Author Topic: Hyperbolic Hyperbole or Interstellar Interloper? ('Oumuamua)  (Read 26682 times)

Offline JasonAW3

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #120 on: 11/15/2017 08:48 PM »
The two values imply that 1I/'Oumuamua has an axial ratio of 4.1 to 6.9
They note in the paper that this is pretty far outside the normal range for known solar system objects in this size range. For perspective, I'd think of Itokawa as an example of a fairly oblong asteroid, but it's only ~2.

Both APO and DCT seem to support this extreme lightcuve (and IIRC there were hints from earlier observation) so it's not likely to be totally in error.

Anybody do a spectrograph of the reflected light yet?
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Offline hop

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #121 on: 11/15/2017 09:35 PM »
Anybody do a spectrograph of the reflected light yet?
Yes, see this post and the second paper in this post. Others have also obtained spectra that aren't published yet but are generally similar, for example Alan Fitzsimmons tweeted this one.

The tl;dr is that it's featureless (no obviously identifiable absorption features) with a red slope (reflects more at longer wavelengths than shorter ones). This is similar to some asteroids and KBOs, but that doesn't necessarily mean they are made of the same stuff.

Offline eric_astro

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #122 on: 11/15/2017 09:36 PM »
You'd need to be moving about 27 km/s in relation to the sun at infinity to catch up with Oumuamua, or 50km/s at 1AU.

To get to Proxima B would then take another 47,000 years.

But if you woke up in 47,000 years, Proxima would be at about 3 light years from earth!

Online KelvinZero

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #123 on: 11/15/2017 11:20 PM »
The two values imply that 1I/'Oumuamua has an axial ratio of 4.1 to 6.9
They note in the paper that this is pretty far outside the normal range for known solar system objects in this size range. For perspective, I'd think of Itokawa as an example of a fairly oblong asteroid, but it's only ~2.

Both APO and DCT seem to support this extreme lightcuve (and IIRC there were hints from earlier observation) so it's not likely to be totally in error.
Weird. Surely this would be a binary? A ratio of 6.9 would be like a skinny finger.

Offline Mongo62

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #124 on: 11/16/2017 01:42 AM »
Interstellar Interloper 1I/2017 U1: Observations from the NOT and WIYN Telescopes

We present observations of the interstellar interloper 1I/2017 U1 ('Oumuamua) taken during its 2017 October flyby of Earth. The optical colors B-V = 0.70±0.06, V-R = 0.45±0.05, overlap those of the D-type Jovian Trojan asteroids and are incompatible with the ultrared objects which are abundant in the Kuiper belt. With a mean absolute magnitude HV = 22.95 and assuming a geometric albedo pV = 0.1, we find an average radius of 55 m. No coma is apparent; we deduce a limit to the dust mass production rate of only ∼ 2×10^−4 kg s−1, ruling out the existence of exposed ice covering more than a few m2 of the surface. Volatiles in this body, if they exist, must lie beneath an involatile surface mantle ≳0.5 m thick, perhaps a product of prolonged cosmic ray processing in the interstellar medium. The lightcurve range is unusually large at ∼2.0±0.2 magnitudes. Interpreted as a rotational lightcurve the body has semi-axes ∼230 m × 35 m. A ∼6:1 axis ratio is extreme relative to most small solar system asteroids and suggests that albedo variations may additionally contribute to the variability. The lightcurve is consistent with a two-peaked period ∼8.26 hr but the period is non-unique as a result of aliasing in the data. Except for its unusually elongated shape, 1I/2017 U1 is a physically unremarkable, sub-kilometer, slightly red, rotating object from another planetary system. The steady-state population of similar, ∼100 m scale interstellar objects inside the orbit of Neptune is ∼10^4, each with a residence time ∼10 yr.
« Last Edit: 11/16/2017 01:44 AM by Mongo62 »

Offline hop

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #125 on: 11/16/2017 02:25 AM »
Weird. Surely this would be a binary? A ratio of 6.9 would be like a skinny finger.
I'm not sure a binary helps much, naively two roughly spherical components of similar composition only gives you the equivalent of 2. You have a binary with elongated components, or a contact binary with a large "bridge" of loose material, but that's still pretty weird.

The authors suggest it could have been distorted by spin or close encounters in the parent system, but those processes should apply to solar system bodies too, so it's not obvious to me those explanations make it much less of an outlier.

They conclude albedo differences are unlikely to explain it, because the colors don't seem to vary, though the paper Mongo62 just posted suggests it could be a combination.

Looking back at the Knight et al DCT paper, they gave ~3 as a lower limit, because they didn't sample enough of the curve to say more.

Online KelvinZero

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #126 on: 11/16/2017 03:57 AM »
Weird. Surely this would be a binary? A ratio of 6.9 would be like a skinny finger.
I'm not sure a binary helps much, naively two roughly spherical components of similar composition only gives you the equivalent of 2. You have a binary with elongated components, or a contact binary with a large "bridge" of loose material, but that's still pretty weird.
Thanks. I hadn't realised that. How about a crater or hard edged facet?

This link says "comparable to the most elongated Solar System objects" implying it is not unheard of. Have we imaged anything like that?
https://en.wikipedia.org/wiki/1I/%CA%BBOumuamua

Offline hop

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #127 on: 11/16/2017 05:15 AM »
How about a crater or hard edged facet?
Without trying to analyze specific shapes, it seems safe to assume you can get extreme light curves with the right combination of shape and surface properties. IMO the weirdness isn't that you can't make a rock do this, it's that the first interstellar rock we see also happens to be at the extreme.
Quote
This link says "comparable to the most elongated Solar System objects" implying it is not unheard of. Have we imaged anything like that?
https://en.wikipedia.org/wiki/1I/%CA%BBOumuamua
I don't know. The Jewitt et al paper Mongo62 posted today says
Quote
However, we note that the 5 km diameter asteroid 4116 (Elachi) shows a range of 1.6 magnitudes (b/a = 4.3:1) that is almost as large (Warner and Harris 2011).
I would expect this was the most extreme example they knew of and felt was reliable. Notably, it's a much larger object. You might expect small objects to be able to have more extreme shapes, since they are less affected by self gravity.

It's also important to remember that the ratio inferred from a light curve gives a lower limit, because it depends on the viewing geometry. In the extreme example of the pole is facing you at 0 phase angle (sun behind you), the light curve would be flat regardless of the shape.

Offline Mongo62

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #128 on: 11/17/2017 01:13 AM »
Is 1I/2017 U1 really of interstellar origin?

Here we investigate the possibility that the asteroid 1I/2017 U1 actually is a Solar System object, currently expelled from the Solar System by the recent encouter with a Solar System planet. We show that this possibility is extremely unlikeley and that 1I/2017 U1 really is an interstellar object.

Col-OSSOS: Colors of the Interstellar Planetesimal 1I/2017 U1 in Context with the Solar System

The recent discovery by Pan-STARRS1 of 1I/2017 U1 (`Oumuamua), on an unbound and hyperbolic orbit, offers a rare opportunity to explore the planetary formation processes of other stars, and the effect of the interstellar environment on a planetesimal surface. 1I/`Oumuamua's close encounter with the inner Solar System in 2017 October was a unique chance to make observations matching those used to characterize the small-body populations of our own Solar System. We present near-simultaneous g′, r′, and J photometry and colors of 1I/`Oumuamua from the 8.1-m Frederick C. Gillett Gemini North Telescope, and gri photometry from the 4.2 m William Herschel Telescope. Our g′r′J observations are directly comparable to those from the high-precision Colours of the Outer Solar System Origins Survey (Col-OSSOS), and offer unique diagnostic information for distinguishing between outer Solar System surfaces. Substantial, correlated near-infrared and optical variability is present, with the same trend in both near-infrared and optical. Our observations confirm that 1I/`Oumuamua rotates with a double-peaked period of 8.10±0.42 hours and is a highly elongated body with an axial ratio of at least 5.3:1, implying that it has significant internal cohesion. 1I/`Oumuamua's color is at the neutral end of the range of observed g−r and r−J solar-reflectance colors, relative to asteroids, more distant minor planets, and to the trans-Neptunian populations measured by Col-OSSOS. The color of the first interstellar planetesimal is like the colors of the Solar System, in particular some of the dynamically excited objects of the Kuiper belt and the less-red Jupiter Trojans.

Offline hop

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #129 on: 11/17/2017 03:02 AM »
Col-OSSOS: Colors of the Interstellar Planetesimal 1I/2017 U1 in Context with the Solar System
They touch on the earlier question of how rare such elongated objects are:
Quote
Small asteroids with 1I/‘Oumuamua’s degree of elongation are rare but not unknown; examples include the ~ 200-300 m diameter Near-Earth Asteroids 2001 FE90 and 2007 MK13, both with lightcurve amplitudes ≥ 2.1 magnitudes

Online plutogno

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #130 on: 11/18/2017 07:20 AM »
Is 1I/2017 U1 really of interstellar origin?

from this paper:

Quote
up to now no outer Solar Solar system asteroid has never been detected, contrary to comets which are very common

as far as I know, a few Oort cloud asteroids have been detected. see for example https://en.wikipedia.org/wiki/2005_VX3 and https://en.wikipedia.org/wiki/List_of_Solar_System_objects_by_greatest_aphelion#TNOs_with_an_aphelion_larger_than_200_AU

Online ugordan

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #131 on: 11/18/2017 09:04 AM »
Is 1I/2017 U1 really of interstellar origin?

Here we investigate the possibility that the asteroid 1I/2017 U1 actually is a Solar System object, currently expelled from the Solar System by the recent encouter with a Solar System planet. We show that this possibility is extremely unlikeley and that 1I/2017 U1 really is an interstellar object.

This talks about the chances of it passing near the hypothetical Planet 9. Even if it did, how would that explain the 26 km/s of heliocentric boost when the orbital velocities hundreds of AU from the Sun are mere fractions of that.

Offline Mongo62

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #132 on: 11/20/2017 01:14 AM »
On the dynamical history of the recently discovered interstellar object A/2017 U1 - where does it come from?

A/2017 U1 is the first interstellar object recorded inside the Solar System. We try to answer the obtrusive question: where does it come from? After a careful search in the close vicinity of the Sun we looked a bit further. Finally, we have checked over 200 thousand stars and found just a handful of candidates. If we limit our investigation to the Sun surroundings within about 30 pc, the most probable candidate for the A/2017 U1 parent stellar habitat is a star UCAC4 535-065571 but GJ 876 cannot be completely ruled out. However, the origin of A/2017 U1 from a more distant source is still an open question.

Offline Mr. Scott

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #133 on: 11/20/2017 01:42 AM »
Is 1I/2017 U1 really of interstellar origin?

from this paper:

Quote
up to now no outer Solar Solar system asteroid has never been detected, contrary to comets which are very common

as far as I know, a few Oort cloud asteroids have been detected. see for example https://en.wikipedia.org/wiki/2005_VX3 and

Quote
up to now no outer Solar Solar system asteroid has never been detected, contrary to comets which are very common

as far as I know, a few Oort cloud asteroids have been detected. see for example https://en.wikipedia.org/wiki/2005_VX3 and https://en.wikipedia.org/wiki/List_of_Solar_System_objects_by_greatest_aphelion#TNOs_with_an_aphelion_larger_than_200_AU

The Oort Cloud is supposed to be between 5000-100000 AU.  Those objects are orders of magnitude inside.  Your list is outer Kuiper Belt perhaps?

The Oort Cloud is still a theory without proof.  Still seems implausible to me that our oceans were formed by it. 

Interstellar objects seem like a much more fruitful possibility for discovery.  Although (again) there is no proof, there have to be mini asteroid objects zooming by much faster than this one.   1000 km/sec would be interesting to find in that they are just so hard to detect.
« Last Edit: 11/20/2017 01:43 AM by Mr. Scott »

Offline Bynaus

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #134 on: 11/20/2017 05:59 AM »
Is 1I/2017 U1 really of interstellar origin?

from this paper:

Quote
up to now no outer Solar Solar system asteroid has never been detected, contrary to comets which are very common

as far as I know, a few Oort cloud asteroids have been detected. see for example https://en.wikipedia.org/wiki/2005_VX3 and https://en.wikipedia.org/wiki/List_of_Solar_System_objects_by_greatest_aphelion#TNOs_with_an_aphelion_larger_than_200_AU

Asteroid in this context means a rocky, ice-free body (i.e., which would not produce a tail when doing a fly-by of the sun). The densities of TNOs suggest that at least most of them have a contribution of ice which is substantial enough to affect their density. The ecliptic, long-period comets are likely derived from the TNOs, and they do form a tail.

1I/2017 U1 seems to have a color similar to P/D-type asteroids in the solar system, which are common in the outer asteroid belt and among trojans. While they might be water-rich (as in hydrated minerals which can also be identified in the spectrum), they are not in general thought to have substantial contributions from water ice.

Offline hop

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #135 on: 11/20/2017 06:27 AM »
The ecliptic, long-period comets are likely derived from the TNOs, and they do form a tail.
A few rocky (edit: or no/extremely low activity) apparent Oort cloud bodies have been seen, e.g. 1996 PW and C/2014 S3 (PANSTARRS) (though the later did show some activity)
« Last Edit: 11/20/2017 06:28 AM by hop »

Offline Phil Stooke

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #136 on: 11/20/2017 07:15 AM »
"The Oort Cloud is still a theory without proof.  Still seems implausible to me that our oceans were formed by it. "

You might be thinking about this the wrong way.  Not that the oceans came from the Oort cloud... but that many icy objects were scattered by the giant planets: those scattered outwards form the Oort cloud.  Those scattered inwards either fall into the Sun, or hit a planet (thereby delivering a bit of ocean), or get another gravity assist which flings them back out.  Still lots of nuances to figure out, isotopes etc., so the story can be refined.  But you are not really bringing an ocean in from the Oort cloud.

Offline Bynaus

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #137 on: 11/20/2017 05:31 PM »
https://www.nature.com/articles/nature25020

Quote
A brief visit from a red and extremely elongated interstellar asteroid

None of the approximately 750,000 known asteroids and comets is thought to have originated outside our Solar System, but formation models suggest that orbital migration of the giant planets ejected a large fraction of the original planetesimals into interstellar space1. The predicted interstellar number density2 of icy interstellar objects of 2.4 × 10−4 au−3 suggested that these should have been detected by surveys, yet hitherto none had been seen. Many decades of asteroid and comet characterization have yielded formation models that explain the mass distribution, chemical abundances and planetary configuration of today’s Solar System, but until now there has been no way to tell if our Solar System is typical. Here we report observations and subsequent analysis of 1I/2017 U1 (‘Oumuamua) that demonstrate the extrasolar trajectory of ‘Oumuamua. Our observations reveal the object to be asteroidal, with no hint of cometary activity despite an approach within 0.25 au of the Sun. Spectroscopic measurements show that the object’s surface is consistent with comets or organic-rich asteroid surfaces found in our own Solar System. Light-curve observations indicate that the object has an extreme oblong shape, with a 10:1 axis ratio and a mean radius of 102±4 m, assuming an albedo of 0.04. Very few objects in our Solar System have such an extreme light curve. The presence of ‘Oumuamua suggests that previous estimates of the density of interstellar objects were pessimistically low. Imminent upgrades to contemporary asteroid survey instruments and improved data processing techniques are likely to produce more interstellar objects in the upcoming years.

10:1! That's even more extreme than the first estimates... That elongated cylinderoid shape will have the web go crazy... perhaps we should have sticked to "Rama" for the name! :)

Offline redliox

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #138 on: 11/20/2017 06:27 PM »
https://www.nature.com/articles/nature25020

Quote
A brief visit from a red and extremely elongated interstellar asteroid

None of the approximately 750,000 known asteroids and comets is thought to have originated outside our Solar System, but formation models suggest that orbital migration of the giant planets ejected a large fraction of the original planetesimals into interstellar space1. The predicted interstellar number density2 of icy interstellar objects of 2.4 × 10−4 au−3 suggested that these should have been detected by surveys, yet hitherto none had been seen. Many decades of asteroid and comet characterization have yielded formation models that explain the mass distribution, chemical abundances and planetary configuration of today’s Solar System, but until now there has been no way to tell if our Solar System is typical. Here we report observations and subsequent analysis of 1I/2017 U1 (‘Oumuamua) that demonstrate the extrasolar trajectory of ‘Oumuamua. Our observations reveal the object to be asteroidal, with no hint of cometary activity despite an approach within 0.25 au of the Sun. Spectroscopic measurements show that the object’s surface is consistent with comets or organic-rich asteroid surfaces found in our own Solar System. Light-curve observations indicate that the object has an extreme oblong shape, with a 10:1 axis ratio and a mean radius of 102±4 m, assuming an albedo of 0.04. Very few objects in our Solar System have such an extreme light curve. The presence of ‘Oumuamua suggests that previous estimates of the density of interstellar objects were pessimistically low. Imminent upgrades to contemporary asteroid survey instruments and improved data processing techniques are likely to produce more interstellar objects in the upcoming years.

10:1! That's even more extreme than the first estimates... That elongated cylinderoid shape will have the web go crazy... perhaps we should have sticked to "Rama" for the name! :)

I have to agree with that statement.  So far it apparently has a long shape, has no coma, and is solid like rock or metal.  It would be easy to presume it could be a spaceship.  However, it hasn't slowed down and is behaving like a rock from outer space.  It's intriguing enough that this is the first interstellar visitor, although if it were artificial it's acting either dead or passive...

If it were a passive observer (be it benign or covert invader), from its POV what views could it have had of our solar system during this visit?  Aside from the sun (in a vague sense), it didn't exactly fly by any of the planets akin to our probes...but still...what could it have noticed?
« Last Edit: 11/20/2017 06:28 PM by redliox »
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Offline Star One

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Re: Hyperbolic Hyperbole or Interstellar Interloper?
« Reply #139 on: 11/20/2017 06:57 PM »
Is 1I/2017 U1 Really of Interstellar Origin?

http://iopscience.iop.org/article/10.3847/2515-5172/aa9af2/meta

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