Transcript for scene 28 of the video " Kepler Today - Part 1 - The Science Revolution" by Rolf Witzsche - Ice Age Ahead not Global Warming  

A third set of epicycles dark matter

And since this isn't quite sufficient to explain the gravitational hold on a distant star, a third set of epicycles has been invented, which is imagined as a ring of dark matter strung around the perimeter of the galaxy as a type of external attractor, that is of course invisible too.