Origin of planetary rings.

The present investigation shows that the origin of planetary rings, such as those of Saturn and Uranus, might have been related to the action of gravitational and magnetic forces in a very early (plasma) phase of the formation of the presatellite disks. An early phase characterized by a rotating central body, a global and (nearly) axisymmetric magnetic field, and a surrounding axisymmetric gas-plasma envelope is considered. It is pointed out that only in the Saturnian and Uranian Systems, the inner boundary of the presatellite disk can have been situated well inside the Roche limit. The consequences of this condition are examined.