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Thread: 'Oumuamua, possible internal composition?

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    'Oumuamua, possible internal composition?

    We know that our Strange Visitor is tumbling, and we know how fast, so is it possible to determine a minimum possible material strength working from that? Combine that with the tarry Carbon laden surface spectra, and we might come up with a rough framework of possible interior material compositions.
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    "It has significant elongation and rotation rate, so it is thought to be metal-rich with a relatively high density."
    https://en.wikipedia.org/wiki/%CA%BBOumuamua

    Not sure how much more we might glean.

    But really, it's only rotating every 8 hours. And only 230 metres long. It wouldn't have to be very strong to overcome such forces.
    Last edited by DaveC426913; 2018-Oct-01 at 02:28 AM.

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    How long have we had the capability and sky coverage to detect objects like Oumuamua?

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    Quote Originally Posted by CaptainToonces View Post
    How long have we had the capability and sky coverage to detect objects like Oumuamua?
    It's less to do with 'capability' and much more to do with luck.
    We can certainly image such things, but we are not scanning the entire sky all the time. There might be other objects in our SS right now, that we could resolve, but just don't happen to be pointing the right scope in the right direction at the right time.

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    Quote Originally Posted by DaveC426913 View Post
    It's less to do with 'capability' and much more to do with luck.
    We can certainly image such things, but we are not scanning the entire sky all the time. There might be other objects in our SS right now, that we could resolve, but just don't happen to be pointing the right scope in the right direction at the right time.
    To put the question in terms of your chances, what I'm asking is what were the chances of Oumuamua being detected in 2017 when it was, compared to the chances of a similar object being detected, 5 years ago, 10 years ago, 20 years ago, and 50 years ago? Were the chances in 2017 twice as high as in 2012? 20% higher? Were the chances of detection in 2017 10 times higher than they were 20 years ago? That is the nature of my question.

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    It says on Wikipedia that objects like Oumuamua should pass inside Earth's orbit several times a year and that there are probably 10,000 such objects inside the orbit of Neptune at any given time.

    Is that true?

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    could its mass be at all determined by any deviation in its orbit due to solar wind? Would the difference in orbit due to inertia vs solar windforce be measurable?
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    Quote Originally Posted by CaptainToonces View Post
    It says on Wikipedia that objects like Oumuamua should pass inside Earth's orbit several times a year and that there are probably 10,000 such objects inside the orbit of Neptune at any given time.

    Is that true?
    I could not find the statement you refer to in the wikipedia article on Oumuamua. It is likely referring to the presence of small asteroids and comets that are a part of the solar system and definitely not to interstellar visitors such as Oumuamua. Can you pinpoint which portion of which article you found the statement in?

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    Quote Originally Posted by Eclogite View Post
    I could not find the statement you refer to in the wikipedia article on Oumuamua. It is likely referring to the presence of small asteroids and comets that are a part of the solar system and definitely not to interstellar visitors such as Oumuamua. Can you pinpoint which portion of which article you found the statement in?
    I cannot speak for Wikipedia, but see here for a reference to a paper that does in fact mention 10,000 interstellar objects inside Neptune’s orbit. I have not kept up to date since to see if that paper might have been refuted, rejected or challenged.
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    Quote Originally Posted by Eclogite View Post
    I could not find the statement you refer to in the wikipedia article on Oumuamua. It is likely referring to the presence of small asteroids and comets that are a part of the solar system and definitely not to interstellar visitors such as Oumuamua. Can you pinpoint which portion of which article you found the statement in?
    It's the very last sentence in the article. Source they cite is a BBC television program.

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    Does anybody know by how much it is accelerating compared to what is expected from gravity?

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    Quote Originally Posted by slang View Post
    I cannot speak for Wikipedia, but see here for a reference to a paper that does in fact mention 10,000 interstellar objects inside Neptune’s orbit. I have not kept up to date since to see if that paper might have been refuted, rejected or challenged.
    The number density estimate is based on this one detection. OK that is better than no information at all, but there are still enormous uncertainties attached to it.

    Also this is the density of interstellar objects greater than 100 metres. There should be even more smaller ones.

    What does that mean for interstellar travel? It sounds like it could be a lot more hazardous than envisaged with all these rocks floating around?

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    Quote Originally Posted by kzb View Post
    The number density estimate is based on this one detection. OK that is better than no information at all, but there are still enormous uncertainties attached to it.
    Of course. But the number on Wikipedia was not in error in the sense that something else was meant, thus "definitely not to interstellar visitors" was not correct. It's no biggie to me, I just remembered reading, being surprised about, and linking to the paper before.
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    Quote Originally Posted by slang View Post
    I cannot speak for Wikipedia, but see here for a reference to a paper that does in fact mention 10,000 interstellar objects inside Neptune’s orbit. I have not kept up to date since to see if that paper might have been refuted, rejected or challenged.
    As I posted my query on the number I said to myself "why are you using the word definitely. You know better than to make absolute statements. You'll just get egg on your face." But I ignored the implicit advice. Thank you for the link. Definitely interesting, though I am always skeptical of extrapolating from a single instance.

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    Here is a paper that says there are probably 10 trillion (with a TR) interstellar comets per cubic interstellar parsec.


    http://adsabs.harvard.edu/cgi-bin/bi...J.....92..171T

    Capture of 20 km/s approach velocity interstellar comets by three-body interactions in the planetary system

    Torbett, M. V.
    Astronomical Journal (ISSN 0004-6256), vol. 92, July 1986, p. 171-175. (07/1986)

    Interstellar comets with velocities at infinity of 20 km s-1 can be captured by three-body interactions within the planetary system. A semianalytic method is presented indicating that Jupiter is the only planet capable of scattering these comets into bound orbits. The time-averaged cross section for this process seems to be roughly five times the area of Jupiter. With an observational upper limit on interstellar comets of ≡ 10^13 [per cubic parsec], the resulting capture rate amounts to only one comet every 60 Myr.
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    So it is, or is not, travelling away from the Sun faster than gravity + solar radiation expects?

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    Quote Originally Posted by CaptainToonces View Post
    So it is, or is not, travelling away from the Sun faster than gravity + solar radiation expects?
    I've never heard anything about that in any report or story. Surely such a very obvious anomaly would have been highlighted if it was doing that?
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    Quote Originally Posted by Noclevername View Post
    I've never heard anything about that in any report or story. Surely such a very obvious anomaly would have been highlighted if it was doing that?
    As far as I know it is so small so as difficult to observe now that it's between Jupiter and Saturn.

    However there was a paper released by legitimate astronomers stating that the pace away from the Sun was faster than could be explained by gravity, and solar radiation may or may not be the cause.

    Let's see if i can find a link, from: https://www.usatoday.com/story/news/...rd/1900213002/

    Sorry about the link to USA Today article which is filled with ads and low on information.

    "The paper said if solar radiation pressure is the reason "Oumuamua" is moving at high speeds, it represents "a new class of thin interstellar material" either made naturally or through artificial means.

    The paper's authors, which include Avi Loeb, chair of Harvard's astronomy department, suggest the object could be a "lightsail" used to propel spacecraft with solar energy."

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    The paper first describing the unusual motion of Oumuamua was published in Nature (Micheli, Nature, 559, 223, 2018), so one can't read it without a subscription. The authors didn't post a preprint to arXiv, either. Rats.

    But this subsequent paper

    https://arxiv.org/abs/1810.11490

    may give you enough information to answer some of your questions.

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    What is our ability to observe the position of Oumuamua now that it is between Jupiter and Saturn? Do we have any telescopes powerful enough to position such a small object that far away?

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    Quote Originally Posted by CaptainToonces View Post
    What is our ability to observe the position of now that it is between Jupiter and Saturn? Do we have any telescopes powerful enough to position such a small object that far away?
    Last time 'Oumuamua was borderline observable was when it was still mag 27.5 mag (the limit of Hubble Space Telescope for fast-moving objects). This was in December 2017/January 2018.

    Source:
    http://www.stsci.edu/hst/phase2-public/15405.pdf
    Last edited by glappkaeft; 2018-Nov-28 at 06:15 PM. Reason: added link

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    The fact that it is accelerating slightly more than expected is reminiscent of the Pioneer anomaly.

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    Quote Originally Posted by Exposed View Post
    The fact that it is accelerating slightly more than expected is reminiscent of the Pioneer anomaly.
    Except that Pioneer was slowing down.... now thought due to its power supply and the heat produced by it "pushing back" on the probe. Instead, something seems to be pushing outward on/from 'Oumuamua.

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    If the extra boost was caused by solar radiation pressure, then wouldn't there have also been an unexpected slowdown in its approach towards the Sun? Or were we not even yet observing it at that point?

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    Quote Originally Posted by CaptainToonces View Post
    If the extra boost was caused by solar radiation pressure, then wouldn't there have also been an unexpected slowdown in its approach towards the Sun? Or were we not even yet observing it at that point?
    If I am not mistaken, we did not see it until after perihelion.

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