Always amazes me how people won't acknowledge there is plenty of things we humans don't know. I didn't think this was clickbait, it's just some interesting ideas based on our limited knowledge of something, nothing pretentious or over reaching IMO
We have knowledge of probability. The probability of the interstellar object being a light sail is equal to the probability of the flying spaghetti monster existing.
So in other words, the probability is not Zero. Meaning it is very much worth considering and this article is legit.
We have knowledge of probability. The probability of the interstellar object being a light sail is equal to the probability of the characteristics matching a known light sail. That's not zero, since it's lining up. It's low enough that it's discountable by many people, to be sure, but not zero.
Probability allows you to say with confidence that the object cannot or is very unlikely to be certain things. For example, unlikely that the object is a sperm whale or a giant statue of liberty.
That's because we can be reasonably sure that no sperm whale is going to fly by from outer space, for obvious reasons.
On the other hand, we have essentially no knowledge about what can possibly be flying around out there and thus your claim that it is extremely unlikely to be an artificial object is not based on anything but your own conviction that this is the case.
Probability allows you to say something with confidence if you have information to work out the probability. If you have no information then you have no probability.
I think that our knowledge of the universe does allow me to conclude with some degree of certitude that it is highly unlikely to find a whale on an extra-solar trajectory.
On the other hand, we know nothing about the sort of objects that could exist out there and about the possibility of alien civilisations.
I am not saying that it is likely or unlikely to be a light sail because the fact is that we don't know enough to assign a likelihood. That's as unbiased as can be.
But that's not what happens: proposed alien technology always approximately tracks human technological development.
I'm having trouble finding it at the moment, but somewhere out there is a pretty good article that points out that even though more people are now carrying cameras than ever before, UFO sightings have basically fallen off a cliff. They rose with the advent of jet aircraft and the space age, and then fell away in the era of drones. (The ones that I found in search results weren't the one I was thinking of.)
"Lightsail" is being floated as a possible explanation for this because we've recently imagined that technology. A few decades earlier, and nobody would imagine it as an explanation; a few decades later, and we'll have some other favorite new possible explanation that we can't imagine now.
'proposed alien technology always approximately tracks human technological development'
Or to put it another way, humans conceptualize, observe and measure based on what they currently know and the tools they have.
My point again is we all to often fill the vacuum of what we don't know with 'the extent of our knowledge and experience is the extent of the entire universe'.
Centauri Dreams can be highly speculative at times but it definitely does not do clickbait.
Note that the title on that article is actually "‘Oumuamua, Thin Films and Lightsails". I suppose it might have been different when submitter submitted it, but that seems unlikely.
This is a law, I think, maybe with the capital L and maybe with very few exceptions: every headline that states a yes or no question can be truthfully answered with 'no'.
This low-quality subthread happened because the submitter posted the article with a tarted-up title ("Is the interstellar object Oumuamua a lightsail from an alien civilization?") We've since changed the title back.
Doing that to titles is explicitly against the HN guidelines and eventually will cause an account to lose submission privileges.
Judging from New Horizon's targeting capabilities and assuming the "discarded" light sail still has guidance then I'd conclude our aim could be amazingly good!
I think that's the right answer, as it got closer the exact parameters for the slingshot could be refined with images of the system taken a few lightdays out with a strong camera. So we just need that robot really.
Given Oumuamua's well documented non-gravitational acceleration, what was the cause? That's the key question this article – and the paper it cites – are investigating.
Comet-like off-gassing has been mostly ruled out due to the lack of observed dust or gas around the object, as well as lack of effect on spin. The paper suggests that a highly reflective 0.3mm-thick film 20m in diameter could be consistent with the observed acceleration. This also happens to be similar in dimensions to lightsails that we've proposed (and in a few cases deployed) here on/around Earth.
Of course, it's just one hypothesis. Could the acceleration be due to some other effect, like the Pioneer anomaly? Sure. Unfortunately, there's no way to ever confirm it given that the object is beyond our ability to observe or catch. But it's still very interesting speculation.
It’s a fascinating mystery, but I gotta say that’d make a crappy lightsail, considering that even at our current tech level we could make a much lighter one if we could manufacture it in space. (The experiments that have flown were all constrained to survive launch and unfolding.)
Hm, say you are designing a light sail for interstellar travel. Instead of having it be made of thin film and actuators capable of swinging these sails like on a sail boat... because actuators are more likely to die after millennia in space:
say you instead make the space craft tumble but make the sails able to change their albedo (how reflective they are). If you wanted to make a course correction, you'd alternate how reflective they were. If you wanted a push away from a sun, you'd make the side facing a sun bright. If you wanted to fall in more towards a sun, you'd make the side facing a sun dark. Would that work?
How much do light sails depend on brightness (light pressure) vs just absorbing molecules in the Solar wind?
Edit: Wikipedia says light pressure from photons is most of the effect, but still I can't figure out the difference between a black body sail and a reflective sail.
Wouldn't a perfect absorber facing the sun directly get half the light pressure of a perfect reflector? I'm assuming after it heats up to equilibrium it emits in all directions (no net momentum from emission, so you're left with absorption only).
Assuming a uniform thickness and density, is the acceleration of a light sail not independent of area? I get the impression that the radius given is an upper limit based on the apparent magnitude and assuming a high albedo.
The light curve indicates that the object is tumbling, so a thin sheet would rarely (if ever) be oriented approximately optimally to act as a sail. I have not figured out how the authors have taken this into account in their calculation - could it be as simple as halving the area to give an effective value?
Perhaps the acceleration is consistent with tumbling if it just-so-happened to tumble (slowly) into a sailable angle at around the time the acceleration was noted, or is tumbling fast enough for things to average out?
> "Comet-like off-gassing has been mostly ruled out due to the lack of observed dust or gas around the object"
This is a new one on me, I'm not aware of any rigorous lower limits on off gassing which have actually ruled it out as the source of the acceleration. Do you have any citations?
While I find it highly unlikely, it does raise an interesting point about Fermi's Paradox, which is that even if there were enough alien life out there for its discarded light sails to go hurtling through our solar system every once in a while, we might not get any more evidence of it than this article demonstrates. So, it's almost certainly not a light sail, but even if it were, we would never know.
Fermi's paradox demonstrates it's almost certainly not a light sail. For it to be a light sail which was observed by chance by our totally unprepared observatories after a window of less than a century but also consistent with all our observations of the universe, we would need to hypothesize that we got extraordinarily lucky to observe a super-rare artifact, or that countless (or one vast) interstellar, pan-galactic civilization throwing out light sails in every direction constantly which also collectively choosing for millions/billions of years to avoid any kind of stellar engineering or direct colonization or Dyson sphere-like artifacts or even atmosphere composition tweaks visible on exoplanet spectrographs all carefully preserving the illusion of a 100% dead cosmos in every inch of our Hubble volume, or that alternately, interstellar civilizations are super common and in fact routinely throw out solar sails all the time, but some sort of interstellar-capable Great Filter kills them almost instantly before they can have any visible effects, leaving just a bunch of spreading artifacts. (And this Great Filter can't be any of the usual ones like asteroids or nukes or pandemic or development of intelligence.)
Or that this was a relatively nearby civilization, and the light sail was intentionally headed toward our solar system (like a few of our proposed interstellar missions to Alpha Centauri).
That falls under the 'we got ludicrously lucky' category: in the entire galaxy of billions of stars over billions of years we just happened to arise exactly simultaneous with the other civilization in time to see it? (Also, if it was coming from a nearby solar system, why did it pass right through, do nothing, and is at rest with respect to the galaxy? I also think if its trajectory led straight to a nearby star system with any potential for life, someone would've noted that.)
It probably is true. And it might surprise you, but papers leave things out all the time... Even things that can be calculated. Shocking, I know. And that wouldn't be in the paper anyway because the Fermi Paradox & Great Filter is not hard science but still half philosophy.
Exoplanet atmospheres can be studied by the transit spectroscopy method. This is how water has been detected, for example. Still no oxygen or any other signatures of life. Lots of hostile atmospheres, though: https://en.wikipedia.org/wiki/Extraterrestrial_atmosphere#Ex...
Or it's a small piece of a larger, rarer piece of equipment that broke up. Or something we don't really have the imagination for. It's far too early to make absolute statements about what is and isn't possible wrt ETI.
As another comment pointed out, the actual title of this article is ‘Oumuamua, Thin Films and Lightsails. While the question "Could ‘Oumuamua be debris from a technological civilization, a discarded lightsail?" occurs in the article, this title does the article a clickbaiting disservice.
("Is the interstellar object Oumuamua a lightsail from an alien civilization? " at the time of this comment)
Yes, that title broke the site guidelines, which ask: "Please use the original title, unless it is misleading or linkbait; don't editorialize." We've since reverted it.
All: Accounts that do that eventually lose submission privileges on HN, so please don't!
My understanding is that the authors of the paper were speculating that this object might be debris from an encounter with another star that later flew by our sun by mere coincidence.
As far as I can see, the observed hyperbolic trajectory doesn't seem consistent with a scenario where the target of the sail's payload would be our solar system.
Although unlikely to be a lightsail I think, this reminds me of the Rama series by Arthur C. Clark. I really wish someone like HBO, Netflix, or Starz would pick that series up and make a show out of it.
He wants to make it into a movie though. I hope he is considering a high-level TV series a la Game of Thrones. I feel like there are a lot of nuances that would get lost if made as a movie or series of movies.
A series that lasted more than one season? Brilliant!
Devil's advocate would raise the example of Dune perhaps, with a fairly decent IMO SyFy network TV miniseries, a lot more nuanced than the film and far more from the novel but didn't have the staying power of either of the two film versions. (Not that any of the film versions or the miniseries seems to be broadly loved)
in a short time, may be even in our lifetime, we'll probably be able to set up manufacturing and sending out of the light sails like this just as a task performed 24x7 by several weaving/printing machines planted on some asteroid having needed raw materials. Given even today's technology something like on scale of hundreds of thousands of such sails can be produced yearly. We just have to get up there.
> In fact, the strong correlation between ʻOumuamua's velocity and the local standard of rest might mean that it has circulated the Milky Way several times and thus may have originated from an entirely different part of the galaxy.
Paging Elon Musk, Jeff Bezos, et al: the next time one of these objects appears, we should try to capture it somehow, or at least divert its trajectory enough that it stays in the solar system and we can study it further. Nabbing one of these things would be a spectacular achievement, comparable to the moon landings, and would likely be of significant scientific value.
Based on my understanding of the Falcon Heavy launch and objectives this is an unfair characterization. The plan was never to put the car in orbit around Mars or hit the planet directly. The plan was to prove that Falcon Heavy can move a payload with the weight of the car at least as far as Mars. Shooting it into the asteroid belt demonstrates the capability of the rocket.
Capturing this object would have required the effort of multiple Apollo prgrams in a timeframe that is shorter by orders of magnitude. It’s far beyond the capabilities of Musk, Bezos and anyone alive today. Pulling it off would make the Moon landing look like parallel parking.
Given how weird, and apparently unexplainable, various aspects of this object are, shouldn't we be moving heaven and earth to investigate the possibility of some kind of mission to it? From what I've read, there are ideas at least for how we might launch a spacecraft capable of catching up with it. Given the potential of what we could learn, wouldn't that be a better way to spend a few billion dollars than a return to the moon? (of course, ideally we'd do both, but...)
This is one of the biggest motivations for going (and staying) on the Moon, Mars, and so on. Going after this object is not just an issue of money. Intercepting objects in space is really hard. Intercepting objects that are hauling ass away and have already shown an ability to exhibit let's say 'aberrant acceleration', when we don't currently have the technology developed, let alone tested and refined, to intercept it makes the entire idea perhaps not impossible, but extremely unlikely to succeed.
By contrast when we have ships moving regularly between Earth, Mars, the Moon, and wherever else - we'll have much more infrastructure and technological development enabling us to have a much better chance of being able to rapidly react to the next 'weird thing' we see in space. And seeing how many weird things we're already starting to observe now that we've just barely begun to be able to open our eyes, I expect this is just the beginning. Consider we still lack the technology to determine whether or not there is some giant super-earth floating around in our own solar system. Sometimes in space it's much easier to see things billions of light years away than it it is to see something right next door.
It makes sense you would jettison your light sail before starting deceleration approaching earth. That means the things they jettison would pass by us first while the actual spaceship is still slowing down.
If you jettisoned lightsail while approaching solar system it would get SLOWED down by Sol's light compared to the main mass of the craft. We would see the ship first and only then the sail.
Solar sails to be effective would have to be much larger than the craft itself, and also very reflective (by definition), though the reflection don't have to omnidirectional (stealth aircraft/ship principle -- make it reflect a lot but only in very specific direction so that it seems dark to most observers).
Given this, the craft would most likely PRECEDE the sail but would also be smaller and darker and we would most likely not be able to spot it.
Using a dinky star for acceleration is not going to get you real fast. There could have been a targeted beam to accelerate the craft. And the craft carries fuel for deceleration only.
You can get right up to relativistic velocities if you first sundive as close as you can while keeping your sail folded and protected by a heatshield, and then deploy your sail right next to the sun.
But anyway, if you carry a solar sail to accelerate, why would you not use the same sail to decelerate as much as possible too?
Especially if you are going to a star roughly same or higher luminosity, you should have no problem braking with the sail. Also, you probably absolutely need to break with sails since you don't want to carry much fuel to break. Any reasonable amount of fuel required to break will be orders of magnitude more than the payload -- reducing effectiveness of sails by same factor.
If it was a large hollow body, then it would have particular resonant frequencies. Is there such a thing as a resonance sail? Total speculation, but I think such a thing would work the opposite of a lightsail, in that it would tend to go toward bodies than emanated it's resonant frequency, rather than be pushed away by radiation.
Please bear in mind, the spectra of Oumuamua is very similar to that of a D-type asteroid (organics and carbon), which isn't consistent with it being highly reflective.
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So in other words, the probability is not Zero. Meaning it is very much worth considering and this article is legit.
That same probability applies to the light sail.
On the other hand, we have essentially no knowledge about what can possibly be flying around out there and thus your claim that it is extremely unlikely to be an artificial object is not based on anything but your own conviction that this is the case.
Probability allows you to say something with confidence if you have information to work out the probability. If you have no information then you have no probability.
I think that our knowledge of the universe does allow me to conclude with some degree of certitude that it is highly unlikely to find a whale on an extra-solar trajectory.
On the other hand, we know nothing about the sort of objects that could exist out there and about the possibility of alien civilisations.
I am not saying that it is likely or unlikely to be a light sail because the fact is that we don't know enough to assign a likelihood. That's as unbiased as can be.
I'm having trouble finding it at the moment, but somewhere out there is a pretty good article that points out that even though more people are now carrying cameras than ever before, UFO sightings have basically fallen off a cliff. They rose with the advent of jet aircraft and the space age, and then fell away in the era of drones. (The ones that I found in search results weren't the one I was thinking of.)
"Lightsail" is being floated as a possible explanation for this because we've recently imagined that technology. A few decades earlier, and nobody would imagine it as an explanation; a few decades later, and we'll have some other favorite new possible explanation that we can't imagine now.
The article wasn't terrible, though.
Or to put it another way, humans conceptualize, observe and measure based on what they currently know and the tools they have.
My point again is we all to often fill the vacuum of what we don't know with 'the extent of our knowledge and experience is the extent of the entire universe'.
We have no idea about what we don't know...
Note that the title on that article is actually "‘Oumuamua, Thin Films and Lightsails". I suppose it might have been different when submitter submitted it, but that seems unlikely.
https://en.wikipedia.org/wiki/Betteridge%27s_law_of_headline...
https://news.ycombinator.com/item?id=17978737
Doing that to titles is explicitly against the HN guidelines and eventually will cause an account to lose submission privileges.
https://news.ycombinator.com/newsguidelines.html
How good is our aim across 4.4 light years?
Genuine question, this is well outside my wheelhouse.
Comet-like off-gassing has been mostly ruled out due to the lack of observed dust or gas around the object, as well as lack of effect on spin. The paper suggests that a highly reflective 0.3mm-thick film 20m in diameter could be consistent with the observed acceleration. This also happens to be similar in dimensions to lightsails that we've proposed (and in a few cases deployed) here on/around Earth.
Of course, it's just one hypothesis. Could the acceleration be due to some other effect, like the Pioneer anomaly? Sure. Unfortunately, there's no way to ever confirm it given that the object is beyond our ability to observe or catch. But it's still very interesting speculation.
say you instead make the space craft tumble but make the sails able to change their albedo (how reflective they are). If you wanted to make a course correction, you'd alternate how reflective they were. If you wanted a push away from a sun, you'd make the side facing a sun bright. If you wanted to fall in more towards a sun, you'd make the side facing a sun dark. Would that work?
How much do light sails depend on brightness (light pressure) vs just absorbing molecules in the Solar wind?
Edit: Wikipedia says light pressure from photons is most of the effect, but still I can't figure out the difference between a black body sail and a reflective sail.
And also, maybe some of the stored and emitted heat can be directed somehow.
Something of that size (area) and weight doesn't seem like some kind of naturally occurring object though.
Even if it is a piece of debris, that is super, super interesting.
Eh, who am I kidding, even if it was produced through some natural process, that is still interesting.
The light curve indicates that the object is tumbling, so a thin sheet would rarely (if ever) be oriented approximately optimally to act as a sail. I have not figured out how the authors have taken this into account in their calculation - could it be as simple as halving the area to give an effective value?
This is a new one on me, I'm not aware of any rigorous lower limits on off gassing which have actually ruled it out as the source of the acceleration. Do you have any citations?
I'm fairly certain we can't detect that yet even if they had.
("Is the interstellar object Oumuamua a lightsail from an alien civilization? " at the time of this comment)
All: Accounts that do that eventually lose submission privileges on HN, so please don't!
As far as I can see, the observed hyperbolic trajectory doesn't seem consistent with a scenario where the target of the sail's payload would be our solar system.
https://en.wikipedia.org/wiki/The_Dark_Forest
Devil's advocate would raise the example of Dune perhaps, with a fairly decent IMO SyFy network TV miniseries, a lot more nuanced than the film and far more from the novel but didn't have the staying power of either of the two film versions. (Not that any of the film versions or the miniseries seems to be broadly loved)
> In fact, the strong correlation between ʻOumuamua's velocity and the local standard of rest might mean that it has circulated the Milky Way several times and thus may have originated from an entirely different part of the galaxy.
Why was this changed in the HN submission? It sounds much more click-baity than it is.
By contrast when we have ships moving regularly between Earth, Mars, the Moon, and wherever else - we'll have much more infrastructure and technological development enabling us to have a much better chance of being able to rapidly react to the next 'weird thing' we see in space. And seeing how many weird things we're already starting to observe now that we've just barely begun to be able to open our eyes, I expect this is just the beginning. Consider we still lack the technology to determine whether or not there is some giant super-earth floating around in our own solar system. Sometimes in space it's much easier to see things billions of light years away than it it is to see something right next door.
Perhaps the main ship is on the way!
Solar sails to be effective would have to be much larger than the craft itself, and also very reflective (by definition), though the reflection don't have to omnidirectional (stealth aircraft/ship principle -- make it reflect a lot but only in very specific direction so that it seems dark to most observers).
Given this, the craft would most likely PRECEDE the sail but would also be smaller and darker and we would most likely not be able to spot it.
But anyway, if you carry a solar sail to accelerate, why would you not use the same sail to decelerate as much as possible too?