Rare view shows big changes for Uranus

Strange things are happening to the rings of Uranus, that little blue planet way out there in the solar system.

It has rings and moons, and once every 42 years, the planet's tilted angle lets earthbound observers briefly catch three edge-on views of the rings.

The time for the rare views is now, and astronomers from the University of California-Berkeley and the SETI Institute in Mountain View, Calif., has seen some dramatic changes -- some rings are growing brighter, at least one is fading away and another is either newly formed or unexpectedly moving outward from the planet by thousands of miles.

At the same time, a broad, diffuse cloud of microscopic dust particles seems to be pervading the entire ring system.

Imke de Pater, a UC planetary astronomer, and Mark Showalter at the SETI Institute, who has been studying Uranus for 20 years, reported Thursday in the online journal Science Express that the changes are by no means fully understood.

De Pater said in an interview that "the ring system looks completely different" from the way it did 21 years ago when the Voyager 2 spacecraft flew past Uranus and photographed its rings and moons.

"The rings are exquisite now," de Pater said, "and the innermost ring, called zeta, seems to have moved since Voyager flew past."

Back then, she said, the Voyager images in 1986 showed that the zeta ring surrounded the planet about 23,000 miles out, but now the latest infrared images from the powerful Keck telescope atop Mauna Kea in Hawaii show that the same ring is nearly 25,000 miles out.

"We're starting to realize that studying the rings and moons of Uranus is more like studying the weather than planetary geology," Showalter said. "Things are moving."

Uranus itself, the seventh planet from the sun, was discovered in 1791, but its rings were not detected until 1977.