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An object like Oumuamua originates in a solar system. This object has roughly the inertia of everything else there. I can imagine stuff on the edge of the accretion zone for a star that...WANDER off...

But come blazing into our system with enough energy to exit again? My only guess for something like that is stellar collisions.

What is a more informed answer?

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    $\begingroup$ A cluster of chaotically orbiting massive objects will often end up ejecting some of them at above escape velocity. $\endgroup$
    – ikrase
    Apr 18, 2022 at 6:46
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    $\begingroup$ If it has enough energy to come into our system, then it will have enough energy to get back out again 99.99% of the time because: conservation of energy. $\endgroup$ Apr 20, 2022 at 5:33

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The answer to 'how can it come blazing in with enough energy to exit again' is that if it started outside the solar system it would have been unusual for it to NOT leave again, since it would have accelerated towards the sun, then slowed down again by exactly the same amount on departure and left with the same velocity it started with, possibly in different direction.

The key here is gravity assists which can produce quite marked changes in the orbits of smaller bodies encountering gas giants, either causing collisions or boosting them away. This will tend to happen a lot in early system formation as gas giants clear their orbits. A more recent example is the way the Voyager and Pioneer vehicles did not intrinsically have enough thrust to escape the solar system but by getting assists from the gas giants 'stole' energy from the solar system to depart.

While departure velocity from the parent system will be low, the future encounters will tend to be with stars having markedly differing orbital velocities around the galactic core, so the process is unlikely to happen in reverse. This means the number of objects (and chance of one passing through our solar system) would tend to increase with time.

Determining actual source of 'Oumuamua is constrained by the available information, but a possible answer is a long period comet had an encounter with a Jupiter equivalent and was gravity assisted beyond the parent solar system escape velocity.

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  • $\begingroup$ Yeah, my point was that a merely wandering object that has ended up leaving a system would be captured by another, instead of being able to leave that one as well. $\endgroup$ Apr 18, 2022 at 18:15
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    $\begingroup$ @ChrisB.Behrens momentum is conserved and that drifting object has a lot of potential energy by being out of a gravity well, it can easily turn that into kinetic energy then back into potential energy on departure as long as it doesn't randomly get a gravity assist from Jupiter or Saturn. And even then per Roger woods answer the high relative velocities between stars mean even a drifter will arrive at the sun with more velocity than anything man made. $\endgroup$ Apr 19, 2022 at 8:15
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This is a very generic answer: A gravitationally bound system has a tendency to become more compact. As this happens, the gravitational potential energy becomes more negative. The energy that is lost ends up mainly as heat caused by collisions and friction. However, energy is also lost because of the tendency for small bodies to reach escape velocity and be cast out of the system.

A non-catastrophic gravitational interaction between two solid bodies tends to leave their kinetic energies more similar after the interaction than before (equipartion theorem). So the lower mass object usually ends up with higher velocity. Due to the natural distribution of velocities, many small objects can achieve escape velocity and will leave their original system.

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Assume that 'Oumuamua was gently ejected from whatever environment it formed in. Then, how is it that it entered the solar system at 26.33 km/s?

This is actually expected. The velocity dispersion of stars in the solar neighborhood is 10's of kilometers per second. So, 'Oumuamua's velocity relative to the solar system is typical for the stuff that is flying around in our part of the galaxy. Even if its original velocity relative to its parent system was low, that system was probably moving pretty fast relative to the Sun, and therefore 'Oumuamua was, too.

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    $\begingroup$ Ah, yeah. Assuming that stars have similar velocities is boneheaded. $\endgroup$ Apr 19, 2022 at 15:15
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    $\begingroup$ @ChrisB.Behrens Not so boneheaded when you appreciate that the dispersion is relative to orbital motion around the galaxy of ~250 km/s. $\endgroup$
    – John Doty
    Apr 19, 2022 at 16:03
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Look at what has happened in our solar system:

56 objects that we know of have had gravitational slingshots that boosted them to higher than system escape velocity and they are now wanderers amongst the stars.

5 of these ejections were carefully engineered by NASA, but Jupiter has the power to eject on it's own and has been observed to do so once.

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    $\begingroup$ Jupiter's also done the same to quite a few naturally-occurring comets that we've observed. $\endgroup$
    – Vikki
    Apr 18, 2022 at 4:54
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    $\begingroup$ A study from 2011 claims that there's a high probability that our system originally had 5 giants, but one of them got thrown out of the system. Young Solar System's Fifth Giant Planet? by David Nesvorny. I have a few more details here: astronomy.stackexchange.com/a/48296/16685 $\endgroup$
    – PM 2Ring
    Apr 18, 2022 at 9:31
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    $\begingroup$ @Vikki I know plenty of comets have encountered Jupiter, I wasn't aware of any being yeeted clear out of the system by it. $\endgroup$ Apr 18, 2022 at 14:43
  • $\begingroup$ @LorenPechtel: Example. $\endgroup$
    – Vikki
    Apr 18, 2022 at 20:37
  • $\begingroup$ @Vikki, interesting to know whether Saturn also helped C/1980 E1 although not by as much as Jupiter. $\endgroup$ Apr 19, 2022 at 15:56
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Orphan planets are more common than thought before:

Stars and even black holes likely harbor "rogue," or "nomad," planets that were kicked out of the star systems where they were born, new simulations suggest. At the same time, a separate study suggests nomad planets are much more common than thought.

https://www.nationalgeographic.com/culture/article/120224-rogue-nomad-planets-stars-black-holes-space-science

Try creating your own "escaped planet":

https://academo.org/demos/orbit-simulator/

If you decrease the mass of the planet while approaching the sun (for example if the body is split in parts by gravity forces), the pieces will be launched away.

enter image description here

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