* Astronomy

Uranus's recently discovered outermost ring is bright blue.

The blue ring is associated with the small moon Mab.
Saturn also has a blue outer ring.

"The outer ring of Saturn is blue and has Enceladus right smack at its brightest spot, and Uranus is strikingly similar, with its blue ring right on top of Mab's orbit" - Imke de Pater, professor of astronomy at the University of California at Berkeley.

Uranus has eleven rings. These rings are made of large rocks up to 10 meters wide.
The other rings are a reddish colour due to them being composed of larger particles that reflect red light, or they contain iron. The blue colour may also be the result of absorption of red light by methane.

The colour of Saturn's blue ring is due to small particles ejected into space by Enceladus as it orbits around the planet. But the same probably isn't true for Uranus.
Uranus' newly discovered moon, Mab, is a small, dead, rocky ball only about 24 kilometres across — one-twentieth the diameter of Enceladus.
However, scientists suspect that both of these rings are subject to forces acting on dust in the rings, which allow the tiny particles to survive while the larger ones are captured by their moons.
These fragments are subject to forces that push them away or toward the planet out of the moon's orbit. The result is a ring of small particles, each only a fraction of a human hair in width, that reflect and scatter mostly blue light.


This schematic view shows the outer rings of Saturn (top) and Uranus (bottom), with each ring system scaled to a common planetary radius.

"This model can be transferred directly to what we now see in Uranus. Although we still need to understand the details of the process" - Imke de Pater

The study is detailed in Friday's issue of the journal Science.