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The largest satellite of Pluto; also known as Pluto I. It orbits 19 570 km from Pluto's centre in 6.387 days. Its orbital period and its axial rotation are the same as the rotation period of Pluto itself, so Charon not only keeps one face permanently turned towards Pluto but also hangs stationary over one point on its surface. Charon is 1210 km in diameter, over half the size of Pluto. Its mass is approximately one-tenth that of Pluto, and the barycentre of the system lies above Pluto's surface. Charon's density is about 1.7 g/cm3, suggesting a composition of rock and ice. Water ice has been detected on its surface. Charon was discovered in 1978 by the American astronomer James Walter Christy (1938– ).

Subjects: Astronomy and Astrophysics.

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