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Interstellar Interloper, Coming in from the great beyond
fredk
post Nov 21 2017, 01:06 AM
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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.
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dudley
post Nov 21 2017, 02:31 AM
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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
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fredk
post Nov 21 2017, 05:26 AM
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You can read in the original Nature paper linked in the ESO release that c is unconstrained from the lightcurve.
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moustifouette
post Nov 21 2017, 09:29 AM
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QUOTE (fredk @ Nov 21 2017, 07:26 AM) *
You can read in the original Nature paper linked in the ESO release that c is unconstrained from the lightcurve.


I may break some rule, but I can't help noting that a galatical battleship wreck fits the shape.
wink.gif
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Floyd
post Nov 21 2017, 01:36 PM
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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).


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Floyd
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Explorer1
post Yesterday, 12:17 AM
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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?
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dudley
post Yesterday, 03:22 AM
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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.
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TheAnt
post Yesterday, 03:20 PM
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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. biggrin.gif
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Ron Hobbs
post Yesterday, 05:16 PM
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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!
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dudley
post Yesterday, 08:15 PM
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QUOTE (TheAnt @ Nov 22 2017, 04:20 PM) *
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. biggrin.gif


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.
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Gladstoner
post Today, 12:03 AM
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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.
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dudley
post Today, 02:16 AM
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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.
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Gladstoner
post Today, 06:36 AM
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QUOTE (dudley @ Nov 22 2017, 08:16 PM) *
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.
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