The formal name "Nix", from the Greek goddess of darkness and night, and mother of Charon, was announced on June 21, 2006 on IAU Circular 8723, where the designation Pluto II is also given. Together with Hydra, Pluto's third moon, the initials are those of the "New Horizons" probe. The initial proposal was to use the Classical spelling Nyx, but to avoid confusion with the asteroid 3908 Nyx, this was changed to "the Egyptian spelling of the Greek name".