DescriptionNix Moon is a natural satellite of Pluto, with a diameter of 49.8 km (30.9 mi) across its longest dimension. It was discovered along with Pluto's outermost moon Hydra on 15 May 2005 by astronomers using the Hubble Space Telescope and was named after Nyx, the Greek goddess of the night. Nix is the third moon of Pluto by distance, orbiting between the moons Styx and Kerberos. Nix was imaged along with Pluto and its other moons by the New Horizons spacecraft as it flew by the Pluto system in July 2015. These images reveal a large reddish area on Nix that is likely an impact crater. Nix was independently discovered by Max Mutchler and Andrew Steffl, members of the Pluto Companion Search Team, using the Hubble Space Telescope. The New Horizons team had suspected that Pluto and its moon Charon might be accompanied by other moons, hence they used Hubble to search for faint moons around Pluto in 2005. Since Nix's brightness is about 5,000 times fainter than Pluto, long exposure images were taken in order to find it. The discovery images were taken on 15 May 2005 and 18 May 2005. The discoveries were announced on 31 October 2005, after confirmation by precovering archival Hubble images of Pluto from 2002. The two newly announced moons of Pluto were subsequently provisionally designated S/2005 P 1 for Hydra and S/2005 P 2 for Nix. The moons were informally referred to as P1 and P2, respectively by the discovery team. The name Nix was approved by the International Astronomical Union (IAU) and was announced on 21 June 2006 along with the naming of Hydra in the IAU Circular 8723. Nix was named after Nyx, the Greek goddess of darkness and night and mother of Charon, the ferryman of Hades in Greek mythology. The two newly named moons were intentionally named that the order of their initials N and H honors the New Horizons mission to Pluto, similarly to how the first two letters of Pluto's name honors Percival Lowell. The original proposal for the naming of Nix was to use the classical spelling Nyx, but to avoid confusion with the asteroid 3908 Nyx, the spelling was changed to Nix, the Coptic spelling of the name. The adjectival form of the 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. 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 have coalesced into the moons of Pluto. However, the collisional hypothesis cannot explain how Nix maintained its highly reflective surface.

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