Particle properties and processes in Uranus' rings.

The Uranian rings provide some confirmations but also many new challenges for ring physics. Current analytic and numerical models can explain many details, but must be extended to be fully realistic. Occultation observations of the ∊ ring are interpreted to yield an effective size of the ring particles that exceeds 70 cm, a surface mass density that exceeds 80 g cm^-2 and a ring vertical thickness greater than tens of meters for solid ice particles. As proposed for regions of the other known ring systems, new ring material can be continually created by the destruction of small moons near the rings. This phenomenon may explain the youthful appearance of the Uranian rings. Otherwise, the confinement of the rings over the age of the solar systems requires some strong mechanism which is yet to be understood.