Pluto and Charon from the Hubble Space Telescope

Aggiornamento del 19 Agosto 2006: il Sistema "Plutone-Caronte", sino a ieri considerato un sistema equiparabile a quello Terra-Luna (in cui Plutone, al pari della Terra, è il Corpo Maggiore e Caronte, invece ed al pari della Luna, quello minore e dunque SOLO Satellite del primo), in accordo ad una decisione dell'International Astronomical Union (IAO) è stato ora rubricato come "Doppio Pianeta".

Caption IAU originale:"Both Pluto and Charon each are large enough (massive enough) to be spherical. Both bodies independently satisfy the definition of “planet”. The reason they are called a “double planet” is that their common centre of gravity is a point that is located in free space outside the surface of Pluto. Because both conditions are met: each body is “planet-like” and each body orbits around a point in free space that is not inside one of them, the system qualifies to be called a “Double Planet”.