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Nix (moon) facts for kids

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Plutonian system.jpg
Artist conception of Hydra (foreground),
Pluto and Charon (background),
and Nix (bright dot center left)
Discovered by Hubble Space Telescope
Pluto Companion Search Team 
Discovered in June 2005
Nictian orbital characteristics
Semi-major axisa 48 675 ± 120 km
Eccentricity 0.002 ± 0.002
Orbital period 24.856 ± 0.001 d
Inclinationb 0.04° ± 0.22°
Parent body Pluto
Physical characteristics
Mean diameter 46 − 137 km
Mass 5×1016 − 2×1018 kg
Mean density unknown
Rotation period unknown
Axial tilt unknown
Albedo 0.04 − 0.35 (assumed)
Apparent magnitude 23.38 to 23.7 (measured)
Surface temp. 33-55 K
Atmosphere none

a Relative to the Pluto-Charon barycenter.
b Relative to Pluto's equator (also Charon's orbital plane).
c Based on assumed albedo.

Pluto system 2005 discovery images
Discovery images of Nix and Hydra

Nix is a non-spherical moon of Pluto. It was found along with Hydra in June 2005 by the Hubble Space Telescope Pluto Companion Search Team.

The discovery images were taken on May 15, 2005 and May 18, 2005; the moons were independently found 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 from photographs archived in 2002. The moon were designated S/2005 P 1 (Hydra) and S/2005 P 2 (Nix).

The moon follows a circular orbit in the same plane as Charon. It takes 24.9 days to circle around Pluto.

Although its size has not been directly measured, the moon is calculated to have a diameter of between 46 km, if its reflectivity is similar to Charon's 35%, and 137 km, if it has a reflectivity of 4%, like the darkest Kuiper belt objects. Nix is slightly fainter than Hydra, suggesting that it is somewhat smaller in size. In the discovery image, Nix is 6,300 times fainter than Pluto.

Early research appeared to show that Nix was reddish like Pluto and unlike the other moons, but more recent reports have been that it is grey like the remaining moons.

Nix is to be visited along with Pluto by the New Horizons mission in 2015.

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".

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