  We consider solutions of the repulsive Vlasov-Poisson system which are a
combination of a point charge and a small gas, i.e.\ measures of the form
$\delta_{(\mathcal{X}(t),\mathcal{V}(t))}+\mu^2d{\bf x}d{\bf v}$ for some
$(\mathcal{X}, \mathcal{V}):\mathbb{R}\to\mathbb{R}^6$ and a small gas
distribution $\mu:\mathbb{R}\to L^2_{{\bf x},{\bf v}}$, and study asymptotic
dynamics in the associated initial value problem. If initially suitable moments
on $\mu_0=\mu(t=0)$ are small, we obtain a global solution of the above form,
and the electric field generated by the gas distribution $\mu$ decays at an
almost optimal rate. Assuming in addition boundedness of suitable derivatives
of $\mu_0$, the electric field decays at an optimal rate and we derive a
modified scattering dynamics for the motion of the point charge and the gas
distribution.
  Our proof makes crucial use of the Hamiltonian structure. The linearized
system is transport by the Kepler ODE, which we integrate exactly through an
asymptotic action-angle transformation. Thanks to a precise understanding of
the associated kinematics, moment and derivative control is achieved via a
bootstrap analysis that relies on the decay of the electric field associated to
$\mu$. The asymptotic behavior can then be deduced from the properties of
Poisson brackets in asymptotic action coordinates.
