QUESTION: I would like to know if the particles and rocks forming the rings are now slowly falling into Jupiter, and eventually the rings will be gone? ANSWER from Elias Barbinis on April 14, 1997: Jupiter's rings are formed by charged particles of various sizes. Most of these particles are very tiny (about 1 micron across). There are two forces that are exerted on these particles by Jupiter: a gravitational force and an electromagnetic force. The gravitational force is stronger than the electromagnetic force for particles with size of 1 micron and it provides the centripetal accelaration that is required to keep these particles in circular motion around Jupiter. Throughout their lifetime these particles are ground down by the energetic particles that are abundant in Jupiter's magnetosphere and eventually they become so small (about 0.03 micron across) that the electromagnetic force overpowers the gravitational force and the particles leave the rings and fall into Jupiter's atmosphere. The lifetime of these particles is about 1000 years, which is very short in a cosmological sense. However, Jupiter's rings are a permanent feature because these tiny particles are regenerated continually by collisions of interplanetary micrometeoroids with boulder-size objects within the rings.