Thomas, P.C. (2007). "Hyperion and its Cousins: Sponges, Landslides, Layers, and Ridges." Eos Trans. AGU 88(52) Fall Meet. Suppl., Abstract P12B-03 INVITED.


Abstract
Cassini's exploration of the Saturn system has given detailed views of small, irregularly-shaped satellites from ~10 to 135 km-mean radius that orbit within the rings to Phoebe orbiting nearly 100 times further from Saturn. The spongy appearance of Hyperion, reflecting a high density of well-preserved 2-10 km craters, may derive from a combination of effects of low porosity and Hyperion's size on generation of impact crater ejecta. Smaller, porous moons in the Saturn system do not show similar effects with available data. Low gravity is not a deterrent to downlsope processes: these dominate the surface of Telesto which is essentially self-buried in debris. Ring-related satellite Atlas and (probably Pan) shows a distinct two-component surface that may represent different stages of accretion. These satellites, and other ring-related ones are shaped such that parts of their surfaces have almost zero escape velocity and thus may retard further accretion, leaving them in balance with hyper velocity impact effects. Phoebe is distinct from the more icy inner satellites, with higher density, probably much lower porosity, and some layering of icy and rocky components. Comparisons to recent data on comets and small asteroids suggests much remains to be learned regarding crater formation and removal on low-gravity objects.