The Puzzle of the Pluto Satellite System
The dwarf planet Pluto has a fascinating satellite system with five known members: Charon, Styx, Nix, Keberos, and Hydra. The innermost satellite Charon is about 1/8 as massive as Pluto, and the Pluto-Charon system is in a dual synchronous state, which is the endpoint of tidal evolution. The orbits of the four small satellites are nearly circular and coplanar with Charon's orbit, with orbital periods nearly in the ratios 1:3:4:5:6. These properties suggest that the small satellites were debris from the same impact event that placed Charon in orbit and had been pushed to their current positions by being locked in orbital resonances with Charon as Charon's orbit was expanded by tidal interactions with Pluto. I will discuss the tidal evolution of Pluto-Charon and show that the placing of the small satellites at their current orbital positions by resonant transport is unlikely. I will also discuss some alternative scenarios for the origin of the small satellites.