A new perspective on the irregular satellites of Saturn – II. Dynamical and physical origin

The origin of the irregular satellites of the giant planets has been long debated since their discovery. Their dynamical features argue against an in situ formation suggesting that they are captured bodies, yet there is no global consensus on the physical process at the basis of their capture. In this paper, we explore the collisional capture scenario, where the actual satellites originated from impacts occurred within Saturn's influence sphere. By modelling the inverse capture problem, we estimated the families of orbits of the possible parent bodies and the specific impulse needed for their capture. The orbits of these putative parent bodies are compared to those of the minor bodies of the outer Solar system to outline their possible region of formation. Finally, we tested the collisional capture hypothesis on Phoebe by taking advantage of the data supplied by Cassini on its major crater, Jason. Our results presented a realistic range of solutions matching the observational and dynamical data.