Nix is a
natural satelliteA natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
of
PlutoPluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
. It was discovered along with
HydraHydra is the second outermost known natural satellite of Pluto. It was discovered along with Nix in June 2005, and is to be visited along with Pluto by the New Horizons mission in July 2015.- Discovery :...
in June 2005, and is to be visited along with Pluto by the
New HorizonsNew Horizons is a NASA robotic spacecraft mission currently en route to the dwarf planet Pluto. It is expected to be the first spacecraft to fly by and study Pluto and its moons, Charon, Nix, Hydra and S/2011 P 1. Its estimated arrival date at the Pluto-Charon system is July 14th, 2015...
mission in July 2015.
Discovery
Nix was found by the
Hubble Space TelescopeThe Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
Pluto Companion Search Team, composed of Hal A. Weaver, S. Alan Stern, Max J. Mutchler, Andrew J. Steffl,
Marc W. BuieMarc W. Buie is an astronomer at Lowell Observatory in Flagstaff, Arizona. He grew up in Baton Rouge, Louisiana and went on to get a B.S. in Physics from Louisiana State University in 1980. After that he switched fields and earned his Ph.D. in Planetary Science from the University of Arizona in...
, 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
precoveriesPrecovery is a term used in astronomy that describes the process of finding the image of an object in old archived images or photographic plates, for the purpose of calculating a more accurate orbit...
from 2002. The moons were
provisionally designatedProvisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calculated...
S/2005 P 1 (Hydra) and
S/2005 P 2 (Nix).
Orbit
The moon follows a circular orbit in the same plane as
CharonCharon is the largest satellite of the dwarf planet Pluto. It was discovered in 1978 at the United States Naval Observatory Flagstaff Station. Following the 2005 discovery of two other natural satellites of Pluto , Charon may also be referred to as Pluto I...
. Its orbital period of 24.9 days is close to a 1:4
orbital resonanceIn celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
with Charon, but the timing discrepancy is 2.7%, which suggests that there is no active resonance. A hypothesis explaining such a near-resonance is that it originated before the outward migration of Charon following the formation of all four known moons, and is maintained by the periodic local fluctuation of 9% in the Pluto–Charon gravitational field strength.
Physical characteristics
Although its size has not been directly measured, the moon has been calculated to have a diameter of between 46 km, if its
geometric albedoThe geometric albedo of an astronomical body is the ratio of its actual brightness at zero phase angle to that of an idealized flat, fully reflecting, diffusively scattering disk with the same cross-section....
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
HydraHydra is the second outermost known natural satellite of Pluto. It was discovered along with Nix in June 2005, and is to be visited along with Pluto by the New Horizons mission in July 2015.- Discovery :...
, 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
PlutoPluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
and unlike the other moons, but more recent reports have been that it is grey like the remaining satellites.
Name
The formal name "Nix", from the Greek goddess of darkness and night, and mother of
CharonIn Greek mythology, Charon or Kharon is the ferryman of Hades who carries souls of the newly deceased across the rivers Styx and Acheron that divided the world of the living from the world of the dead. A coin to pay Charon for passage, usually an obolus or danake, was sometimes placed in or on...
, was announced on June 21, 2006, on
IAUThe International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...
Circular 8723, where the designation
Pluto II is also given. Together with Hydra, Pluto's third moon, the initials are those of the
New HorizonsNew Horizons is a NASA robotic spacecraft mission currently en route to the dwarf planet Pluto. It is expected to be the first spacecraft to fly by and study Pluto and its moons, Charon, Nix, Hydra and S/2011 P 1. Its estimated arrival date at the Pluto-Charon system is July 14th, 2015...
probe. The initial proposal was to use the classical spelling Nyx, but to avoid confusion with the
asteroidAsteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
3908 Nyx3908 Nyx is an Amor and Mars-crosser asteroid. It was discovered by Hans-Emil Schuster on August 6, 1980, and is named after Nyx, the Greek goddess of the night, after which Pluto's moon Nix is also named...
, the spelling was changed to Nix. The USGS Gazetteer of Planetary Nomenclature states that Nix is the "Egyptian spelling,"
while Jürgen Blunck explains it as the "Spanish translation" of the Greek name.
External links