thumb|300px|Diagram illustrating the orbits of the irregular satellites of Saturn, with major groups and moons labeled. The inclination and semi-major axis are represented on the Y and X-axis, respectively. The satellites with inclinations below 90° are [[prograde orbit|prograde, those above 90° are retrograde. The X-axis is labeled in terms of Saturn's Hill radius.]]

The Norse group (or family or cluster; also simply referred to as the retrograde moons) comprises the retrograde irregular satellites of Saturn. They are unlikely to have a common origin as a single collisional family and their orbital parameters are very widely dispersed; more probably they are composed of a number of dynamical clusters with more homogeneous orbital and physical parameters. As of April 2026, there are 210 known members, making it by far the largest group of Saturn's confirmed moons. The Norse group is dominated by moons that are smaller in size, which could be indicative of a recent catastrophic collision event within the population. Ten of the satellites received official names in August 2022.

General characteristics

thumb|upright=1.5|268 irregular moons of Saturn plotted by semi-major axis and inclination . The Norse group (left) is color-coded into four different subgroups proposed by Ashton et al.

Overall, their orbital elements are very broadly distributed, with inclinations between 136° and 178°. The cause of the steep size distribution was later narrowed down solely to a specific section of the retrograde population, proposed as the "Mundilfari subgroup". though Mundilfari's inclination also differed enough from the rest of the group to be questionable.

In 2008, Nicholson et al. split the retrograde satellites into three groups, but made no attempt to justify their potential shared dynamic origins, simply roughly sorting them by inclination alone. Each group was centred on a moon and their inclination. Their groups were the Phoebe group with an inclination around 175° (Phoebe, Suttungr, Thrymr, Ymir, and Fornjot), the Mundilfari group with an inclination at 168° (Mundilfari, S/2004 S 7, Aegir, S/2004 S 12, S/2004 S 13, Hati, Fenrir, and S/2004 S 17), and the Skathi group with an inclination at 153° (Skathi, Narvi, Farbauti, Bergelmir, and Bestla). They did not provide exhaustive lists of all members in their groups, and commented that nine newly discovered satellites at the time all fell into their inclination groupings but did not specify which moons went into which groups.

Also in 2008, Turrini et al. pointed out that members from a potential Phoebe family would likely be collisionally removed by the moon itself, which argues against the existence of the family. As half of all potential collisions between irregular moons would involve Phoebe due to its large size, this produces a "sweeping effect" that they presumed was probably the cause of a lack of known moons with semi-major axes around Phoebe's. They proposed that it was not related to any of the other known irregular moons, noting that none of the other satellites had compatible colours. Using an algorithm called the Hierarchical Clustering Method, they found several retrograde "families", which did not cover all 27 of the known retrograde satellites at the time. A group was qualified as a viable family if it passed the condition that the members were close enough in their orbital elements to potentially have a shared collisional origin with realistic dispersion velocities (≤200 m/s). Six of these were found to be acceptably realistic. The six groups were:

  • Bergelmir and S/2006 S 1
  • Mundilfari, S/2004 S 13, and S/2004 S 17
  • Kari and S/2006 S 3
  • Aegir, S/2004 S 12, and Hati
  • Fornjot, Loge, and Fenrir
  • Narvi and Bestla

They also made larger groups of moons that merged multiple families and previously left-out moons that they called "clusters", that they said could be groups composed of multiple generations of collisional fragments. One of the clusters passed their acceptance criterion, "cluster A", which was composed of Mundilfari's group, Jarnsaxa, and Aegir's group.

Ashton et al. (2021) chose to split off the Norse satellites with inclinations within 3° of Phoebe's into a "Phoebe subgroup", comprising 11 out of 46 total, and suggested that the remainder of the Norse group could likely be subdivided further.

</references>

  • Scott S. Sheppard - SaturnMoons
  • Outer Moons of Saturn - tilmanndenk
  • Robert Johnston: Orbital and dynamical data for solar system planets and satellites