Self-gravity wakes:
The critical distance of roughly 2.5 planetary radii is called the Roche limit. Within the Roche limit, tidal forces make it impossible for two like-sized bodies orbiting Saturn to collide and merge to form a larger body. Short-lived aggregates of ring particles called self-gravity wakes can form within the Roche limit, but they last for only about the time they take to complete one orbit around Saturn (less than an Earth day). [“Saturn’s Rings,” Dr. Luke Dones, The Planetary Report (September Equinox 2017, paywall).]
Typos mine. And since I am referencing Saturn, here’s a gratuitous picture.
This stunning false-color view of Saturn’s moon Hyperion reveals crisp details across the strange, tumbling moon’s surface. Differences in color could represent differences in the composition of surface materials. The view was obtained during Cassini’s close flyby on Sept. 26, 2005.
[NASA/JPL]
