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Uranus' new ring has scientists seeing blue.

Blue may be a color that most of us can feel, but the solar system's seventh planet is feeling it, too--in its recently discovered outermost ring, making it just the second known blue ring in the solar system.

Saturn's E ring is the only other known example of a blue planetary ring. The blue rings of Saturn and Uranus are associated with small moons.

Research by the Space Science Institute at the University of California, Berkeley, indicates that the particles in the blue ring around Uranus likely are produced by impacts on Mab, one of Uranus' smallest moons. Mab is embedded within the blue ring. It is suspected that both rings owe their color to gravitational forces acting on dust in the rings that allow smaller particles to survive while larger ones are recaptured by the moon.

Combining ground-based near-infrared observations from the Keck Telescope in Hawaii and visible-light photos taken by the Hubble Space Telescope, scientists discovered two faint rings, located well outside of Uranus' main ring system. The outer ring is centered on the orbit of the tiny moon Mab and is blue, while the other, which orbits between the moons Rosalind and Portia, is red. Rings around the giant planets in our solar system--Jupiter, Saturn, Uranus, and Neptune--typically are reddish because they contain many large particles that mostly reflect longer (red) wavelengths of light.

It has been hypothesized that meteoroid impacts on the surface of Enceladus--one of Saturn's moons--scatter debris into its orbit in a broad range of sizes. While larger pieces remain within the moon's orbit and eventually are swept up by the moon, smaller particles are subject to subtle forces that push them toward or away from the ringed planet, out of the moon's orbit. These forces include pressure from sunlight, magnetic torques acting on charged dust particles, and the influence of slight variations in gravity due to the equatorial bulge of Saturn.

The net result is a broad ring of smaller particles, less than one-tenth of a micron across--a thousandth the width of a human hair--that scatter and reflect predominantly blue light. This theory can be transferred directly to what is being seen near Uranus.
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Publication:USA Today (Magazine)
Geographic Code:1USA
Date:Jun 1, 2006
Words:361
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