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This question already has an answer here:

I'll have to ask an elementary level question about orbital motion and the mass/gravity that influences it.

In solar systems, the large mass of the sun pulls on the planets and we see the velocity of the outer planets traveling far slower than the inner planets because the mass in the rest of the solar system is far lower than the mass of the sun. If dark matter is spread throughout a galaxy, and not just at the center, would that not be like having massive planets in the outer part of a solar system, like a lot of jupiters that can have an effect on the planetary motion of the outer planets in the solar system? i.e. if there were a lot of jupiters in the outer regions of a solar system, would they cause the velocity of the outer planets to speed up, like we see in a galaxy with dark matter located throughout the galaxy?

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marked as duplicate by user36790, John Rennie, Jon Custer, Qmechanic Sep 15 '16 at 6:56

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    $\begingroup$ Probably a duplicate. See answe in physics.stackexchange.com/q/107764 $\endgroup$ – Bob Bee Sep 14 '16 at 18:40
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    $\begingroup$ Possible duplicates: physics.stackexchange.com/q/1008/2451 and links therein. $\endgroup$ – Qmechanic Sep 14 '16 at 18:43
  • $\begingroup$ @BobBee I don't think it is a duplicate of that question: it seems to be asking whether the solar solar system is affected by dark matter, while I think this question is asking whether solar systems with a lot of distant mass -- lots of Jupiters -- would have markedly different rotation curves for other planets. $\endgroup$ – tfb Sep 14 '16 at 18:44
  • $\begingroup$ @tfb I have to say that the answers provided by DavePhDa and Alan under the proposed duplicate are fine and explicit answers to this question: the size of the possible effect is below the sensitivity of current measurements so we can only tell you the theoretical answer. $\endgroup$ – dmckee Sep 14 '16 at 19:14
  • $\begingroup$ @dmckee And I think the theoretical answer is what they are after: how are the rotation curves of galaxies (or planetary systems) dependent on their mass distributions, not how our solar system's curve in how much dark matter we expect to exist, which is obviously 'not very much at all'. $\endgroup$ – tfb Sep 14 '16 at 19:30
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Yes, it would, provided that those outer planets are more distant from the sun than the dark "Jupiters" you are considering. If the "Jupiters" are more distant than the outer planets and the "Jupiters" are spherically symmetric around the sun, they will make no difference to the motion of the outer planets according to the the Shell Theorem.

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  • $\begingroup$ I think you meant to write, in the last sentence, that a spherical distribution outside the imaginary shell where the outer plants are would just have no gravitational effect inside that shell $\endgroup$ – Bob Bee Sep 15 '16 at 1:00

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