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Interstellar Interloper, Coming in from the great beyond
Holder of the Tw...
post Oct 27 2017, 01:40 PM
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They finally found a chunk of something coming into the Solar System. Something much bigger than cosmic rays or dust particles.

Asteroid/comet in hyperbolic trajectory
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Gladstoner
post Oct 27 2017, 06:47 PM
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The estimated eccentricity of 1.19 (per Wikipedia), along with no interaction with any planets, would certainly confirm it.

I assume the object's velocity and trajectory will be adequate for calculating the galactic orbit -- inbound and outbound. It is stated that the object was coming from the direction of Vega. That is the direction of the sun's motion in the galaxy, which means the sun was likely overtaking the object, which would mean the object was traveling slightly slower than the sun, which would mean the object's 'perigalactic' distance was closer to the Milky Way's center (smaller semimajor axis).

Interesting times....
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Paolo
post Oct 27 2017, 07:04 PM
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I was surprised at first by the "low" eccentricty, which almost looks parabolic. I was expecting something more extreme like e=4. then I remembered that for e=sqrt(2), which is about 1.4 the asymptotes are perpendicular to each other, and 1.2 does no longer look that parabolic.

I think we are seeing a rare event: the object is largeish and it passed relatively close to the Earth and Sun.

be sure to check Andy Rivkin's tweets ( https://twitter.com/asrivkin ). He has posted some interesting considerations. concerning e.g. the object's color and asteroidal/cometary nature
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fredk
post Oct 27 2017, 07:05 PM
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QUOTE (Gladstoner @ Oct 27 2017, 07:47 PM) *
The estimated eccentricity of 1.19 (per Wikipedia), along with no interaction with any planets, would certainly confirm it.

Unless the uncertainty in the eccentricity is comparable to 0.19. There've been several measurements which I'd guess would normally pin down the eccentricity quite well, but if there's coma activity perhaps not so well. I haven't heard an estimate of the uncertainty but have heard comments from those involved that more observations are needed before we can be sure it's extrasolar.
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Paolo
post Oct 27 2017, 07:13 PM
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the error bar for eccentricity is actually quite small right now. see for ex. https://projectpluto.com/temp/2017u1.htm

QUOTE
e 1.1938645 +/- 0.00211
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fredk
post Oct 27 2017, 07:32 PM
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Thanks for that reference, Paolo.

Still, there have been several cautionary comments, eg from S&T:
QUOTE
"If further observations confirm the unusual nature of this orbit," notes Gareth Williams, the MPC's associate director, "this object may be the first clear case of an interstellar comet."


Or from New Scientist:
QUOTE
“It could be that it’s coming from outside the solar system, but it’s really hard to tell,” says Simon Porter, also at the Southwest Research Institute. Further observations in the next couple weeks will make the picture clearer.


Maybe these are older comments or perhaps people were concerned it was a piece of a comet that had broken up, so may have gotten a boost near perihelion. Anyway now the S&T story says it is pointlike and hence an asteroid, not a comet.
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Gladstoner
post Oct 27 2017, 07:51 PM
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For reference, a list of all 'hyperbolic' comets:

https://en.wikipedia.org/wiki/List_of_hyperbolic_comets

The eccentricities are all 1.00 or lower, which are very close to parabolic (e=1). These are either first timers or extremely long-period comets whose orbits were influenced by planetary perturbations or outgassing effects. This includes initially vigorous comets like Kohoutek (1973) and ISON. A/2017 U1, on the other hand, is apparently inert and avoided planetary encounters.
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Holder of the Tw...
post Oct 27 2017, 09:09 PM
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QUOTE (fredk @ Oct 27 2017, 02:32 PM) *
Still, there have been several cautionary comments...


Professional overcaution in print, particularly for breakthrough first time observations, is understandable and commendable. But seriously ... there really isn't much doubt here.
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Paolo
post Oct 28 2017, 05:16 AM
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many of these articles were written before a second round of astrometric data was published and when orbital uncertainties would still allow a local origin. the second round confirmed that the object is indeed interstellar (Rivkin is calling it a "xenoasteroid", I really hope this name sticks).
some additional details from National Geographic: First Rock From Outside the Solar System Sails Past Earth

and a couple of papers that will now need to be re-written:
Realistic Detectability of Close Interstellar Comets
An Observational Upper Limit on the Interstellar Number Density of Asteroids and Comets
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JRehling
post Oct 28 2017, 09:48 PM
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The challenges are obvious, but it would be nice to have a mission that catches this thing from behind and gives us a close look before it goes back to the interstellar void.
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TheAnt
post Oct 28 2017, 10:46 PM
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QUOTE (JRehling @ Oct 28 2017, 11:48 PM) *
The challenges are obvious, but it would be nice to have a mission that catches this thing from behind and gives us a close look before it goes back to the interstellar void.


Serious challenge is the middle name, as it moves at an insane speed.
Lets see:
A: If we would be able to coerce a number of universities to build cubesats.
B: Find and identify a similar object before perihelion.
C: And last but not least important, get Bezos or Musk to provide a launcher they might be building for some other purpose.
Each cubesat would be able to do a very fast flyby, and piecemeally adding information - yes perhaps for a similar object that turn up in the future.

But to play tag with A/2017 U1?
Even if we had a launcher and spacecraft ready on the launchpad, would we even be able to reach it before it pass the orbit of Neptune?
It depend on the launcher, if it got an upper stage, or if it's one of the largest launchers currently in use.

Now we know these objects do exist, I bet some people will at least start thinking on how to get a sample of an object from another solar system.
The value and pricetag of one such sample return mission would be literally *cough* astronomical.

Even though a sample return flight might not need to return at the same neck breaking speed, so an upgraded ION drive might do.
The latest variety of a Hall drive yield 5,5 Newton only after it's fed 102 kilowatts by a current of a whopping 250 Amperes!
That will require solar panels the size of a football field as the craft have an easier task to intercept the object further out than close to the Sun, or a special built miniature nuclear powerplant.
Lets see, one ASRG 'Advanced Stirling radioisotope generator' would provide 130W so we only need to strap on just less than 800 of those.
The 'Kilopower' that's being studied might yield 10 KW - so just about ten of those latter ones would be needed.
Well we can only dream, now I have handwaved enough Phlebotinum powered gadgets for this thread or enough for the entire forum for the next couple of years! wink.gif

Now wait this is interesting: A/2017 U1 arrived from a direction 6° from the solar apex, the Sun moves at 20 km/s through its interstellar medium.
So depending on where this object originated - it might actually have been moving comparatively slowly!
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Gladstoner
post Oct 28 2017, 11:12 PM
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I recall reading several years ago about a year-round 'meteor shower' radiant that was due to the earth encountering more-or-less random interplanetary debris as all revolved around the sun. The radiant would constantly shift eastward at it maintains a fixed elongation with the sun.

As it turns out, these are called 'apex meteors' (see: http://www.skyandtelescope.com/observing/r...random02112015/ ).

Now consider A/2017 U1. It just happens to be approaching from a direction close to the solar apex (direction of sun's movement) near Lyra. Compare the solar apex:

Attached Image


to the asteroid's position (red x) up to 400 years ago:

Attached Image


Could this be analogous to a galactic-scale 'meteor radiant'?
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JohnVV
post Oct 28 2017, 11:58 PM
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using the HORIZONS telnet ( yes telnet from the 70's) service i was able to grab a copy of the SPICE data bsp file

visualizing it using Celestia
( you could also use Cosmagrapha-spice on the PDS ftp servers )

( note- the mesh in the first 2 images is 100% synthetic )


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JRehling
post Oct 30 2017, 12:48 AM
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TheAnt,

Truly reaching this object will be quite difficult, but compared to sending a mission (much less a sample return!!!) to another star's system, it's outrageously easy.

I think getting mere in situ isotopic analysis of heavier elements from an object like this would be extraordinarily valuable, and an examination of the morphology of chondritic material in an object like this (if there is such a thing) would weigh mightily in addition to that.

Certainly it would be easier to target a future such object while it is close to the inner solar system, but we may have to wait decades for something like that… the mission would practically have to be ready on the pad for such an object to appear, and this certainly confounds conventional mission planning. Catching this one from behind fits more traditional planning but may require extraordinary resources.

I might guess that the way ahead will be to develop the capability to target much smaller interlopers… there is presumably a power law relating size and frequency, and there must be interloping objects on a regular basis if one can lower the size requirement sufficiently.

To take an entirely different approach, perhaps some of this material survives impact and rather than targeting a fast-flying body we could try to find such material that has already impacted the Moon or some other ancient, airless body. However, the velocities and energies involved may end that hope from the get-go.
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Gladstoner
post Oct 30 2017, 05:40 AM
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Path of approach of A/2017 U1 plotted in Voyager II:

Attached Image


(Solar apex marked with yellow X)

Attached Image
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