Outer Ring System
In 2003–2005, the Hubble Space Telescope detected a pair of previously unknown rings, now called the outer ring system, which brought the number of known Uranian rings to 13. These rings were subsequently named the μ and ν rings. The μ ring is the outermost of the pair, and is twice the distance from the planet as the bright η ring. The outer rings differ from the inner narrow rings in a number of respects. They are broad, 17,000 and 3,800 km wide, respectively, and very faint. Their peak normal optical depths are 8.5 × 10−6 and 5.4 × 10−6, respectively. The resulting equivalent optical depths are 0.14 km and 0.012 km. The rings have triangular radial brightness profiles.
The peak brightness of the μ ring lies almost exactly on the orbit of the small Uranian moon Mab, which is probably the source of the ring’s particles. The ν ring is positioned between Portia and Rosalind and does not contain any moons inside it. A reanalysis of the Voyager 2 images of forward-scattered light clearly reveals the μ and ν rings. In this geometry the rings are much brighter, which indicates that they contain much micrometer-sized dust. The outer rings of Uranus may be similar to the G and E rings of Saturn as E ring is extremely broad and receives dust from Enceladus.
The μ ring may consist entirely of dust, without any large particles at all. This hypothesis is supported by observations performed by the Keck telescope, which failed to detect the μ ring in the near infrared at 2.2 μm, but detected the ν ring. This failure means that the μ ring is blue in color, which in turn indicates that very small (submicrometer) dust predominates within it. The dust may be made of water ice. In contrast, the ν ring is slightly red in color.
Read more about this topic: Rings Of Uranus
Famous quotes containing the words outer, ring and/or system:
“Once conform, once do what other people do because they do it, and a lethargy steals over all the finer nerves and faculties of the soul. She becomes all outer show and inward emptiness; dull, callous, and indifferent.”
—Virginia Woolf (1882–1941)
“He will not idly dance at his work who has wood to cut and cord before nightfall in the short days of winter; but every stroke will be husbanded, and ring soberly through the wood; and so will the strokes of that scholar’s pen, which at evening record the story of the day, ring soberly, yet cheerily, on the ear of the reader, long after the echoes of his axe have died away.”
—Henry David Thoreau (1817–1862)
“My advice to people today is as follows: If you take the game of life seriously, if you take your nervous system seriously, if you take your sense organs seriously, if you take the energy process seriously, you must turn on, tune in, and drop out.”
—Timothy Leary (b. 1920)