Oumuamua may be an alien lightsail?

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BWV
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Discussed here
https://www.centauri-dreams.org/2018/10/29/on-oumuamua-thin-films-and-lightsails/

referencing this paper by Baily & Loeb @ Harvard Smithsonian Center for Astrophysics

’Oumuamua (1I/2017 U1) is the first object of interstellar origin observed in the Solar system. Recently, Micheli et al. (2018) reported that ’Oumuamua showed deviations from a Keplerian orbit at a high statistical significance. The observed trajectory is best explained by an excess radial acceleration ∆a ∝ r −2 , where r is the distance of ’Oumuamua from the Sun. Such an acceleration is naturally expected for comets, driven by the evaporating material. However, recent observational and theoretical studies imply that ’Oumuamua is not an active comet. We explore the possibility that the excess acceleration results from Solar radiation pressure. The required mass-to-area ratio is m/A ≈ 0.1 g cm−2 . For a thin sheet, this requires a width of w ≈ 0.3−0.9 mm. We find that although extremely thin, such an object would survive an interstellar travel over Galactic distances of ∼ 5 kpc , withstanding collisions with gas and dust-grains as well as stresses from rotation and tidal forces. We discuss the possible origins of such an object.
https://arxiv.org/pdf/1810.11490.pdf
 
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  • #2
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"We have shown that the observed non-gravitational acceleration of ’Oumuamua, may be explained by Solar radiation pressure."
I think this part is important. Is it possible that there can be any other explanations ?. Also I think its also important to think how it can be so thin ? If its alien lightsail then where it is going ?
 
  • #3
stefan r
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"We have shown that the observed non-gravitational acceleration of ’Oumuamua, may be explained by Solar radiation pressure."
I think this part is important. Is it possible that there can be any other explanations ?. Also I think its also important to think how it can be so thin ? If its alien lightsail then where it is going ?

There can be other explanations. If you assume their calculated density of 0.1 g/cm2 then you do not need much gas to accelerate.

An alien popped balloon works better than an alien light sail. Accelerating a light weight object requires much less gas so failure to detect gas would be expected. For example, if the density is 1 g/cm2 you get 90% acceleration from gas and 10% light pressure. Instead of a balloon you could use a foam or aerogel.

... If its alien lightsail then where it is going ?
Imagine asking that question on an island when you observe a polymer bag drifting by in the wind. A garbage bag or shopping bag would be my first two guesses based on experience with litter in the USA. Trying to decipher the original purpose without getting a sample would be challenging.
You could also consider wind dispersed seeds. Cottonwood trees and dandelions do not likely know where they are sending seeds, perhaps "down wind". Wind dispersed pollen has a target destination but the tree hits the target by shotgun strategy. You can speculate on what evolutionary advantages a tree gains by causing human allergies but it is not likely to generate a good model of a tree.
 
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  • #4
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Imagine asking that question on an island when you observe a polymer bag drifting by in the wind. A garbage bag or shopping bag would be my first two guesses based on experience with litter in the USA. Trying to decipher the original purpose without getting a sample would be challenging.
You could also consider wind dispersed seeds. Cottonwood trees and dandelions do not likely know where they are sending seeds, perhaps "down wind". Wind dispersed pollen has a target destination but the tree hits the target by shotgun strategy. You can speculate on what evolutionary advantages a tree gains by causing human allergies but it is not likely to generate a good model of a tree.

Thanks for your explanation.

Well you are right on that matter, I thought that, we can calculate its trajectory and find out that maybe its headed to another solar system.
 
  • #5
rootone
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Well if it's some kind of exploratory craft, it appears to have decided that the solar system wasn't that interesting.
 
  • #6
Michael Price
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Didn't I read somewhere that there is one of these 'Oumuamua-type excursions into the Solar System every day, it's just that they go unobserved and unrecorded? It would seem unlikely that they are all alien artifacts, or even a small percentage of them. Or the universe would be crawling and overrun with Ancient Civilizations.
 
  • #7
DrStupid
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Or the universe would be crawling and overrun with Ancient Civilizations.

Unless the artifacts are Berserkers.
 
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  • #8
Sanborn Chase
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The actual imaging I've been able to see doesn't show a rocky uneven "rock" but rather a uniform shape. Could this be due to a low resolution?
 
  • #9
glappkaeft
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The actual imaging I've been able to see doesn't show a rocky uneven "rock" but rather a uniform shape. Could this be due to a low resolution?

Do you have any links to these "actual images"? I don't think there is optical system in existence that is even close to being able to resolve 'Oumuamua at the distances involved even at closest approach.
 
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  • #10
Algr
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Will intercepting Oumuamua with a probe ever be possible? Or is it too fast? Too hard to find where it will go in that time?
 
  • #11
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Will intercepting Oumuamua with a probe ever be possible? Or is it too fast? Too hard to find where it will go in that time?
Its not possible to send a probe. Its too fast
 
  • #12
Sanborn Chase
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I'm sorry, but I can't find the image I saw months ago. I think it was a radar image; could Arecibo resolve it?
 
  • #13
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Didn't I read somewhere that there is one of these 'Oumuamua-type excursions into the Solar System every day, it's just that they go unobserved and unrecorded? It would seem unlikely that they are all alien artifacts, or even a small percentage of them. Or the universe would be crawling and overrun with Ancient Civilizations.
Its possible i guess. Its hard to believe that it can be some sort of ailen lightsail...since it has not emitting radio signals..
 
  • #14
Sanborn Chase
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I agree "alien probe" would be towards the end of my list.
 
  • #15
stefan r
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Its possible i guess. Its hard to believe that it can be some sort of ailen lightsail...since it has not emitting radio signals..

The paper written on it just says thin film accelerated by sunlight. If you assume artificial objects made by a civilization, then trash is by far the most likely object we will see.
If a radio used a light sail to slow down it might make make sense to jettison the sail after passing the Sun. The sail could have tether launched a small probe which then made a close pass on one of the planets. All of the planets were on the same side of the Sun this year.
 
  • #16
LURCH
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If this object were venting volatiles from the side being warmed by the Sun, this could result in a reaction force that might mimic acceleration from solar pressure. Could these two scenarios be differentiated by observation? What I mean is; could we tell the difference, just by looking, between an object so light that it gets noticeable acceleration from solar wind, and a much heavier object being accelerated by reaction force from the venting of volatiles? Would the cloud created by so much venting necessarily be visible to us?
 
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  • #17
TEFLing
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Actual observations of 10:1 varying light curve from 25 to 27 October 2017, four or five months after the object entered the inner solar system, and more than a month after it swung around closest to the Sun:

https://i.postimg.cc/TPVSsppY/Oumuamua-light-curve-25-to-27-October-2018.png

Oumuamua light curve - 25 to 27 October 2018.png
 

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  • #18
LURCH
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Wow, that looks remarkably consistent to me. Is that normal? Specifically; is it normal for the signal to remain so uniform from one end to the other? I know it’s only a spread of about two days, but at the speed this thing was going, surely by the end of observation on the 27th we were seeing it from a significantly different angle from the one we saw at the beginning of the graph, on the 25th, right? Please, someone with more experience take a look at that chart and tell me if it looks normal. Not that we have much to which to compare regarding, “normal compared to other extrasolar objects we’ve observed passing through our system “, but do asteroids and burned out comets usually look like that?
 
  • #19
metiman
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Does anyone else find this to be the most compelling possibility of alien contact since the Wow! signal? I find it a lot more compelling actually. I am a bit disappointed with the unenthusiastic response from many scientists.

There really has never been anything like this in human history and we were alive to see it. At the very least it is the first interstellar object we have ever seen up close, but it is sufficiently weird that the hairs on the back of my neck...well. It really could be an alien probe. So far at least that is a very real possibility and I think that is worth admitting. Absolutely no evidence can rule that out at this point.

What I would like to see is what data we have that makes this possibility less likely. The first disappointment for me is that it is traveling so slow. Only 26 km/sec or 0.000087c. Well below what even our primitive tech could accomplish if we had infinite money. Even we could get up to 0.05c with nuclear pulsed Orion ships or more speculative but promising designs like fission fragment or nuclear salt water.

It has always been assumed that any aliens who made contact with us would be far more advanced because we are so primitive that if they were any less advanced they could not communicate with us or even find us and a similar level of science development is just utterly improbable.

But we don't really know much about this object aside from maybe its overall mass and size, interstellar trajectory with active adjustments, and its weird changing albedo. Has anyone checked to see if the albedo changes are nonrandom? Maybe they say Hello World or Prepare to be exterminated, Earthlings.

If it is an alien probe its subtle behavior and low speed could be explained by it being part of a swarm program. Maybe hundreds of thousands of slow and basic solar sail crafts were manufactured and launched to explore the galaxy. Maybe it releases a mini probe too small for us to detect to explore each system and report back with neutrino or gamma ray laser pulses or some other communication system way beyond our level.

Even in the unlikely event the miniprobe used microwave RF transmission it would be above 100 Ghz and would be directed away from us so even if we were listening at such high frequencies that are mostly absorbed by our thick atmosphere we wouldn't detect it.

If it actually does try to make contact with us I would imagine it would try several methods limited by cost and mass considerations and the fact that maybe they cannot predict what RF or EM frequencies could make it through our atmosphere. Even if the source civ is or was alive it may or may not be life as we know it. They may not assume a thick Nitrogen Oxygen mix. Surely laser pulses would be a safe bet though. We should be looking for those as well as 77Ghz, 29-32 Ghz, and 9-12 Ghz microwave pulses coming from a likely perihelion transfer solar orbit.

It is possible that the mini-probes do not have sufficient intelligence or detection capabilities to decide on their own if they detect a planet with life or intelligent life and that they just transmit back neutrino pulses or whatever with images and spectroscopy and other analytic data upon arrival. If that's the case we may not know for hundreds of years about the probe's presence due to the round trip communication times. Any system with intelligent life is very unlikely to be closer than 100 ly even if intelligent life is very abundant in our galaxy.

If it is an alien artifact of some kind and did not drop a payload will we be able to detect if it turns around and comes back in an omgwtf double take pattern in 50-250 years from now? Or even sooner if it is a smart enough device to see that there is something very very odd about the third planet?
 
  • #20
metiman
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Another now obvious explanation for its slow speed just occurred to me. It could have been decelerating for many years bevore arriving here for its solar slingshot. The alien civ would want its solar system tour to be slow enough to take photos and do spectroscopy. You would not want to enter the system at 0.7c or whatever they are capable of. Now the question is will it burn its thrusters again to accelerate when it gets past the final planet in its trajectory?

Or maybe it is just a solar sail probe. But wait...can we measure the small acceleration or deceleration that a solar sail around the size of the object would experience? Would a solar sail not have a slightly different trajectory around the sun than either a normal asteroid or a cigar shaped vehicle without a sail? It would be a powered object rather rather than a passive one.

Btw I am excited by the possibility but I am not making any claim whatsover that this is in fact an alien artifact. I would bet large sums of money on our not seeing an object like this again in any of our lifetimes though. I am skeptical of the several times per year idea. Interstellar objects are probably rare and ones whose trajectories just happen to intersect with other star systems are rarer still I would imagine. Before this I believe the general consensus was that they did not exist at all. Now all of a sudden they are supposed to be routine. Right. Any theories on how such an object might attain escape velocity from its solar orbit in the first place?
 
  • #21
LURCH
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From all of the articles that I've read, the issue is not slow speed, but the current slowing of speed. What has people interested is not the velocity at which the object is moving, but the fact that that velocity is changing. It is therefore undergoing some kind of propulsion.
 
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  • #22
metiman
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Yes well in the Why It May Be an Artifact column that, along with its oddly changing albedo is the most compelling evidence which even if explained by the irregularly wobbling cigar shape theory is I think unlike the albedo of any known local object.

Also the fact that it is the first and after an entire year still the only interstellar object we have ever seen and that its trajectory was just so perfect, aiming for a close flyby with the Goldilocks zone of the inner planets, of Earth and Mars, and then slingshotting around the sun just inside the orbit of Mercury just close enough to the sun for a nice gravity assist or Oberth burn but not so close as to require special materials or elaborate solar shielding. At 0.255 AU its perihelion is almost exactly what NASA would have planned and did plan with Helios A and B with perihelions of 0.31 AU and 0.29 AU respectively. It is pretty much exactly what we would expect an alien starship to look like too. Although if it is a wobbly cigar that argues against an actively piloted ship.

After taking the time to examine all the admittedly limited data I think it it really may be an alien artifact of some kind because any other explanation seems unlikely as well. If it is natural it is entirely unlike anything we have seen before. It is not a comet or an asteroid and it is much too small to be a planetoid.

We don't have any way to explain how a natural object could present this way. We just dont. The data is just not consistent with any natural explanation. I was thinking it could be an icy asteroid like sort of an asteroid-comet hybrid but we have never seen such an object and then why no tail or outgassing and the changing albedo would not fit unless it were an irregularly wobbling long cigar shaped icy asteroid which is again totally unlike any natural object we have ever seen. But maybe the Lyra mission will catch up with it and the images it sends back will be of a perfect ice cylinder, like a sort of 2001 monolith but made of ice. The reddish color may argue against an ice surface though. For all we know it is a monolith but perhaps cranberry red. This seems a lot more like science fiction than anything real. Are we inside a narrative now?

It is amazing but I actually think it being an alien artifact is the only explanation we currently have that would fit all the data. An old derelict ship with a solar sail or an active probe that is cigar shaped and wobbling for some reason. The fact that we can't trace its trajectory from or toward anything in particular seems to argue against it being actively piloted at least and the wobbling does too.

But if it is an active object it may not even turn on its main method of propulsion within a solar system. Once it gets past Neptune though maybe it will turn on its Improbability Drive and light up the sky with blue Cherenkov radiation or make gravity wave ripples that shake the planets slightly like a large ship wake leaving a harbor. Then it may change its trajectory for another perfect slingshot around Barnards star or Ross 128 or even make a short hop over to Alpha Centauri.
 
  • #23
metiman
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What if in 100 years we build our own probe driven by a fission fragment propulsion system that can quickly catch up to this slow and supposedly passive object but when we arrive at where it should be it just isn't there?
 
  • #24
rootone
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If it was an alien probe it would almost certainly have as part of it's mission an agenda to detect life supporting planets.
Earth is such a planet and it didn't seem to be interested.
Also, it has long been suspec6ted that there could be some fairly large chunks of stuff existing in interstellar space.
Leftover stuff form forming of solar systems, possibly even whole planets that got ejected from a solar system
 
  • #25
metiman
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It would probably be more efficient to use a mothership that dropped smaller probes that themselves would slow down and do the complex orbital manuevers to start sending back data and images either using the mothership as a relay station or send the digital data back many light years themselves using advanced alien tech. These smaller probes could be the size of a pack of cigarettes and would be far too small to be seen unless they wanted to reveal themselves by aiming a transmitter at us. Probably a laser.

So it may have dropped a payload of micro-probes already or it could be a derelict ship, a failed mission launched millions of years ago. Even advanced aliens are not immune to things going badly wrong. Technology is not always enough to prevent failure as stone age cave dwellers might observe if they were here now. The failed interstellar mission idea seems particularly compelling to me.
 
  • #26
metiman
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I am almost 50 now and for most of my life I think the consensus has been that interstellar objects were highly speculative and extremely rare and that we should not really ever expect to see any. I guess sort of like intergalactic objects might be regarded now. Sure now it is easy to point to past theories that mostly only science fiction authors paid attention to and say well of course. So far the predictions that we would start seeing more of these objects now that we are looking for them have failed.

The Ice Limit by Douglas Preston and Lincoln child featured an interstellar asteroid and I remember how far fetched and speculative it seemed when I read it at the time. Of course being the entertaining but trashy but fun writers that they are they pushed it even farther than that but it was just science fiction until now. Were there really a lot of scientists predicting we would start seeing these things? I guess I should just check an old astronomy textbook, but I think not. I think the next editions of many astronomy and astrophysics textbooks are going to have the word Oumuamua in them now. Of course if we do catch up with this thing one day and it is a million year old ship or monolith or ice sculpture or something even stranger then interstellar asteroids will remain in the realm of science fiction.
 
  • #27
stefan r
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I'm sorry, but I can't find the image I saw months ago. I think it was a radar image; could Arecibo resolve it?
no resolution.

NASA released an artist's image. That is the official picture.
 
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  • #28
Sanborn Chase
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If the difficulties of doing so could be surmounted, could an Earth-based sub-millimeter VLBI system resolve it? I feel sure many of the variables of this case present a formidable challenge for such an array to do so, but would the sheer resolving power exist? Thanks.
 
  • #29
stefan r
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If the difficulties of doing so could be surmounted, could an Earth-based sub-millimeter VLBI system resolve it? I feel sure many of the variables of this case present a formidable challenge for such an array to do so, but would the sheer resolving power exist? Thanks.
If oumuamua had 2 cell phones broadcasting the vlbi would be a good system for figuring out where they were with respect to each other. I think they can get down to a milliarcseconds. A milliarcsecond would have given 2 pixels the long way and would be back to 1 pixel on short side.
I am not sure how much radio wavelengths were bouncing off of Oumuamua. The signal needs to exceed the background noise.
 
  • #30
the fact that it is the first and after an entire year still the only interstellar object we have ever seen

Oh boy, *entire year* and we didn't see another one? I'm sure you know that in the last 400 years, this one is the first. Why are you surprised we didn't see two in 1 year timespan? Telescopes do improve, but not THAT fast.

If it is natural it is entirely unlike anything we have seen before. It is not a comet or an asteroid and it is much too small to be a planetoid.

We don't have any way to explain how a natural object could present this way. We just dont. The data is just not consistent with any natural explanation.

What are you talking about?
Its behavior is explained quite well by a theory that it's an oblong chunk of rock.
 
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  • #31
I am almost 50 now and for most of my life I think the consensus has been that interstellar objects were highly speculative and extremely rare

No, this wasn't the consensus. Interstellar objects were expected to be seen inevitably. A number of similar objects probably flew through our system undetected in the last ~200 years. As large survey telescopes become more numerous, we finally saw one.
 
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  • #32
Sanborn Chase
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Could a VLBI system be used to "paint" such an object? Has anyone used the system as a radar?
 
  • #34
sophiecentaur
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No, this wasn't the consensus. Interstellar objects were expected to be seen inevitably. A number of similar objects probably flew through our system undetected in the last ~200 years. As large survey telescopes become more numerous, we finally saw one.
The advent of digital imaging and the use of space telescopes had meant that the flow of useful data has increased many orders of magnitude. Even the management of the data has improved and so any worker who wants a certain type of data can find it and analyse it. It's not surprising that new objects are being found on an almost daily basis where they were found very infrequently in the days of Messier and his pals.
 
  • #35
Sanborn Chase
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Sophiecentaur said"...so any worker who wants a certain type of data can find it and analyse it."
Whoa! I think he's correct about our increase in data and our ability to organize and analyse it, but is it that simple? Could the bane of the Information Age be searching for that last bit of confirming data from the previous work of others?
 

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