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Oumuamua revisited

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#1 Sketcher

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Posted 06 August 2019 - 03:17 PM

We have some knowledge of Oumuamua, many inferences, and plenty of unknowns:

 

1.  Oumuamua moved quickly through our inner solar system, zipping past Earth (the planet it came closest to) at an observed velocity that implied an interstellar origin.

 

2.  Working backwards, it's been inferred that Oumuamua entered our solar system from the Local Standard of Rest for our region of the galaxy.

 

3.  It was observed as a pinpoint object -- devoid of any observable out-gassing.

 

4.  Its color has been measured as being reddish.

 

5.  Its brightness varied by a factor of 10, undergoing a regularly repeating pattern that was never observed to change in any significant manner.  The latter being one reason for questioning out-gassing as the explanation behind Oumuamua's non-gravitational acceleration.

 

6.  It was observed to move outward, away from the sun, at a somewhat greater speed than can be accounted for by gravitational effects alone.

 

7.  It's been inferred that Oumuamua was in a tumbling motion (inferred from the brightness variations).

 

8.  An early inference (from the light variations) was that Oumuamua might be about 10 times longer in one dimension than it is in another.

 

9.  It's been inferred that Oumuamua is a dense, solid, rocky object, perhaps with some metal in its composition -- inferred from the need for structural integrity if it is indeed tumbling with a 7 to 8 hour period.

 

10.  Out-gassing has been hypothesized to explain the non-gravitational acceleration by some, and ruled out, or questioned, by others 

 

11.  Radiation pressure has been hypothesized to explain the non-gravitational acceleration; but for this to be workable, Oumuamua would have to have a density of about 0.001 grams per cubic centimeter -- comparable to the density of air -- which might be difficult to reconcile with #9 above.

 

So, where are we in explaining the nature of this object?  Is it composed of "dark matter"?  Is it a lattice structure composed of hydrogen ice?  Is it a craft powered by a sail?  Is it a discarded, empty shell of some kind -- like a child's giant party balloon, or a thin-skinned, empty fuel tank, cargo container, etc?  How much faith should we put in the various inferences that have been made?

 

Isn't this object unique enough, interesting enough, and with enough scientific potential to justify a mission for a closer look and examination?  The old elongated rock scenario seems to be less likely now than something else.  Most of those "something else" alternatives would seem, in my opinion, to be justification enough to mount a mission to catch up with Oumuamua for a closer look.



#2 RadioAstronomer

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Posted 06 August 2019 - 03:28 PM

We have some knowledge of Oumuamua, many inferences, and plenty of unknowns:

 

1.  Oumuamua moved quickly through our inner solar system, zipping past Earth (the planet it came closest to) at an observed velocity that implied an interstellar origin.

 

2.  Working backwards, it's been inferred that Oumuamua entered our solar system from the Local Standard of Rest for our region of the galaxy.

 

3.  It was observed as a pinpoint object -- devoid of any observable out-gassing.

 

4.  Its color has been measured as being reddish.

 

5.  Its brightness varied by a factor of 10, undergoing a regularly repeating pattern that was never observed to change in any significant manner.  The latter being one reason for questioning out-gassing as the explanation behind Oumuamua's non-gravitational acceleration.

 

6.  It was observed to move outward, away from the sun, at a somewhat greater speed than can be accounted for by gravitational effects alone.

 

7.  It's been inferred that Oumuamua was in a tumbling motion (inferred from the brightness variations).

 

8.  An early inference (from the light variations) was that Oumuamua might be about 10 times longer in one dimension than it is in another.

 

9.  It's been inferred that Oumuamua is a dense, solid, rocky object, perhaps with some metal in its composition -- inferred from the need for structural integrity if it is indeed tumbling with a 7 to 8 hour period.

 

10.  Out-gassing has been hypothesized to explain the non-gravitational acceleration by some, and ruled out, or questioned, by others 

 

11.  Radiation pressure has been hypothesized to explain the non-gravitational acceleration; but for this to be workable, Oumuamua would have to have a density of about 0.001 grams per cubic centimeter -- comparable to the density of air -- which might be difficult to reconcile with #9 above.

 

So, where are we in explaining the nature of this object?  Is it composed of "dark matter"?  Is it a lattice structure composed of hydrogen ice?  Is it a craft powered by a sail?  Is it a discarded, empty shell of some kind -- like a child's giant party balloon, or a thin-skinned, empty fuel tank, cargo container, etc?  How much faith should we put in the various inferences that have been made?

 

Isn't this object unique enough, interesting enough, and with enough scientific potential to justify a mission for a closer look and examination?  The old elongated rock scenario seems to be less likely now than something else.  Most of those "something else" alternatives would seem, in my opinion, to be justification enough to mount a mission to catch up with Oumuamua for a closer look.

If I'm not mistaken the object is moving way too fast to send a mission. 



#3 photoracer18

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Posted 06 August 2019 - 03:31 PM

Assuming we could even catch it at this point, I say yes.



#4 DaveC2042

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Posted 06 August 2019 - 04:04 PM

Look, it's fun to speculate, but all the evidence says it's a rock. A very interesting rock, but a rock nonetheless.
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#5 Sketcher

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Posted 06 August 2019 - 04:31 PM

If I'm not mistaken the object is moving way too fast to send a mission. 

Oumuamua's speed certainly does create some difficulties to overcome; but a mission might still be a possibility.  Try Googling "Project Lyra".



#6 MikeMiller

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Posted 06 August 2019 - 04:48 PM

Oumuamua's speed certainly does create some difficulties to overcome; but a mission might still be a possibility.  Try Googling "Project Lyra".

New Horizons is going 23 km/s and it needed a gravitational slingshot from Jupiter to get there. 

 

Oumuamua is going 26 km/s at nearly a right angle to the plane of the solar system, and it is already past Neptune's orbit. Even if we launched a Delta IV today we are not going to catch it in any reasonable amount of time. And with the amount of time it would take to prepare a mission, the rock is going to be long gone.


Edited by MikeMiller, 06 August 2019 - 04:49 PM.


#7 Sketcher

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Posted 06 August 2019 - 09:03 PM

Look, it's fun to speculate, but all the evidence says it's a rock. A very interesting rock, but a rock nonetheless.

All the evidence?  A rock?

 

Some of the calculations suggest that out-gassing can not account for the non-gravitational acceleration; and therefor radiation pressure must be responsible.  But for radiation pressure to work, the object would need to have a density comparable to air.  It would take a most unusual rock indeed to have such a density -- and be elongated -- and be tumbling with a period of 7 to 8 hours -- and still hold itself together.

 

But of course, the light variations are factual.  On the other hand, we don't really know if the object is elongated.  We don't really know if it's tumbling.  Some of the inferences that have been made may not be accurate/correct.  The fact of the matter is that much remains unknown.

 

Probability might point in the direction of a rocky (asteroidal or cometary) body, but the evidence seems to be a bit less conclusive.



#8 Mister T

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Posted 07 August 2019 - 06:41 AM

It is most definitely a rock.

A spacecraft would have hauled arse outta here, on full power, after it got a look at what passes for sentient beings !!



#9 llanitedave

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Posted 07 August 2019 - 09:07 AM

All the evidence?  A rock?

 

Some of the calculations suggest that out-gassing can not account for the non-gravitational acceleration; and therefor radiation pressure must be responsible.  But for radiation pressure to work, the object would need to have a density comparable to air.  It would take a most unusual rock indeed to have such a density -- and be elongated -- and be tumbling with a period of 7 to 8 hours -- and still hold itself together.

 

But of course, the light variations are factual.  On the other hand, we don't really know if the object is elongated.  We don't really know if it's tumbling.  Some of the inferences that have been made may not be accurate/correct.  The fact of the matter is that much remains unknown.

 

Probability might point in the direction of a rocky (asteroidal or cometary) body, but the evidence seems to be a bit less conclusive.

Be patient.  There will be others, and at some point we'll have the capability of visiting them.


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#10 Jim_V

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Posted 07 August 2019 - 09:50 AM

Oumuamua is an interesting object, which really ( at least from my perspective) shows how much we really do not understand about the universe and the objects contained there in. About how more there is to learn.  We can contemplate possible narratives to explain the motion/speed/composition of the object. However those speculative possibilities again enforce my original point of our lack of knowledge.



#11 polyfractal

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Posted 18 August 2019 - 08:30 PM

Be patient.  There will be others, and at some point we'll have the capability of visiting them.

++

 

Once the Large Synoptic Survey Telescope is up and running, they are optimistically hoping to find upwards of one extrasolar asteroid per year (based on some educated guesses, how frequently our own solar system ejects asteroids e.g. when Jupiter flings them out, etc). Exciting times to come as we find more of these objects.

 

The acceleration issue is interesting, although probably just outgassing.  But what I find a lot more interesting is the shape of Oumuamua.  Last I heard astronomers were narrowing down the estimate to ~6:1 axis ratio, which is interesting because it's so rarely found in our own solar system.  You'd sorta expect the first extrasolar object we'd see would be pretty "average" in shape, so it's cigar-shape is especially interesting.  Are we misunderstanding something about formation? Does some phenomenon (gravitational stretching, etc) happen when rocks are launched out of a solar system?  Lots of neat questions :)

 

 

 Is it composed of "dark matter"?

Just a note, Oumuamua is by definition not dark matter, since dark matter according to our current theories does not interact with electromagnetic radiation.  So we wouldn't have been able to see Oumuamua if it were dark matter :)



#12 DaveC2042

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Posted 18 August 2019 - 09:45 PM

++
...But what I find a lot more interesting is the shape of Oumuamua. Last I heard astronomers were narrowing down the estimate to ~6:1 axis ratio, which is interesting because it's so rarely found in our own solar system. You'd sorta expect the first extrasolar object we'd see would be pretty "average" in shape, so it's cigar-shape is especially interesting. Are we misunderstanding something about formation? Does some phenomenon (gravitational stretching, etc) happen when rocks are launched out of a solar system?


Isn't it possibly as simple as it being debris from a collision, rather than something formed by accretion?

#13 polyfractal

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Posted 18 August 2019 - 10:20 PM

Isn't it possibly as simple as it being debris from a collision, rather than something formed by accretion?

Yep, I believe there's a whole host of papers working off the collision/ejecta scenario.  Not an expert, but my understanding is that it requires some unusual circumstances to generate an elongated shape.  E.g. the spin of Oumuamua indicates it is probably monolithic (since a rubble pile that size wouldn't be able to sustain the rotation/tumbling without flying apart).  In our solar system, ~100m long, thin monoliths are relatively rare because collision events that generate 1km-100m bodies tend to result in many collisions which randomly "round out" the asteroids.

 

So something that generated a long fragment like Oumuamua would need to eject it quickly before it has a chance interact with other bodies.  But the forces involved need to be constrained to some degree... a supernova near a planet would just atomize all the mass without ejecting shards.  I think there are a bunch of theories that all seem plausible though:  Mars-mass planet tidally disrupted by getting too close a star in a binary system, the fragements getting ejected all over the cosmos.  Large comet tidally disrupted after zipping by a gas giant or other large planet.  Debris from a new solar system in formation. etc etc.

 

There are some theories that it's a contact binary, but I think those are less likely due to the tumbling.

 

And there are a bunch of papers on how it was originally spheroidal in shape, but a millenia of bombardment by interstellar particles selectively eroded Oumuamua to it's current shape.

 

All in all, lots of neat things to think about.  Shame we only saw it for a few weeks!


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#14 goodricke1

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Posted 19 August 2019 - 02:00 PM

what I find a lot more interesting is the shape of Oumuamua.  Last I heard astronomers were narrowing down the estimate to ~6:1 axis ratio, which is interesting because it's so rarely found in our own solar system.  You'd sorta expect the first extrasolar object we'd see would be pretty "average" in shape, so it's cigar-shape is especially interesting.

 

The most distant object we've visited in our own outer Solar System, Ultima Thule, was also a pretty unexpected shape. It's possible that objects at the edge of stellar systems - which would the most likely interstellar candidates - have a wider variety of shapes, as the processes that 'round them out' in the inner system aren't as prevalent out in the boondocks. Also, it's now believed that a pancake shape is equally as likely for 'Oumuamua as a cigar shape.


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#15 polyfractal

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Posted 19 August 2019 - 02:28 PM

The most distant object we've visited in our own outer Solar System, Ultima Thule, was also a pretty unexpected shape. It's possible that objects at the edge of stellar systems - which would the most likely interstellar candidates - have a wider variety of shapes, as the processes that 'round them out' in the inner system aren't as prevalent out in the boondocks. Also, it's now believed that a pancake shape is equally as likely for 'Oumuamua as a cigar shape.

Yeah that's a good point.  I suppose we have a pretty limited view of "average" given we mostly see inner-system bodies :)



#16 MikeMiller

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Posted 20 August 2019 - 10:49 AM

Yeah that's a good point.  I suppose we have a pretty limited view of "average" given we mostly see inner-system bodies smile.gif

An astronomer, a physicist and a mathematician are on a train in Scotland.
The astronomer looks out of the window, sees a black sheep standing in a field, and remarks, "How odd. Scottish sheep are black."
"No, no, no!" says the physicist.
"Only some Scottish sheep are black."
The mathematician rolls his eyes at his companions' muddled thinking and says, "In Scotland, there is at least one field, containing at least one sheep, at least one side of which appears black from here."


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#17 BillP

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Posted 25 August 2019 - 09:40 PM

Isn't it possibly as simple as it being debris from a collision, rather than something formed by accretion?

 

 

Here is an interesting new take on it - https://arxiv.org/abs/1901.08704




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