Apr 7 2006
From The Space Library
Imke de Pater of the University of California, Berkeley, and a team of astronomers, reported in Science that they had determined that the outermost ring of the planet Uranus is bright blue. Saturn is the only other planet in the solar system known to possess a blue outer ring. In December 2005, astronomers Mark R. Showalter and Jack J. Lissauer, had reported the discovery of two of Uranus’s moons—Mab and Cupid—and of two new rings. At that time, the astronomers had only determined the color of the innermost red ring. To determine the color of the planet’s outermost ring, the team had combined the ground-based, near-infrared observations of the W. M. Keck telescope in Hawaii with visible-light images captured by the HST. They had analyzed the properties of Uranus’s outermost ring and had drawn a parallel with the blue ring of Saturn. The astronomers speculated that Saturn’s blue ring of small particles was the result of meteoroid impacts on the surface of Saturn’s moon Enceladus, impacts that had scattered debris into the moon’s orbit. The largest particles had remained within Enceladus’s orbit, but various forces, including pressure from sunlight, had pushed the smallest particles out of the moon’s orbit, causing Saturn’s broad ring of smaller scattered particles, which reflect predominantly blue light. De Pater explained that this explanation of the color of Saturn’s outer ring was directly applicable to the blue ring observed around Uranus. However, he cautioned that astronomers did not yet “understand the details of the process.”
Robert Sanders, “Blue Ring Discovered Around Uranus,” University of California at Berkeley press release, 6 April 2006, http://berkeley.edu/news/media/releases/2006/04/06_bluering.shtml (accessed 25 June 2010); see also Imke de Pater et al., “New Dust Belts of Uranus: One Ring, Two Ring, Red Ring, Blue Ring,” Science 312, no. 5770 (7 April 2006): 92-94.
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