moons of Pluto

Pluto and its four known moons. P4 was the latest to be discovered, in 2001

Pluto has four known moons. The innermost of these and by far the largest is Charon, discovered in 1978. All three of the smaller moons were discovered from observations by the Hubble Space Telescope: the first two, Hydra (S/2005 P1) and Nix (S/2005 P2), in 2005, and the third, S/2011 P3, in 2011. All the moons move in retrograde, coplanar, and nearly-circular orbits around Pluto. Nix, S/2011 P3, and Hydra appear to be in 1:4:5:6 orbital resonances, respectively, with the Charon-Pluto orbital period.

moon	semimajor axis (km)	orbital period (days)	orbital eccentricity	orbital inclination (^o)	diameter (km)
Charon	17,536 ± 3	6.387	0.0022	0.001	1,207 ± 3
Nix	48,708	24.85	0.0030	0.195	46 – 137
S/2011 P3	~59,000	32.1	~0	?	13 – 34
Hydra	64,749	38.21	0.212	0.006	61 – 167

Related category

• PLANETS AND MOONS

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