Charon (moon)

Charon (/ˈkɛərən/ or /ˈʃærən/), known as (134340) Pluto I, is the largest of the five known natural satellites of the dwarf planet Pluto. It has a mean radius of 606 km (377 mi). Charon is the sixth-largest known trans-Neptunian object after Pluto, Eris, Haumea, Makemake and Gonggong.[20] It was discovered in 1978 at the United States Naval Observatory in Washington, D.C., using photographic plates taken at the United States Naval Observatory Flagstaff Station (NOFS).

Charon
Charon in true color, imaged by New Horizons
Discovery
Discovered byJames W. Christy
Discovery date22 June 1978
Designations
Designation
Pluto I[1]
Pronunciation/ˈkɛərən/[2] or /ˈʃærən/[3][note 1]
Named after
Discoverer's wife, Charlene, and Χάρων Kharōn
S/1978 P 1
AdjectivesCharonian /kəˈrniən, ʃə-/[4][5][6]
Charontian, -ean /kəˈrɒntiən/[7][8][9]
Charonean /kærəˈnən/[10][11]
Orbital characteristics [12]
Epoch 2452600.5
(2002 Nov 22)
Periapsis19,587 km
Apoapsis19,595 km
19591.4 km (planetocentric)[13]
17181.0 km (barycentric)
Eccentricity0.0002[13]
6.3872304±0.0000011 d
(6 d, 9 h, 17 m, 36.7 ± 0.1 s)
0.21 km/s[note 2]
Inclination0.080° (to Pluto's equator)[13]
119.591°±0.014° (to Pluto's orbit)
112.783°±0.014° (to the ecliptic)
223.046°±0.014° (to vernal equinox)
Satellite ofPluto
Physical characteristics
Mean radius
606.0±0.5 km[14][15] (0.095 Earths, 0.51 Plutos)
Flattening<0.5%[16]
4.6×106 km2 (0.0090 Earths)
Volume(9.32±0.14)×108 km3 (0.00086 Earths)
Mass(1.586±0.015)×1021 kg[14][15]
(2.66×10−4 Earths)
(12.2% of Pluto)
Mean density
1.702±0.017 g/cm3[15]
0.288 m/s2
0.59 km/s
0.37 mi/s
synchronous
Albedo0.2 to 0.5 at a solar phase angle of 15°
Temperature−220 °C (53 K)
16.8[17]
1[18]
55 milli-arcsec[19]

With half the diameter and one eighth the mass of Pluto, Charon is a very large moon in comparison to its parent body. Its gravitational influence is such that the barycenter of the Plutonian system lies outside Pluto, and the two bodies are tidally locked to each other.

The reddish-brown cap of the north pole of Charon is composed of tholins, organic macromolecules that may be essential ingredients of life. These tholins were produced from methane, nitrogen and related gases released from the atmosphere of Pluto and transferred over 19,000 km (12,000 mi) to the orbiting moon.[21]

The New Horizons spacecraft is the only probe that has visited the Pluto system. It approached Charon to within 27,000 km (17,000 mi) in 2015.


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