Retrograde Predominance of Small Saturnian Moons Reiterates a Recent Retrograde Collisional Disruption

Abstract We report the discovery and careful orbital determination of 64 new irregular moons of Saturn found in images taken using the Canada–France–Hawaii Telescope from 2019 to 2021, bringing the total number of Saturnian irregulars to 122. By more than doubling the sample of Saturnian irregular moon orbits, including pushing to smaller sizes, we can now see finer detail in their orbital distribution. We note the emergence of potential subgroups associated with each of Siarnaq and Kiviuq within the Inuit group. We find that in the inclination range 157 ∘ –172 ∘ , the ratio of smaller moons (diameters less than 4 km) to larger moons (diameters greater than 4 km) is significantly larger than that of any other inclination range in the retrogrades. We denote this subset of the Norse group as the Mundilfari subgroup after its largest member. The incredibly steep slope of the Mundilfari subgroup’s size distribution, with a differential power law index of q = 6, strengthens the hypothesis in E. Ashton et al. that this subgroup was created by a recent catastrophic collision, <10 8 yr ago.