  The New Horizons mission has provided resolved measurements of Pluto's moons
Styx, Nix, Kerberos, and Hydra. All four are small, with equivalent spherical
diameters of $\approx$40 km for Nix and Hydra and ~10 km for Styx and Kerberos.
They are also highly elongated, with maximum to minimum axis ratios of
$\approx$2. All four moons have high albedos ( $\approx$50-90 %) suggestive of
a water-ice surface composition. Crater densities on Nix and Hydra imply
surface ages $\gtrsim$ 4 Ga. The small moons rotate much faster than
synchronous, with rotational poles clustered nearly orthogonal to the common
pole directions of Pluto and Charon. These results reinforce the hypothesis
that the small moons formed in the aftermath of a collision that produced the
Pluto-Charon binary.
