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Outermost ring of Uranus is blue

The recently discovered outermost ring of gas giant Uranus is a bright blue, scientists said Thursday. The rare blue hue is probably created by a small moon called Mab that orbits just inside the ring The ring and the moon Mab were only discovered in 2005 by the Hubble Space Telescope.

Saturn is the only other planet with an identified blue outer ring in the solar system. All other rings — such as those around Jupiter, Saturn, Uranus and Neptune — sport a reddish color because they are composed of larger particles that reflect red light. The particles themselves may also be reddish, possibly from iron.

The color of Saturn’s blue ring has been credited to the tiny particles spewed into space by Enceladus as it orbits around the planet. But the same probably isn’t true for Uranus, scientists say. Uranus’ moon, Mab, is a small, dead, rocky ball only about 15 miles (24 kilometers) across — one-twentieth the diameter of Enceladus.

The scientists, however, 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.

The team’s explanation is that the outer ring is made of very fine water ice particles, mostly less than a tenth of a micrometre across. They are too small to scatter long-wavelength infrared light, but visible wavelengths can bounce off the particles - especially at the shorter blue end of the spectrum.

The view of Uranus will soon be clearer because, as seen from the Earth, the rings are changing their angle. In 2007 the ring will be edge on, and 100 times brighter. Then it should be possible to obtain a better image and confirm the curious colour of Uranus’ outermost ring.

posted by: kyawoo at 20:37 | link | comments |
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