  How did Pluto's recently discovered minor moons form? Ward and Canup propose
an elegant solution in which Nix and Hydra formed in the collision that
produced Charon, then were caught into corotation resonances with Charon, and
finally were transported to their current location as Charon migrated outwards.
We show with numerical integrations that, if Charon's eccentricity is
judiciously chosen, this scenario works beautifully for either Nix or Hydra.
However, it cannot work for both Nix and Hydra simultaneously. To transport
Nix, Charon's eccentricity must satisfy e_C< 0.024; otherwise, the second order
Lindblad resonance at 4:1 overlaps with the corotation resonance, leading to
chaos. To transport Hydra, e_C > 0.7 R_p/a_C > 0.04; otherwise migration would
be faster than libration, and Hydra would slip out of resonance. These two
restrictions conflict. Having ruled out this scenario, we suggest an
alternative: that many small bodies were captured from the nebular disk, and
they were responsible for forming, migrating and damping Nix and Hydra. If this
is true, small moons could be common around large Kuiper belt objects.
