  Pluto's recently discovered minor moons, Nix and Hydra, have almost circular
orbits, and are nearly coplanar with Charon, Pluto's major moon. This is
surprising because tidal interactions with Pluto are too weak to damp their
eccentricities. We consider an alternative possibility: that Nix and Hydra
circularize their orbits by exciting Charon's eccentricity via secular
interactions, and Charon in turn damps its own eccentricity by tidal
interaction with Pluto. The timescale for this process can be less than the age
of the Solar System, for plausible tidal parameters and moon masses. However,
as we show numerically and analytically, the effects of the 2:1 and 3:1
resonant forcing terms between Nix and Charon complicate this picture. In the
presence of Charon's tidal damping, the 2:1 term forces Nix to migrate outward
and the 3:1 term changes the eccentricity damping rate, sometimes leading to
eccentricity growth. We conclude that this mechanism probably does not explain
Nix and Hydra's current orbits. Instead, we suggest that they were formed
in-situ with low eccentricities.
  We also show that an upper limit on Nix's migration speed sets a lower limit
on Pluto-Charon's tidal circularization timescale of >10^5 yrs. Moreover,
Hydra's observed proper eccentricity may be explained by the 3:2 forcing by
Nix.
