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Could 'Oumuamua be an icy fractal aggregate ejected from a protoplanetary disk? (syfy.com)
509 points by Santosh83 on Feb 19, 2019 | hide | past | web | favorite | 225 comments

At least this makes sense. Perhaps calling it a fractal is an unnecessary spin, but if it is linbaity enough to cover the spaceship theory I'm in.

More than a fractal, it is better to imagine it as a pile of recently fallen snow is a day with the correct climate (cold?), so the snow accumulates but it doesn't compact too much. So the density is much smaller than the density of ice that has been in a glaciar for years under a lot of pressure. Since the gravity is too low, it will no compact too much.

The main difference is that it's not a pile of real snowflakes, ut a pile of dust "snowflakes". Otherwise, the ice in the real snowflakes would have been partially evaporated by the sun and it will be classified as a comet.

Anyway, it would be interesting to read more technical details about the plausibility of this. Can the dust pile survive the micrometeorites? Does the color profile match a dust pile object. I really don't like the starship hypothesis paper, but at least it contains a good analysis of many of the (secondary) objections.

It makes more sense to call it a fractal rather than a pile. In the paper they reference, it is suggested that particles can form fractal like structures through a diffusion limited aggregation process[0]. One very important result in planetary science is the observation by the astronaut Donald Pettit of granular materials aggregating together in microgravity[1]* . In the experiment[2], it appears that some of the resulting structures resemble those formed in a diffusion limited aggregation process.

*It is also worth noting that this experiment was entirely ad-hoc and came about from Don basically just playing around with stuff in microgravity




For example, bismuth crystals grow in an interesting way and, like h20 are less dense as a solid than a liquid. At the utterly extreme temperature/pressure environments expereinced in the universe, it isn't hard to believe there are solids out there we can't begin to predict at present. Below are some 3D crystal growths at SEM and macro scales for earth examples



"Perhaps calling it a fractal is an unnecessary spin,"

It is, or at least calling it self-similar is, as well as what the image implies: https://www.youtube.com/watch?v=gB9n2gHsHN4 That's a 3Blue1Brown video explaining why "fractal" and "self-similar" are not the same thing.

That video is about how "self-similar" is not sufficient for fractal. (The rest of the requirement is some notion of fine detail at every scale, which the video focuses on.)

It is widely agreed that self-similarity is required for fractal, although often interpreted as quasi/statistical/multiple similarity


Put another way, some things are self-similar but lack detail (for example, a straight line), and some things have detail but not similar detail at all scales (for example, a meterstick with ticks at every millimeter) and some things have infinite detail but no similarity (for example, purely entropic noise that cannot be compressed or expressed as a structure)

The core idea of a fractal is something having fractional dimension. It just happens that the ones we know of are self-similar. If we had a formula that generated different shapes ad infinitum, I would also call that a fractal.

It may be "self-similar" in a particular mathematical way, but fractal does not imply "self-similar" in the way people expect.

I think you meant "not necessary".

And can that loose pile of dust survive even a slight rotation. If it is long and thin, the dust near the tips should separate.

There are mechanisms by which tiny particles may bond over time without becoming more dense. The only prerequisite is that individual atoms or molecules can move on the surface of the particles. This is true for a wide range of conditions, but usually is extremely slow.

The article claims that if it has the snowflake properties it isn’t long and thin and still produces what we saw.

> More than a fractal, it is better to imagine it as a pile of recently fallen snow

But snow flakes are fractals.

And snow ‘falls’ in gravity. This aggregated somehow else.maybe by tenuous electrostatic attraction (some ice particles get positively ionized when a photo kicks out an electron, some get negatively ionized when an electron attaches to them, & cetera and eventually they clump together to make a roughly electrical neutral object. The. Hydrogen bonds kick in once it’s electrically neutral (assuming it’s made of water or other polar molecules).

Why does it have to be something else? Couldn't the particles have precipitated gravitationally inside a smallish dust cloud?

But a pile of snow is not.

It's Wired. They have to use "fractal" a few times an issue or their articles of incorporation call for a new board.

It’s Phil Plait on the Syfy blog Bad Astronomer, not Wired. He does occasionally get a bit click-baity in his headlines but the content is pretty solid, particularly on the subject of omuamua

Oh wow, you're right. I saw the green-underlined all-caps text and assumed Wired. That and the word fractal.

Funny you mention that. I seem to remember them classifying it as a “meme that died from overexposure” in their regular feature sometime back in 1997 or thereabouts.

> It seems far more likely that objects like 'Oumuamua are relatively rare, and that means it likely came from someplace close by (if it came from farther away, the odds are even lower we'd ever see one).

Ok, it's on my list of things to do this year to actually learn how statistics work, but my naive reaction to this supposition, which I read is "the fact that we have encountered Oumuamua means that it's likely it didn't come from far away, because if it did, it's less likely we would have encountered it," is: We did encounter it. Just this one, ever. How can we draw any statistical information from that? Either we encountered it, or didn't, how does that have any bearing on the statistical probability of seeing it?

Here's a quote by Feynman on the topic: “You know, the most amazing thing happened to me tonight... I saw a car with the license plate ARW 357. Can you imagine? Of all the millions of license plates in the state, what was the chance that I would see that particular one tonight? Amazing!”

I believe what you're getting at is the Ludic Fallacy, which could probably apply here. That said, whether it's a fallacy in the science or in the reporting, it's hard to say. I have a degree in statistics, and I'd say I spent half the time learning stats, and half the time learning to use language precisely to avoid overgeneralizing stats.

There's a really great TED talk about how even very educated people get it wrong when talking about stats: https://www.ted.com/talks/peter_donnelly_shows_how_stats_foo...

Suppose you know nothing about license plates and I tell you that license plates work one of two ways, either every license plate reads "ARW 357" (it's just a meaningless tradition) or every plate has six randomly selected numbers and letters and there's equal probability that either explanation is true. THEN you observe a single car with a single license plate with the value "ARW 357".

Does this single observation tell you anything about reality? I would argue that it does - it should strongly suggest to you that you're in the "every car is ARW 357" reality. Similarly, if you draw a ball from an urn and it's red, and you know you've drawn either from the "urn of red balls", or the "urn of one million green balls and one red one" you should be pretty confident you've drawn from the "urn of red balls".

If one theory can explain your observations but the explanation is highly unlikely, and another theory explains your observations and the explanation is likely, the second theory is more likely to be correct all else equal.

"Does this single observation tell you anything about reality? I would argue that it does - it should strongly suggest to you that you're in the "every car is ARW 357" reality."

I think this scenario is incoherent after thinking about it for a minute. You say "there is equal probability that either explanation is true" but you imply that you, the storyteller, know something about license plates. Probability is a description of incomplete knowledge, so whose knowledge are we talking about, yours or mine?

I see no reason (in my hypothetical ignorance) to exclude the possibility you know I will see "ARW 357" next even if all license plates are different.

The license plate example is a kind of nonsense magic example to just use the same things that the parent comment was talking about - you should also factor in to your analysis the absurdity of issuing an identical plate to every car, etc.

Instead, consider the example with the urns. I think that's a lot more realistic and illustrates the problem.

Maybe there is some process that makes the red ball to always go to the top, so the probability of finding it is larger than one to million.

In both cases you do not have enough information to make any conclusions.

>In both cases you do not have enough information to make any conclusions.

That's why the field of statistics exists in the first place.

Ok, this explanation makes a lot of sense.

However, are we able to reduce down our understanding of "which universe we're in" in such simple terms? I think I'd understand better if I knew how long we've been capable of detecting oumuamuas.

It depends on your priors. If you set it up properly the evidence for either model from one sample would be weak. You shouldn't be confident in either model after one trial, but you can eliminate some models, i.e. all balls are green.

You're correct about choosing between theories, but I think what's being challenged here is how we're determining if something is unlikely or not given our imperfect knowledge...and how it was described in the article. I'm not making the case for aliens here.

Why is it so trendy to discount the possibility of aliens? Your comment and the article have specific, nearly-foremost intent to do that.

There's no evidence it is aliens. Obviously it could be, and it's unlikely there are not such things in our universe.

It just seems more appropriate to say "there's no evidence it is related to alien tech." Everyone having to say "it's NOT aliens" seems like some sort of cultural phenomenon.

I don’t follow. If my “ancient aliens” theory says that Stonehenge should occur on 50% of planets, would you automatically favor it over any theory that sets steeper odds?

If I had confidence that you'd formed that theory without prior knowledge of the existence of Stonehenge, then the fact that you'd predicted Stonehenge would indeed be making your theory look pretty good!

In fact that is an essential part to how theories are evaluated. Not just by what they explain, but by what they predict.

Most theories on physics are evaluated this way. "We theorize that light is a particle, which would explain these properties of light, and means we should expect to see these other properties of light if we test them." If further observation of light matches those properties you predicted then that's pretty good evidence that your theory is on the right track.

So the UFO people are right? They predicted this sort of thing all along, without any prior knowledge of Oumuamua. I don’t recall hearing about fractal comets before?

We're going to need to think carefully about what is covered by "this sort of thing".

If your ancient aliens theory didn't actually predict "Stonehenge", but predicted that the aliens would have left "all sorts of cool weird stuff", and then you point at Stonehenge and say "see, that's the sort of cool stuff I mean", then I'm no longer impressed by the predictive power of your ancient aliens theory.

Predictions have to be precise for a theory to be supported by them: they can't be vague generalities. cf. astrologers, who "predict" the future by predicting nothing.

I predict “aliens would leave all sorts of cool weird stuff” and you predict “nope just more rolling hills”.

My theory is wrong, but it assigns higher likelihood to Stonehenge than yours. That’s why I don’t like the license plate example.

Well, "my" theory is also pretty wrong if it doesn't allow for the human civilisation that built Stonehenge.

A theory that is wrong will sometimes predict correct things by accident. That's unavoidable, but we a) have statistical methods for modelling how often things go right by chance, and b) have a philosophy of science in which theories are forever tentatively held: your aliens theory might beat any theory which says Stonehenge is impossible, but will soon be replaced by a theory which explains Stonehenge more economically.

I have no degree in statistics. But I know for sure that any statistics is just meaningless numbers if you have no hypothesis behind it. At the same time the only method to deal with single observation I know is bayesian statistics. As I understand this statistics have an answer "observation of Oumuamua raises probability that there are many objects like this in the interstellar space".

We can suggest that there are N classes of objects in space, we picked one at random, and it happens to be Oumuamua belonging to the class of Oumuamua-like. To one of N classes. The more some class is common, the more probability for us to see element from this class. Here we can use Bayes' theorem and conclude that the fact of observation of Oumuamua is a weak evidence that the class of Oumuamua-like is more common in the interstellar space than any other class.

It is a weak evidence, and I dont know how much is it. But the point is this evidence points to an ordinariness of objects like Oumuamua not to a rareness.

The license plate story is useful, but it does not address the uniqueness problem. We see lots of license plates, and there's nothing particularly special about most combinations of characters. We see lots of rocks, too, but until Oumuamua they were all solar. The distinction between solar and nonsolar is meaningful; indeed, many astronomers have wanted to see a rock from outside the solar system for a long time.

Say your prior is that something has a 1 in 1 million chance of happening in any given year.

You start monitoring it. Year 1, the thing happens. Which is more likely:

1. You've encountered a 1/1,000,000 event

2. Your prior is incorrect and the thing happens more often than once every million years?

Without more information we can't actually answer this question with certainty, but "re-evaluate your priors" would absolutely be a thing one might suggest in response to this event.

Unfortunately, LIGO encountered the 1/1,000,000 almost as soon as it was powered on and they've been waiting for another one like it. Probabilities are funny things ...

I don’t understand this comment... It’s true that the first event occurred after only two days but ligo have 11 events over two running periods at this point.


I was under the impression from an interview that the first event that LIGO caught was held up so long before release because it was such a stupidly rare occurrence.

Even as there are eleven observed events so far, that is from 2 trillion galaxies in the observable universe [1]. So at 100 billion stars per galaxy [2] a guesstimate is that we are talking about 200 billion trillion stars. Seems even divided by eleven it seems pretty rare. (Not sure if the detector can “see” all those stars though.)

[1] https://en.m.wikipedia.org/wiki/Observable_universe

[2] https://www.livescience.com/56634-how-many-stars-are-in-the-...

What does 1/1000000 even mean? One every million seconds, every million minutes, every million years?

It means "outcome with low prior probability". Just that and nothing more. Seriously.

Presume I have a machine that, when you press a button, will either light up the red light bulb or the green light bulb. Usually, the red light bulb lights up, but the green bulb will if and only if one of the following two things are true: #1. The lottery ticket in your pocket is the winner of the big jackpot #2. It's raining.

You press the button. The light bulb turns green. There's no windows to check for rain or internet to check for winning numbers. You have no further information beyond the fact that the light bulb turned green.

Which is more likely to be the case: That you're now a millionaire, or that you should grab an umbrella as you leave?

We know we saw 'Oumuamua (the green light). We now can construct many models for why we might see such results. The probability that we would see the results given the model (lotteries or rain) can be used to infer what the true model most likely is.

As soon as you have internet you will check lottery results first. It's more exciting.

Is there a chance that both are true, cause the weather here was pretty shitty on my way into work...

We did encounter it during the short timeframe in which we would be able to detect it. Could be a once every 20 years occurrence, that would make it quite frequent.

Let's consider two scenarios:

1) Somebody starts flipping a coin they claim is fair. You're not sure whether or not that's true. It comes up with 10 heads in a row.

2) Somebody tells you there's a 1 in 10,000 chance of something happening each day. You're not sure whether or not this is true. It happens tomorrow.

Which, if either, do you think has reasonable evidence to begin to doubt the claimed odds are the real odds? Which do you think is better evidence of the proposed claim being false?

With the logic you expressed in your post you might suggest the first is better evidence of a false claim, but it's not. The odds a fair coin going 10 heads in a row is 1 in 2^10, or 1 in 1024. Even though it's 10 'events', it's ultimately just a 1 in 1024 happening if we assume a fair coin. By contrast the second event is about an order of magnitude less likely to have happened by chance. So even though the second event is only one happening, it's more likely that that event is not a 1 in 10,000 event than it is that the coin is not fair.

I'm not sure whether that sentence from the article actually makes sense.

But to answer your question more generally: you start with some model, with one or more parameters for which you don't know the value. e.g. "the galaxy contains N uniformly spread out interstellar objects that are big enough to see if they happen to come within 1 AU of Earth."

Then we start watching the sky, and after 10 years we see 1 such object.

Then for each possible value of N, you could calculate the probability of observing exactly 1 such object during a decade. One particular value of N is going to give us the highest likelihood of getting that result. We call that value the "maximum likelihood estimate" for N.

While I do love the "ejected from another star" idea, the probabilities of something being ejected from another star in the correct direction AND being captured by our Sun is so vanishingly small that it's far, far, FAR* more likely to be a remnant of when our own star formed.

For a humorous take on what can be done with a sample size of 1:


Certainly, any new information is going to radically adjust the posterior probabilities, but you can still make some tentative inferences.

A quick scan didn't reveal my favorite sample size 1 statistic. If you sample serial numbers starting from 1 and sample N, the best guess is that there are 2N examples.

This was worked out in WW II for estimating tank production.

What we can say statistically is that, if there was no intention behind this object's trajectory, then it is more likely to have come from a nearby system. We can even say how much more likely.

In fact, an argument that it's more likely to have come from somewhere nearby holds even if it was sent by design. Conscious beings are more likely to want to explore the stuff they can reach sooner, and they are more likely to succeed at reaching nearby things. But without knowing their engineering constraints and their preferences, we can't quantify that like we can the random ejection scenario.

Another way to state this would be that given our current understanding of the universe, most objects that get close enough for this kind of encounter will have a nearby origin.

I'd take issue a different way.

It seems far more likely that objects like 'Oumuamua are relatively rare, and that means it likely came from someplace close by (if it came from farther away, the odds are even lower we'd ever see one).

I'd rather look at the density of Oumuamua-like objects in space. First, it seems like these objects rarer than some things but dense enough for us to have seen them.

Their "terminal density" comes when their rate of production managers to equal their rate of consumption. Who knows how they're produced but I'd assume they are consumed when they are gravitationally captured by a solar system - actually flying into a sun is much less likely I'd assume. Such gravitational capture is more likely if these objects are moving at a similar speed to the solar system they encounter.

The one thing we know about Oumuamua is it seemed to speed up as it left the solar system. This factor might imply that the chances of capture wind-up very low. Now, the rate of production could be low and thus life-span could be high. A high lifespan implies this came from far away. I could be wrong on the consumption chances. But still, I think arguments about how far these travel would do better with such life span analysis than with the quote argument, whose implications are foggy imo.

As to whether the thing is a product of alien intelligence? If the very low density analysis is correct, if such a thing could behave as Oumuamua did, then that too might be a good spacecraft design. Which is to say, the amount of information we have is low that making absolute answer seems pretty hard here.

We're not 'drawing statistical information' from the observation itself, simply saying that if it is the case that such objects come from interstellar space and are relatively rare, it is more probable to encounter one that originated nearby than it is to encounter one that came from far away. With those assumptions, you can arrive at this conclusion without observing such an object at all.

I don't know much about statistics, but I can add that the time period matters. If we only started observing space yesterday, and saw it, it would be weird to say "it's rare", but we've been observing space for, I don't know, up to 400 years? (counting since invention of telescope, 1608)

I don't think an object like this could have been spotted until relatively recently.

But how recently have we developed the capability to:

- observe this thing at all

- accurately measure it's velocity and acceleration

- understand that it's velocity and acceleration were unusual?

This type of object could only really have been seen when it was. It was picked up as part of a full-sky survey that year, the firsts time such a thing had been done at sufficient resolution to detect an object like 'Oumuamua.

A number that I saw quoted earlier was that it is expected that around 3 of these things go through the solar system every day. This one just happened to be the one caught by the survey, which itself required a bunch of coincidences since it means catching multiple pictures of the same object in different locations so as to establish a trajectory, so an ability to detect is not just resolution, but also timing and orbital trajectory.

> but we've been observing space for, I don't know, up to 400 years? (counting since invention of telescope, 1608)

We've been observing space 'forever'. Pre-telescope observers had quite accurate star maps (of the naked-eye stars, obviously) and were fully aware of the complex movements of the planets. Their models of the movements were good enough for predictions even if the underlying explanatory causal models were sometimes wrong.

Well, there is this entire science describing the universe and how it works you see, and that science makes certain prediction about things like how easy it is to kick something out of a star system and how likely a rock thrown in a random direction on the other side of the galaxy is to hit a our particular sun.

In this instance it seems like what's more interesting is what it possibly is rather than what it probably is.

No one can say for certain what Oumuamua actually is-- other than it is "a surprise".

What it really is, IMHO, is a call to action for better instrumentation so that the next time one of these things pays us "a visit", we're in a position to find out more about it.

The LSST, which goes online (hopefully) next year, will greatly improve our ability to detect faint transient objects such as Oumuamua. It's expected that a number pass through the inner solar system each year, if we can find a and compare a number of them that will give us a better sense of whether Oumuamua is a remarkable object or not.


AFAIK we don’t have many satellites around the other planets. I think we need many more. Each planet could have at least one telescope, comms satellite, etc

Mars and Jupiter have orbiters and Saturn had one until recently (Cassini). But what good do those do? They are planetary science missions, largely useless for observing very distant objects.

I think what you are proposing is having a bunch of large space telescopes around planets. But this might not help very much. All the planets are in the plane of the ecliptic. Interstellar objects are not going to be aligned with the plane of the ecliptic.

For stuff like this. For stuff we can’t even fathom yet. The world didn’t need the amazing diversity of organisms that it has, but then we can’t imagine a world without it. The “swarm” offers a lot more than just numbers, but it also offers numbers. Arguing against each planet having observatory abilities and comms is not that far from dismissing all progress on the basis that “well were already pretty well off.”

You have to weigh it against the very finite budget of space programs. NASA does this as their decadal surveys. There is no shortage of ideas and serious concepts.

The difficulty of putting Hubble or JWST sized telescopes in orbit of other plants is immense. They need constant maintenance as well and will take years to reach their intended targets.

B612/Sentinel has been "in the works" for at least 8 years, but still doesn't have consistent funding. This would be in a Venutian orbit to looks for near Earth objects. https://en.wikipedia.org/wiki/Sentinel_Space_Telescope

IMHO, a more useful location for a space telescope rather than in orbit around another planet would be phased 6 months off of Earth at 1 AU. This would let us continuously observe the "sun side" of space.

I don’t see this as a this or that calculation. I see this as a civilization-level infrastructure project /imperative/. We should have some basic support infrastructure built up around our solar system. So many things would be easier and new avenues opened.

And better rocket come 'space ship' preparedness. You can only learn so much about things from millions of miles away regardless of your resolution. It's a very serious problem that our space program has severely regressed. In 1969 we put men on the moon and brought them back home safely. In 2019, we struggle to send a man on a flyby around the moon!

It's frustrating because we already have the technology to be able to achieve basic intercepts here, even if they were at high velocity. The only thing in the way is a dilapidated space program.

Manned exploration may have reached a zenith in 1969, but science did not. In 1969, the field of planetary science did not really yet exist. Since then, we have done flybys of every planet, intercepted comets and asteroids, put orbiters around many of them, landed probes on more, and even had robots driving around! A ton of science has happened since 1969.

We also learn far more from robot/probe missions per million dollars spent than manned missions. The Mars rovers have explored for years on end (albeit slowly) while a manned mission to Mars and back may only be able to stay for a few days. I personally would love to see us walk on the Moon and Mars in my lifetime as I was not around in 1969, but the science can be performed just as well if not better with modern robotics without even needing to bring them back.

This is a particularly good example of the problem.

NASA provides regular updates from Curiosity here. [1] What you might find there is that problems are never ending and that progress is very very slow. As an example one of the primary missions of the Curiosity rover was to try to drill into the surface of objects on the planet to start getting some basic idea of what was going on. The problem is that after superficially activating the drill 15 times, it broke. The drill feed mechanism became disabled. The most likely culprit is some dust or other particle caused a critical brake to get stuck. This is a 10 minutes fix for a human on site. For the rover? Countless minds at NASA spent years working out a solution and came up with a solution that is not really sustainable and still leaves major issues with sample collection. That solution, limited though it may be, is as much a testament to the capability of NASA's engineers as it is to the major limitations of probes and rovers. The Planetary Society had a really nice write up on this here [2].

Opportunity recently died after more than 15 years on Mars. An absolutely remarkable achievement for a rover with a planned mission length of 90 days! However, even then it's death may be premature. One of the most likely culprits for its demise is that after a substantial dust storm, which it went into hibernate during, its solar panels were left covered with dust. A Martian janitor with a broom could fix in about 10 seconds, but for a rover - it's time to enter the long sleep. Another side of the story is that during its long life, Opportunity was only able to travel 28 miles, a bit less than 2 miles a year. You end up getting a very limited view of what's going on. Curiosity, for comparison, has managed 12.5 miles of travel in its 6.5 years since landing.


Finally there is one last major point to be made. We don't know the cost of manned missions. We can speculate on the cost of sending the first man, but I mean once we actually get into the 'normal' phase of putting men on other planets much as we do to e.g. the ISS today. We currently spend about $70 million per person to send them up, and that's a greatly inflated price as we rely on foreign suppliers. But even at that price, sending a man into orbit on a station intercept for $70 million is something that at one time would have been unthinkable.

We will likely see that price drop the single digit millions of dollars, at least in real cost, before the end of this decade. And getting to orbit in space is 90% of the battle. There's an old quote that once you get into orbit you're halfway to anywhere. And that's pretty much true. There will be a serious up front cost for setting up habitation systems but once these are established, I think there's a very strong argument to be made that humans will quickly become cheaper than rovers.

And finally this all completely ignores the human aspect. Putting a man on the moon shaped an entire generation of people with hope, optimism, and a sharp increase in the drive towards scientific pursuits. In a world of needless division, petty diversion, and increasing pessimism towards pretty much everything - you can not overstate how monumental an effect there will be to once again start putting people on other planets.

[1] - https://mars.nasa.gov/msl/mission/mars-rover-curiosity-missi...

[2] - http://www.planetary.org/blogs/emily-lakdawalla/2017/0906-cu...

I would not disagree, though the Soviet Union had already put a probe within the atmosphere of Venus in 1967. In 1970 they landed a probe on its surface!! They were called the Venera [1] probes. They also returned audio and picture from the surface of Venus. Absolutely remarkable if you're never heard it before. This [2] is the sound of the probe coming down through Venus' atmosphere, its landing, the lens cap (for the camera) popping off, the deploying of the drill, and then the drilling of course. In my opinion that remains arguably the most remarkable achievement in planetary science in our solar system. Although it must be said that that audio came much later than the earlier probes. "Much later" being about 40 years ago.

I think the recent discovery/confirmation that our moon has substantial reserves of water ice emphasizes the difficulties with technology outside of manned exploration. There's a lot of information you can obtain from probes and other forms of remote observation, but it tends to be extremely specialized and very limited. This is not something we should be discovering 40 years after landing on it -- water was confirmed in 2009.

[1] - https://en.wikipedia.org/wiki/Venera

[2] - https://www.youtube.com/watch?v=8jZDW53U8qQ

Solar Defense Force!

So, an interstellar dust bunny.

I wonder if it will find a resting place in some dark corner of the universe, maybe behind a black hole somewhere just out of our sight clinging tenuously to the outstretched arm of some far-off spiral galaxy and resisting every effort to slurp it back into the vacuum.

"Interstellar dust bunny" is a fantastic phrase.

Your comment made me smile.

Thanks. It doesn't add much to the discussion but I thought at the time that it might be a reasonable analogy based on the author's speculations. Of course we may also have just missed the opportunity to save the Who's. Sadly though, they couldn't all yell loudly enough for us to hear them over here on our rocky speck.

Can we please name the space probe we'll launch to explore it "Dyson"? After Freeman Dyson, of course.

Not that I get my science from SyFy but this particular hypothesis of a ice/dust composite doesn't survive the 'thermal / tidal' test. Which is that an object of that density would deform due to the tidal forces imparted by the Sun as it changed direction. I've yet to see a paper that suggests its profile changed at all before, during, or after the solar system transit.

We didn't detect it until it was leaving. So we have no data to compare to in order to even begin to speculate if it changed shape at its periapsis.

In Oumuamua defense, it hasn't seen this much of Sun to be impressed or inflicted by its thermal power. 25. kilometers. per. second. It went in and out before Sun could do its damage.

However, the idea of a porous surface like a snowflake or sponge or something doesn't add up because of exact speed it travels. Even if this is just ice/dust composite, with that kind of speed, it would be disintegrated by having its surface polished with cosmic energy long before it could reach 25km/s.

I hope we won't see another one. This one was so close to Earth it wasn't funny. And traveled so quick we wouldn't have time to call all family members to tell them we love them. Its nothing like meteor; even big one would just drop flat on earth, raise all dust for next 30,000 years, throw us back into stone age or close to extinction and some form of human life looking nothing like we do today would argue 250,000 years from now what caused the first human near-extinction. No. You're talking about razor-sharp thin and lightweight object traveling with insane speed. Upon impact, it would either penetrate Earth surface exploding inside the core, like any hollow bullet does, or it would cut Earth in half like a high power laser and deform itself on way out. Either way this wouldn't be your near extinction experience. This would be like all of sudden Earth spliced in half and both parts going away, while you are either being drown with oceans hundreds feet of water tall due to lack of gravity, or crushed by weight of same ocean who happened to froze in the upper atmosphere, caught some gravity and smashed on the top of you. I don't want to even think about super hot lava thrown everywhere without gravity it would be like spraying venom from a giant snake.

I have no idea how something like that would look like when Earth split in two, and no movies of that kind of extinction has ever been done. But something tells me it would be far from an easy death and I would rather carry on suicide pill in my tooth like they did during WW2, rather than witness such literal Hell on Earth.

> In Oumuamua defense, it hasn't seen this much of Sun to be impressed or inflicted by its thermal power. 25. kilometers. per. second. It went in and out before Sun could do its damage.

…it was (and still will be) in the solar system for quite a while. The Solar System is big.

> it would be disintegrated by having its surface polished with cosmic energy long before it could reach 25km/s

…no? Relative to cosmic energy, it might as well be at rest.

> Upon impact, it would either penetrate Earth surface exploding inside the core, like any hollow bullet does, or it would cut Earth in half like a high power laser and deform itself on way out.

I suggest you read up on high velocity impacts: https://en.wikipedia.org/wiki/Impact_depth

I read it. It doesn't make a difference that majority of meteors burn in atmosphere and barely hit Earth surface. Oumuamua may have traveled through earth atmosphere and hit Earth undamaged. The difference is obviously like day and night.

> It doesn't make a difference that majority of meteors burn in atmosphere and barely hit Earth surface. Oumuamua may have traveled through earth atmosphere and hit Earth undamaged. The difference is obviously like day and night.


Contains some tables with actual numbers (based on a 17km/s impact), including how big of a airburst a non-impacting object makes and how much of a crater an impacting object makes.

You aren't splitting the Earth with something the size we are talking about with any of the estimates of it's size, even at 25km/s, which basically a little over doubles impact energy, the same as a 29% increase in diameter does.

This does not meaningfully change the result; as far as I'm aware you can just change the A/B ratio to account for the density of the atmosphere and treat it as any another layer. Even accounting for this, speed does not have a meaningful effect.

Leaving aside everything else...

> and some form of human life looking nothing like we do today would argue 250,000 years from now what caused the first human near-extinction.

Well, they might, but they would probably be talking about the Toba supervolcano 320,000 years in their past.

> You're talking about razor-sharp thin and lightweight object traveling with insane speed.

Shape is not all that important (though I think that a long tumbling object is more likely to break up break up at altitude), the speed is high, sure, but not so far out of line with typical meteors as to make that big of a difference, and the low density offsets the effects of speed (also makes it more likely to break up at altitude). And the later estimates of it's size are not enormous. It would perhaps be a bag meteor impact, but quite possibly not the worst to hit during the existence of humans.

> Upon impact, it would either penetrate Earth surface exploding inside the core, like any hollow bullet does, or it would cut Earth in half like a high power laser and deform itself on way out.

No, it would do neither of those things: it would either explode in the atmosphere or make a crater on the surface.

You seem to think it is a superstrong heat-resistant stabilized penetrator dart coming point first, rather than a tumbling body of (probably) rock and ice.

This is all predicated on 25 km/s being very fast, which in this case it really isn't. Man made objects like the ISS travel at 7 km/s, so these are relatively achievable speeds, even for humanity.

We can look at meteor impacts, too. The first source I found on the topic said meteors commonly impact with 11- 72 km/s. [1] This happens every day with small objects and we're fine. With bigger objects you'll get extinction events and features like the Chicxulub crater, but no way you'd see anything "penetrate Earth surface ... like any hollow bullet does, or ... cut Earth in half like a high power laser."

The speed of light is 300,000 km/s, more than 10,000 times faster than Oumuamua. An object at 0.1c or even 0.01c would be very threatening, but those are still orders of magnitude faster than Oumuamua.

In short - 25 km/s isn't that fast, don't worry about it. There are plenty of asteroids that could hit us faster than that that we also don't always see!

[1] - https://www.amsmeteors.org/meteor-showers/meteor-faq/

> This is all predicated on 25 km/s being very fast, which in this case it really isn't. Man made objects like the ISS travel at 7 km/s, so these are relatively achievable speeds, even for humanity.

Quite a few spacecraft have reached this speed. Off the top of my head, I think Juno reached something like 70 km/s when approaching Jupiter.

That's pretty meaningless though, the speed of interest is the heliocentric velocity. Juno was accelerating toward the largest planet in the solar system and orbiting it, not doing a gravitational slingshot.

The current record is Voyager 1, which got its speed from a flyby tour of the outer solar system. It is going 17 km/s.


We still don't know what Oumuamua is made off of. I think we can agree anyone would rather be hurt by a baseball flying 10km/hour, than being hurt by a knife that travels 1km/h.

> We still don't know what Oumuamua is made off of.

The fact that it is tumbling and not coming on like a dart along it's long axis means it pretty much doesn't matter what it's made of, aside from it's total mass, it's not going to do some kind of radical penetration or anything else that unusual of it were to hit the Earth.

(Even if it was a stabilized penetrator dart of some kind, AFAIK, that doesn't really change much about surface impact unless you make radically implausible assumptions of composition, but I think it might effect the probability of it making a ground impact rather than an airburst.)

Your intuition of how impacts work falls apart at high speeds.

> cosmic energy

Huh? What's "cosmic energy? Do you mean cosmic rays? Those are actually atoms or electrons moving at an exceedingly high speed. Matter, albeit highly energized matter, but not energy itself.

If that is what you meant, the fact that this object was moving at 25 k/s is a fart in a whirlwind compared to the overall velocity of those atoms/electrons. It would have a virtually identical effect to something moving at 25 kph. Not to mention those particles are too small to really "disintegrate" anything. At best, they would knock a few particles off some of the atoms that comprise the object, perhaps changing a few into another element/isotope. There just isn't enough mass there to do any damage on a macro scale.

this is all nonsense - why are you proclaiming this fantasy as if you were some authority?

The whole situation of us encountering Oumuamua and being unable to gather much information about it reminds me of one of the Lem's short stories about Pilot Pirx in which he encounters an unique alien object and is also struggling with recording data about it.

Here's a quote that works on imagination:

There are times when the human eye can behave like a camera lens, when a momentarily but brilliantly cast image can be not merely recalled but meticulously reconstructed as vividly as if viewed in the present. Minutes later, I could still visualize the surface of that colossus in the flare’s afterglow, its kilometers-long sides not smooth but pocked, almost lunar in texture; the way the light had spilled over its corrugated rills, bumps, and craterlike cavities—scars of its interminable wandering, dark and dead as it had entered the nebulae, from which it had emerged centuries later, dust-eaten and ravaged by the myriad bombardments of cosmic erosion. I can’t explain my certainty, but I was sure that it sheltered no living soul, that it was a billion-year-old carcass, no more alive than the civilization that gave birth to it.

This story (Pirx's Tale) is available on Google Books: https://books.google.com/books?id=n16z06cm1P0C&lpg=PT11&dq=%...

I'm curious about whether an object with a density this low could survive the gravity gradient it experienced during the solar flyby.

As am I. The paper dedicates one sentence to that question:

"... another aspect that needs to be studied is whether its extremely low density could be maintained while in the parent system, during its long interstellar journey, and when entering the solar system."

Without analyzing the structural integrity of such a fluff ball it's tough to give any more or less merit to this concept than the others.

Just how close did it get to the Sun? My memory is that it got about as close as Mercury to the sun. It should have warmed up a fair bit, but the gravity gradients shouldn't be ripping it apart.

Unless it's very large why would there by much of a gravity gradient?

It never came all that close to the sun, so the gradient on different parts of it wouldn't be that extreme.

There wouldn't be a large gradient. But a big ball o' fluff presumably has essentially no internal cohesion; it's sort of like a liquid in that way. So even very small gradient forces could be enough to disperse it.

So lets run the numbers:

At Perihelion it was 38198320 km from the sun = an acceleration of 0.090962666582226 m/s^2

It's 1km long so on the other end the acceleration is 0.090962661819574 m/s^2

Subtract: .000000004762652 m/s^2 which is such a small amount I'm not sure how to put it into context.

Multiply by 1 metric ton = 1/5 weight-force of a single snowflake on earth.

Which means each metric ton of material needs to handle just that much force trying to separate it.

i.e. it won't be ripped apart in the slightest. Over centuries it might elongate a bit (and it's already elongated).

Interesting. Thanks for the analysis.

So, continuing this general line of thought: what's the largest tidal force it would have experienced? Differential solar pressure? Would it have encountered anything on its journey that should have dispersed it?

> what's the largest tidal force it would have experienced?

I have no idea of its past obviously, but near us this would be it, at closest approach to the sun the tidal force is greatest.

> Differential solar pressure?

Solar pressure is very low, it just applies that force for a very long time. It would act to compress it (flatten it), slightly.

But I don't know what orientation it had when approaching the sun. It could have been tumbling and randomized any force.

> Would it have encountered anything on its journey that should have dispersed it?

Vaporization from heating is the only thing energetic enough that I can think of.

But maybe other people can think of other things.

I'm curious about the force/event before it got to our solar system. If the original object was protoplanetary, what kind of forces would be required to knock an object of this current size out of a stars gravitational hold, and into interstellar space? I'm guessing we can assume that due to the current size of this object, it would have had to have been part of a much larger event.

Possibly it didn't? Since we saw it after solar perigee, perhaps it is in it's spread out state and it was more compact while approaching the sun.

and the stress and strain of rotating about its own axis, especially if the optical pressure is not perfectly central, it could speed up to high speeds.

I don't know that this theory is any "weirder" than an alien spacecraft, but it's certainly more plausible.

Plausible or less deniable?

I can't see how it's anywhere near as weird as an alien spacecraft. Interesting article though.

Meteorites form in distinctive nickel-iron crystal patterns (Widmanstatten). I wonder if they would form ‘snowflake’ patterns in conditions of large negative temperature and pressure gradient following a supernova shockwave.

It frustrates me to no end that there was a possibility (however small) that we could have witnessed an alien artifact passing by our planet and we missed it.

The idea it is a fractal structure is not weirder than the idea it is possibly an alien probe sent over the course of hundreds of thousands of years to pass by our Goldilocks-zoned planet for observation.

Does anyone know more about the initiatives by Yuri Milner with respect to this? I heard something like he is helping fund satellites that could specifically be better at looking at 'Oumuamua than our current means?

We can't look at 'Oumuamua any more, with any kind of spacecraft. It's headed out of the solar system. There's absolutely no way we could possibly put together a mission and build a craft and launch it and have it catch up with 'Oumuamua at this point. If we had something ready to launch now, it might be possible to catch up with it, but it would be years before we could have a mission ready to go, and we don't have the propulsion technology necessary to catch up with it after that much time.

This should have been a big wake-up call to have pre-made probe craft ready to launch to investigate anything odd that entered the solar system. But expecting humanity to be that fore-sighted is pure folly.

Oumuamua is traveling at 26kps. For comparison the Voyager probes are traveling at around 17kps.

Even if we had a probe ready today it's already too far and moving too fast to overtake. Even if we had a probe ready when we first detected the object it would have been difficult to intercept with today's technology. It would have to be something like a Falcon Heavy already in orbit and ready to burn at a moment's notice with a tiny probe at the top for gathering the data.

>Even if we had a probe ready when we first detected the object it would have been difficult to intercept with today's technology.

That's the other side of the problem: we didn't detect it until far too late. We should be able to detect objects of this size much, much sooner than we currently do. We're not looking very hard for them, so usually we end up seeing them after they've already whizzed by. There have been way too many times in the last decade or so when we're informed, "hey, we just barely got missed by some big asteroid, and we didn't even see it until it already went by the Earth!" That's just pathetic.

So it follows we should have that, at all times. :-)

That payload is... a lot of teslas worth of cargo. It would need to be built in orbit. A project that size would definitely make a lot of jobs and require a major rebuilding of our space problem. So many downsides.

One of the Breakthrough Starshot probes could do a flyby and take some pictures.

Edit: although, that would involve pointing a 100 gigawatt laser directly at Oumaouma, which might disturb it.

>that would involve pointing a 100 gigawatt laser directly at Oumaouma, which might disturb it

Maybe that would cause it to turn around and come back.

“Oh so you think that’s funny earthlings? Just discovered laser pointers have we? Well guess what!”

If we build prototypes of the Breakthrough project probes in say 5 years there's a real possibility that we can catch it in a decade or two.

We can foresee our lack of foresight- so its not hopeless.

I'm sure there were some people who could foresee the lack of foresight before the collapse of Rome too. It didn't help them.

Weird still is "Oumuamua's velocity (being) within 5 km/s of the median Galactic velocity of the stars in the solar neighborhood" (https://arxiv.org/abs/1710.11364)

That means the system it originated from if a natural object would need to be coincidentally that close to our median local

What are the hypothetical requirements of a craft/probe which could be sent to chase after this object? Could we build something very small but extremely fast perform a fly-by? It kills me to think we've been visited by a mystery I'll never get the answer to in my lifetime.

Yeah, it's slow enough that we could catch up to it. One of the biggest mysteries about it is why it was moving so slowly. Voyager left the solar system at 17,000 m/s. ‘Oumuamua accelerated to a top speed over 87,000 m/s as it was moving toward the sun, but it's slowing down now, and will eventually slow to 26,000 m/s. It will pass the orbit or Uranus early next year.

Note that the Voyager probes are only moving that fast because they got orbital assists. It would take a very big rocket already in orbit to attempt an intercept.

Oh it would be crazy expensive. But we have the tech. (Wait, do we have tech for in-orbit refueling? Anyway we're developing that for Mars missions already so we'll have it soon.)

We resupply the international space station, so even if we couldn't carry great loads of fuel up at a time, orbital refueling is clearly within the realm of the possible.

More interesting would be if we could beam up energy to refuel, but for that we'd probably need yet-to-be-invented drives which use loads of energy per amount of matter to accelerate it further. Kind of like a particle collider but for propulsion.

My bet would be an RTG powering a dozen electric thrusters packing a lot of propellant and a relatively small probe.

Still, it'd mean reaching Uranus' orbit in about a year. That's a lot to ask for.

If we stop and think of it, it'd be a lot of energy to be able to reach Uranus' orbit by next year.

Big rocket or very small probe.

This was answered non-facetiously after discovery: https://arxiv.org/abs/1902.04935

The main proponent of the Oumuamua is an extra-solar object is Harvard astronomer Avi Loeb and there's a great interview with him where he discusses his reasons for his conclusions in a very accessible manner:


Isn't extra acceleration what dark energy is supposed to explain? (Maybe "explain" is the wrong word. :-) I haven't seen anyone say this (probably for some good reason), but maybe 'Oumuamua's acceleration is from the same source? I'm curious what more knowledgeable people have to say about that.

The "acceleration" dark energy is supposed to explain is with regards to the expansion of the universe, which would have very little effect on anything on scales this small.

Dark energy is an expansion of spacetime itself that is uniformly present throughout the entire universe. If it were responsible for ʻOumuamua's acceleration it would have been followed by our entire solar system being shredded down to subatomic particles shortly afterwards - see https://en.wikipedia.org/wiki/Big_Rip

The argument "it's too slow to be a spaceship" makes a lot of unstated economic assumptions. Yes, a bigger sail would be faster. But if you wanted to send a lot of ships to various places, and you were the kind of civilization that makes very long-term investments, smaller probes could be optimal.

I feel like the headline writer tried to spice it up a bit and went too far. Seems much less weird than alien artifact to me.

I mean I'd click on an "Another Oumauamua Theory" headline, but I guess that's not what kids are clicking on these days.

I am just a layman, but it sounds like an object of this structure would be relatively fragile. Would it be able to survive the type of event that would be needed to launch it into interstellar space at the speed it is traveling?

Interestingly enough, it is traveling very slowly with regards to the average motion of all the local stars. You could look at it as just sitting there in the void, slowly drifting until our system zoomed on by and flung it off in a new direction in its wake.

(see point 2 here: https://blogs.scientificamerican.com/observations/6-strange-... and the more detailed discussion of this it links to)

If the object is a loose collection of dust it might very well be the result of something that didn't survive whatever event created it.

What a tragedy that would be to catch it, find that it was created by some extrasolar intelligence, but it's been destroyed.

That sort of event would typically be getting a slingshot[1] boost from a large passing mass. Those wouldn't come anywhere near breaking a normal asteroid but who knows with a fluffy one.


If it does get a push from the sun's light it could reach escape velocity from its home sun in a few million rotations around it...maybe?

Normal solar pressure doesn't tend to speed up an object in its orbit since it comes in perpendicular to the direction of motion. However if the object is rotating it can absorb light on its inner side the re-emit it on its trailing side as that side cools down. This can alter orbits substantially over millions of years.

Makes me think of Rendezvous at Rama[1].

[1] https://en.wikipedia.org/wiki/Rendezvous_with_Rama

I came here for exactly this comment. Props.

OK this is great.

I never gave a moment's credence to the idea that it was an alien spaceship but I really enjoyed reading the thoughtful and well reasoned arguments for and against the idea. For me the space of thought that these arguments created was an interesting experience that gave me an interesting perspective.

So saying "hey no, it's not spaceship... it's weirder than that" (and then arguing that point) is fantastic.

Coming from a planet that launches a lot of alien spaceships, is it that implausible that it could be (or could have been) an alien spaceship?

This. I don't understand why articles like this are so quick to dismiss the chance that it was an alien probe or ship. I feel like it's just to get clicks and make the hypothesis they present seem more plausible.

I totally agree that there is a good chance that it wasn't alien, and we want to identify what it could be if it wasn't, but why dismiss it? Most scientist already believe we are not alone, even though it is unlikely we are close to any other intelligent life. The chance that it was alien should be explored as well, and I know their are scientist who believe it is alien.

I guess after all these years Carl Sagan's observation still makes a lot of sense to me. Extraordinary claims demand extraordinary evidence. So far I've only seen ordinary and interesting evidence.

Huh, literally never thought of it that way. We put a ton of trash into space - someone is probably, at some point in the future, going to say "what the fuck is that" when Voyager goes flashing by!

But ... i thought amazon is going to produce the new series of the Expanse. Or is SYFY going to fork the story with a 'deuteromolecule' ?

I don't find the author's reasoning in the related article[1] that its not a solar sail very convincing. I am not an astrophysicist, but, the author plainly admits that the measurements are within expected bounds of a solar sail.

Instead, the argument is surrounding the psychology of the hypothetical creators of said solar sail, or plausible ways we missed some data. Since we are just speculating at this point, who am I to say?

But to answer some specific criticisms:

- Perhaps the brightness/darkness cycles were the sail turning on and off as a mechanism to control velocity

- Perhaps the 25km/s speed being a crawl for interstellar travel was because it was meant to slow down while passing through our solar system. Either so we might notice it, or so it can collect data while here a bit better.

I am having a hard time understanding how rare an event this space-foam-fractal theory is predicting, but if it's extremely rare a solar sail seems a completely reasonable hypothesis still.

1. https://www.syfy.com/syfywire/is-oumuamua-an-interstellar-sp...

It's far more likely to be a poorly understood natural phenomenon that we will later make sense of. It would be the millionth example of that, compared with the _first ever_ example of life not from Earth (capable of building interstellar tech!). We need very, very strong evidence to overcome this hurdle.

We know for a fact that the universe is filled with strange and interesting dynamics (not involving alien life forms) that we don't always understand at first. We don't yet know where else life may exist in the universe, if at all.

Alien life would be a natural phenomenon, ultimately; on a deep analysis any phenomenon is natural.

We make a differentiation between phenomenon wrought from cognition, but that cognition is - at least in part - a natural phenomenon too.

Is this distinction founded in dualist philosophies(mind-body and/or material-spirit)? Does it make sense to make for monistic materialists?

We might not ultimately recognise alien construction as coming from some intellect, plenty of creatures create structures on Earth (as do physical processes) with high complexity that are not considered to result from cognition.

We don't need to play this pointless semantics game every time the word "natural" is used.

There is an inarguable qualitative difference between the types of objects and materials that can be produced from undirected mechanical and chemical processes and those that can be produced through the work of intelligent, living beings.

In picking this semantic nit, you've completely ignored the actual point made by the GP: we've seen countless examples of new and strange phenomena that end up being described by undirected physical and chemical processes. We have yet to find anything that requires intelligent life to explain, like an interstellar skyscraper would.

It was more a "oh, this is a cool idea [to me, at this instant]".

Particularly I like that it sent me in to thinking of an alien life form that could, maybe like ants, construct a large scale "artefact" - like a solar sail - that we would recognise as being wrought by intelligent life but would actually be the result of some sub-intelligent life form.

I like Fritjof Capra's rendition of Gaia hypothesis (as an idea), but had never really extended the idea of self-ordering, or complex-ordering, to how we might interact with alien constructions.

>In picking this semantic nit, you've completely ignored ...//

Just my reaction to it.

I meant the term "natural" only as a short hand for anything that isn't alien technology. I do agree that even civilization and technology can be viewed as natural.

It's context-depednent. Unnatural doesn't need cognition-dependence, but merely higher complexity than usual -- an arthropod skeleton floating in space is unnatural, in the context of an asteroid, because asteroids are though of as "nartually" arising collisions of rocks, gravity, solar radiation, and the like, but not not the complex processes of animal life.

Uh, what? Plait makes the important point that the light curve is hard to explain without tumbling, and if the "sail" is tumbling the entire acceleration calculation presented in the paper is shit. Kind of a big deal.

Light curve is hard to explain without tumbling, and my suggestion is it could be explained by the solar sail changing it's reflectiveness purposefully.

At that level of detail you could just be chanting "god did it" over and over, it comes out to about the same explanatory power.

>Perhaps the 25km/s speed being a crawl for interstellar travel was because it was meant to slow down while passing through our solar system…

We know how much it’s acceleration as affected by solar pressure because we measured it, and it was very low, similar in scale to that caused by off-gassing of comments. Tiny both by interstellar travel standards, and in terms of its actual velocity.

The way you use ‘solar’ sails for interstellar travel is to propel them using a fixed laser at their point of origin, and possibly another laser to slow them down at their destination. Actual light pressure from a star is way too low to give them useful velocity for interstellar journeys.

> The way you use ‘solar’ sails for interstellar travel is to propel them using a fixed laser at their point of origin, and possibly another laser to slow them down at their destination.

What if someone sent out a bunch of these things to wander the galaxy until they encounter a civilization cable of detecting it and slowing it down? Perhaps it was even sent purposefully after signs of life were detected on earth. That seems like a feasible communication method with today's tech, the galactic equivalent of a station wagon full of hard drives.

I don't find the author's reasoning in the related article[1] that its not a solar sail very convincing

Imagine a pre-industrial civilization that finds a ship's sail that was lost at sea washing up on its shore.

I don't believe the solar sail hypothesis, but I like the fantasy it provokes in my mind.

It's the "I don't want to say aliens because no one will listen to you if you say aliens" conundrum, which does a disservice to the science by pooh-poohing any intelligence-spawned possibilities while wildly speculating on naturally-caused possibilities.

The reality is this is an extremely alien object, no matter if it was formed by intelligent beings or spun off from a star. Maybe this is a solar sail or maybe it is a giant snowflake.

And, contrary to the author's hand-waving, there is nothing that says an enormous, impossibly thin solar sail can't be formed by randomly bashing an infinity of rocks together over a near-infinity of time - after all, LIFE ITSELF comes from just such an action, so pretty much anything is in play if that is the standard!

> here is nothing that says an enormous, impossibly thin solar sail can't be formed by randomly bashing an infinity of rocks together over a near-infinity of time

Nobody is saying that it is impossible, the author is simply saying that it seems unlikely that is the origin. It's Occam's razor, whereby the simplest solution seems to not be alien intelligence or serendipitous solar sails, but rather something that we have seen appear naturally (fractals).

> after all, LIFE ITSELF comes from just such an action, so pretty much anything is in play if that is the standard!

That's how an instance of life came about. A very simple, most likely extremely short-lived, not at all efficient form of life. The advancement to Eukaryotes took ~2 billion years from there, and multicellular life took about another billion years. These happened not by random bashing, but selection pressures.

While a solar sail could happen completely randomly, 'life itself' isn't really a good comparison, since that's not really how it happened. At least not any form of life that is really recognizable as life.

everything is randomly bashing things together; every human is randomly bashing things together. we are similar, but have billions and billions of tiny differences that make up the specific things about us.

everything has selection pressures too: just like life forms exist and thrive in different environments, dust behaves differently at different temperatures and gravities.

life as an event, and specific things that happen thereafter are no less “random” than specific chunks of rock/dust in specific configurations

> life as an event, and specific things that happen thereafter are no less “random” than specific chunks of rock/dust in specific configurations

No. Incremental changes over millions of generations in response to environmental pressures are not "random".

This sliver of dusty ice may have formed in a one-in-a-million random chance, but there's no process that selects for this.

Life is a pretty rare occurrence, as far as we're aware. So I think I can forgive the author for not being sold on the "aliens" conclusion just yet–it's probably a good idea to look for alternative conclusions that might be more likely first.

>Life is a pretty rare occurrence, as far as we're aware.

I don't know where you get this from...just because we have not observed it directly? Based on everything we have learned so far about life here on Earth, it seems entirely reasonable to think that life would be very common throughout the universe.

If our nearby system (star, planets, and all in between) is to serve as an observation parameter to determine the probability of the occurrence of life, life in not very common.

Yes, it is true that you have plenty of life here, but you have it only on a very (and I mean very) thin layer on this floating rock. It seems a lot on the surface (pun intended), but it actually isn't.

It's reasonable to think life is very common. It's also reasonable to think that life might be very rare in the universe, or that we could be alone. Science, so far, hasn't really narrowed down orders of magnitude on some of the potential Great Filters. So it doesn't have that much to say about this question, yet.

(And, if you are willing to invoke some form of the anthropic principle, maybe a universe that can support even one instance of intelligent life is itself incredibly rare in some landscape?)

Are you conflating "common" with "possible"? Study of exonoplanets finds earth-like ones relatively rare, and being Earth-like is still a far cry from.

There may be a large number of life-hposting planets in the Universe, while still fitting current data that they are extremely rare as a fraction of, for example, the region of space reachable by humans, by floating space rocks, or perhaps even the Earth's light-cone.

Something being reasonable to think (while it's also reasonable to think the opposite, no less) and being aware that something is a fact are two very different things.

It's the "I don't want to say aliens because no one will listen to you if you say aliens" conundrum, which does a disservice to the science by pooh-poohing any intelligence-spawned possibilities while wildly speculating on naturally-caused possibilities.

See also: Religion.

Please keep generic ideological tangents, and particularly religious flamewar, off HN. It's all predictable and therefore off topic here.


I just dont understand how a solar sail would function outside the reach of our solar system... assume you have a sail that is equidistant between any stars - but some are bigger than others - and assum that the direction youd like to head, is backed by the weakest or smallest star. How will you get the energy youd be hoping for from these stars? How to orient? Or how to head the direction you want if there arent enough stars behind you to provide the thrust you want/need?

You wouldn't. Solar sails need a handy nearby star, or a less handy giant laser.

You won't get much acceleration from distant and/or dim stars. (Without a giant laser.)

Interestingly, Oumuamua is at the high end of in-system solar sail velocities, and extremely slow for powered inter-system travel.

The velocity profile matches a natural solar sail drifting rather randomly through space or - if you're going to go with "aliens", for the lulz - a probe deployed on the outskirts of the solar system with a low velocity.

It doesn't match the profile of a powered inter-system solar sail.

On a real sailboat, you can go in lots of directions, not just the one the wind is pointing at. You can even go somewhat against the wind.

In a lightsail, if I understand this diagram correctly[1], the imparted momentum is proportional to the sum of the angle of incidence and the angle of reflection. (Which, come to think of it, is exactly how billiards works.) Therefore the sail travels perpendicular to its orientation, no matter where the incoming light came from (as long as it came from that side -- I'm guessing the other side is not reflective).


One of the embedded assumptions I seem to see in discussions about this object is that objects like it (from outside the solar system) are rare.

Is this truly the case, or is it just hard to monitor the paths of the multitude of objects passing by earth?

It is rare because other systems that form these objects are VERY far away (trillions of KMs). Imagine trying to slide a hockey puck from one end of a hockey rink to the other, but have it pass through a small (~1M) circle at the far end from you. If you took 1000 attempts even randomly, you'd probably hit the circle by accident at some point. Now someone else is also shooting at the circle, but they are 50,000KM away. Suffice to say no matter how many attempts that person takes, it will be significantly more rare to see their puck cross through the circle than yours.

> It seems far more likely that objects like 'Oumuamua are relatively rare, and that means it likely came from someplace close by (if it came from farther away, the odds are even lower we'd ever see one).

Rare enough to be a space ship?

Given that we don't know if interstellar spaceships exist I'd say calling them "rare" is a misnomer.

So... in the time in the US where both sides are yelling at each other about being special snowflakes, we have the largest snowflake ever observed just floating by. What a weird coincidence and what a time to be alive!

Ok, I know nothing about space, but looking at this video, it makes me realise something.

Would have it been possible for thie Oumuamua to directly crash into the sun and just... end our solar system? Just like that?

I guess it would be possible that it crashed into the sun, if it had the right trajectory, but it wouldn't have had any effect; the thing is 50 - 130 meters, while the sun is nearly 900.000 KILOmeters in diameter. It would likely have burned up before even reaching the surface of the sun. Even if it was idk, a huge nuclear weapon that detonated before melting, it wouldn't matter because the sun already is a huge fusion nuke. It does coronal mass ejections regularly that, according to a pop sci article I just read, already has more energy than 20 million nuclear weapons - anything that would end the sun would have to be several orders of magnitude stronger.

As Douglas Adams wrote:

> Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space.

An image which accurately shows both the Sun and other objects to size or at the correct distance doesn't give you an accurate measure of scale. Movies which show space sequences and ships flying from one planet to the other don't help, either.

An image of the Solar System which shows both the Earth and Sun in the same image is either distorting the size of the Earth, distorting the distance between the two, or both. Here's one tool that may help...get your scroll wheel warmed up, though:


Or maybe you could visit one of the many to-scale solar system models, and take a walk from a 1-meter-diameter sun 100 meters away to a 1-cm-diameter Earth and continue walking for 30 minutes to the outer planets.

At 1 meter scale for the Sun, Oumuamua is 0.1 microns, or 1/10th the size of a bacteria. If we multiply everything by 10,000 until the object is a 1mm grain of rice, now the Sun is 10 km in diameter, the size of a small city. Nothing the grain of rice could do, no matter how fast it moves or what it's made of, would harm the city-sized ball of fire. Granted, a 130 meter high-density (not Oumuamua) high-velocity asteroid impacting the Earth (100 meter diameter in our scaled-up rice-grain model) would cause significant distress for the very environmentally sensitive organisms clinging in a thin film to its surface (namely, humans), especially near the impact site.

Why would a tiny object crashing into a star "end" the solar system?

> Assuming a size for 'Oumuamua of 50 – 130 meters, what they get is a very low density: About 0.00005 grams per cc.

Do we have example of naturally ocurring space object with such low density?

Half-close? Quarter-close?

Even an aerogel is .0.2g/cc. That sounds implausible to me but so does the solar sail hypothesis. And really we don't have much information about what an interstellar object would be like.

I agree that the proposed density is too low. Anyway, the aerogels are deigned to support their own weight on Earths, wind currents and some moron poking them. The magical aerogel of this object may have lower requirements.

> Do we have example of naturally ocurring space object with such low density?

Depends what you mean by "object. Assuming the mass is mostly protons, that corresponds to a density of ~3e19 particles per cc. In comparison, molecular clouds in the galaxy have regions which are have densities as low as 1e2 particles per cc. And the hot X-ray emitting gas in clusters can be less than 1 particle per cc. There are things which span the gap, including disks around stars.

By object he is probably talking about matter in a solid state which would exclude gas or plasma. Also given Oumuamua's rotation rate the pieces of matter that makes up the object probably has to have some bounds with each other or it would fly apart.

This is ridiculous. It’s intergalactic debris, it could be anything.

I would prefer to see a list of things it could be vs. the hubristic response of leading scientists.

It’s a great example of something unknown.

> I would prefer to see a list of things it could be vs. the hubristic response of leading scientists

But isn't it through what leading scientists deem it could be that we get such a list that you want?

Otherwise, it could be:

- an icy fractal aggregate

- a rock

- a teapot

- a bunny rabbit

- a full-scale replica of the Titanic visible only to bees

- a fortnight's holiday in Benidorm

what I don't understand is this: if the kinetic energy is higher than the potential energy, what is the probability that it would pass the sun so closely? for bound objects this is not so surprising.

either these objects are way more frequent than we think and the reason it passed the sun so closely was simply that these would be the first to be observed, or it almost seems aimed to pass the sun closely?

We do think they're very 'frequent':

"Astronomers estimate that several interstellar objects of extrasolar origin (like ‘Oumuamua) pass inside the orbit of Earth each year, and that 10,000 are passing inside the orbit of Neptune on any given day."


Is it technically correct to call 'Oumuamua an UFO? I mean, it is unidentified so it should apply, right?

Considering its trajectory is more or less ballistic, the F would stand for "Falling".

Disk Not Ejected Properly Eject "Oumuamua" before disconnecting or turning it off.

Fans of The Expanse have known what it is all along...

It's not fat, it's fluffy.


> [Oumuamua as a fractal] is a hypothesis worth investigating ...

tabloid journalists:


I guess the use of 'Bad Astronomy' tag is apt.

It's probably an alien probe disguised as a random rock. It's already transmitted the existence of Earth and its coordinate back to the homeworld. Soon a supernuke will be sent at 0.99C to nip humanity in the bud.

None of this rules out the idea that it is a vessel and or from a civilization

Its not mutually exclusive

Its just clever and now we have hypothesis about how it was done

Off topic, on the writing style: the personal casual style that sprinkles things with "I have to say, I love this." seems to have become incredibly common now in news sources. What's led to this? I always feel like it detracts from the story, and adds nothing unless they've AB tested it and it helps ad revenue?

This is a blog, right? Blogs have always been more informal.

Discourse and language in general has seem to become “dumbed” down in the past 50 years.

The most irritating headlines to me are "No. XXX is not YYY."

This was an amazing deduction.

I dont understand the key component of the article about the radiation from the sun giving it a boost. These scientists were able to make all these deductions about its shape and why from this, but what? How does radiation propel in any circumstance? Are we saying molecules change composition? Electrons moving to another state? What

> How does radiation propel in any circumstance?

It depends on the type of radiation, but two mechanisms jump to mind for me:

The first is direct action of photons, as in a Crookes radiometer. The idea is that the black and white sides of the vanes respond to different types of EM radiation differently. How it actually works is somewhat beyond me (and apparently contentious), but it does work: https://en.wikipedia.org/wiki/Crookes_radiometer

The second is is through boiling. If the side of the object facing the sun were composed of a material that boiled when exposed to sunlight, the boiling off of that material would provide thrust against the object in the same way a rocket provides thrust (by expelling gas).

Note that I am not a physicist, and am not proposing that either of these are the reason for the object's anomalous trajectory - just throwing out two ideas through which radiation could propel an object.

This article explains that aspect of it:


Seriously- its a snow-flake, as in something snow bally like Halley's Comet - that would emit vapours under light pressure? What is this, if you disprove your own thesis in the prelude of your article? Scientific slapstick?

Sounds like it might be a giant rock-dust flake. Maybe the whole thing is held together by vacuum welding?

If you imagine a dirty snowball, then sling it past a star so that all the ice melts and leaves, you might be left with something vacuum welded together, but very fluffy for its size. Perhaps the same time that it lost all its volatiles is also what ejected it from some system, a slingshot around some other star.

That wouldn't be terribly different from how Aerogels are made.

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