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The currently known Galactic globular cluster population extends out to amaximum galactocentric distance of $\sim$ 145 kpc, with the peculiarity thatthe outermost clusters predominantly have an inward velocity. Orbit averagingfinds that this configuration occurs by chance about $6\%$ of the time,suggesting that several globular clusters with positive radial velocitiesremain undiscovered. We evaluate the expected number of undiscovered clustersat large distances under the assumption that the cluster population has asmooth radial distribution and is in equilibrium within the Milky Way's virialradius. By comparing the present day kinematic properties of outer clusters torandom orbital configurations of the Galactic globular cluster system throughorbit averaging, we estimate a likelihood of $73\%$ of there being at least oneundiscovered globular cluster within the Milky Way. This estimate assumes thecurrent population is complete out to 50 kpc, and increases to $91\%$ if thepopulation is complete out to 150 kpc. The likelihood of there being twoundiscovered clusters is between $60\%$ and $70\%$, with the likelihood ofthere being three undiscovered clusters being on the order of $50\%$. The mostlikely scenario is that the undiscovered clusters are moving outwards, whichresults in the outer cluster population being consistent with an equilibriumstate. Searches for distant and possibly quite low concentration and very lowmetallicity globular clusters will be enabled with upcoming deep imagingsurveys.

The Likelihood of Undiscovered Globular Clusters in the Outskirts of the Milky Way