name is Nictian (cf. Russian Никта Nikta). The names of features on the bodies in the Pluto system are related to mythology and the literature and history of exploration. In particular, the names of features on Nix must be related to deities of the night from literature, mythology, and history. Origin Pluto's smaller moons, including Nix, were thought to have formed from debris ejected from a massive collision between Pluto and another Kuiper belt object, similarly to how the Moon is believed to have formed from debris ejected by a large collision of Earth. The ejecta from the collision would then coalesce into the moons of Pluto. However, the collisional hypothesis cannot explain how Nix maintained its highly reflective surface. Physical characteristics Nix has an elongated shape, with its longest axis measured at across and its shortest axis across. This gives Nix the measured dimensions of . It is the third-largest moon of Pluto, being slightly smaller than Hydra. Early research appeared to show that the surface of Nix is reddish in color. Contrary to this, other studies show that Nix is spectrally neutral, similar to the small moons of Pluto. The neutral spectrum of Nix signifies that water ice is present on its surface. Nix also appeared to vary in brightness and albedo, or reflectivity. The brightness fluctuations were thought to be caused by areas with different albedos on the surface of Nix. Images of Nix from the New Horizons spacecraft show a large reddish area approximately across, which could explain the two conflicting measurements of Nix's surface color. The reddish area is thought to be a large impact crater where the reddish material was ejected from underneath Nix's water ice layer and deposited on its surface. In this case, Nix would likely have regoliths originating from the impact. Another explanation suggests that the reddish material may have originated from a collision with Nix and another object with a different composition. However, there were no significant color variations on other impact craters on Nix. The water ice present on the surface of Nix is responsible for its high reflectivity. Trace amounts of frozen methane may be also present on the surface of Nix, and could be responsible for the presence of reddish material, likely tholins, on its surface. In this case, tholins on the surface of Nix may have originated from the reaction of methane with ultraviolet radiation from