Suggests that the determinations of position and/or speed were incorrectly measured.

You can read the paper , which I linked a few post back. It doesn't appear that any errors of the sort mentioned were likely, given the degree of care taken. If you find any fault in their methodology, I'd like to learn of it.

The 'Flyby Effect', which affected several of our space probes rounding the Sun, was somewhere suggested as a possible source of the extra speed. I looked into this, but found that, it would be unlikely to account for more than a few hundred kilometers, in the length of time concerned.

100,000 kilometers, cosmically speaking, is not too much to be off. I haven't read the research myself, but as I understand it, they're still pouring over the data as best they can, and will probably be arguing and disagreeing over assertions for quite some time. Possibly forever.

However, scientifically speaking, it is better to suggest a natural conclusion (asteroid, comet) than to suggest an unnatural one without stronger evidence. Merely having an odd orbit and traveling faster than expected are not enough to claim it was an alien spacecraft. Extraordinary claims require extraordinary evidence.

Reviewing the articles from a few months ago about Oumuamua, one is struck with how firm was the asteroidal interpretation. Now that we have seen enough acceleration to put it 100,000 kilometers farther out in space than expected, there is this effort to fit it into the comet mold, even if it doesn't fit very well.

Alternately, some have suggested that it is an asteroid, but is being affected by the Yarkovsky Effect. This seems far too negligible to have moved an asteroid to anywhere near this extent, in a matter of months. I understand that it is typically measured in distances of one or a few kilometers per year.

One also wonders if it had a magnetic field which interacted with the solar magnetic field to produce some unexpected forces.

100,000 kilometers, cosmically speaking, is not too much to be off. I haven't read the research myself, but as I understand it, they're still pouring over the data as best they can, and will probably be arguing and disagreeing over assertions for quite some time. Possibly forever.

However, scientifically speaking, it is better to suggest a natural conclusion (asteroid, comet) than to suggest an unnatural one without stronger evidence. Merely having an odd orbit and traveling faster than expected are not enough to claim it was an alien spacecraft. Extraordinary claims require extraordinary evidence.

Besides the decidedly hyperbolic orbit of Oumuamua, and its poorly-explained acceleration, we have the extreme oddity that it may be as much as 10 times as long as it is wide. I'm not claiming that it is settled that Oumuamua is an interstellar space vehicle, of course, but these do seem an extraordinary set of facts about this object.

This fascinating possibility was entertained by both the SETI Institute and the Breakthrough Listen project , as evidenced by their repeated radio monitoring of Oumuamua, for any intelligent signals it might be emitting.

Reviewing the articles from a few months ago about Oumuamua, one is struck with how firm was the asteroidal interpretation. Now that we have seen enough acceleration to put it 100,000 kilometers farther out in space than expected, there is this effort to fit it into the comet mold, even if it doesn't fit very well.

Alternately, some have suggested that it is an asteroid, but is being affected by the Yarkovsky Effect. This seems far too negligible to have moved an asteroid to anywhere near this extent, in a matter of months. I understand that it is typically measured in distances of one or a few kilometers per year.

One also wonders if it had a magnetic field which interacted with the solar magnetic field to produce some unexpected forces.

The discussed letter to the journal Nature mentions that magnetic interaction of Oumuamua with the Sun was considered, but was found inadequate to explain the acceleration of the object. For details on this, please consult the letter, which I linked, a few posts back.

No matter what, it most likely isn't coming back to give us another chance at identifying it. IF it is a spaceship ain't it a hoot that we were totally ignored.

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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

If we assume, for the sake of discussion, that Oumuamua is a space vehicle, it could have been a 'dry run' to see how we'd react. Since there was interest, and even the realization that it could be a spacecraft, yet no panic, we could be in for a more conspicuously artificial object, the next time. For all we know such a thing could be on its way to us right now, just waiting for us to discover it.

If this were to occur, it would probably turn up in an astronomical survey. This is the main reason I keep track of the latest news about near- Earth, and other unusual asteroids and comets. Such a space vehicle could be interpreted as a comet or asteroid, at first, just as Oumuamua was.

NASA has discovered a 2 asteroids system, which rotate around their center of mass. They were detected by using Arecibo as a planetary radar and Green Bank as a telescope which received the radio waves reflected by the asteroids. You can read about this on the NASA site.
Tullio

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Captain's log: "Helpless Dodos aplenty, all waiting to be plucked.. Easy protein source added to fleet's trade route."

Just sayin'.

No matter what, it most likely isn't coming back to give us another chance at identifying it. IF it is a spaceship ain't it a hoot that we were totally ignored.

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Apr 3, 1999 - May 3, 2020

We'd probably give them severe indigestion, if not food poisoning! The biochemistry of life evolving independently on another world would very probably be so different, that it would be incompatible with our own. Then, too, one suspects that beings able to master the problem of interstellar spaceflight could very likely synthesize whatever food they needed, seemingly a much simpler task.

Captain's log: "Helpless Dodos aplenty, all waiting to be plucked. Easy protein source added to fleet's trade route."

We'd probably give them severe indigestion, if not food poisoning!

That's why I'm loading-up with low-quality fast foods - to make their gastronomical/gastrointestinal lives as miserable as possible.

The biochemistry of life evolving independently on another world would very probably be so different, that it would be incompatible with our own. Then, too, one suspects that beings able to master the problem of interstellar spaceflight could very likely synthesize whatever food they needed, seemingly a much simpler task.

Very reasonable hypothesises that would be even truer if they happen to be cybernetic in nature, but I'm not taking any chances; just in case they prove to have biochemically compatible organics, I've resolved to generously down fast foods with the most abrasive canadian whiskeys available (alas, no more Jack Daniel thanks to the absurdist trade war going on amongst traditional economical partners). As to the heightened probability that this regimen might kill me long before any alien invasion occurs, this is probably a topic for another time and place.

Before any moderator calls me back to order, I'm now returning the thread to its usually more serious (which I enjoy reading) considerations.

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Apr 3, 1999 - May 3, 2020

There are so many possible theories regarding the existence of ET and the forms they might take and right now one is as good as any other..

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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

Liked the video. :)


Karen Meach , Astronomer, astrobiologist , - TED TALKS - Oumuamua

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The probability that the interstellar object Oumuamua is a comet, is explored in a new scientific paper. They find that it's unexpectedly high rate of speed is very unlikely to be explained by cometary outgassing.

Due to the elongated shape of the object, it should have spun faster and faster, to the point of flinging itself to pieces. Since it neither fragmented, nor appeared to increase its rate of rotation, some other cause of its retreating from the inner solar system at a faster rate than expected should be considered.

Oumuamua appears stranger and stranger, the more carefully we examine it. The natural explanations proposed have all been found wanting.

Please find a link to the refered-to paper, below:

https://arxiv.org/pdf/1809.06389.pdf

It's interesting to read these papers.
One suggests that the non-gravitational acceleration could be accounted for if the object was a comet that was outgassing volatile material. The other paper shows that no outgassing was detected and if there had been then this would affect the rate of rotation (which didn't change), suggesting it's more likely to be a solid asteroid; which then undermines the comet theory.
One possibility that was discussed, and would fit the data, is that the acceleration is due to the pressure of the solar wind. However, for this to work, the object would need to have a density "3 or 4 orders of magnitude lower than an asteroid". The density of an asteroid isn't well established, but is estimated to be around 2g/cm^-3 (If it was pure ice, it would have a density of 1g/cm^-3). In other words, in order to have a much lower density of ~2-20mg^cm-3 it would have to be hollow.
Just for comparison, the heat shield tiles of the space shuttle had a density of 140mg^cm-3 so the object would have to be unrealistically low density (even for a spacecraft) for this idea to work.
(EDIT: Silly me. it would have a density of 140mg^cm-3 if it was made entirely of shuttle tiles. Whereas real spaceships just have a thin skin of tiles, so a hollow 'asteroid' might indeed get as low as 20mg^cm-3).
However, I really fail to see the point of a ship coming all the way across interstellar space to just pass us by for a month and go on its way. Seems like you'd want to hang around and make more observations of us than that. Unless it drops off a probe at each system it encounters for long-term observations......

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The path of Oumuamua through the inner solar system was well understood. Any added velocity, gained by passing near the Sun, or Earth, were already taken into account. Quite beyond this, the object was determined to be departing at a faster than expected velocity. A 'non-gravitational' force was required to explain this. None of these forces, as it turns out, properly explains the actual motion of Oumuamua.

Given this, plus the odd, very elongated shape of the the object, a shape that was already known to minimize impacts with interstellar debris, the case for an interstellar spacecraft doesn't seem to be so very unreasonable.

It's interesting to read these papers.
One suggests that the non-gravitational acceleration could be accounted for if the object was a comet that was outgassing volatile material. The other paper shows that no outgassing was detected and if there had been then this would affect the rate of rotation (which didn't change), suggesting it's more likely to be a solid asteroid; which then undermines the comet theory.
One possibility that was discussed, and would fit the data, is that the acceleration is due to the pressure of the solar wind. However, for this to work, the object would need to have a density "3 or 4 orders of magnitude lower than an asteroid". The density of an asteroid isn't well established, but is estimated to be around 2g/cm^-3 (If it was pure ice, it would have a density of 1g/cm^-3). In other words, in order to have a much lower density of ~2-20mg^cm-3 it would have to be hollow.
Just for comparison, the heat shield tiles of the space shuttle had a density of 140mg^cm-3 so the object would have to be unrealistically low density (even for a spacecraft) for this idea to work.

To be sure, some asteroids are apparently riddled with voids, which renders them less dense than if they were entirely solid. But, as you point out, an object made up of 99 percent or even 99.9 percent of hollow spaces is very unlikely. It is also, very probably, structurally unstable.

All known non-gravitational sources of thrust were considered, but found unsatisfactory. The cometary outgassing scenario was apparently the last resort, and was advanced despite the lack of the expected evidence for it, in the form of conspicuous entrained dust.

Now we see that even in the improbable case of pure outgassing, without dust, the spin of the object should have been markedly affected. Observations establish that it was not so affected.

A Scientific American article which I read in Italian translation on Le Scienze online magazine says that Oumuamua may be the dead relic of an extinct civilization and suggests to go looking for more objects of this kind.
Tullio

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I think it is this article.
How to Search for Dead Cosmic Civilizations
If they’re short-lived, we might be able to detect the relics and artifacts they left behind
https://blogs.scientificamerican.com/observations/how-to-search-for-dead-cosmic-civilizations/