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