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Two Questions:

1) Are rogue planets in motion, i.e. are they just wandering freely in space or stationary?

Rephrased 1) Do rogue planets have defined path or a one which can be anticipated? I understand that they cannot be at absolute rest as they are moving along with the galaxy.

2) Do rogue planets rotate around their axes?

If they are in motion, and they outnumber the stars in our galaxy, why our solar system never had a guest?

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1 Answer

up vote 3 down vote accepted

1) this question has no real answer as it depends on the reference frame being used. It is very unlikely that they will be stationary except in their own reference frame.

rephrased 1) In theory their paths can be calculated precisely if you know their speed and the positions and motions of all other bodies (also gas and dust clouds) that might influence their motion. Practically, you will not have that knowledge, as most non-stellar bodies that the rogue planet may encounter will be very dim and you will not be able to detect them. On the other hand space is for the most part empty, so you might reasonably expect their paths to be quite predictable (within a limited time frame). They'll probably be in orbit (either an elliptical, parabolic, or hyperbolic) around the centre of the milky way.

2) yes, they will probably have some angular momentum left from where they formed.

Space is very large so it is not very likely that one will appear in our solar system in our lifetime. And of course we do not know if none ever moved through the solar system.

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I agree that the wording of Q1 was somewhat ambiguous. I rephrased it. –  Farhan Jan 30 at 14:56
    
Of course if a rogue planet did pass through any planetary system there is the possibility of capture. For example, Sedna may be a captured rogue dwarf planet--though it is probably more likely that it is part of an extended scattered disk or inner Oort Cloud. –  called2voyage Feb 6 at 19:17
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