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Featured B First Interstellar Asteroid Found

  1. Oct 31, 2017 #1
    The first asteroid ever seen from another solar system is whizzing through our own, and astronomers are racing to observe the visitor before it slips away.

    Links: Nature

    Sky and Telescope
     
  2. jcsd
  3. Oct 31, 2017 #2

    tony873004

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  4. Nov 1, 2017 #3

    Vanadium 50

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    I don't think there is any evidence that this came from "another solar system". It could be from, e.g. our own Oort cloud.
     
  5. Nov 1, 2017 #4

    tony873004

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    It's travelling about 25 km/s too fast to have come from the Oort Cloud.
    It came from the most likely direction that an interstellar object would come from. i.e. if the solar system were a car, and this was a raindrop, it hit our windshield.
    It came in with a speed typical for what we would expect from an interstellar object.
     
  6. Nov 1, 2017 #5
    It did not come from the Oort cloud.

    As stated in the Nature story, the orbit is clearly hyperbolic; its eccentricity is 1.20, which is safely above 1.00. Furthermore, as shown in the animation in the Nature story, the object never passes close to a giant planet whose gravitational pull could have altered an elliptical orbit and made it hyperbolic.

    Bottom line: this object did indeed come from another solar system.
     
  7. Nov 1, 2017 #6
    Does it need a solar system to form an asteroid?
     
  8. Nov 1, 2017 #7

    OmCheeto

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    I had loads of fun this morning figuring out where the "25 km/s" number came from.
    I think I did my maths correctly, as I came up with a figure of 25.7 km/sec.

    Another number I came up with was, that if it was from Vega, it would have taken 580,000,000 years to travel that distance.
    Though, as indicated by another of your simulations, Vega was probably nowhere near where it came from, that far back.
    (Our galaxy looks like a busy airport when you look at it in 1000years/increment timescales. Freakin' stars flying everywhere!)

    ps. Any idea who runs "projectpluto.com"? They seem to know what they are talking about:"Pseudo-MPEC" for A/2017 U1

    [edit: millions of millions sounded too much like Sagan]
     
    Last edited: Nov 1, 2017
  9. Nov 1, 2017 #8
    Actually, it took only 290,000 years to travel the 25-light-year distance from Vega, although as correctly noted, the star wasn't "there" 290,000 years ago.

    According to this paper, the asteroid's speed before feeling the Sun's pull was 26.2 kilometers per second.
     
  10. Nov 1, 2017 #9

    OmCheeto

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    Thank you for the maths correction.


    2017.11.01.interstellar.maths.error.png
    kilometer ≠ meter​

    But now I'm still off by a factor of 2. :H
     
  11. Nov 2, 2017 #10

    Vanadium 50

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    These are both arguments that this body isn't in a permanent orbit with such parameters. I accept that. But why is it impossible to have been perturbed into this trjectory from the Oort cloud? Note that if you want to claim it's from a different solar system, you have the same problem - you need to give it enough velocity to eject it from that solar system.

    Since you need this to happen either way, how can you use this to reject the source that is closer?

    If we had an ensemble of such objects and we could make a distribution, I would find this argument compelling. But I have seen statistical arguments applied to a single data point fail too often to put much stock in them.
     
  12. Nov 2, 2017 #11

    Astronuc

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    Toward the bottom of the Nature article is the statement "The asteroid came from the direction of the constellation Lyra, which is roughly where our Solar System is heading."

    From where would elements such as C, N, O, Si, Fe, and/or Ni be formed?

    Also from the Nature article,
    The object does not appear to be 'icy'. Wouldn't an Oort object be more likely 'icy'?

    On the other hand,
    Ref: https://en.wikipedia.org/wiki/Oort_cloud#Structure_and_composition

    Given the dimness of such objects, perhaps we have missed such objects in the past, say more than 200 years ago.
    https://en.wikipedia.org/wiki/History_of_the_telescope#Optical_telescopes
     
  13. Nov 2, 2017 #12
    There are approximately pi x 10**7 seconds in a year. Try that and see if you get the right answer.

    Take a look at the trajectory of the asteroid in the Nature story. Notice that the asteroid does NOT pass close to any giant planet; therefore, there's nothing in our solar system that could have perturbed an Oort cloud object that was originally on an elliptical orbit onto a highly hyperbolic orbit--unless you believe there's a Planet X located far above the solar system.

    But there are plenty of giant planets in OTHER solar systems that could have ejected the asteroid.
     
  14. Nov 2, 2017 #13

    russ_watters

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    This debate is very interesting to me. What I'm hearing is that the vast majority of Oort Cloud objects we encounter are thrown at us at relatively low velocity. This would be because when you have an interaction between an asteroid and object of much larger size, there is a range of delta-V's that can be applied, and that range starts at zero and goes up from there. So a high [delta-]V object coming from the Oort Cloud is unlikely.

    But a high velocity object from another solar system is also rare because the same logic about velocity distribution applies. The only difference between the scenarios is that the object would have gotten thrown "up" from another solar system vs "down" from our Oort Cloud.

    ...of course, while there are a lot more "up" velocity vectors than "down" ones, there are also a lot more other solar systems out there at those other velocity vectors. So perhaps all velocity vectors are roughly equally covered, making the likelihood of this being from another solar system higher than from the Oort Cloud?
    My understanding is that it can either be very large and far away or smaller and closer. While there aren't believed to be any Jupiter-sized objects in the Oort Cloud, we already know there are many Pluto+ sized objects. So a close encounter would be able to fire an object away/toward us at high velocity.
     
  15. Nov 2, 2017 #14

    Vanadium 50

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    Exactly.

    That is true. But they are also farther away. It's not clear to me which effect wins: more sources, or a closer source.
     
  16. Nov 2, 2017 #15

    russ_watters

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    It isn't clear to me either, but looking at angles tells me the extrasolar origin is probably more likely:

    In order to fire an asteroid into the inner solar system at high velocity, it has to be in a tight window, say 10 degrees. The other 99% of velocity vectors (made up numbers) eject it without reaching the inner solar system for us to see it....and of course, the one we se is also being ejected after its flyby.

    So that would tell me if all solar systems are similar, that for every 1 we see at high velocity from our own, we should see 100 from other solar systems.

    ...i do suppose though that this assumes the galaxy is dense enough that given enough time, all asteroids ejected from one solar system will eventually pass through another. Its Olbers' paradox with asteroids.
     
  17. Nov 2, 2017 #16

    tony873004

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    Objects in the Oort Cloud would move with speeds in the 100s of meter/second. There's no way two of them are going to interact, sending one of them off with a speed of 26 km/s.

    It's possible that a star passed through the Oort Cloud and perturbed some objects. But it would have to get really close to an object to give it 26 km/s of speed. Objects in the Oort Cloud are so spread out that a star passing through would likely not get close to any individual object, just like our spacecraft pass through the asteroid belt without encountering any asteroids, unless we aim for them.

    Also, the objects in the Oort Cloud are comets. This object is an asteroid. So it likely didn't come from the Oort Cloud.

    Because it could have been ejected from the star's planetary region, rather than from it's Oort Cloud. In our Solar System we've seen Jupiter do it (https://twitter.com/tony873004/status/913997533570985985), and have reason to believe that during the formation of the Solar System, lots of stuff got ejected into interplanetary space. It doesn't need to be ejected from the other solar system at high speed either. It could be ejected with a velocity at infinity of 1 m/s. But if this other solar system was moving at 26 km/s with respect to the Sun, that's how fast the asteroid will encounter the Sun. This asteroid's inbound velocity is typical to the velocity distribution of solar neighborhood stars.
    https://arxiv.org/abs/1710.11364



    It's not a statistical argument. Even with 0 data points it's to be expected that we will encounter interstellar objects more frequently in the direction of our motion. That's why when they manufacture cars, they put the wipers on the front window without ever having seen a single raindrop hit the car.
     
  18. Nov 2, 2017 #17
    Pardon my poor eyes if I missed it, but given that we've detected large bodies in space not associated with any star why does it have to be from another system?

    Two scenarios come to mind, and there are probably more, of course.

    1. It was thrown out of another solar system, crossed interstellar space, and found its way here. (No "guiding" implied there.)

    2. It was already in space, but not near another star. As Sol passed it was pulled in. (Does not imply the visitor was stationary itself.)

    3. ...
     
  19. Nov 2, 2017 #18

    tony873004

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    Large enough bodies like brown dwarfs can form the same way stars do, from clouds of hydrogen and other elements.
    Smaller large bodies such as planets were probably formed in a solar system and then ejected.
    Asteroids don't spontaneously assemble themselves from interstellar gas and dust.

    It was not stationary. It was moving at 26 km/s. Sol accelerated it to 88 km/s. Now its on the way out, and sol is decelerating it. It will slow back down to 26 km/s as it leaves the solar system.
     
  20. Nov 2, 2017 #19
    There's no scenario where the body could have formed outside a solar system?
    "(Does not imply the visitor was stationary itself.) "
     
  21. Nov 2, 2017 #20

    russ_watters

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    Ok, so this is something I misunderstood about the gravitational slingshot. I thought you could gain more speed by getting closer to the massive object, with no limit. But googling, I see a limit of 2x the large object's velocity. That makes it very difficult for an object to gain such a large velocity while in the Oort cloud.
     
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