I will love the light for it shows me the way, yet I will endure the darkness for it shows me the stars. — Og Mandino

po_Uranus-RingsThe planet Uranus has a system of rings intermediate in complexity between the more extensive set around Saturn and the simpler systems around Jupiter and Neptune.

The rings of Uranus were discovered on March 10, 1977, by James L. Elliot, Edward W. Dunham, and Douglas J. Mink. More than 200 years ago, in 1789, William Herschel also reported observing rings; some modern astronomers are skeptical that he could have actually seen them, as they are very dark and faint – others are not.

By 1978, nine distinct rings were identified. Two additional rings were discovered in 1986 in images taken by the Voyager 2 spacecraft, and two outer rings were found in 2003–2005 in Hubble Space Telescope photos. They are probably composed of water ice with the addition of some dark radiation-processed organics.

The majority of Uranus’s rings are opaque and only a few kilometers wide. The ring system contains little dust overall; it consists mostly of large bodies 0.2–20 m in diameter. However, some rings are optically thin: the broad and faint 1986U2R/ζ, μ and ν rings are made of small dust particles, while the narrow and faint λ ring also contains larger bodies. The relative lack of dust in the ring system is due to aerodynamic drag from the extended Uranian exosphere—corona.

The rings of Uranus are thought to be relatively young, at not more than 600 million years old. The Uranian ring system probably originated from the collisional fragmentation of a number of moons that once existed around the planet. After colliding, the moons probably broke up into numerous particles, which survived as narrow and optically dense rings only in strictly confined zones of maximum stability.

The mechanism that confines the narrow rings is not well understood. Initially it was assumed that every narrow ring had a pair of nearby shepherd moons corralling them into shape. However, in 1986 Voyager 2 discovered only one such shepherd pair (Cordelia and Ophelia) around the brightest ring.