Origin and evolution of the Saturn system

As was the case for Jupiter, Saturn formed either as a result of a gas instability within the solar nebula or the accretion of a solid core that induced an instability within the surrounding solar nebula. In either case, the protoplanet's history can be divided into three major stages: early, quasi-hydrostatic evolution (stage 1); very rapid contraction (stage 2); and late, quasi-hydrostatic contraction (stage 3). The irregular satellite Phoebe was most likely captured by gas drag experienced in its passage through a bloated Saturn, just prior to the onset of stage 2. The nebular disk served as the birthplace of Saturn's regular satellites and probably the ring material. As Saturn's excess luminosity declined during the early portion of stage 3, water was able to condense at progressively closer distances to the center of the system and water clathrates and hydrates were able to form. Despite the comparatively small size of the inner satellites of Saturn, a number (especially Dione and Rhea) may have experienced significant expansion and melting during the first ≡1×10⁹ yr. During the early history of the Saturn system, giant impact events may have catastrophically disrupted most of the original satellites of Saturn. This may be responsible, in part, for the occurrence of Trojans and coorbital moons in the Saturn system. Titan's atmosphere formed from hydrates and clathrates. Over the age of the solar system, a nontrivial amount of atmospheric nitrogen and much more methane than is presently in the atmosphere have been lost.