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The satellite galaxies of the Milky Way (MW) define a vast polar structure(VPOS), a thin plane perpendicular to the MW disc. Proper motion (PM)measurements are now available for all of the 11 brightest, `classical'satellites and allow an updated analysis of the alignment of their orbitalpoles with this spatial structure. The coherent orbital alignment of 7 to 9 outof 11 satellites demonstrates that the VPOS is a rotationally stabilizedstructure and not only a pressure-supported, flattened ellipsoid. This allowsus to empirically and model independently predict the PMs of almost allsatellite galaxies by assuming that the MW satellite galaxies orbit within theVPOS. As a test of our method, the predictions are best met by satellites whosePMs are already well constrained, as expected because more uncertainmeasurements tend to deviate more from the true values. Improved and new PMmeasurements will further test these predictions. A strong alignment of thesatellite galaxy orbital poles is not expected in dark matter based simulationsof galaxy formation. Coherent orbital directions of satellite galaxies are,however, a natural consequence of tidal dwarf galaxies formed together in thedebris of a galaxy collision. The orbital poles of the MW satellite galaxiestherefore lend further support to tidal scenarios for the origin of the VPOSand are a very significant challenge for the standard LCDM model of cosmology.We also note that the dependence of the MW satellite speeds on Galactocentricdistance appear to map an effective potential with a constant velocity ofapproximately 240 km/s to about 250 kpc. The individual satellite velocitiesare only mildly radial.

The rotationally stabilized VPOS and predicted proper motions of the Milky Way satellite galaxies