Pluto has four known natural satellites (Charon, Nix, Hydra and S/2011 P1. (provisional name, also known as P4, identified by the Hubble Space Telescope in 2011).
Nix is the third largest known natural satellite of Pluto. It was discovered along with Hydra in June 2005.
Based on estimated size, Nix is the 48th largest moon in the Solar System currently known.
Discovery
Nix was found by the Hubble Space Telescope's Pluto Companion Search Team, which is composed of Hal A. Weaver, Alan Stern, Max J. Mutchler, Andrew J. Steffl, Marc W. Buie, William J. Merline, John R. Spencer, Eliot F. Young, and Leslie A. Young.
The discovery images were taken on May 15, 2005, and May 18, 2005; the moons were independently discovered by Max J. Mutchler on June 15, 2005, and Andrew J. Steffl on August 15, 2005.
The discoveries were announced on October 31, 2005, after confirmation by precoveries from 2002.
Naming
Nix was provisionally designated S/2005 P2. Nix the moon, was named after Nyx the Greek goddess of darkness and night, and mother of Charon.
The initial proposal was to use the classical spelling Nyx, but to avoid confusion with the asteroid 3908 Nyx, the spelling was changed to Nix. The USGS Gazetteer of Planetary Nomenclature states that Nix is the "Egyptian spelling", of the Greek name.
Stats
Diameter (mean): ~91.5 (46 – 137) km
Semi-major axis: 48,708 km
Orbital Period: 24.86 days
Rotation Period: Unknown
Physical properties
Nix's size has not been directly measured. Calculations based on its brightness give it a diameter of between 46 km, if its geometric albedo is similar to Charon's 35 percent, and about 137 km, if it has a reflectivity of 4 percent like the darkest Kuiper belt objects.
Nix is slightly fainter than Hydra, suggesting that it is somewhat smaller in size.
Exploration Status
The arrival of the New Horizons Spacecraft to Plutonian System in July 2015 is highly anticipated. The true size of Nix and other new discoveries will be revealed.
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