Rings of Rhea 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
Definition of planet spherical under its own gravity but not large enough to fuse. This definition would add 19 moons to the list of planets in our Solar System. The discovery since 1992 of extrasolar planets, or planet-sized objects around other stars ( such planets in planetary systems including multiple planetary systems as of ), has widened the debate on the nature of planethood in unexpected ways. Many of these planets are of considerable size, approaching the mass of small stars, while many newly discovered brown dwarfs are, conversely, small enough to be considered planets. The material difference between a low-mass star and