Giant Impact?

Explanation: The 'Giant Impact' model for the formation of Pluto's moons. 1: a Kuiper belt object nears Pluto; 2: the KBO impacts Pluto; 3: a debris disk/ring forms around Pluto; 4: the debris aggregates to form Charon; 5: Pluto and Charon relax into spherical bodies.


Image credit: Wikipedia.