Interstellar Interlopers, Coming in from the great beyond Options

[Holder of the Tw...]

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

[Gladstoner]

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....

[Paolo]

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

[fredk]

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.

[Paolo]

the error bar for eccentricity is actually quite small right now. see for ex. https://projectpluto.com/temp/2017u1.htm

e 1.1938645 +/- 0.00211

[fredk]

Thanks for that reference, Paolo.

Still, there have been several cautionary comments, eg from S&T:

"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:

“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.

[Gladstoner]

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.

[Holder of the Tw...]

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.

[Paolo]

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

[JRehling]

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.

[TheAnt]

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!

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!

[Gladstoner]

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:



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



Could this be analogous to a galactic-scale 'meteor radiant'?

[JohnVV]

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 )

[JRehling]

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.

[Gladstoner]

Path of approach of A/2017 U1 plotted in Voyager II:



(Solar apex marked with yellow X)

[Gladstoner]

I gather that it would be prudent to give this region of the sky some extra scrutiny in minor planet/comet surveys. At least the earlier detection of an approaching interstellar object would be more likely. How nice would it have been for Hubble to be ready (or JWST in the future)?.... not that 2017 U1 would have been detected any earlier.

[Paolo]

that was fast!

Palomar Optical Spectrum of Hyperbolic Near-Earth Object A/2017 U1

We present optical spectroscopy of the recently discovered hyperbolic near-Earth object A/2017 U1, taken on 25 Oct 2017 at Palomar Observatory. Although our data are at a very low signal-to-noise, they indicate a very red surface at optical wavelengths without significant absorption features.

[Floyd]

Path of approach of A/2017 U1 plotted in Voyager II: (Solar apex marked with yellow X)

The spiral motion is due to the relative motion of ??? I'm not quite understanding the reference frame.

[Ames]

The spiral motion is due to the relative motion of ??? I'm not quite understanding the reference frame.

Earth - Parallax.
Apparent motion against the background stars.

[TheAnt]

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....

I agree in full about the value of getting such a sample, it would add to the knowledge about our own Kupier or Oort belt also.
And that was the reason I did that back-of-envelope type of calculation.
Only to find that a sample return would require a spacecraft of Frankensteinian proportions, so for several reasons not within a magnitude of our current capabilities.

That's why I mentioned cubesats/U-class spacecrafts first, cheap components built by any interested university, comparatively easy to store and to be sent by the dozen.
So yes, in situ or remote by a small craft that might even fly in formation is possible, one of the cubesats might even be sent to collide to get additional data.

Smaller objects will indeed be more frequent, but harder to find at the distance needed to get our interceptor on the way in time.
In addition, fragment of comets might have similar orbits making the tracking even harder.

Now a search for any such that might have impacted on the Moon or any other object without an atmosphere is worth thinking about.
Even though the shattered remains would be a bit less pristine, extremely heated up rather, it would still be possible to get some data.

After my previous post I realized one kind of probe in development that indeed would be able to reach A/2017 U1 - the sail in development by Breakthrough Starshot.
And that is a much more realistic target for such a spacecraft, accelerated to 30-50 Km/s instead of 50 000 km/s or whatever they hope for.
Even that tiny proposed transmitter ½ W or whatever, might be able to send the data back - a nice advantage.
Ooops! I better stop, all of a sudden I appear to be a supporter or Phlebotinum technology! =)

[Gladstoner]

After my previous post I realized one kind of probe in development that indeed would be able to reach A/2017 U1 - the sail in development by Breakthrough Starshot.
And that is a much more realistic target for such a spacecraft, accelerated to 30-50 Km/s instead of 50 000 km/s or whatever they hope for.
Even that tiny proposed transmitter ½ W or whatever, might be able to send the data back - a nice advantage.
Ooops! I better stop, all of a sudden I appear to be a supporter or Phlebotinum technology! =)

Interesting!

FWIW, here is an ephemeris of A/2017 U1 for the next century in ~half-year increments (from JPL HORIZONS). Shown are object position date, sky coordinates, magnitude, distance from sun in AU (range), and range rate.

Date__(UT)__HR:MN R.A._(ICRF/J2000.0)_DEC APmag r rdot
***************************************************************************

2017-Jan-01 00:00 18 10 48.25 +24 14 08.4 30.25 5.480932452578 -31.5363755
2017-Jul-03 00:00 15 32 00.23 +53 39 52.0 25.78 1.889032162719 -38.5709524
2018-Jan-02 00:00 23 31 39.21 +09 15 17.0 27.69 2.865905946364 35.3016311
2018-Jul-04 00:00 00 54 46.46 +24 45 49.3 30.73 6.310209706508 30.9243218
2019-Jan-03 00:00 23 47 03.93 +19 48 22.3 32.33 9.492071071897 29.4799470
2019-Jul-05 00:00 00 23 59.88 +24 55 04.3 33.48 12.56469466334 28.7362338
2020-Jan-04 00:00 23 49 03.67 +21 41 49.5 34.36 15.57559887711 28.2766783
2020-Jul-05 00:00 00 13 38.17 +24 54 51.9 35.07 18.54638060269 27.9624986
2021-Jan-04 00:00 23 49 51.33 +22 31 22.7 35.69 21.48873606470 27.7322127
2021-Jul-06 00:00 00 08 21.67 +24 54 13.9 36.22 24.40982212577 27.5556680
2022-Jan-05 00:00 23 50 17.39 +22 59 32.2 36.69 27.31424412971 27.4149317
2022-Jul-07 00:00 00 05 08.78 +24 53 44.4 37.11 30.20527197114 27.3002568
2023-Jan-06 00:00 23 50 33.95 +23 17 50.3 37.50 33.08517864084 27.2043140
2023-Jul-08 00:00 00 02 58.39 +24 53 22.8 37.84 35.95579599000 27.1233533
2024-Jan-07 00:00 23 50 45.19 +23 30 43.4 38.17 38.81844478692 27.0537124
2024-Jul-08 00:00 00 01 23.90 +24 53 06.4 38.46 41.67432291663 26.9940086
2025-Jan-07 00:00 23 50 53.11 +23 40 17.5 38.75 44.52427964797 26.9421107
2025-Jul-09 00:00 00 00 11.88 +24 52 51.7 39.00 47.36918076463 26.8974383
2026-Jan-08 00:00 23 50 58.77 +23 47 39.5 39.26 50.20960167493 26.8581905
2026-Jul-10 00:00 23 59 15.03 +24 52 37.3 39.48 53.04620010132 26.8240801
2027-Jan-09 00:00 23 51 02.95 +23 53 29.1 39.71 55.87935864384 26.7937684
2027-Jul-11 00:00 23 58 28.92 +24 52 22.6 39.91 58.70958668171 26.7673787
2028-Jan-10 00:00 23 51 06.18 +23 58 12.2 40.12 61.53711806064 26.7437097
2028-Jul-11 00:00 23 57 50.79 +24 52 07.6 40.30 64.36234819915 26.7228467
2029-Jan-10 00:00 23 51 08.78 +24 02 05.6 40.49 67.18540107417 26.7036419
2029-Jul-12 00:00 23 57 18.82 +24 51 53.1 40.66 70.00659655710 26.6863708
2030-Jan-11 00:00 23 51 11.07 +24 05 21.9 40.84 72.82596926704 26.6701114
2030-Jul-13 00:00 23 56 51.68 +24 51 39.7 40.99 75.64376934851 26.6552907
2031-Jan-12 00:00 23 51 13.17 +24 08 10.1 41.16 78.45995555855 26.6409568
2031-Jul-14 00:00 23 56 28.49 +24 51 28.1 41.30 81.27473208547 26.6274029
2032-Jan-13 00:00 23 51 15.19 +24 10 36.3 41.45 84.08799925892 26.6136987
2032-Jul-14 00:00 23 56 08.47 +24 51 18.6 41.58 86.89992433998 26.6004116
2033-Jan-13 00:00 23 51 17.15 +24 12 45.7 41.73 89.71036367251 26.5869003
2033-Jul-15 00:00 23 55 51.03 +24 51 11.5 41.85 92.51947003209 26.5737846
2034-Jan-14 00:00 23 51 19.01 +24 14 41.6 41.99 95.32708409903 26.5603725
2034-Jul-16 00:00 23 55 35.67 +24 51 06.7 42.10 98.13338319320 26.5474188
2035-Jan-15 00:00 23 51 20.72 +24 16 26.1 42.23 100.9382376756 26.5345316
2035-Jul-17 00:00 23 55 21.92 +24 51 03.3 42.34 103.7418799516 26.5227040
2036-Jan-16 00:00 23 51 22.18 +24 18 00.5 42.46 106.5442180234 26.5115771
2036-Jul-17 00:00 23 55 09.45 +24 51 00.3 42.56 109.3455395567 26.5019409
2037-Jan-16 00:00 23 51 23.34 +24 19 25.2 42.68 112.1457872309 26.4931472
2037-Jul-18 00:00 23 54 58.00 +24 50 56.9 42.78 114.9452816962 26.4858139
2038-Jan-17 00:00 23 51 24.25 +24 20 41.3 42.89 117.7439584064 26.4793249
2038-Jul-19 00:00 23 54 47.43 +24 50 52.5 42.98 120.5421316165 26.4743190
2039-Jan-18 00:00 23 51 24.93 +24 21 49.2 43.09 123.3397045015 26.4699764
2039-Jul-20 00:00 23 54 37.69 +24 50 47.1 43.18 126.1369684489 26.4666519
2040-Jan-19 00:00 23 51 25.50 +24 22 50.1 43.28 128.9337854645 26.4634958
2040-Jul-20 00:00 23 54 28.70 +24 50 40.7 43.36 131.7304236184 26.4610408
2041-Jan-19 00:00 23 51 26.03 +24 23 45.0 43.46 134.5267014939 26.4585773
2041-Jul-21 00:00 23 54 20.46 +24 50 33.8 43.54 137.3228545106 26.4565905
2042-Jan-20 00:00 23 51 26.56 +24 24 35.1 43.63 140.1186566277 26.4542362
2042-Jul-22 00:00 23 54 12.92 +24 50 27.1 43.71 142.9143240201 26.4519119
2043-Jan-21 00:00 23 51 27.19 +24 25 21.5 43.80 145.7095951991 26.4488311
2043-Jul-23 00:00 23 54 06.06 +24 50 20.9 43.88 148.5046609684 26.4455781
2044-Jan-22 00:00 23 51 27.89 +24 26 04.9 43.96 151.2992201805 26.4415150
2044-Jul-23 00:00 23 53 59.82 +24 50 15.8 44.03 154.0934496632 26.4371469
2045-Jan-22 00:00 23 51 28.68 +24 26 46.2 44.12 156.8870283178 26.4317178
2045-Jul-24 00:00 23 53 54.10 +24 50 11.8 44.19 159.6801401032 26.4258816
2046-Jan-23 00:00 23 51 29.51 +24 27 25.9 44.27 162.4724718766 26.4192610
2046-Jul-25 00:00 23 53 48.83 +24 50 09.1 44.33 165.2642466500 26.4127921
2047-Jan-24 00:00 23 51 30.32 +24 28 03.9 44.41 168.0551860974 26.4061158
2047-Jul-26 00:00 23 53 43.88 +24 50 07.1 44.48 170.8455768218 26.4000655
2048-Jan-25 00:00 23 51 31.06 +24 28 40.1 44.55 173.6351989204 26.3942348
2048-Jul-26 00:00 23 53 39.16 +24 50 05.4 44.61 176.4244060000 26.3894526
2049-Jan-25 00:00 23 51 31.66 +24 29 14.1 44.69 179.2130070134 26.3852944
2049-Jul-27 00:00 23 53 34.62 +24 50 03.4 44.75 182.0013795829 26.3824557
2050-Jan-26 00:00 23 51 32.13 +24 29 45.5 44.82 184.7893297743 26.3802049
2050-Jul-28 00:00 23 53 30.25 +24 50 00.8 44.88 187.5772360404 26.3789347
2051-Jan-27 00:00 23 51 32.52 +24 30 14.6 44.95 190.3648762331 26.3778834
2051-Jul-29 00:00 23 53 26.08 +24 49 57.5 45.00 193.1526084366 26.3776262
2052-Jan-28 00:00 23 51 32.85 +24 30 41.4 45.07 195.9401713849 26.3774871
2052-Jul-29 00:00 23 53 22.10 +24 49 53.7 45.13 198.7278960412 26.3778679
2053-Jan-28 00:00 23 51 33.18 +24 31 06.2 45.19 201.5154800279 26.3779210
2053-Jul-30 00:00 23 53 18.36 +24 49 49.5 45.24 204.3032353277 26.3780759
2054-Jan-29 00:00 23 51 33.54 +24 31 29.6 45.31 207.0908264328 26.3776450
2054-Jul-31 00:00 23 53 14.86 +24 49 45.5 45.36 209.8785399827 26.3771736
2055-Jan-30 00:00 23 51 33.96 +24 31 52.0 45.42 212.6659979793 26.3759706
2055-Aug-01 00:00 23 53 11.62 +24 49 41.8 45.47 215.4534686765 26.3744406
2056-Jan-31 00:00 23 51 34.45 +24 32 13.7 45.53 218.2405487454 26.3718108
2056-Aug-01 00:00 23 53 08.61 +24 49 38.8 45.58 221.0274973699 26.3686251
2057-Jan-31 00:00 23 51 34.99 +24 32 35.1 45.64 223.8138932763 26.3644430
2057-Aug-02 00:00 23 53 05.81 +24 49 36.6 45.69 226.6000064676 26.3600162
2058-Feb-01 00:00 23 51 35.56 +24 32 56.3 45.75 229.3854289017 26.3548746
2058-Aug-03 00:00 23 53 03.16 +24 49 35.1 45.79 232.1704758092 26.3497464
2059-Feb-02 00:00 23 51 36.11 +24 33 17.2 45.85 234.9547887149 26.3443557
2059-Aug-04 00:00 23 53 00.61 +24 49 34.2 45.89 237.7387558508 26.3396530
2060-Feb-03 00:00 23 51 36.60 +24 33 37.5 45.95 240.5220705249 26.3353909
2060-Aug-04 00:00 23 52 58.09 +24 49 33.2 45.99 243.3051736701 26.3323038
2061-Feb-03 00:00 23 51 36.98 +24 33 56.8 46.05 246.0877883402 26.3298305
2061-Aug-05 00:00 23 52 55.60 +24 49 31.9 46.09 248.8703861956 26.3284595
2062-Feb-04 00:00 23 51 37.27 +24 34 14.8 46.15 251.6526845958 26.3275742
2062-Aug-06 00:00 23 52 53.13 +24 49 30.0 46.19 254.4351439185 26.3277427
2063-Feb-05 00:00 23 51 37.49 +24 34 31.5 46.24 257.2174488946 26.3283175
2063-Aug-07 00:00 23 52 50.71 +24 49 27.5 46.28 260.0000394086 26.3296212
2064-Feb-06 00:00 23 51 37.68 +24 34 47.0 46.33 262.7825631934 26.3308361
2064-Aug-07 00:00 23 52 48.37 +24 49 24.4 46.37 265.5654372282 26.3323923
2065-Feb-06 00:00 23 51 37.85 +24 35 01.4 46.42 268.3482733287 26.3336897
2065-Aug-08 00:00 23 52 46.12 +24 49 21.0 46.46 271.1314623971 26.3351963
2066-Feb-07 00:00 23 51 38.06 +24 35 15.0 46.51 273.9145733456 26.3361683
2066-Aug-09 00:00 23 52 44.01 +24 49 17.6 46.55 276.6979746497 26.3369434
2067-Feb-08 00:00 23 51 38.31 +24 35 28.2 46.60 279.4812060583 26.3368044
2067-Aug-10 00:00 23 52 42.03 +24 49 14.4 46.63 282.2646177022 26.3362287
2068-Feb-09 00:00 23 51 38.62 +24 35 41.2 46.68 285.0477139224 26.3346920
2068-Aug-10 00:00 23 52 40.19 +24 49 11.6 46.72 287.8308317662 26.3327335
2069-Feb-09 00:00 23 51 38.98 +24 35 54.3 46.77 290.6134657804 26.3297552
2069-Aug-11 00:00 23 52 38.46 +24 49 09.4 46.80 293.3959708719 26.3263162
2070-Feb-10 00:00 23 51 39.36 +24 36 07.4 46.85 296.1778614745 26.3221299
2070-Aug-12 00:00 23 52 36.80 +24 49 07.7 46.88 298.9595424847 26.3181184
2071-Feb-11 00:00 23 51 39.74 +24 36 20.6 46.93 301.7405769084 26.3140978
2071-Aug-13 00:00 23 52 35.19 +24 49 06.3 46.96 304.5214341643 26.3107922
2072-Feb-12 00:00 23 51 40.06 +24 36 33.5 47.01 307.3017298453 26.3078283
2072-Aug-13 00:00 23 52 33.57 +24 49 04.9 47.04 310.0819918084 26.3058512
2073-Feb-12 00:00 23 51 40.33 +24 36 45.7 47.08 312.8618603634 26.3044613
2073-Aug-14 00:00 23 52 31.95 +24 49 03.1 47.11 315.6418739165 26.3042195
2074-Feb-13 00:00 23 51 40.53 +24 36 57.3 47.16 318.4216565204 26.3045300
2074-Aug-15 00:00 23 52 30.33 +24 49 01.0 47.19 321.2017384038 26.3056751
2075-Feb-14 00:00 23 51 40.69 +24 37 08.0 47.23 323.9817161684 26.3069288
2075-Aug-16 00:00 23 52 28.74 +24 48 58.4 47.26 326.7620959899 26.3086960
2076-Feb-15 00:00 23 51 40.84 +24 37 18.1 47.31 329.5424355575 26.3104561
2076-Aug-16 00:00 23 52 27.20 +24 48 55.4 47.33 332.3232149080 26.3125811
2077-Feb-15 00:00 23 51 41.00 +24 37 27.5 47.38 335.1039531217 26.3143279
2077-Aug-17 00:00 23 52 25.73 +24 48 52.3 47.41 337.8851064850 26.3159741
2078-Feb-16 00:00 23 51 41.19 +24 37 36.6 47.45 340.6661631250 26.3169159
2078-Aug-18 00:00 23 52 24.34 +24 48 49.3 47.48 343.4475583501 26.3175945
2079-Feb-17 00:00 23 51 41.43 +24 37 45.6 47.52 346.2287409193 26.3174539
2079-Aug-19 00:00 23 52 23.05 +24 48 46.5 47.55 349.0101221132 26.3168540
2080-Feb-18 00:00 23 51 41.72 +24 37 54.7 47.59 351.7911284179 26.3151602
2080-Aug-19 00:00 23 52 21.86 +24 48 44.2 47.61 354.5721698930 26.3127923
2081-Feb-18 00:00 23 51 42.05 +24 38 04.1 47.65 357.3526656288 26.3094031
2081-Aug-20 00:00 23 52 20.73 +24 48 42.3 47.68 360.1330427424 26.3057455
2082-Feb-19 00:00 23 51 42.40 +24 38 13.7 47.72 362.9127467774 26.3015826
2082-Aug-21 00:00 23 52 19.65 +24 48 41.0 47.75 365.6922599466 26.2975583
2083-Feb-20 00:00 23 51 42.74 +24 38 23.4 47.79 368.4710831365 26.2934393
2083-Aug-22 00:00 23 52 18.57 +24 48 39.9 47.81 371.2497695288 26.2900171
2084-Feb-21 00:00 23 51 43.04 +24 38 33.0 47.85 374.0278720167 26.2871290
2084-Aug-22 00:00 23 52 17.48 +24 48 38.8 47.88 376.8059860250 26.2853655
2085-Feb-21 00:00 23 51 43.28 +24 38 42.2 47.91 379.5836783193 26.2842374
2085-Aug-23 00:00 23 52 16.37 +24 48 37.4 47.94 382.3615591870 26.2840748
2086-Feb-22 00:00 23 51 43.46 +24 38 51.0 47.98 385.1391871696 26.2843147
2086-Aug-24 00:00 23 52 15.24 +24 48 35.7 48.00 387.9171567196 26.2853453
2087-Feb-23 00:00 23 51 43.61 +24 38 59.1 48.04 390.6949897075 26.2866869
2087-Aug-25 00:00 23 52 14.12 +24 48 33.6 48.06 393.4732557222 26.2886114
2088-Feb-24 00:00 23 51 43.75 +24 39 06.7 48.10 396.2514440776 26.2904232
2088-Aug-25 00:00 23 52 13.02 +24 48 31.2 48.12 399.0301005893 26.2923505
2089-Feb-24 00:00 23 51 43.89 +24 39 14.0 48.16 401.8086806126 26.2939102
2089-Aug-26 00:00 23 52 11.96 +24 48 28.7 48.18 404.5877061803 26.2954949
2090-Feb-25 00:00 23 51 44.05 +24 39 21.0 48.22 407.3665956339 26.2965449
2090-Aug-27 00:00 23 52 10.97 +24 48 26.2 48.24 410.1458442877 26.2972620
2091-Feb-26 00:00 23 51 44.25 +24 39 27.9 48.28 412.9248423800 26.2970596
2091-Aug-28 00:00 23 52 10.03 +24 48 23.9 48.30 415.7040726003 26.2962758
2092-Feb-27 00:00 23 51 44.48 +24 39 35.0 48.33 418.4829013260 26.2945387
2092-Aug-28 00:00 23 52 09.16 +24 48 22.0 48.36 421.2618006803 26.2923453
2093-Feb-27 00:00 23 51 44.73 +24 39 42.3 48.39 424.0401357992 26.2893477
2093-Aug-29 00:00 23 52 08.33 +24 48 20.4 48.41 426.8184085677 26.2860161
2094-Feb-28 00:00 23 51 45.00 +24 39 49.8 48.45 429.5960196202 26.2821596
2094-Aug-30 00:00 23 52 07.51 +24 48 19.1 48.47 432.3735266968 26.2785692
2095-Mar-01 00:00 23 51 45.24 +24 39 57.3 48.50 435.1503861705 26.2752485
2095-Aug-31 00:00 23 52 06.69 +24 48 17.9 48.52 437.9272188157 26.2728050
2096-Mar-01 00:00 23 51 45.45 +24 40 04.7 48.56 440.7035255146 26.2709070
2096-Aug-31 00:00 23 52 05.85 +24 48 16.6 48.58 443.4799688578 26.2699776
2097-Mar-02 00:00 23 51 45.60 +24 40 11.7 48.61 446.2560672260 26.2696723
2097-Sep-01 00:00 23 52 04.97 +24 48 15.0 48.63 449.0324857663 26.2703844
2098-Mar-03 00:00 23 51 45.71 +24 40 18.3 48.66 451.8087176126 26.2716587
2098-Sep-02 00:00 23 52 04.09 +24 48 13.1 48.68 454.5854073946 26.2736797
2099-Mar-04 00:00 23 51 45.80 +24 40 24.4 48.72 457.3620210856 26.2758314
2099-Sep-03 00:00 23 52 03.21 +24 48 10.8 48.74 460.1391793005 26.2783048
2100-Mar-05 00:00 23 51 45.88 +24 40 30.1 48.77 462.9163092806 26.2806896
2100-Sep-04 00:00 23 52 02.35 +24 48 08.3 48.79 465.6940016740 26.2832937
2101-Mar-06 00:00 23 51 45.97 +24 40 35.4 48.82 468.4716483939 26.2855656
2101-Sep-05 00:00 23 52 01.53 +24 48 05.6 48.84 471.2498134738 26.2875956
2102-Mar-07 00:00 23 51 46.08 +24 40 40.7 48.87 474.0278568717 26.2888765
2102-Sep-06 00:00 23 52 00.76 +24 48 03.1 48.89 476.8063215535 26.2897021
2103-Mar-08 00:00 23 51 46.24 +24 40 46.0 48.92 479.5845365105 26.2897072
2103-Sep-07 00:00 23 52 00.05 +24 48 00.7 48.94 482.3630197312 26.2891443
2104-Mar-08 00:00 23 51 46.43 +24 40 51.4 48.97 485.1410794424 26.2875876
2104-Sep-07 00:00 23 51 59.39 +24 47 58.7 48.99 487.9192381246 26.2853353
2105-Mar-09 00:00 23 51 46.65 +24 40 57.1 49.02 490.6968133300 26.2821900
2105-Sep-08 00:00 23 51 58.77 +24 47 57.0 49.04 493.4743527262 26.2787755
2106-Mar-10 00:00 23 51 46.88 +24 41 03.0 49.07 496.2512093005 26.2751210
2106-Sep-09 00:00 23 51 58.16 +24 47 55.6 49.08 499.0279908145 26.2717729
2107-Mar-11 00:00 23 51 47.09 +24 41 09.1 49.11 501.8041110989 26.2685871
2107-Sep-10 00:00 23 51 57.55 +24 47 54.3 49.13 504.5802409108 26.2660913
2108-Mar-11 00:00 23 51 47.27 +24 41 15.0 49.16 507.3558400948 26.2642288
2108-Sep-10 00:00 23 51 56.91 +24 47 53.0 49.18 510.1316121800 26.2634340
2109-Mar-12 00:00 23 51 47.42 +24 41 20.7 49.21 512.9070210537 26.2633402
2109-Sep-11 00:00 23 51 56.25 +24 47 51.4 49.23 515.6827674142 26.2640801
2110-Mar-13 00:00 23 51 47.52 +24 41 26.1 49.26 518.4583011834 26.2651943
2110-Sep-12 00:00 23 51 55.58 +24 47 49.6 49.27 521.2343053782 26.2668710
2111-Mar-14 00:00 23 51 47.62 +24 41 31.1 49.30 524.0101933775 26.2687672
2111-Sep-13 00:00 23 51 54.92 +24 47 47.5 49.32 526.7866151287 26.2710698
2112-Mar-14 00:00 23 51 47.70 +24 41 35.8 49.35 529.5629516554 26.2732699
2112-Sep-13 00:00 23 51 54.27 +24 47 45.3 49.36 532.3398291243 26.2753969
2113-Mar-15 00:00 23 51 47.80 +24 41 40.4 49.39 535.1165962531 26.2770413
2113-Sep-14 00:00 23 51 53.65 +24 47 43.0 49.41 537.8938521977 26.2784625
2114-Mar-16 00:00 23 51 47.92 +24 41 44.9 49.44 540.6709136313 26.2793283
2114-Sep-15 00:00 23 51 53.08 +24 47 40.8 49.45 543.4483523707 26.2797139
2115-Mar-17 00:00 23 51 48.08 +24 41 49.5 49.48 546.2254569839 26.2791708
2115-Sep-16 00:00 23 51 52.55 +24 47 38.9 49.50 549.0027868624 26.2778808
2116-Mar-17 00:00 23 51 48.26 +24 41 54.2 49.52 551.7796202594 26.2756504
2116-Sep-16 00:00 23 51 52.06 +24 47 37.2 49.54 554.5565143382 26.2728739
2117-Mar-18 00:00 23 51 48.46 +24 41 59.2 49.57 557.3327542246 26.2694791
2117-Sep-17 00:00 23 51 51.59 +24 47 35.9 49.58 560.1089334275 26.2658555

[Explorer1]

If only it had been noticed earlier, before closest approach... At any rate, a good argument for more wide field observations, even if interception remains implausible for this particular body.

[HSchirmer]

I agree in full about the value of getting such a sample, it would add to the knowledge about our own Kupier or Oort belt also.
And that was the reason I did that back-of-envelope type of calculation.
Only to find that a sample return would require a spacecraft of Frankensteinian proportions, so for several reasons not within a magnitude of our current capabilities.

Curious, getting a sample doesn't necessarily mean matching velocity, does it?
"Sample return" could be as simple as something crossing the projected path.

If we do get enough lead time in the future, are there any protocols about a obtaining a "reverse kinetic" sample?
That is, launch a 10kg steel manhole cover into the path of our 50,000 km/s visitor, kaboom, and then analyzing the debris?

[TheAnt]

Curious, getting a sample doesn't necessarily mean matching velocity, does it?
"Sample return" could be as simple as something crossing the projected path.

Well my idea for the cubesat sized craft where one would collide would be for only getting a spectra of the gas and flash of the collision.

But yes sample return might be remotely possible, lets imagine the impacting cubesat is basically a ceramic brick with only a minimum of controlling electronics and miniature thrusters.
Then other cubesat's that fly in formation might have a piece of aerogel on one or several sides.
None of the cubesat's will have any significant propulsion on its own as they would be KISS devices.
But if the trajectory is planned well and it need to be - as any part of the small craft would be literally vaporized by any +20km/s impact -and that would be game over.
Celestial mechanics would eventually bring the cubesat or the aerogel parts back to the vicinity of Earth - for retrieval by another craft.
Now this is again wild speculation, and I guess the real pro's here can poke as many holes in this idea that it look like swizz cheese. =)

[HSchirmer]

I guess the real pro's here can poke as many holes in this idea that it look like swizz cheese. =)

Following up on that - here's a stupid question-
Why isn't this comet falling into the sun?
How likely (or unlikely) are hyperbolic path, parabolic path, orbit, or crash?


I understand that Kuiper and Oort objects start with angular momentum, which you can't get rid of, so they just don't "fall into the sun"
But, our other interstellar visitors don't start in orbit, so, what's the likelihood that they miss the sun?

In retrospect, it may be a fundamental property of orbits, the number of possible paths through the "hill sphere" of gravitational influence is is always going to be much larger than the number of possible paths that impact the object,
but are there any empirical calculations of how likely a parabolic orbit is, compared to a collision?

[fredk]

It just depends on the velocity distribution of interstellar objects. If it really is interstellar, and so unbound to the sun, then that just means it's got a hyperbolic or (borderline bound) parabolic orbit. Closed orbit means bound, so not interstellar (barring having been perturbed by another body to become bound).

The boundary (parabolic) means it approaches zero velocity (relative to the sun) at large distances. The velocity distribution of interstellar objects is going to be broad, certainly not peaked near zero, so generically you'd expect them to come in on hyperbolic orbits.

And collisions are going to be rare - the sun's a tiny target on the interstellar (or even solar system) scale. Again, generically the objects will have angular momentum relative to the sun - it would take fine-tuning (ie dead-centre collision) for them to have zero angular momentum.

[ngunn]

I'd like to know the miss distance of its approach trajectory, in other words the distance from the sun to the asymptote of the orbit. If my mental estimate is about right there must be about a thousand of these things passing though the orbit of Neptune every few years.

[fredk]

That's called the impact parameter. It's just sqrt[(e + 1)/(e - 1)]r_p, where e is the eccentricity and r_p the perihelion distance. Plugging in the elements gives about 3.3 r_p, or about 0.85 AU, for the impact parameter.

So there should be 8 times as many such objects coming in with impact parameters inside double that, ie 1.7 AU. Etc. Double the distance means 1/4 the brightness (at the same observation distance). Anyway, the prospects should be not bad for spotting more farther out if we can reach the required sensitivity...

[JRehling]

I think the two most important kinds of scrutiny for such an object would be:

1) Isotopic analysis of heavy elements.
2) Millimeter scale resolution of chondritic (or the equivalent?) material.

Those would tell us something about how the system evolved differently from ours. We still don't understand what flash-fried the chondrules in our solar system, and seeing another analogue would be tremendously interesting.

The kinds of things you'd see from a flyby would certainly be interesting, but in this regard it's "just another" very small icy body, perhaps not very different from ones in our solar system, but whatever it's like, it wouldn't necessarily tell us about its system, just as a comet nucleus in our solar system doesn't tell you much about Saturn or Venus.

So I think a very valuable mission would be one that landed and performed in situ analysis of the stuff within an arm's reach. Perhaps lithobraking solves the hard problem of the delta-v. Have a small payload encased in concentric shells of crushable shield to spread out the impact delta-v over a longer time. The failed Deep Space 2 probes to Mars would be the closest analogue – 2.4 kg per probe, intended to survive impact. There, though, the delta-v was much less, there was some aerobraking, and – again – they failed despite that. But if you had many hundreds of kg of shield devoted to permitting the survival of a ~3 kg probe, maybe this gets easier.

[HSchirmer]

I'd like to know the miss distance of its approach trajectory, in other words the distance from the sun to the asymptote of the orbit. If my mental estimate is about right there must be about a thousand of these things passing though the orbit of Neptune every few years.

I'm curious whether the outbound path will take it anywhere near VGR1, VGR2 or New Horizons...
Also curious to know whether any heliopause measurements detected any shockwave or disturbance when this thing was inbound,
which might help identify what happens when it passes back out of sol-space to interstellar-space on the outbound trajectory.

Fun tangent - is there a theoretical maximum for speed from gravity assist orbits?
Say, hypothetically, we launch a ion-engine probe so that it gets a gravity assist ▲v from the moon, breaks earth orbit and heads for the Sun and Mercury.
Gravity assist from the Sun kicks in huge ▲v and gravity assist from Mercury aims it back towards the moon.
Gravity assist from the moon kicks in more ▲v and sends it back towards the Sun and Mercury.
Repeat as necessary.
Using 2 large airless bodies to "play catch" and get repeated gravity assists from a star, how fast can you get?

[Phil Stooke]

I'm afraid that's not quite how it works. To get from Mercury to the Moon you are increasing heliocentric velocity. To get from the Moon to Mercury you are reducing it. No net gain from bouncing back and forth.

More seriously, you need big objects to make this work best. Massive objects. So you might attempt a close solar flyby (probably allowed only by a Jupiter flyby to begin with... note that we are reducing heliocentric velocity here). The Sun gives a big boost (especially if you can add a rocket burn at closest approach), targeted to give a second Jupiter flyby. That is designed to give another boost - it will need to be low above the cloudtops, but Juno shows us we can do it). Then it's off out of the solar system.

I'm not sure that this would really work especially well given the need for thermal shielding mass at the Sun. Maybe lightsails would give better final velocity.

Phil

[fredk]

The sun also doesn't help. The slingshot mechanism relies on the three-body scenario: slinging around one object (eg Jupiter) in orbit around another (eg the sun). When you approach the sun all you'll do is continue outwards in the same orbit you were on moving inwards (apart from any slowing due to friction). That's a two-body problem and the only solutions are the conic sections.

[HSchirmer]

The sun also doesn't help. The slingshot mechanism relies on the three-body scenario: slinging around one object (eg Jupiter) in orbit around another (eg the sun). When you approach the sun all you'll do is continue outwards in the same orbit you were on moving inwards (apart from any slowing due to friction). That's a two-body problem and the only solutions are the conic sections.

Hmm, guess I have my frames of reference crossed up.

Thinking of Cassini, Venus-Venus-Earth-Jupiter gravity assist, curious that you can get a gravity assist from a planet that has less heliocentric speeed.
Guess I'm missing something.

I had though that, (way oversimplifying) with an idealized "hairpin orbit" you get a sligshot boost of roughly 2x the approach velocity between the object and the planet.
That way, you "shoot an arrow in the air" and grab "2U" each time you hairpin around the moon or mercury.
Guess that doesn't quite work.

So, if we want "ludicrous speed" to intercept something, we have to fall back to Pascahal-B, where US cold war nuclear testes (may have) launched a manhole at 6x escape velocity...

Attached image(s)

 

[fredk]

For the sun, the outgoing speed will clearly be the same as the ingoing, in the frame of the sun (ie, for the frame in which U = 0 in your sketch). But the point is that that's the relevant frame, since it is the speed relative to the sun that we're talking about maximizing.

The sun won't help, but I don't know how large a boost you might practically achieve given multiple passes of planets such as Jupiter etc...

[Paolo]

I'm curious whether the outbound path will take it anywhere near VGR1, VGR2 or New Horizons...

2017 U1 was coming from the general direction of the solar apex and V1, V2 and NH (and Pioneer 11) are all going in the general direction of the apex, so they must have come close (like tens of AU close) in the inbound leg

[Paolo]

and a second arXiv paper:
Kinematics of the Interstellar Vagabond A/2017 U1

The initial Galactic velocity vector for the recently discovered hyperbolic asteroid A/2017 U1 is calculated for before its encounter with our solar system. When the velocity is compared to the local stars, A/2017 U1 can be easily ruled out as co-moving with any of the dozen nearest systems, i.e. it does not appear to be associated with any local exo-Oort clouds (most notably that of the Alpha Centauri triple system). The object's velocity is within 5 km/s of the mean Galactic velocity of the stars in the solar neighborhood (<25 pc), so its velocity would appear to be typical for that of a body whose velocity was drawn from the Galactic velocity distribution of the local stars. These calculations strengthen the interpretation that A/2017 U1 has a distant extrasolar origin, but not among the very nearest stars.

[Gerald]

... Perhaps lithobraking solves the hard problem of the delta-v. Have a small payload encased in concentric shells of crushable shield to spread out the impact delta-v over a longer time. The failed Deep Space 2 probes to Mars would be the closest analogue – 2.4 kg per probe, intended to survive impact. There, though, the delta-v was much less, there was some aerobraking, and – again – they failed despite that. But if you had many hundreds of kg of shield devoted to permitting the survival of a ~3 kg probe, maybe this gets easier.

Overcoming the speed of sound within the solid material of the shield would certainly be a challenge. Longitudinal forces in solids usually are transmitted with about the speed of sound of the solid medium. So, the mechanism would need something faster, like electromagnetic fields.

[nprev]

Going back to the object itself, interesting that it seems to be fairly red. First thing that brings to mind is thiolins, so maybe this thing used to be an Oort Cloud denizen somewhere else. A thick layer of that stuff may have been enough to prevent significant outgassing as well (plus it's definitely not spending much time in the inner Solar System to get really warmed up).

Hopefully additional spectra will reveal some absorption details, maybe even some delayed outgassing if the body has significant thermal inertia.

[Gladstoner]

Going back to the object itself, interesting that it seems to be fairly red. First thing that brings to mind is thiolins, so maybe this thing used to be an Oort Cloud denizen somewhere else. A thick layer of that stuff may have been enough to prevent significant outgassing as well (plus it's definitely not spending much time in the inner Solar System to get really warmed up).

Hopefully additional spectra will reveal some absorption details, maybe even some delayed outgassing if the body has significant thermal inertia.

Would tholins indicate an icy body, or could they also form on carbon-rich material (C-type asteroids)?

[Gerald]

You'll probably need an environment, where light and mostly reduced, hydrogen-rich molecules like CH4 and NH3 don't escape easily, such that they can react under energetic radiation to more complex compounds like the broad class of tholins. Within a low-gravity environment, this will probably require low temperatures.
Carbon taken allone would result in black, soot-like compounds.

[Gladstoner]

Are there asteroids in the inner solar system with a similar reddish color?

It's just odd how a tiny 500-foot object with a KBO-like color comes in from the deep, passes 0.25 AU from the sun, and remains intact with no detectable outgassing. After many years of following comets, my money would have been on a break-up of the object just before perihelion.

[Gerald]

A coating of a few microns of a pigment like tholins should provide the visible color of the object. The interior may well be rocky. The color of tholins will also win over the colors of translucent minerals like silicates in a mineral-tholin mix.
A considerable portion of the material of a stellar system is probably ejected during the first few millions of years after its Jeans collapse,
A rocky body of the inner stellar system may travel through outer parts or interstellar dust clouds, and collect a coating of tholins.
Tholins should survive for some time in an inner stellar system, before they will be degraded by stellar wind or micrometeorites.
That's just one out-of-the-hip scenario. There are certainly many more of varying likelihood.

Amalthea seems to be dark red. It's not in the inner solar system. But it's an example of a small red body with the potential to be ejected by close encounters or collisions. The composition of the interior of a small body depends mostly on its origin. An outer layer may have accreted later, in a new environment.

[JRehling]

A/2017 U1 had no observed coma, so it had little in the way of volatiles, at least near the surface. It could have had volatiles below a darker "crust" that didn't break through, but a dark object passing 0.2 AU from the Sun should have heated up quite a bit. It might be a chip off some exosystem's version of Mars. The surface color might be a thin coating or go all the way down. It's certainly spent a lot of time in interstellar space, which may have caused slow but thorough transformations that nobody's yet imagined.

I'd guess that in future decades we'll be able to spot much smaller versions of this thing which visit the solar system with considerable frequency and we'll start to explore them. There's a lot of untapped potential for huge light-bucket telescopes to monitor the skies and then things that are dimmer and dimmer will be detected earlier. If the size distribution of interstellar objects is like that of the asteroids in our solar system, then at some size threshold, there seemingly must be interstellar interlopers every year. But the process of interstellar travel might introduce some unimagined selection effects. For one, reaching the escape velocity of a star may be extremely violent.

[fredk]

Makes me wonder about capture: some extremely small percentage of these interstellar interlopers will become bound to the sun through an inverse slingshot encounter with Jupiter or other planets. So there must be some now orbiting the sun (or planets). Of course identifying them long after they've left their initial hyperbolic orbit would be insanely hard.

[Gladstoner]

It has been hypothesized that comet 96P/Machholz could be a captured extrasolar object based on its unusual composition and, to a lesser degree, its unusual orbit. However, there are possible solar-system-origin scenarios that could explain these anomalies.

Even a slight possibility that this comet could be interstellar should bring this comet to the top of the list of potential exploration targets.

[nprev]

Amalthea seems to be dark red. It's not in the inner solar system. But it's an example of a small red body with the potential to be ejected by close encounters or collisions.

Amalthea's a bit of a special case, though. Its reddish color (plus some yellows, as I recall) is likely due to deposition of Ionian volcanic ejecta over time. Volcanically active large moons may be common around Jovians, but we have no data one way or another. Also, I don't see a close moon of a gas giant being knocked out of orbit in one piece considering the acceleration required to accomplish just that alone (to say nothing of achieving system escape velocity) not to mention doing so without shaking off all the ejecta deposits...

Probability and observations to date seem to strongly favor this thing being an asteroid or a relatively rocky TNO-equivalent. Again, hopefully better spectral data will be acquired to help constrain the composition and possibilities.

[Gerald]

I wouldn't call the ejection of a small Jovian moon as a likely origin. But take an eccentric Amalthea equivalent with a slingshot or a resonant encounter with an Earth-sized hot moon around a gas giant, and consider the Oberth effect near periapsis.
All I wanted to say is, that there may exist many unlikely scenarios that sum up to a non-negligible probability. When we look at exoplanets, there are all conceivable scenarios of stellar systems, such that we can't simply extrapolate our solar system as representative.
Just observing a red color and lack of sublimation doesn't constrain the scenarios of the origin of the body very much. All we know is, that probably several meters of the top layer don't contain relevant amounts of volatiles, and the material of the top few microns looks red.

[Paolo]

I suspect that the xenoasteroid's redness has something to do with its exposure for millions of years to energetic cosmic rays and to its surface being mostly untouched ever since it abandoned its original solar system. keep in mind, that since then, it should have encountered mostly minuscule interstellar dust particles.

[nprev]

Pity we'll never get a high-res image of it. Its cratering history might provide some clues about where in its parent system it originated, and any truly fresh ones could provide clues about the density of meteor-sized objects in the interstellar medium (unless it got whacked by junk entering our system).

[HSchirmer]

I suspect that the xenoasteroid's redness has something to do with its exposure for millions of years to energetic cosmic rays and to its surface being mostly untouched ever since it abandoned its original solar system. keep in mind, that since then, it should have encountered mostly minuscule interstellar dust particles.

Or Dave Lister finally finished that paint job...

Attached thumbnail(s)

 

[Gerald]

I wonder, how this observation of an extrasolar asteroid connects to interstellar dust, as observed by Ulysses in 1992.
All models I've been coming across ignore the presence of interstellar grains much larger than one micron.
So, there arise two straightforward questions:
- Can the interstellar asteroid be regarded as a particular large dust grain of a population of interstellar dust? and
- Do explanations of the grain size distribution of interstellar dust ignore interstellar asteroids as a significant supply of material?

Taken together, needs the "IDGSDF" to be extended to the grain size of asteroids in order to obtain a proper model of interstellar dust?

[Paolo]

IIRC interstellar grains are mostly supposed to form in dust clouds and be expelled by stellar winds, or in supernova explosions, while exocomets and exoasteroids are ejected by good old gravitational perturbations. So the origins of these bodies (if you can call interstellar dust "body") are different.
we have also seen our solar system produce its interstellar comets, for example comet Bowell in 1980 and possibly comet Lexell in the late 18th century (which may or may not have been expelled from the solar system). I remember reading an article in Sky & Telescope (but it may have been a different magazine) in 1997 or 98 explaining that expulsion from the solar system is a common fate for planet-crossing asteroid such as near Earth objects.

[Gerald]

The paper I mentioned above says at the end of page 1, that there is a discrepancy between the expected residence time of 2.5 Gyrs of a dust grain in the ISM and the expected lifetime of 0.5 Gyrs of a dust grain. Then they try to overcome this discrepancy by grain growth in cold molecular clouds (subsection 4.2):

The only possible site of grain growth in the ISM are the dense molecular clouds of the cold phase of the ISM (Draine 1990).

With the presence of interstellar comets and asteroids, I'm not sure, whether this conclusion is evident, since new grains could also form by collisions of small dust grains with these larger bodies, such that we should get a secondary population of interstellar dust grains made of debris, possibly statistically comoving with the (rogue) asteroids and comets. If this turns out to be realistic, we should get information about "interstellar interlopers" by the analysis of interstellar dust.
Since there may exist many such unbound small bodies, some useful result regarding an origin could only be obtained, if these small bodies form themselves a more or less comoving cloud, inducing such a co-motion into the according presumed debris made of interstellar dust.

[HSchirmer]

So, there arise two straightforward questions:
- Can the interstellar asteroid be regarded as a particular large dust grain of a population of interstellar dust? and
- Do explanations of the grain size distribution of interstellar dust ignore interstellar asteroids as a significant supply of material?

Taken together, needs the "IDGSDF" to be extended to the grain size of asteroids in order to obtain a proper model of interstellar dust?

One of the more interesting things I'd come across about fine dust, is that within the solar system,
magnetic field effects can be much stronger than gravity or radiation.

That does suggest that, depending on what sort of dust you have, (i.e. A) whether the grains have an internal magnetic field, B ) they are susceptible to having a field induced, C) they're non magnetic) you could get some interesting magnetic attraction effects.

[Paolo]

a new naming convention for interstellar objects: meet I/2017 U1 'Oumuamua.

https://www.minorplanetcenter.net/mpec/K17/K17V17.html

[stevesliva]

You omitted the 1, which when you get down to things like 2 Pallas and 4 Vesta, is a neat bit of history.

1I/'Oumuamua

So when Rama arrives in 2130 (Arthur C. Clarke), it will be 367I/Rama

[JRehling]

In our solar system, small (asteroid) and very small (dust) solid particles occupy a continuous distribution of size and occurrence, but there are many factors that hold constant in our solar system that will not hold for small bodies created galaxy-wide, and there are still more factors that will not hold constant for bodies that have crossed interstellar distances, and there is yet another striking selection effect in the fact that this thing survived a near-brush with the Sun.

The oldest stars in the universe would have no metals in them, just hydrogen and helium. There's no way to make a solid body out of those elements, so the source star has to be second generation, at least. But it might come from a system that has plentiful oxygen but nothing so heavy as iron or even silicon. Systems that are older will have fewer heavier elements, which would mean no rocks or even dust for the bodies in that system to begin accreting around. But it seems impossible for something made only of ice to survive that passage by the Sun, or even to be red. A younger system will have more of the elements to explain this thing's nature, but less time for the interstellar journey to have taken place. A lot of these factors are easy to mention in qualitative terms but are unconstrained quantitatively.

Other selection effects: Possibly the existence of giant planets that could have enabled a gravity assist to eject them this far, this fast. And that constrains the source star in ways that we don't yet understand. Juno and the newly-observed neutron star collision are both opportunities to learn the basics of how elemental/planet creation depends upon the stuff (nuclear chemistry) that's available.

So, there's a lot to learn about a lot. If anything, I think this discovery makes it seem worthwhile to prepare for future bodies, and if possible, to catch them and do in situ compositional analysis before they make any close approaches to the Sun.

[Paolo]

a good update on what's known about 'Oumuamua, cortesy of Sky & Telescope:
Update on ‘Oumuamua, Our First Interstellar Object

and ideas for a reconnaissance mission using existing or near-term technology
Project Lyra: Sending a Spacecraft to 1I/'Oumuamua (former A/2017 U1), the Interstellar Asteroid

[HSchirmer]

a good update on what's known about 'Oumuamua, cortesy of Sky & Telescope:
Update on ‘Oumuamua, Our First Interstellar Object

and ideas for a reconnaissance mission using existing or near-term technology
Project Lyra: Sending a Spacecraft to 1I/'Oumuamua (former A/2017 U1), the Interstellar Asteroid

Might be "a day late and a dollar short" but could Cassini have caught up to Oumuaroua?
Probably not, because Oumuamua and Saturn are on different sides of the sun now, (would require a slingshot past Jupiter and the sun IIRC)

But as a "what if" question, let's say that Oumuamua was heading towards Saturn...
There was an article "Cassini Saturn-escape trajectories to Jupiter, Uranus, and Neptune" which mentioned a possible Uranus or solar escape trajectories for a Cassini extended mission, so given enough computing time and slingshots, it appears Cassini could match that velocity.

[djellison]

The spacecraft would not have survived the trip. Remember - the reason Cassini was scuttled was because it was almost out of fuel for attitude control.

[hendric]

With all the hot Jupiters we've discovered, I would expect that this object is more likely from the inner portion of its source solar system, scattered to a Galactic orbit by an approaching Big Brother.

Maybe it's not a stripped extrasolar Oort Cloud member, but rather an extrasolar Vulcanoid!

That would explain the lack of outgassing during the close approach, it's already been "cooked dry". Don't know enough about asteroid spectrography to talk about if it could be as red as it is with limited organics. Maybe Alan Stern can comment?

[Hungry4info]

With as deep in their star's gravitational wells as they are, it would be quite a feat for a hot Jupiter to kick an asteroid out of its planetary system that wasn't already on a highly eccentric orbit.

[HSchirmer]

With as deep in their star's gravitational wells as they are, it would be quite a feat for a hot Jupiter to kick an asteroid out of its planetary system that wasn't already on a highly eccentric orbit.

Well, I think the idea is a Nice model, gas giant forms at the snowline, then makes it's way to the inner orbit by gas drag,
or by dumping excess angular momentum by scattering asteroids or comets.

It's counter-intuitive, gas giants don't have retro-rockets to slow them down and spiral in, so their method of braking is tossing asteroids around.
-edit- It's sort of a solar system version of the gravel run-outs you have for trucks that loose their brakes - tossing small rocks around is a way to scrub off speed.

[hendric]

Well, my assumption was that the source solar system had a lighter mass sun, such as a red dwarf. Should be much easier for a hot jupiter in that situation to knock about protoplanetoids during its dive from the outer parts to the inner parts. Considering how compact some of these systems are, multiple encounters of the same or other Jupiter class planets in the same system is entirely likely.

[JRehling]

Hot Jupiters are relatively rare. We discovered so many of them early in the exoplanet discovery process because there are two observational biases favoring them: size and proximity to their star, both factors favored by both the Doppler method and the transiting method. There are only about 0.06 Jupiter-sized planets per sunlike star with periods <500 days, and even fewer in the "hot" bin.

The most common kind of star, red dwarfs, have few Jupiter-sized planets at all, so far as we know. Sunlike stars are less common, but have more Jupiter-sized planets. Still larger stars are still rarer, but may have more, if the trend continues.

We're almost totally ignorant about the frequency of planets distant (>10 AU) from stars. We know that they exist (Fomalhaut b, Uranus, Neptune) but not their frequency.

All told, we can't possibly have a good handle on the various observational biases: How many stars of what size have planets of what size at what distances, and potential interloper population at what distances, and at what times in the evolutionary history of the system. We only have very partial information to begin to answer this. The dynamics follow universal laws that are well understand, but most of the rest is unconstrained now. We know the planet population function only for the more common kinds of star and only for relatively close-in orbits (~500 days for Earths and Super-Earths, out to ~10 AU for giant planets). And then there are biases allowing the body's survival and having made the long journey here. Unknowns on top of unknowns.

It does seem likely that this body is "baked" / rocky and not comet-like. Empirical observations FTW!

[fredk]

Here's a twist - a paper looking at the possibility that the interloper is a chunk of dark matter: Could 1I/'Oumuamua be macroscopic dark matter?

There are two mass ranges for such lumps allowed by gravitational lensing and cosmic microwave background constraints. The paper is pretty sketchy, but it seems that the lower mass range (around 10^15 g) would imply that many more of these should've been seen, so that range should be ruled out. The heavier mass range (around 10^22 g) is potentially ruled out by the fact that such a heavy mass would produce noticable perturbations on the orbits of solar system bodies. (The heavy range corresponds very roughly to masses in the range of a small moon such as Pandora to a mid-sized moon such as Iapetus.)

So the idea may not work, which might be interesting as a new constraint on certain types of dark matter.

[nprev]

Well...at least it's a testable hypothesis if they claim it would have caused perturbations of the inner system during its passage. Short of that, you could use Occam's Sledgehammer to eliminate it...no need for fine work provided by the Razor...

[dudley]

Examination of the light curve of Oumuamua as it rotates is now reported to suggest an object 30 meters wide by 180 long. That's a remarkably long, thin object, about the shape of a thick cigar; length to width ratio 6 to 1. That's over twice the longest, thinest asteroid known to inhabit our solar system.

[TheAnt]

Examination of the light curve of Oumuamua as it rotates is now reported to suggest an object 30 meters wide by 180 long. That's a remarkably long, thin object.....

It might also be a darker area that seemingly gives that result.
If that is correct it might be a shard from some kind of collision, or perhaps even from uneven heating when it passed close to its primary star when it got ejected.

@nprev: "Occam's Sledgehammer" Yes I felt that paper was bordering on too speculative. That the first interstellar object also have to be something really spectacular.
Then again, it's good science to check even on less likely possibilities.

[Explorer1]

Examination of the light curve of Oumuamua as it rotates is now reported to suggest an object 30 meters wide by 180 long. That's a remarkably long, thin object, about the shape of a thick cigar; length to width ratio 6 to 1. That's over twice the longest, thinest asteroid known to inhabit our solar system.

Very interesting/strange...How can something like that stay together? It's not a rubble pile like Itokawa (which is bigger), so it must be more solid?

I wonder what Arthur C. Clarke would say...

[fredk]

It's not entirely clear what Occam would say about this. We know dark matter exists, but have no idea what form it takes. There's been no sign of the "nominal" WIMPS yet, so "chunks" are a real possibility (medium-sized black holes are currently popular, which, being black, we wouldn't've seen).

Another point against the dark matter hypothesis I forgot to mention is that Oumuamua was moving about a tenth the speed expected for typical dark matter particles, but apparently at a not-surprising speed for an interstellar interloper.

The other side of this is: what do we expect for the local density/distribution of asteroids/comets kicked out of extrasolar systems? Surely there must be some estimates of this. Of course any such estimates would span a wide range since the details are very unclear, but if the estimates are that we'd expect to see such an interloper no more often than once in, say, 10 000 years, then the observation of one would be an important data point and perhaps point to other possibilities (if not a gross misunderstanding of solar systems). On the other hand, a predicted rate consistent with one per decade or so would support such an origin. Has anyone seen such estimates?

[dudley]

Very interesting/strange...How can something like that stay together? It's not a rubble pile like Itokawa (which is bigger), so it must be more solid?

I wonder what Arthur C. Clarke would say...

The spectra of the object suggested similarities to D and P class asteroids. These are made of silicates, carbon, and perhaps some ice in their interiors. I don't know how well such material would bear spinning, once every 8 hours, if formed into such a long thin shape. Seeing no asteroids belonging to our own solar system that come anywhere near this shape, I'm inclined to suspect that such an object would be likely to fly apart, or be knocked apart by impacts.

[Ron Hobbs]

ESO has a press release out today with an artist's impression of 'Oumuamua. It looks very much like the proverbial needle in a haystack.



https://www.eso.org/public/news/eso1737/

I bet Arthur Clarke would have fun seeing this discovery.

[Gerald]

Possibly a collision fragment. But figures of equilibrium of gravitationally bound polytropes allow for elongated Jacobi ellipsoids, too.

[dudley]

The differences in reflectivity, through the course of its rotation, are held to imply that the object is at least 10 times longer than it is wide. If the two ends don't align directly with Earth, which would be quite a coincidence, the elongation would be even greater, we're told. The 'fat cigar' has become quite a thin one! Not a contact binary, it seems. The object is reported to be spinning too rapidly for this to be a stable configuration. The article, linked below, has some even less probable explanations for the object.

BBC Article

[fredk]

It's worth pointing out that the lightcurve brightness range (a factor of ten) determines the ratio of only two axes (on the assumption its shape is roughly ellipsoidal). So for axis length ratios a:b:c they can say that a:b is roughly 10:1, but c is unconstrained. So the shape could be crudely slab-shaped, if c ~ a (or cigar-shaped if c ~ b ). I don't know if formation scenarios would be any easier for a 10:1 thickness slab vs the cigar.

The authors also claim that it's unlikely to be roughly spherical with albedo markings explaining the lightcurve. But perhaps a combination of both would be easier to swallow: a less extreme cigar or slab together with albedo markings.

Either way I'd think there are prospects to learn more about this, since that paper shows a lightcurve over only less than a day in total. A cigar configuration lightcurve would be sensitive to the angle between line of sight and spin axis, so data over a longer stretch may tell us whether geometry or albedo or some combination is the best explanation.

[dudley]

The linked article is a few days old, so has the old 6:1 aspect ratio. However, they do characterize the dimensions as 30 by 30 by 180 meters, which sounds cigar-, rather than slab-shaped.

NOAO article

[fredk]

You can read in the original Nature paper linked in the ESO release that c is unconstrained from the lightcurve.

[Floyd]

There must be Psyche-like bodies in other systems. A metal fragment could certainly have that shape, but could its surface turn that particular red (definitely not thinking iron rust red).

[Explorer1]

Have we confirmed (from any 'precovery images') that there is no coma, and there wasn't even at perihelion? Would any observatory have been looking in the right direction back then, or even before?

[dudley]

The trend in thinking about this object now, is that it is quite dense. Presumably, it has to be dense, so it won't spin itself to pieces, given its fairly rapid rotation, and strange shape. The spectra taken of this object suggested a likeness to class D and P asteroids in our solar system. However, these aren't very dense at all, only about 1.4 times that of water. A very peculiar object, all around.

[TheAnt]

So we have to accept that 1I/2017 U1 truly have one remarkable shape.
According to one hypothesis it could have been formed from metal during the early phase of a stellar system in making, when the cores of small asteroids were molten.
In that case it had been 'squirted' out as two minor blocs collided.

The other one already proposed here is that it's a shard, it does not necessarily need to be caused by a collision.
Temperature swings can have rocks crack also, and so it might have left the parent body in a less dramatic way.

But I got one of my own, based on nothing else but garage physics and my experience of sandblasting.
That is that it started out as an oval object, since then have been eroded by micrometeorites and so have gotten the current shape.

And yes I agree, Arthur C. Clarke would have been amused to write an essay on this one.

[Ron Hobbs]

The artwork from M. Kornmesser at ESO is the APOD for 11/22/2017. The write-up mentions 'Oumuamua's resemblance to the craft in Clarke's story.

A remarkable find!

[dudley]

So we have to accept that 1I/2017 U1 truly have one remarkable shape.
According to one hypothesis it could have been formed from metal during the early phase of a stellar system in making, when the cores of small asteroids were molten.
In that case it had been 'squirted' out as two minor blocs collided.

The other one already proposed here is that it's a shard, it does not necessarily need to be caused by a collision.
Temperature swings can have rocks crack also, and so it might have left the parent body in a less dramatic way.

But I got one of my own, based on nothing else but garage physics and my experience of sandblasting.
That is that it started out as an oval object, since then have been eroded by micrometeorites and so have gotten the current shape.

And yes I agree, Arthur C. Clarke would have been amused to write an essay on this one.

A 'squirting out' of molten material, which forms, essentially, a cylinder, strikes me as surprisingly organized. A multitude of roundish blobs seems likelier.

If Oumuamua is a shard, one wonders why we don't see its like in asteroids belonging to our solar system. Granted, a long history of collisions would probably break up a long thin asteroid into smaller pieces. But wouldn't more recent collisions make ones that we could still observe?

Long shards recently cracked off larger asteroids in our solar system by cycles of heat and cold should still be observable, too, shouldn't they? The closest we have seems to be Eros, but it's only about 3 times longer than it is wide; more of a 'potato' than a 'thin cigar'.

Fine particles in space could erode an asteroid, but would probably do so evenly across its surface. Its rotation should facilitate that, as would the multidirectional distribution of the particles.

[Gladstoner]

Objects in our solar system have been subjected to billions of years of impacting, turning many of them into loose rubble piles. Perhaps 1I/2017 U1 escaped this destructive process by being ejected from its system very early on.

[dudley]

Perhaps Oumuamua was ejected from its home system very early. If so, it seems that it should have retained the ices that primordial objects subject to ejection are expected to have. Oumuamua had no coma and no tail, so seems bereft of ice.

Shouldn't comparatively recent asteroid collisions, or spallings in our solar system have produced some long, thin shards, like Oumuamua, that haven't been broken up yet, say, in the last few million years? We don't find any, though.

[Gladstoner]

Shouldn't comparatively recent asteroid collisions, or spallings in our solar system have produced some long, thin shards, like Oumuamua, that haven't been broken up yet, say, in the last few million years? We don't find any, though.

Perhaps if they come from the relatively undisturbed interiors of larger asteroids.

[Gerald]

As far as I understood, any detectable cometary activity has been ruled out. So, there shouldn't be much deviation from a Kepler orbit.

[nprev]

ADMIN NOTE: Two posts in violation of rule 1.3 removed.

[TheAnt]

A 'squirting out' of molten material, which forms, essentially, a cylinder, strikes me as surprisingly organized. A multitude of roundish blobs seems likelier.
If Oumuamua is a shard, one wonders why we don't see its like in asteroids belonging to our solar system. Granted, a long history of collisions would probably break up a long thin asteroid into smaller pieces. But wouldn't more recent collisions make ones that we could still observe?

Agreed that those 2 ideas were less likely, and why I looked for a third explanation.
We do have a handful of elongated asteroids in Sol system, even that we've studied close like Eros, Ida and Itokawa and then we've got good radar images of Kleopatra.
And all those are elongated indeed. Perhaps there's more of a smaller size that we simply have not had gotten a good look at yet - it's not unheard of 1I/2017 U1 happen to be a notch longer.

Now the explanation might be in any of those areas that make Oumuamua different from asteroids in the solar system.
So my idea of interstellar sandblasting assumed that Oumuamua might have started out something like those mentioned above.

There might be other ones, the event that had it ejected could have caused a breakup of somewhat larger body.
The ultra low temperatures in interstellar space combined with small colliding objects when the object is ultra cooled could be another factor.

Well lets see if any of the astronomer and or physicists comes up with a hypothesis.

[dudley]

The length of Oumuamua was first given as 180, and later as 400 meters. Recognizing that it is a point source, can this wide range of values be solely attributed to interpretation of like data? Could the object have changed its rotational orientation with respect to Earth? We're told that the less directly its ends align with Earth, as it spins, the less its brightness will vary, and so the less elongated it will seem. Could its ends align with Earth better now, than formerly, causing the longer length estimate?

[nprev]

I haven't seen error bars for any of these measurements, but they have to be getting larger by the hour as the object recedes. It's important to note that what we're likely seeing in the press are best-guess median numbers instead of what is really known, which would be a set of constrained ranges plus or minus for each dimension, and the resolution range given this thing's small size and large distance is likely at best several tens of meters...and decreasing. To my knowledge there haven't been any truly high-precision measurements to date such as stellar occultation observations.

In the end, all we can really say that we know with high confidence is the rotation period, that it's probably markedly non-spherical (although large surface albedo variations are not ruled out and may therefore modulate how far out of round it is), and that it has spectral attributes that resemble those of some groups of asteroids. And, of course, that it's of extrasolar origin.

[fredk]

Adding to nprev's comments, the lightcurve only pins down the ratios of the axes (and only roughly). To estimate actual dimensions, all they can do is compare the observed brightness (since it's only a point source) with assumptions about how dark the surface is (albedo). A different assumption for the albedo gives different dimensions (eg with darker albedo it must be larger to appear as bright from earth). So that may explain part of the variation out there.

[JRehling]

In real estate, the three most important things are location, location, location.

With fragments from another place, the three most important things are selection bias, selection bias, selection bias.

Meteorites found on Earth are disproportionately irons because they (1) Survive the trip and (2) Are easily distinguished from terrestrial rocks.

Meteorites from Mars appear to be disproportionately from volcanic surfaces because, it's been hypothesized, they (1) Survive the trip and (2) Begin their departure from Mars at high elevation, already above some of the martian atmosphere.

So if this thing from outside the solar system looks very odd, we have to consider that it has been through several rounds of exceptional selection, and therefore selection bias. Its inbound velocity of 26 km/s relative to the Sun would indicate, if it escaped from earthlike distance from a sunlike star an initial velocity of about 70 km/s. Not a lot of structures would survive that. So it may be less surprising to see that it's remarkably rigid: Snowballs aren't going to survive the trip that it survived.

[Floyd]

Excellent point on multiple rounds of exceptional selection.

[Paolo]

I remember reading an article in Sky & Telescope (but it may have been a different magazine) in 1997 or 98 explaining that expulsion from the solar system is a common fate for planet-crossing asteroid such as near Earth objects.

turns out it was a paper in Nature in 1994: Asteroids falling into the Sun where it is shown that expulsion from the solar system is the second most likely fate of NEOs. Even Toutatis was computed to be injected in a hyperbolic trajectory in the paper. Since it was published, we have better understanding of how the Yarkovsy effect is more efficient in moving object to the resonant areas and replenish the NEO population than collisions, mentioned in the paper.

[HSchirmer]

A/2017 U1 had no observed coma, so it had little in the way of volatiles, at least near the surface. It could have had volatiles below a darker "crust" that didn't break through, but a dark object passing 0.2 AU from the Sun should have heated up quite a bit. It might be a chip off some exosystem's version of Mars. The surface color might be a thin coating or go all the way down. It's certainly spent a lot of time in interstellar space, which may have caused slow but thorough transformations that nobody's yet imagined.

I'd guess that in future decades we'll be able to spot much smaller versions of this thing which visit the solar system with considerable frequency and we'll start to explore them. There's a lot of untapped potential for huge light-bucket telescopes to monitor the skies and then things that are dimmer and dimmer will be detected earlier. If the size distribution of interstellar objects is like that of the asteroids in our solar system, then at some size threshold, there seemingly must be interstellar interlopers every year. But the process of interstellar travel might introduce some unimagined selection effects. For one, reaching the escape velocity of a star may be extremely violent.

https://www.nature.com/articles/s41550-017-0361-4.epdf?referrer_access_token=Tv9RQYVZTfUOErHaUga4wtRgN0jAjWel9jnR3ZoTv0PcZvQWL5Z-R4Pni3X6og8peG3Rn-XTaAylcyVMjW1tWwY3l34gQKTwe31gWMPPHhEgp-C7DNSLtS7xKRF0ZepVCvzXiiOND3IZLksD176yGOWWBk0HdDnSqmjrLfFWwvHLSg1yjnizORiTdn0S3u
2h83v2EKfs-pNVvrFczQjveJ9dd2V6Dr4iSmtcmg959UlmyNoK6006UlQ8oAg5dUQOjAJxzCCP14FpFFLiuj2OiQ8qW
kEzTkVaR45J9J-7RpVD6nn2jbr-sdgEOCoUsdUE&tracking_referrer=www.spiegel.de://https://www.nature.com/articles/s41...=www.spiegel.de


"We've discovered that this is a planetesimal with a well-baked crust that looks a lot like the tiniest worlds
in the outer regions of our solar system," Bannister said in a statement.
"It has a greyish/red surface and is highly elongated, probably about the size and shape of the Gherkin skyscraper in London."

Ok, so we've been visited by an interstellar version of a state-fair battered and deep-fried pickle?
Chrunchy crust on the outside, moist on the inside?

[Gerald]

This seems to be within the possible scenarios on the basis of the noisy data.
But lack of evidence regarding the interior appears to be a pretty thin basis to conclude "moist" in the interior.
I'd be pretty sure, that we'll also see different interpretations in the future.

[JRehling]

It seems like the number of possible hypotheses is hard to bound, but one that comes to mind would be that it is a body that was once part of another planetary system that was ejected via gravity assists and has taken a long time to cross interstellar distances.

A gravity assist adds a velocity less than the orbital velocity of the assisting (large) planet to the assisted (small) object.

For this object to get such a large velocity before arriving at our system would require some very exceptional circumstances – compared to anything in our system. It seems that the velocity of the assisting object must have been very high. So one scenario would be a double star system or a system with a hot Jupiter that accelerated a small object that got in the right place at the right time. This would necessarily imply a passage close to at least one star, although that passage could have been arbitrarily brief and the star need not necessarily be as hot as Sol.

By no means does this discussion exhaust the possibilities, but it seems to be copacetic with our knowledge of planetary systems around dwarf stars. I don't know how one could quantify the possibility that it might come from a system very atypical of ones we currently know of.

[nprev]

We've got evidence that many systems have planets extremely close to their stars, and not all are hot Jupiters. In fact, entire systems have been found that would fit within Earth's orbit. This may increase the probability of ejection due not only to greater velocities imparted during encounters but a significantly higher probability of multiple encounters over time.

For example, I can easily see an object like this in a close-packed system whipped into a cometary orbit by one encounter and then experiencing another at some later time that either resulted in outright ejection or caused it to pass so close to its host star that ejection resulted. This would be even more likely if the initial perturbation kept its orbit within the local ecliptic plane since such systems are likely bound very close to that due to tidal effects.

A fast, close stellar passage might even be expected to produce the hypothesized 'baked Alaska' composition here; burnt on the outside, raw on the inside.