CFHT UM2025 - Presentation Details
Abstract Details
Title: CFHT discoveries of 200 saturnian moons
Presenter: Brett Gladman
Abstract:
Over the last six years, the Canadian, French, and Tawianese TACs have invested a moderate amount of telescope time to search for faint saturnian irregular moons (on large eccentric planetocentric orbits that are highly inclined to the planet's heliocentric orbital plane). CFHT Mepagrime was able to take 3-hour sequences that were "Shift and Stacked" at rates corresponding to saturnian irregulars to reach magnitudes of about 26, corresponding to moons with diameters in the range of 3 km. The first results from the 2019-2021 campaign suggested that the size distribution of the detections was extremely steep, which is indicative of the presence of a recent collision somewhere in the system which has generated many fragments that have not yet had time to mutually collide and grind the size distribution down towards a shallower (collisional equilibrium) slope. It appeared that this steep size distribution was largely confined to a small subsection of the retrograde orbital space, near the moon Mudilfari (which itself had been discovered by CFHT in 2000 along with 11 others). Additional CFHT time was awarded as multiple nights in each of three sequential dark runs in late 2023. By having multiple nights per dark run and several nearby dark runs, the orbital linking process was much easier to perform even to slightly fainter magnitudes (and thus slightly smaller moons). This search was wildly successful, yielding the announcement of a staggering 128 new saturnian irregulars on March 11, 2025 by the IAU Minor Planet Center. The hypothesis of a fresh (last 100 Myr) collisional family appears to have been verified, for that majority of the new smallest moons again concentrate into this restricted region of the parameter space. A moon of at least tens of km must have been disrupted to provide the current collisional family, with Mundilfari the largest remnant. The other known saturnian clusters (the Inuit and Gallic inclination groups) have also acquired new members, with the Kiviuq sub-group of the Inuit group receiving the greatest increase, showing that the giant planet irregular moon groups are the surviving members of an intense collisional cascade that has been operating over the entire age of the Solar System. The largest saturnian irregular, Pheobe (known for more than a century), does not apper to host a concentrated collisional fragment, indicating that is likely the fortunate grandfather in the system that has luckily escaped a major collision.