Collaborative work on the dynamics of co-orbitals of the Saturnian moons has continued throughout the year, with Fathi Namouni (Observatoire de la Côte d'Azur, Nice, France) and Maria Helena Moreira Morais (Observatório Astronómico de Coimbra, Santa Clara, Portugal). This research seeks to explain why we see co-orbitals associated with two of the moons, Dione and Tethys, but not Mimas and Enceladus.
During the year, we have successfully modified the MERCURY integrator to simulate the tidal evolution of such orbits. An initial batch of simulations (without tides) using the CONDOR mini-cluster has shown that co-orbitals of all four satellites are stable with the exception of `shallow' co-orbitals of the satellite Mimas. `Deep' co-orbitals are, however, all stable. This strengthens our suspicion that tidal evolution of the orbits is mainly responsible for the picture we see today. Future work will focus on determining the exact cause of the instability that precludes co-orbitals of Mimas and Enceladus. Since tidal evolution and capture into resonance are not time-reversible, it should be possible to place interesting constraints on the orbital history of the satellites though the absence or otherwise of co-orbitals.