Did you know there are 13 rings around Uranus?

Ring in Mab’s oribit intriguingly similar to Saturn’s blue ring in Enceladus’ orbit

The outermost ring of Uranus, discovered just last year, is bright blue, making it only the second known blue ring in the solar system, according to a report this week in the journal Science.

Perhaps not coincidentally, both blue rings are associated with small moons.

"The outer ring of Saturn is blue and has Enceledus right smack at its brightest spot, and Uranus is strikingly similar, with its blue ring right on top of Mab’s orbit," said Imke de Pater, professor of astronomy at the University of California, Berkeley. "The blue color says that this ring is predominantly submicron-sized material, much smaller than the material in most other rings, which appear red."

The authors of the paper in the April 7 issue of Science are de Pater, Mark Showalter of the SETI Institute in Mountain View, Calif.; Heidi B. Hammel of the Space Science Institute in Boulder, Colo.; and Seran Gibbard of Lawrence Livermore National Laboratory in California.

The similarity between these outer rings implies a similar explanation for the blue color, according to the authors. Many scientists now ascribe Saturn’s blue E ring to the small dust, gas and ice particles spewed into Encedadus’ orbit by newly discovered plumes on that moon’s surface. However, this is unlikely to be the case with Mab, a small, dead, rocky ball, about 15 miles across – one-twentieth the diameter of Enceladus.

Instead, the astronomers suspect both rings owe their blue color to subtle forces acting on dust in the rings that allow smaller particles to survive while larger ones are recaptured by the moon.

"We know now that there is at least one way to make a blue ring that doesn’t involve plumes, because Mab is surely too small to be internally active," said Showalter. He and astronomer Jack Lissauer of NASA Ames Research Center in Mountain View, Calif., discovered Mab in Hubble Space Telescope images in 2003.

The likely scenario to explain Saturn’s blue ring was proposed before plumes were discovered last November as the Cassini spacecraft flew by Enceladus. As modeled for the E ring, meteoroid impacts on the surface of Enceladus scatter debris into its orbit, probably in a broad range of sizes. While the 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 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.



[link to www.innovations-report.com]

"The rings are extremely dark—the Bond albedo of the rings' particles does not exceed 2%. 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..."

[link to en.m.wikipedia.org]

interesting
6+7
9+4