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Rogue planets can be designated as rogue planets due to one of two possible scenarios: 1) the "rogue planet" formed as a sub-brown dwarf, or 2) the planet was ejected from its home star system. I want to make it clear that here, I'm interested in objects of the second category - objects that are similar to the planets we find in our solar system.

Could a rogue planet, having been ejected from its home star system, be gravitationally re-captured by another star system? If so, would it be likely to disrupt other bodies in the stellar system (I know this depends on size; let's say that the rogue planet is a "Hot Jupiter")?

I realize that we don't know a whole lot about these objects (let's face it, we only know of a handful), so I'm not looking for examples, but any logical answers would be pretty helpful.

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voting without commenting is fine and should be the norm. As to your question, I think your first paragraph contains an error: you are interested in objects of the second category (not first); please correct. –  Walter Sep 5 at 9:39
    
@Walter Thanks for the correction; I should have seen that before. –  HDE 226868 Sep 6 at 20:05

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For a start, the hot jupiters (HJ) are not similar to the planets of the Solar system (they are much hotter and very close to their host star). It's essentially impossible for HJs to be ejected away from their star's sphere of influence. The reason is that they are gravitationally rather tightly bound to their star, so that any gravitational interaction with a third body that would gain them enough energy for ejection needs to be closer than is possible without it leading to a collision with that third body.

So rogue planets that didn't form independent of a star must have been much less bound to their parent star, similar to the outer planets of the Solar system. Of course, once ejected (free-floating), such an object can in principle be re-captured into another planetary system or a binary system. However, this is quite unlikely, since the planet must move with a velocity very close to that of its capturer. Also, it must involve a third body (either another planet or star bound to its capturer) to absorb (into its orbit) the orbital energy (and angular momentum) released by the capture.

The only possibility is that the planet was ejected very early on, when the stellar association / group / open cluster within which it was born had not yet been dissolved. Then it may find another home with one of the other members of that association.

I don't think that anybody has estimated the actual probabilities for this to happen, but why are you interested?


As a side remark, it seems clear that orbiting planets form from / in gas discs surrounding protostars, but it's not clear whether brown dwarves cannot also form this way. Whether or not an object formed this way becomes a gas planet, a brown dwarf, or even a star depends entirely on its mass and not the formation process.

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