S.A. Stern (1992). "The Pluto-Charon system". Annual Review of Astronomy and Astrophysics30: 190. doi:10.1146/annurev.aa.30.090192.001153. Bibcode: 1992ARA&A..30..185S. "Charon's orbit is (a) synchronous with Pluto's rotation and (b) highly inclined to the plane of the ecliptic.".
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S.A. Stern (1992). "The Pluto-Charon system". Annual Review of Astronomy and Astrophysics30: 190. doi:10.1146/annurev.aa.30.090192.001153. Bibcode: 1992ARA&A..30..185S. "Charon's orbit is (a) synchronous with Pluto's rotation and (b) highly inclined to the plane of the ecliptic.".