Astronomers using The Hubble telescope have imaged two additional bodies in the Pluto/Charon system. All 4 bodies orbit a centre of gravity that lies just above the surface of Pluto. Interestingly the orbits of Charon, P1 and P2 (as the new moons are designated) have a 12:2:3 orbital resonance. For each 12 orbits Charon completes, P2 completes 2 orbits and P1 completes 3. This implies that the moons where formed from a collision event that ejected material that later coalesced into the bodies. The gravity in the system isn’t strong enough for captured P1 & P2 to have formed the resonant orbits in the time the Solar System has been in existence. There is more info in this weeks Nature. If you don’t have access there are many other sources on the Internet. It’ll be interesting when the New Horizons mission gets to the Pluto/Charon system in July 2015.
This story is covered in this weeks Nature Podcast as well.