If anyone knows a reference that discusses this question, please post a citation. Naively it seems that any central mass would attract DM from the mass's general vicinity so that an approximately spherically symmetric accumulation would develop over time about the central mass. This seems to be accepted as the explanation of why the velocities of stars (or gas) within spiral galaxies do not exhibit a Newtonian pattern. Since the planets of our solar system DO have a Newtonian pattern, there must not be any such DM halo. But, why not?