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Thread: Interstellar Comet

  1. #121
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    A curious coincidence in the comet paper was the factor of 10^-6 which also shows up in Anderson's flyby paper where they suggested an empirical formula that fitted some of the earlier flyby results but did not work for some latter flybys.

  2. #122
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    Interesting TED Talk about Oumuamua.
    https://www.youtube.com/watch?v=rfi3w9Bzwik

  3. #123
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    Looking at some numbers

    Wondering if there is some connection between the A_1 of the comet paper's fitted free parameter of 5.01X10^(-6) and Anderson's K of 3.099X10^(-6) which is derived from a formula giving a dimensionless value:
    K=2 w_earth X R_earth/c where w is the angular rotational velocity in rads/sec and R is Radius of earth and c is the speed of light.

    It is assumed that radius is measured from the core to the surface of earth and not to the top of the atmosphere.

    A caveat is that we have no accurate similar measure of the comet prior to solar closest approach. It seems probable that it had at least one prior hyperbolic encounter in its home stellar system in order to escape to visit our system. Unknown if it had other encounters before arriving in our system. So it is unknown if it had some anomaly before arriving here. A measurement of anomaly prior to solar encounter would allow a better measurement of gain or loss of anomaly due to post solar encounter.

    So consider the extreme case where no anomaly was present before solar encounter and solve for the effective solar radius.

    The Sun rotates about 27 times slower than the Earth. A_1/K_earth=1.617 which suggests that the effective radius for the sun is around 278,400 kilometers which is about .4 of the total solar radius within the radiative zone. This is where the density is a bit above the density of water but less than gold. ( https://solarscience.msfc.nasa.gov/interior.shtml )

    The authors suggestion that there might be material coming off the comet that is below current detection levels to account for the apparent non-gravitational acceleration might require IN SITU observations to either confirm or rule out their hypothesis. Considering the possible shape of the comet being up to 10:1 allows the suggestion that it might be a surface shard from a larger high rotation body that got too close to the Roche limit of a larger body getting a large gravity assist. A surface shard would not have suffered subduction which could leave microfossils, if present, still intact. A sample return mission would give an idea of what constitutes the visitor from another system. If there is no evidence to support comet like activity that could be seen upon approach, then a lab can test for a possible violation of UFF by comparing the fall of an earth rock to a sample from the anomalous comet.

  4. #124
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    A new paper today casting doubt on outgassing for the non-gravitational force. Spin evolution that would accompany it appears to be too small to be plausible:

    SPIN EVOLUTION AND COMETARY INTERPRETATION OF THE INTERSTELLAR MINOR OBJECT 1I/2017 ’OUMUAMUA

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

    They do not forward an alternative interpretation to explain the force.

  5. #125
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    A headline article today about Oumuamua from physics world:

    Interstellar object ‘Oumuamua is an asteroid, not a comet argues astrophysicist
    https://physicsworld.com/a/interstel...strophysicist/

    This is about the above arxiv paper on spin evolution.

    The mystery deepens a bit when applying the Anderson formula to Oumuamua. The value between the ingoing and outgoing can only produce values between the extremes of 2 to -2. The angle was estimated to be around 66 degrees. So if the Earth flyby model is applied, which is similar to a one time change near perigee, like an impulse, the amount of Delta v anomaly accrued would only be around 10% of the total anomaly observed. The authors of the comet like paper also noted that a one time impulse was improbable when compared to either r^(-2) or r^(-1) force gleaned from observations made over different times. Solar pressure seems unlikely unless the comet was hollow.

    Oumuamua may be a more pure and less complicated form of the flyby anomaly. The sun is the only relevant body and the comet is clearly hyperbolic during the entire event. This may suggest that there is another parameter with regard to Earth flyby anomalies that has not been well considered if hyperbolic speed is required: sphere of influence. None of the Earth flybys increased the overall speed to beyond 42km/sec@earth needed to attain solar escape speed. There are three relevant bodies: Earth, the Sun and the Moon. The anomaly at earth would be truncated once the Sun's sphere of influence begins to dominate because gravity assist was insufficient to bring the craft to solar hyperbolic speed. Perhaps by taking this parameter into consideration might account for some prediction failures of the more favored models.

    It has been noted that the Earth flyby anomalies appear to be not conservative. The Oumuamua anomaly which appears to reveal either a r^(-2) or r^(-1) force might allow a restoration of conservation. This would be similar to gravity assist where a spacecraft gains or loses speed while the planets loses or gains an imperceptible mount of speed. The example that comes to mind is in Mahdavi's A520 paper where there was noted a darkened core of dark matter and a dimmer core of dark matter in galaxy cluster 5 that seemed to balance each other. While all galaxy clusters were ram stripped, the other galaxy dark cores appeared not to be dimmed. Mainly cluster 5 was at a different angle from the others. Total dark matter effect seems to be conserved while there appears a darkening/dimming but conserving effect happened between 5 and 3 (the dark core of A520). Within the dark matter particle paradigm,where DM is independent of baryons, there has been considered self interacting dark matter and within this there is a recent resonant self interacting DM that helps the core/cusp and too-big-to-fail problems. These, however, are large scale only attempts that would not work at the level of a comet and star. The reverse is not ruled out. The flyby anomalies could occur at the large scale as well as small scale.

    There has been a try at a dark matter interpretation of the flyby anomaly that centered on an earthbound two fluid dark matter interacting with a craft without regard to a hyperbolic requirement but orbiting spacecraft did not see the anomaly and small anomalies seen in the more eccentric orbits seem to cancel out.

    There have been modified classical inertia theories but they have not always been successful.

    A dark matter intensity conservation interpretation would require that dark matter inertia would be inherent in baryons but in addition to its classical inertia.

    In Oumuamua's case, the angle allowed an interaction where the comet's dark matter was dimmed while the Sun's dark matter became imperceptibly darker. This would allow the comet to escape faster than it should as observed. Rather than invoking an additional r^(-2) force, part of the dark inertia has been altered. The possibility of either darkening or dimming can explain the independence from the classical gravity assist.

  6. #126
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    So it is more like a pancake,, flat and not spindle shaped?

  7. #127
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    Quote Originally Posted by publiusr View Post
    So it is more like a pancake,, flat and not spindle shaped?
    I didn't notice anyone saying that. Can you point out where you think that was implied?
    Forming opinions as we speak

  8. #128
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    The possibility of a more pancake was brought up in the above link to the TED talk. Before posting the link to the spin evolution paper, it was important to read it in light of pancake shape. They gave 4 independent reasons for their conclusions and only 1 was with regard to shape.

  9. #129
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    It might be a long shot considering dispersion also due to solar pressure and Yarkovsky effect, but comet paper's authors stated it might be below detection levels to see a tail. A possible search out of the ecliptic might be done by the Next Generation VLA looking for the faint trailL
    Science with an ngVLA: High-resolution imaging of comets
    https://arxiv.org/abs/1810.07867

  10. #130
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    Project Lyra looks at the challenges of a mission to Oumuamua:
    Project Lyra: Sending a Spacecraft to 1I/'Oumuamua (former A/2017 U1), the Interstellar Asteroid
    https://arxiv.org/abs/1711.03155
    Trying to bring back a sample would be especially challenging. After landing and getting a sample having used fuel to arrive, slow down, and land, you are going out of the solar system at 26km/sec. Even with initial fuel to start back, we might need one or two more craft to relay the sample to perigee near Earth.

  11. #131
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    The solar pressure hypothesis for a non-gravitational force is reviewed. The possibility was mentioned in the earlier comet paper. Featured is the thickness of between 0.3-0.9 mm There is a discussion about whether rotation or tidal forces would disallow the thin shell. Tensile strength is discussed. Solar pressure would slightly slow the craft prior to closest approach. A constraint not considered is the possible effect of heat upon the tensile strength. Coming in at near 0.25 AU inside the orbit of Mercury might soften, melt, or vaporize some compounds. Could there be an oven effect if the surface is closed? Would there be some modulation in the spin evident in the observations during the closer points to the sun if the object melted and deformed the shape before freezing out at further distances?

    COULD SOLAR RADIATION PRESSURE EXPLAIN ’OUMUAMUA’S PECULIAR ACCELERATION?

    https://arxiv.org/abs/1810.11490

  12. #132
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    Quote Originally Posted by borman View Post
    The solar pressure hypothesis for a non-gravitational force is reviewed. The possibility was mentioned in the earlier comet paper. Featured is the thickness of between 0.3-0.9 mm There is a discussion about whether rotation or tidal forces would disallow the thin shell. Tensile strength is discussed. Solar pressure would slightly slow the craft prior to closest approach. A constraint not considered is the possible effect of heat upon the tensile strength. Coming in at near 0.25 AU inside the orbit of Mercury might soften, melt, or vaporize some compounds. Could there be an oven effect if the surface is closed? Would there be some modulation in the spin evident in the observations during the closer points to the sun if the object melted and deformed the shape before freezing out at further distances?

    COULD SOLAR RADIATION PRESSURE EXPLAIN ’OUMUAMUA’S PECULIAR ACCELERATION?

    https://arxiv.org/abs/1810.11490
    If it is a discarded or escaped piece of space engineering it would be designed to withstand these things.

    Also it has been calculated that such objects would survive many kpc of journey distance through the galaxy.

    Is it likely that an object this size with a thickness of a fraction of a millimetre could be of natural origin ?

    Here we have our first sight of ET space junk ?
    Last edited by kzb; 2018-Oct-31 at 12:19 PM.

  13. #133
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    An extraterrestrial artifact? It's not out of the question. If a comet shed enough material to affect its motion through space, to the extent observed in Oumuamua, its rate of rotation should apparently have been visibly changed. This object was closely watched, but the rotation rate was reportedly unchanged.

  14. #134
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    Quote Originally Posted by Ross 54 View Post
    An extraterrestrial artifact? It's not out of the question. If a comet shed enough material to affect its motion through space, to the extent observed in Oumuamua, its rate of rotation should apparently have been visibly changed. This object was closely watched, but the rotation rate was reportedly unchanged.
    Apparently, no outgassing was detected. Given that, we only have radiation pressure to change its course.

    For radiation pressure to have achieved the magnitude of deviation observed, the object can only be a fraction of a millimetre thick.

    It's reportedly several hundred metres in other dimensions. You have to ask what natural explanation could there be for such a large thin structure. Also it would require a certain degree of physical strength to survive tidal forces, which again points to non-natural origin.

    Of course the fraction of millimetre thickness only comes from the course change, and assuming it all comes from radiation pressure, but perhaps that is all mistaken.

  15. #135
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    Astronomers from Harvard University have suggested it might a UFO.

    https://edition.cnn.com/2018/11/06/h...ntl/index.html

    A mysterious cigar-shaped object spotted tumbling through our solar system last year may have been an alien spacecraft sent to investigate Earth, astronomers from Harvard University have suggested.

    The object, nicknamed 'Oumuamua, meaning "a messenger that reaches out from the distant past" in Hawaiian, was first discovered in October 2017 by the Pan-STARRS 1 telescope in Hawaii.

    Since its discovery, scientists have been at odds to explain its unusual features and precise origins, with researchers first calling it a comet and then an asteroid, before finally deeming it the first of its kind: a new class of "interstellar objects."
    I am because we are
    (African saying)

  16. #136
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    Quote Originally Posted by selvaarchi View Post
    Astronomers from Harvard University have suggested it might a UFO.

    https://edition.cnn.com/2018/11/06/h...ntl/index.html
    If it was a laser sail or similar, surely it would be going a lot faster?

    At the speed it was going, the journey time from even one of the closer stars would be millennia.

    Personally I think it is more likely space junk. Some kind of stellar shield off a space colony. Apparently such things could survive intact in interstellar space for many millions of years.

  17. #137
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    Quote Originally Posted by kzb View Post
    If it was a laser sail or similar, surely it would be going a lot faster?
    Not necessarily. Remember that Robert Forward's sail was staged:
    https://space.stackexchange.com/ques...n-a-solar-sail

    A thought experiment:

    If a breakthough starshot mini-probe were fired backwards from 'Oumuamua --towards Earth, say--what would be visible is the parent object accelerating, while the mini probe might not be visible. Or if a thin tether were backspun to release a microprobe so it wouldn't fly out of the solar system.

    This would all result in an acceleration of 'Oumuamua, which seems the case.

    Straining at gnats here, mind you. Very big IFS

    Mini-probe has laser signal sent to sail--that bounces back to homeworld.

    Cue optical SETI?
    Last edited by publiusr; 2018-Nov-09 at 06:40 PM.

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