The ?? ring is a rather crowded place with a filling factor near the apoapsis estimated by different sources at from 0.008 to 0.06.[21] The mean size of the ring particles is 0.2???20.0 m,[15] and the mean separation is around 4.5 times their radius.[21] The ring is almost devoid of dust, possibly due to the aerodynamic drag from Uranus's extended atmospheric corona.[2] Due to its razor-thin natur