Evidence for ET?

[Paleophyte]

One of the more interesting anomalies about Oumuamua is that it had a very low velocity relative to the Local Standard of Rest prior to entering our solar system. That might suggest that it wasn't pulled free of another star but formed in interstellar space. I don't know how that might happen but it could very well give rise to something that is neither the asteroids nor comets that we are familiar with. That might account for some of Oumuamua's unusual characteristics.

I disagree.  It seems to me that based on our current knowledge, we should expect extra-solar object ejected from other star systems to commonly possess low relative velocities to local standard of rest.

Here in our solar system a major means to eject an object formed around the sun from the sun’s gravitational influence is through close gravitational interaction between the object and a gas giant, primarily Jupiter, after the object has been initially perturbed into a gas giant crossing elliptical orbit.  A number of comets that have been observed to follow hyperbolic heliocentric trajectories (e>1) due to encounters with Jupiter and Saturn. Although Jupiter’s gravity is powerful enough to slingshot small objects approaching with appropriate encounter geometry to solar escape velocity, it is not powerful enough to do this with any significant margin to spare (e>1, but just barely).   This means as these object follow their Jupiter given escape trajectories, the sun would claw back almost all the extra heliocentric orbital energy imparted by Jupiter before the object can finally escape the sun’s gravity well for good.   So the object will leave with almost zero surplus kinetic energy, and thus very minimal relative velocity with respect to the sun.   So these objects will end up more or less fly in lose formation with the sun in their independent orbits around the Milky Way rather than just zip off at high speed in random directions never to be seen again.

I believe numerical simulation has shown that for a Star such as the sun, it is not difficult to come up with combinations of mass and orbits of gas giant planets that would enable the gas giant to pump other objects in the system up to stellar escape velocity.  But it is much more difficult to come up with plausible combinations of mass and orbits that would enable the gas giant to impart a large amount of surplus kinetic energy to a small object in system beyond what is needed to escape.  So objects thrown out with very little surplus energy should be common.  Objects thrown out with lots of surplus energy sufficient to support galactic orbital vectors substantially different from the parent star would be comparatively uncommon.

The local standard of rest is nothing more than the average velocity of the stars in the broad galactic neighborhood around the sun.  If the escape mechanism powered by a massive planet deep in a star’s gravity well is typical of the star systems in the sun’s neighborhood, then we would expect many of the ejected objects from these systems would end up with very little relative motion to their parent systems.   In other words, we would expect the mean velocity of these interstallar objects to be essentially the same as the local standard of rest.

Just one problem. Almost nothing moves at LSR. There are a couple of different populations of stars moving at different speeds, so almost nothing is going the mean velocity. The Sun is moving something like 10 km/s relative to the LSR, so you'd need a hefty bit of delta-v to leave the solar system with a low velocity relative to LSR. Ditto for most other stars and a complete non-starter for low-metallicity stars, which are really moving. And then you have those weirdoes in retrograde orbits...

So finding an object at low velocity relative to the LSR is odd.

[Anomalocaris]

Surprise! Other things aren't traveling at our speed.

I disagree.  It seems to me that based on our current knowledge, we should expect extra-solar object ejected from other star systems to commonly possess low relative velocities to local standard of rest.

Here in our solar system a major means to eject an object formed around the sun from the sun’s gravitational influence is through close gravitational interaction between the object and a gas giant, primarily Jupiter, after the object has been initially perturbed into a gas giant crossing elliptical orbit.  A number of comets that have been observed to follow hyperbolic heliocentric trajectories (e>1) due to encounters with Jupiter and Saturn. Although Jupiter’s gravity is powerful enough to slingshot small objects approaching with appropriate encounter geometry to solar escape velocity, it is not powerful enough to do this with any significant margin to spare (e>1, but just barely).   This means as these object follow their Jupiter given escape trajectories, the sun would claw back almost all the extra heliocentric orbital energy imparted by Jupiter before the object can finally escape the sun’s gravity well for good.   So the object will leave with almost zero surplus kinetic energy, and thus very minimal relative velocity with respect to the sun.   So these objects will end up more or less fly in lose formation with the sun in their independent orbits around the Milky Way rather than just zip off at high speed in random directions never to be seen again.

I believe numerical simulation has shown that for a Star such as the sun, it is not difficult to come up with combinations of mass and orbits of gas giant planets that would enable the gas giant to pump other objects in the system up to stellar escape velocity.  But it is much more difficult to come up with plausible combinations of mass and orbits that would enable the gas giant to impart a large amount of surplus kinetic energy to a small object in system beyond what is needed to escape.  So objects thrown out with very little surplus energy should be common.  Objects thrown out with lots of surplus energy sufficient to support galactic orbital vectors substantially different from the parent star would be comparatively uncommon.

The local standard of rest is nothing more than the average velocity of the stars in the broad galactic neighborhood around the sun.  If the escape mechanism powered by a massive planet deep in a star’s gravity well is typical of the star systems in the sun’s neighborhood, then we would expect many of the ejected objects from these systems would end up with very little relative motion to their parent systems.   In other words, we would expect the mean velocity of these interstallar objects to be essentially the same as the local standard of rest.

Just one problem. Almost nothing moves at LSR. There are a couple of different populations of stars moving at different speeds, so almost nothing is going the mean velocity. The Sun is moving something like 10 km/s relative to the LSR, so you'd need a hefty bit of delta-v to leave the solar system with a low velocity relative to LSR. Ditto for most other stars and a complete non-starter for low-metallicity stars, which are really moving. And then you have those weirdoes in retrograde orbits...

So finding an object at low velocity relative to the LSR is odd.

Actually, I believe the sun is moving at something like 20-40 km/s relative to LSR.  There are many individual or collections of stars that move at much higher delta V to LSR than the sun, but I believe the majority move at substantially lower delta V to LSR than the sun. So it should not be surprising that if ejection by close in gas giant is an important mechanism for stocking interstellar space with asteroid/comet like objects, than a sizeable fraction would move with the LSR.

If an object just barely escape the solar system, it would approach majority of local stars at initial relative velocities similar to that which Omaouaoua possessed relative to the sun before her trip into the solar system.

[Gawdzilla Sama]

To you.

Our particular solar system is more likely to encounter interstellar objects that’s traveling at a substantial speed with relative to our sun than would be the case with typical stellar systems in our region of the Milky Way.

Our solar system’s motions around Milky Way is not closely following the general flow of stars and interstellar material in our region of the Milky Way.

And whadda fuck does that have to do with what I said?

[Paleophyte]

Actually, I believe the sun is moving at something like 20-40 km/s relative to LSR.  There are many individual or collections of stars that move at much higher delta V to LSR than the sun, but I believe the majority move at substantially lower delta V to LSR than the sun.   So it should not be surprising that if ejection by close in gas giant is an important mechanism for stocking interstellar space with asteroid/comet like objects, than a sizeable fraction would move with the LSR.

If an object just barely escape the solar system, it would approach majority of local stars at initial relative velocities similar to that which Omaouaoua possessed relative to the sun before her trip into the solar system.

The numbers that I saw suggested that only about 0.2% of asteroids ejected from stellar systems should have a peculiar velocity (Seriously? These chuckleheads named the one type of velocity that's intuitive "peculiar"?) as low as Oumuamua's. The error bars on that are probably pretty enormous though.

I just think that an object that formed in interstellar space and doesn't fit into any of the pigeonholes that we're familiar with would go a long way to explaining Oumuamua's oddities.

[Gawdzilla Sama]

I've seen speculation that planets could form without being in orbit around a star. That would mean that smaller objects could be formed in interstellar space as well.

[Anomalocaris]

Actually, I believe the sun is moving at something like 20-40 km/s relative to LSR.  There are many individual or collections of stars that move at much higher delta V to LSR than the sun, but I believe the majority move at substantially lower delta V to LSR than the sun.   So it should not be surprising that if ejection by close in gas giant is an important mechanism for stocking interstellar space with asteroid/comet like objects, than a sizeable fraction would move with the LSR.

If an object just barely escape the solar system, it would approach majority of local stars at initial relative velocities similar to that which Omaouaoua possessed relative to the sun before her trip into the solar system.

The numbers that I saw suggested that only about 0.2% of asteroids ejected from stellar systems should have a peculiar velocity (Seriously? These chuckleheads named the one type of velocity that's intuitive "peculiar"?) as low as Oumuamua's. The error bars on that are probably pretty enormous though.

I just think that an object that formed in interstellar space and doesn't fit into any of the pigeonholes that we're familiar with would go a long way to explaining Oumuamua's oddities.

If our assessment of the density of material in typical interstellar space is accurate, and it appears to be corroborated by multiple independent observations, Then the odds that sufficient amount of material can meet by chance and collect into an object the size of this asteroid over the life of the universe must be pretty slim.

If in fact the condition of material density in interstellar space required to provide high chance of objects like this forming within the age of the universe is common, then it would suggest there is far more interstellar material then we have otherwise found evidences for.

[Paleophyte]

If our assessment of the density of material in typical interstellar space is accurate, and it appears to be corroborated by multiple independent observations, Then the odds that sufficient amount of material can meet by chance and collect into an object the size of this asteroid over the life of the universe must be pretty slim.

Agreed. I'm having a hard time figuring that part out. Perhaps a small gas cloud, far too small to form a star and solar system but large enough to slowly form who knows what under some pretty odd conditions. We know that it had to be at least carbonaceous, so remnants of a nova or supernova. If it had been primordial H-He and come within 0.25 AU of the sun it would have made for a fairly impressive comet.

[ignoramus]

Another nice scientific pragmatic talk.

[purplepurpose]

We already have ET from God's planet. Just look at any diehard believer and you will notice that he is definitely not from this planet.

[Anomalocaris]

I've seen speculation that planets could form without being in orbit around a star. That would mean that smaller objects could be formed in interstellar space as well.

That would be totally different. The sort of “planet” that are believed to form independently of any Star are really miniature star in their own right in terms of composition, just too small to actual ignite or sustain thermal nuclear fussion like normal star. They are still enormous objects, likely on average much more massive than Jupiter.