Globular clusters in the era of precision astrometry
  The study of the kinematics of globular clusters (GCs) offers the possibility
of unveiling their long term evolution and uncovering their yet unknown
formation mechanism. Gaia DR2 has strongly revitalized this field and enabled
the exploration of the 6D phase-space properties of Milky Way GCs, thanks to
precision astrometry. However, to fully leverage on the power of precision
astrometry, a thorough investigations of the data is required. In this
contribution, we show that the study of the mean radial proper motion profiles
of GCs offers an ideal benchmark to assess the presence of systematics in
crowded fields. Our work demonstrates that systematics in Gaia DR2 for the
closest 14 GCs are below the random measurement errors, reaching a precision of
~0.015 mas/yr for mean proper motion measurements. Finally, through the
analysis of the tangential component of proper motions, we report the detection
of internal rotation in a sample of ~50 GCs, and outline the implications of
the presence of angular momentum for the formation mechanism of proto-GC. This
result gives the first taste of the unparalleled power of Gaia DR2 for GCs
science, in preparation for the subsequent data releases.
