  We propose a novel method utilizing stellar kinematic data to detect low-mass
substructure in the Milky Way's dark matter halo. By probing characteristic
wakes that a passing dark matter subhalo leaves in the phase space distribution
of ambient halo stars, we estimate sensitivities down to subhalo masses $\sim
10^7\,M_\odot$ or below. The detection of such subhalos would have implications
for dark-matter and cosmological models that predict modifications to the
halo-mass function at low halo masses. We develop an analytic formalism for
describing the perturbed stellar phase-space distributions, and we demonstrate
through simulations the ability to detect subhalos using the phase-space model
and a likelihood framework. Our method complements existing methods for
low-mass subhalo searches, such as searches for gaps in stellar streams, in
that we can localize the positions and velocities of the subhalos today.
