The Milky Way, Coming into Focus: Precision Astrometry Probes its
  Evolution, and its Dark Matter
  The growing trove of precision astrometric observations from the Gaia space
telescope and other surveys is revealing the structure and dynamics of the
Milky Way in ever more exquisite detail. We summarize the current status of our
understanding of the structure and the characteristics of the Milky Way, and we
review the emerging picture: the Milky Way is evolving through interactions
with the massive satellite galaxies that stud its volume, with evidence
pointing to a cataclysmic past. It is also woven with stellar streams, and
observations of streams, satellites, and field stars offer new constraints on
its dark matter, both on its spatial distribution and its fundamental nature.
The recent years have brought much focus to the study of dwarf galaxies found
within our Galaxy's halo and their internal matter distributions. In this
review, we focus on the predictions of the cold dark matter paradigm at small
mass scales through precision astrometric measurements, and we summarize the
modern consensus on the extent to which small-scale probes are consistent with
this paradigm. We note the discovery prospects of these studies, and also how
they intertwine with probes of the dynamics and evolution of the Milky Way in
various and distinct ways.
