COURTESY W.M. KECK OBSERVATORY This composite view of Uranus seen with its rings edge-on, top, was taken in two infrared wavelengths. The planet is now in a good position for Earth scientists to study its rings.

Uranus shows Earth its rings

Astronomers say the planet's outer bands have changed in time

WAIMEA, Hawaii » Astronomers around the world are buzzing about a rare view of the wispy rings of planet Uranus .

The planet is now in a position, reached only once every 42 years, when the edges of the rings are facing the Earth, which means that a lot of solar glare reflecting from that is avoided. That position, and the power of the Keck II telescope, on Mauna Kea produced very clear images.

Telescopes have to look at the planet roughly 1.8 billion miles from the sun, then focus on rings about as thick as the length of a football field.

When a team led by astronomer Imke de Pater at the University of California at Berkeley did it May 28 using the giant Keck II telescope, they got a surprise.

Not discovered until 1977, not photographed until 1986, the rings have changed. While some of the objects in the rings are the size of boulders, others are specks of dust.

"People tend to think of the rings as unchanging, but our observations show that not to be the case," de Pater said. "There are a lot of forces acting on small dust grains, so it is not that crazy to find that the arrangement of the rings has changed."

The most interesting difference is a broad ring called zeta, which is several thousand miles farther from Uranus than it was 21 years ago when first seen by the Voyager space probe.

De Pater's findings were reported online in Science Express and discussed yesterday at the European Planetary Science Congress 2007 in Potsdam, Germany.