Astro2020 Science White Paper: Science at the edges: internal kinematics
  of globular clusters' external fields
  The outer regions of globular clusters can enable us to answer many
fundamental questions concerning issues ranging from the formation and
evolution of clusters and their multiple stellar populations to the study of
stars near and beyond the hydrogen-burning limit and to the dynamics of the
Milky Way. The outskirts of globular clusters are still uncharted territories
observationally. A very efficient way to explore them is through high-precision
proper motions of low-mass stars over a large field of view. The Wide Field
InfraRed Survey Telescope (WFIRST) combines all these characteristics in a
single telescope, making it the best observational tool to uncover the wealth
of information contained in the clusters' outermost regions.
