EQUATORIAL RIDGE

'Equatorial ridges' are a feature of at least two of Saturn's moons. They are ridges that follow closely the moon's equator. They appear to be unique to the Saturnian system, but it is uncertain whether the two occurrences are related or a coincidence. Both were discovered by the ''Cassini'' probe in 2005.
Ridges have been observed on Saturn's large outer moon, Iapetus, and on a tiny inner moon, Atlas. The ridge on Iapetus is nearly 20 km wide, 13 km high and 1,300 km long. That on Atlas is equally remarkable given the moon's much smaller size and distorts the moon's shape into an odd, UFO-like appearance.
It is not certain how either ridge formed, or whether there is any connection between them. Because Atlas orbits within the rings of Saturn, a likely explanation for its ridge is that it sweeps up ring particles as it orbits, which build up around its equator. This theory is less applicable to Iapetus, which orbits far beyond the rings. One scientist has suggested that Iapetus swept up a ring before being somehow expelled to its current, distant orbit.[1] Others think it was stationary and it is the rings that have been pulled away from it, falling into Saturn's gravity field. But most scientists prefer to assume that Iapetus's ridge was produced by some kind of internal source.