satellite plane problem

The satellite plane problem (which goes by other phrases, such as planes of satellite galaxies problem) is the mystery that observations have suggested that the Milky Way and Andromeda each have satellite galaxies generally within a plane, and each such plane is not the plane of the host galaxy, but tilted in relation to it. If the orientation of a disk galaxy resulted from the rotation the original protogalaxy, then satellite galaxies would form rotating around the same axis and in the manner of gravitationally-bound disks, fall into the same plane. Andromeda and the Milky Way are the two major spiral galaxies for which we have a good view, and in both cases, observation suggests this is not the case, i.e., they demonstrate this problem.