we find that potentially habitable planets are super common but life is not? What if life is rare? If so then with the death of ourselves and maybe a handful of other ecosystems the universe would be barren. Should we feel compelled to protect life by spreading it? Of course we would do that through colonization but that does little for improving diversity. Maybe we would want to seed some planets which we weren’t going to colonize anyway with more primitive microbial life to give it a chance to some day develop into complex life that is different from ourselves.

          In other words, maybe when we get out into the universe we will find that we have a moral imperative to seek out new worlds… and shit on them!

  1. If it was the first known interstellar object, and it was ever possible to take pictures of it why don’t we already have them?
    Sounds obvious to me that if you have a telescope and a limited time to point it at something unique you take the pictures.

      1. Looks like a blurred round rock to me, so it must be an alien artifact. I can imagine the conversation in the alien space sail design department. ‘What do you want the new sail to look like?’. ‘Errr, just make it look like a big rock, but a bit flatter’. Are these the same aliens that built the moon, or the ones that built the pyramids?

        1. Do you really think that you can imply any sort of shape from that blurry image? I think the point is that it was discovered after it had already passed and was too far away for a proper visual-light photo beyond “blurry dot”. I assume that the shape it has been reported to have comes from some other method, maybe radar or something like that. But then.. I suppose I could probably find out by just Googling it huh?

      2. If they got a spectroscopy of the object it should say if it’s artificial as something made by an alien civilization would have a lot of refined metals or materials similar to carbon fiber in it.

  2. Half the errors seem to be from generic spellcheckers not recognising technical terminology, so I don’t hold out much hope for improvement with extra help from artificial stupidity.

  3. If it is an alien solar sail, does that mean there’s an alien spaceship currently marooned in deep space somewhere because it’s lost its sail? I think it’s time for… Space Force to the rescue!!!


  4. This whole thing sounds a lot like Arthur C. Clarke’s classic novel, *Rendezvous With Rama*. It’s about a mysterious asteroid-shaped object that hurtles briefly through the solar system, and the people who try to figure out what it is.

    “Moreover, the discovery of Rama challenged another dogma that Davidson had preached for years. When pressed, he would reluctantly admit that life probably did exist in other star systems; but it was absurd, he had always maintained, to imagine that it could ever cross the interstellar gulfs.

    Perhaps the Ramans had indeed failed, if Commander Norton was correct in believing that their world was now a tomb. But at least they had attempted the feat, on a scale that indicated a high confidence in the outcome. If such a thing had happened once, it must surely have happened many times in this galaxy of a hundred billion suns. And someone, somewhere, would eventually succeed.

    This was the thesis that, without proof but with considerable arm-waving, Dr. Carlisle Perera had been preaching for years.”

  5. A very large object with quite thin walls. It sounds an awful lot like a discarded propellant tank used to send something to our solar system.

    Given that it is huge, and was discarded, it follows that there was a second stage on top (that discarded it).

    That second stage would have made it here much earlier: thousands or millions of years ago.

    Suppose we might be the descendants of its passengers?

    (related must-read: Tchaikovsy’s “Children of Time”, where a civilization sent out ships to seed planets with monkeys and an engineered virus to accelerate their evolution. The story is about how, of course, things don’t go as planned. Highly recommended.)

      1. In the absence of other factors (like, say, a gravity assist, or stage separation happening in a gravity well), it is reasonable to assume the stages might share similar trajectories: You’d want to spend your early stage delta-V to shove your upper stages in a particular direction. You would not change vectors and thrust in a different direction after staging. Now, if the trajectories go anywhere near a gravity well after separation then, yes, they’ll diverge.

        1. Since we’re talking interstellar distances here, if there was any course correction at all to the upper stage after booster separation, they could be in different solar systems.

          1. To take this whole point a bit further:

            If we’re talking about a time difference of thousands to millions of years, the solar system would NOT be any where near its location when the upper stage arrived.

            Quick math puts our solar system velocity at 828,000km/hr. The solar system’s diameter is 2.87E12 km, so it only takes 400 years for the solar system to move into a completely different location. At an arrival time difference of 10,000 years (arbitrarily chosen time period), the solar system would be 25 solar system diameters from where it was when the upper stage arrived.

  6. You are being willfully ignorant if you think there is not concrete evidence that climate change is currently happening. Though, being willfully ignorant seems to be a popular pastime these days.

    1. Climate Change is happening, it’s always has, and has been on a warming trend for over 10,000 years. It’s the manmade CO2 climatology that is shady. All that pollution we spue, is worse than the CO2, 0.1% of the atmosphere. We don’t fully understand this planet, yet we are pretty sure about what flew through our solar system? I’d like to believe that there is life out there, but if they are smart enough to get here, they are probably smart enough to avoid us as well, filthy planet. They would likely have similar limitation, as far as time and speed, to travel great distances. It would take many generations born in space, to get here, none could ever return, just maybe their offspring, of many more generations. And who would even remember such a mission, if they could make it home, and it’s still there?

  7. There are 1938761346345-9825623462985732095834-69734562597865309783560083-0972465235-9378456-908364897345789354903845-0893456-9730845634098573098739587673945867305967364086354083756-903786-98346-9073460873406973460973046973409673049567309678348 rocks in the universe. One just passed by.

    I wrote long form because I don’t know how to do superscript. incase anyone complains :)

    1. Highly made up number as there are too many significant digits like a monkey typing on the first row of the keyboard. I would expect the estimate for these kind of things would be at most 2-3 significant digits and an exponent.

    1. That is indeed the case, though it remains only unexplained because technically no one can prove what we believe is happening actually is. The thermal models done to analyze it are very convincing. However, a small anisotropic heat loss should be negligible for a tumbling object–the forces will cancel themselves out over time. Still, it might be a noticeable effect if something like that were happening here.


  8. Surely it’s pronounced “[Papa] Oom Mow Mow [Dip Dip]”

    Cool theory, here, but surely telescopes and probes coulda got (or should get!) *something* for us to see rather’n merely artist’s renderings. They spotted it *somehow*, no? We can see inside nebulas lightyears away, can pinpoint galaxies billions of lightyears away, but can’t look at something in our own solarsystem?!

    1. Of course there are real images of the thing. How else do you think we discovered it and know its trajectory? Sadly, it’s small and far away. The general public doesn’t have much appetite for pictures showing small blobs of light, and even less for graphs with numbers on them. So science communicators are forced to hire illustrators to make pretty pictures to capture the public’s fickle and feeble imagination. Unfortunately then it leads to clueless dolts saying we don’t have any real pictures of it.

      1. Check this: Wikipedia says all images are nothing more than a point-source of light, a single pixel.
        Rotation, size, shape, etc. have all been determined through the varying intensity of that pixel.
        Graphs show a pseudo-sinusoidal intensity variance at a rate of something like 8hr / cycle.
        Almost like an extremely low frequency carrier-wave.
        Now, let’s say communication is desired over a distance spanning plausible light years. Sending radio transmissions requires a lot of power. The nearby stars, however, can supply communication-worthy power in the form of *light*. Imagine a ship covered in E-Ink, a tiny amount of electricity is required to rotate them e-ink dots. Or one gigantic E-pixel dot whose dark-side is a solar panel. Or, a gigantic Liquid-crystal panel.

        I think it should be pretty obvious where this is going.

        Easy to track and even locate such an object due to its carrier-wave.

        And, from a light-‘source’ like this, communication needn’t be limited to the carrier-rate of 1bit/8hr, variance in each individual sine-wave can easily be picked-up.

        Please click my link and go donate moolah for this huge scientific breakthrough ;)

        1. Neat theory, and has the benefit of the object not needing to know exactly where to point to to send your information.

          But do the arithmetic: provided you know where to point it, a modest laser and decent optics (say, 1 watt into a 15 cm diameter lens) will vastly outshine the reflected light from even kilometer-scale “E-ink” panels.

          A narrow-beam laser also confers some operational security: no point in broadcasting to *everybody* your location. Unless, of course, you’re a navigational hazard or a beacon of some sort.

          1. …exactly…. “providing you know where to point it”.
            Now, say, we think in 2020 that maybe Climate Change will be conquered before our existance is wiped from the face of the earth, and start thinking (again) a little further than one or two generations (a temporal Renaissance from these temporal Dark Ages). Say a solar-sail could get a probe to the nearest likely-habitated planet in twenty lifetimes… By that time, we’ll most-likely have forgotten how/where/if to point that laser. It’s also quite likely we’ll have moved-on from present-day data-encodings, just as few folk are barely aware of Morse-code, today. But, it’s very likely we’ll come back to eyeing that plausibly-habitated planet, even *if* our civilization crumbles and has to be rebuilt from scratch before then. Now, at some point we eye that planet and see a blinkenlight nearby that seems a bit odd… And eye that for a bit, realize it’s not quite ‘natural’ and start to think about it…
            Or, similarly, say we send it not for our own rediscovery, but for that of the inhabitants.
            And, who’s to say other species perceive time as we do…? 8hr to some may be like 200ns to us. But: even our lowly imaging/telescope-technology of yesteryear could pick up a blink-rate of 8hr/cyc, AND it’s a reasonable time-scale to literally be *looking* for, due to the same technology’s looking for moons, etc.

          2. @esot.eric – “And, who’s to say other species perceive time as we do…? 8hr to some may be like 200ns to us.”

            I really, really doubt this.

            People like to go to extremes when it comes to aliens. They either assume that they would be so different from us as to be completely incomprehensible or their imagined aliens are just humans with green skin, antanae, forehead ridges or something like that.

            Sure, nature could take a lot of different paths to end up with different lifeforms but they all have to satisfy a few basic requirements. They must obtain the nutrients needed to grow, repair and power their bodies. They must avoid getting eaten themselves. And they must reproduce.

            Towards that first end, getting nutrients we see on Earth that every ecosystem develops two things, predation and paratism. We even see that in artificial, simulated e-life ecosystems. Predation and parasatism are most likely universal phenomena that appear everywhere that life develops. Imagine a species that develops to move super slow such as the above “8hr is like 200ns” species. They would be sitting ducks! Even if every lifeform on a planet moved that slow it would only a matter of time before some predator evolved to move faster. It wouldn’t even have to be fast. Imagine, what would a 8h3/200ns do against a 1hr/200ns predator? It’s extinction would be guaranteed.

            Of course we don’t have animals evolving into “The Flash” here on Earth. Also, we do have sessile organisms such as plants. Sessile organisms evolve with a different strategy towards life. They have few critical parts “such as brains” that can’t be regrown after being chomped off. Without movement they have no real reason to ever develop intelligence, which is calorically very expensive and so they will not.

            There is variance among our moving organisms such as snails and cheetahs but even these earthly extremes are nothing on the scale where a lifeform might be able to sit and wait for a solar sail to make it across the space between solar systems. I suspect that life prefers the range of speeds that we see in our animals because physics makes anything faster impractical and anything slower would be too vulnerable. This is probably a fairly universal phenomena.

            Of course.. we still do have only a sample set of 1 so I could be wrong….

          3. An incredibly geocentric set of assumptions. Life developed here the way it did because of the environment, and there’s no reason to assume that the same set of qualities would be required for success in a wildly different environment. On our planet, the range of sizes for living beings is dictated by gravity. Different size planet, different size of organisms. On our world, the air is mostly oxygen and nitrogen, and water can be found almost everywhere, and this has a profound effect on how living things developed. Different world, different chemistry. On Earth, there are distinct boundaries between ground, water, and air. On a gas giant, not so much, and this would have a big effect on what it takes for organisms to be mobile. Just scratching the surface, here.

          4. Oh. And to address the need for speed, all life on Earth is based on organic chemistry. Logic gates based on hydrocarbons are ridiculously slow, resulting in the need for highly parallel signal processing. And even then, the speed that thoughts can move is limited by the physical size of the organism, because nerve conduction is an electrochemical process, not an electromagnetic one. As a result, small insects can have much faster reaction times than big, lumbering lizards and mammals. And yet, big, lumbering lizards and mammals continue to thrive. True, it’s only a couple orders of magnitude at most, not dozens. But imagine if life had developed from semiconductors. It could be many orders of magnitude faster in its perceptions and thoughts than organic creatures. Then, go to the other extreme and imagine life whose thoughts are formed by phase changes in a fluid. A “nerve” impulse might be transmitted by a crystal growing from one end of it to the other, taking minutes or hours to reach the “brain”. If that is how life worked, somewhere, then all life there would be similarly glacial. As with organic life, the smaller creatures would be quicker than the larger ones, but if there was no faster mechanism available, then life there – and competition between species – would evolve within this constraint.

          5. @ Grandpooper.

            “They must obtain the nutrients needed to grow, repair and power their bodies. They must avoid getting eaten themselves. And they must reproduce.”

            Like viruses.

            ” Without movement they have no real reason to ever develop intelligence, which is calorically very expensive and so they will not.”

            Group intelligence.

        2. Except that the math doesn’t work here. From the closest star system (4.3 ly), such a small target (by tan function, the angle is so small) would require a telescope that’s much more precise than the diffraction limit to capture a single photon. Just to take a picture of a planet for this star system would require a telescope 2km wide for a wonderful 4×4 pixels picture. Oumuamua is, in comparison, so much smaller than a planet. So, unless you have a closer observer, you can’t do that. Yet, maybe there’s a closer observer that is indeed sending back electromagnetic wave (RF/light) to another closer observer and so on until it reaches the closest star.

          1. I like your thinking!
            This sorta math I am far from doing, but the single-photon scenario seems plausible if not likely.
            Intermediate repeaters sounds like a great solution, if long-range communication is the goal. (as opposed to, say, communication with the plausibly-habitated planet described earlier). Make ’em cheap enough and in vast quantities like esp32 wifi repeater throwies, and their positioners, sensors, and transmitters needn’t be particularly sophisticated nor power-hungry.
            But, really? even a single photon over 4 hours is too much to ask? “wave-particle duality” my a**. This sounds more like nothing more than wavy particles!

    1. Waaaaaayy too big and bulky to get that kind of acceleration from radiation pressure alone. Think more along the lines of a mylar sheet. Has to be highly reflective and have a huge surface area but almost no mass. So ultra thin.

      Probably not aliens, but perhaps there’s some as-of-yet unknown process in the interstellar medium that creates vast micron-thin membranes of high-albedo matter which drift about in space. Some annealed foil of metal formed on the shock front of a supernova? Sparse net of long-chain polymers knit together by interstellar amino acids in a nebula? Who knows, but the fact that we spotted one almost immediately after gaining the tech needed to spot one means they’re probably pretty common out there. Comets make a huge tail when they get close to a star, so we noticed them long ago. Here’s something kind of like a comet that doesn’t.

      1. Came to suggest the same.. a natural solar sail. A supernova or other shockwave running through some sort of cloud…

        I hope nobody was counting on being in the record books for building the largest ever SLA printer!

  9. Solar radiation pressure and the solar wind are two different things, and this Hackaday article mixes the two up.

    The paper referenced in the article to refers to the former, which involves the reflection or absorption of photons from the Sun (or other bright light source) and the pressure that results from that momentum transfer.

    The Kepler mission made use of solar radiation pressure as noted in this article for attitude adjustments, and speculative concepts of interstellar light sails launched with huge laser batteries rely upon the radiation pressure concept. Implosion in some fusion weapons relies upon radiation pressure from x-rays, at least in part.

    The solar wind is the stream of ionized gas (plasma) that escapes from the Sun; it is in some sense the extension of the corona that is visible around the Sun during solar eclipses. The solar wind is fast (hundreds of km/s at 1 AU), but quite tenuous (typically 1-10 particles per cubic cm).

    While reflection or absorbtion of the solar wind can transfer momentum similar to the process involved in radiation pressure, that pressure is several orders of magnitude smaller than radiation pressure for the Sun.

  10. It was probably launched by some eccentric alien billionaire who sent his sailing ship into space to demonstrate the lift capacity of his new heavy lift launch vehicle, shortly before their civilisation collapsed due to ecological overshoot, which explains why we haven’t seen anything else from them.

  11. This is just another instance of the science ‘news’ cycle in action:

    Grad student from the academic publish-or-perish ecosystem comes up with an interesting hypothesis, crunches some numbers, finds that the result doesn’t flat-out invalidate the hypothesis, and writes what in other realms would be a “here’s something interesting to think about” puff piece.

    University PR office strips out all the math and 80% of the reasoning, comes up with an attention-getting subject line for an email, and sends a press release to the news agencies.

    ‘Journalists’ unfettered by such limiting constraints as accuracy or understanding turn the PR office’s subject line into something more suitable to click-whoring standards, write a fanfic about the implications of that, and publish it as ‘science news’.

    Public discussion drains any remaining vestige of fact or logic out of the subject.

    If the original author is unlucky, the matter gets enough attention that someone wants to do a follow-up article and comes looking for quotes. Then the poor shlemazel is stuck having to make what amounts to a retraction of what someone else said, while not pissing off the PR office, which is high-fiving itself for drawing attention to the university. If they’re really unlucky, the whole thing annoys some alumnus donor, at which point the PR office throws the original author under the bus and starts making pious noises about ‘responsible publication’ and ‘institutional credibility’.

    Not a fan, do not want.

    1. It doesn’t end there though.

      You also get alien conspiracy theorists and similar that might glom on to the idea, weave it into their imagined history and perpetuate it for generations to come.

      And then there’s the young-earthers who will point at it and claim that [The Scientists] say that exactly this IS what happened and it’s crazy(er than what they believe?) and that proves that science is wrong!

    2. An alternative system might be that people never publish mere hypothesis and so unless the original ‘thinker’ has the time, ability and resources to test the hypothesis themselves nobody else does either.

      Which system will better fuel scientific progress?

  12. Calvin, to Hobbs (paraphrase)–
    “I think the surest sign that intelligent life exists elsewhere in the universe is that it has stayed completely away.”

    Corollary: if you find something which is obviously, unquestionably of or from an intelligent extraterrestrial civilization, it isn’t.

  13. Nothing to see here, just your garden variety moron who thinks he’s a genius and has the whole world figured out. Takes a special kind of powerful, bitter stupidity to think you’re smarter than like 97% of climate scientists and know better with your hunches and anecdotes than all the evidence the entire human civilization has gathered. Round up every neuron in a brain and devote them exclusively to arrogance, leaving aside a few hundred for breathing and maintaining a heartbeat and you have this guy.

    This is the kind of pure, cruel dumbness that has the power to ruin the whole world.

  14. Small correction you might want to make:
    Solar wind refers to the high energy particles coming from the sun. It is what blasts material off comets and gives them their tails.
    Solar Radiation Pressure is the mechanism that solar sails use for propulsion and what Kepler and Hubble and a few others running when components such as reaction wheels failed.

  15. They saw the property listed in the Real Estate section the HHGTTG’s Classifed Ads and did a quick drive by to see if it was worth contacting a Vogon Real Estate agent. I’m guessing by the way they quickly turned around, they had seen enough.
    The property will now probably be seized by “Eminent Domain” for a new interstellar freeway.

  16. Since there are so many free-floating rocks in the universe, could it be that this one just underwent a series of random gravity-assists? Hence it’s speed.

    Or even just one really lucky one, close to a star of some kind …

  17. Overlooking that it’s probably just a outer space floating planetesimal shard that collided with another Oort Cloud body eons ago, it looks like an impressive strategy for an alien culture to execute as a random exoplanet probe. Just out there drifting and returning (or phoning home) at some time in the distant future like our Voyager Probes.

    Let’s just say, in the spirit of Dr. Ehman’s theory for his August 15, 1977 Wow! Signal as being a theoretical alien exoplanet Hydrogen Line RADAR sweep throughout the galaxy, that this is just another strategic endeavor for them to randomly discover other life like us. The idea being to let loose a millimeter thick 700′ disk propelled only by only star wind.

    It has no emissions as it only records data to store and forward several eons later, like something from Star Trek IV. Except it’s onboard A.I. starts up the “go home” or “phone home” program in a few eons. No live control.


    Who knows, maybe even a plausible explanation for Deimos and Phobos at Mars can be conjectured in this venue about alien probes. They both look like shards too.

      1. @NoseyNick – Yes but a fatter potato like version. One of them (or both?) appear to be partially hollow. And Phobos has an enigmatic solitary “tower” rock formation (near Stickney Crater) , as if it was a 300′ high disguised antenna (radome) to phone home with..

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