Rings of Rhea - Interpretation

Interpretation

Cassini's flyby trajectory makes interpretation of the magnetic readings difficult.

The obvious candidates for magnetospheric plasma-absorbing matter are neutral gas and dust, but the quantities required to explain the observed depletion are far greater than Cassini's measurements allow. Therefore the discoverers, led by Geraint Jones of the Cassini MIMI team, argue that the depletions must be caused by solid particles orbiting Rhea:

An analysis of the electron data indicates that this obstacle is most likely in the form of a low optical depth disk of material near Rhea’s equatorial plane and that the disk contains solid bodies up to ~1 m in size.

The simplest explanation for the symmetrical punctuations in plasma flow are "extended arcs or rings of material" orbiting Rhea in its equatorial plane. These symmetric dips bear some similarity to the method by which the Rings of Uranus were discovered in 1977. The slight deviations from absolute symmetry may be due to "a modest tilt to the local magnetic field" or "common plasma flow deviations" rather than to asymmetry of the rings themselves, which may be circular.

Not all scientists are convinced that the observed signatures are caused by a ring system. No rings have been seen in images, which puts a very low limit on dust-sized particles. Furthermore, a ring of boulders would be expected to generate dust that would likely have been seen in the images.