The Rings and Moons of Uranus
The Uranian ring system was discovered in 1977 during
observations of a stellar occultation by the planet. The
star was observed to blink out briefly five times before
moving behind the planet and again five times afterward,
indicating
that the planet was encircled by five narrow rings.
Subsequent Earth-based observations indicated that
there were actually nine major rings. Working outward
from the planet, they are named 6, 5, 4, Alpha, Beta, Eta,
Gamma, Delta, and Epsilon. In 1986 the Voyager 2
spacecraft acquired additional occultations and also our
best images of the ring system. The Voyager cameras
detected a few additional rings and also showed that
the nine major rings are surrounded by belts of fine dust.
Like Jupiter's, the rings of Uranus are very dark but like Saturn's they are composed of fairly large particles ranging up to 10 meters in diameter in addition to fine dust. There are 11 known rings, all very faint; the brightest is the Epsilon ring. Shepherd Moons are important in maintaining the Epsilon ring. The Uranian rings were the first after Saturn's to be discovered. This was of considerable importance since we now know that rings are a common feature of large planets, not a peculiarity of Saturn alone.
Uranus' Satellites
Uranus has 20 named moons plus 1 recently discovered one which
as yet has not been given an official name.
Unlike the other bodies in the solar system which have names from classical
mythology, Uranus' moons take their names from the writings of Shakespeare and
Alexander Pope. They form three distinct classes:
the 11 small very dark inner ones discovered by Voyager 2, the 5 large
ones (above), and the newly discovered much more distant ones.
Most have nearly circular orbits in the plane of Uranus'
equator (and hence at a large angle to the plane of the ecliptic);
the orbits of the outer 4 moons are much more elliptical (non-circular).
Miranda, Ariel, Umbriel, Titania and Oberon are the 5 main major moons of Uranus, ranging is size from 236 to 761 km in radius (still rather small: Earth's Moon is 3400 km).
Miranda is about half water ice and half rocky material and the
surface is all mixed up with heavily cratered terrain intermixed with
weird grooves, valleys and cliffs. In 1986, Voyager 2 passed closest to
Miranda than any other moon. Scientists were being viewed on LIVE TV as
the first images where being read down. Explaining the bizarre hitherto
unknown terrain proved quite an embarrassment and the usual impressive
and esoteric technical jargon of the scientists gave out. They resorted
to using such terms as "chevron", "race track", and "layer cake" to
describe Miranda's unique features.
There are no more missions planned to Uranus and Neptune. The data from Voyager 2 may be all we have for a very long time. However, groundbased images can still be quite revealing! See here