Rings of Uranus one of which, Mab, shares its orbit with the outermost newly discovered μ ring. As currently understood, the ring system of Uranus comprises thirteen distinct rings. In order of increasing distance from the planet they are: 1986U2R/ζ, 6, 5, 4, α, β, η, γ, δ, λ, ε, ν, μ rings. They can be divided into three groups: nine narrow main rings (6, 5, 4, α, β, η, γ, δ, ε), two dusty rings (1986U2R/ζ, λ) and two outer rings (ν, μ). The rings of Uranus consist mainly of macroscopic particles and little dust, although dust is known to be present
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