Origin of the Local Group satellite planes
  We attempt to understand the planes of satellite galaxies orbiting the Milky
Way (MW) and M31 in the context of Modified Newtonian Dynamics (MOND), which
implies a close MW-M31 flyby occurred ${\approx 8}$ Gyr ago. Using the timing
argument, we obtain MW-M31 trajectories consistent with cosmological initial
conditions and present observations. We adjust the present M31 proper motion
within its uncertainty in order to simulate a range of orbital geometries and
closest approach distances. Treating the MW and M31 as point masses, we follow
the trajectories of surrounding test particle disks, thereby mapping out the
tidal debris distribution.
  Around each galaxy, the resulting tidal debris tends to cluster around a
particular orbital pole. We find some models in which these preferred spin
vectors align fairly well with those of the corresponding observed satellite
planes. The radial distributions of material in the simulated satellite planes
are similar to what we observe. Around the MW, our best-fitting model yields a
significant fraction (0.22) of counter-rotating material, perhaps explaining
why Sculptor counter-rotates within the MW satellite plane. In contrast, our
model yields no counter-rotating material around M31. This is testable with
proper motions of M31 satellites.
  In our best model, the MW disk is thickened by the flyby 7.65 Gyr ago to a
root mean square height of 0.75 kpc. This is similar to the observed age and
thickness of the Galactic thick disk. Thus, the MW thick disk may have formed
together with the MW and M31 satellite planes during a past MW-M31 flyby.
