Saturn's rings ever-changing
By MATT WILLIAMS Colorado Daily Staff Writer
Monday, September 5, 2005 7:04 PM MDT An outer ring of Saturn periodically tears apart and is reassembled by the planet's gravitational force, a team of CU-Boulder scientists has found.
Joshua Colwell, science team member for the Ultra Violet Imaging Spectrograph (UVIS) - a $12.5 million instrument designed and built at CU-Boulder that is riding on the Cassini-Huygens spacecraft - said the periodic rearrangement of Saturn's outer "A" ring particle clumps is like marbles orbiting a beach ball.
Colwell said the marbles closest to the ball would orbit more quickly, causing some marble clumps to break apart and the reassemble.
The outermost "A" ring, which is made of clusters as big as a moving vans and as small as dust grains, has particles that are largest near the middle of the ring and smaller clusters near the edges, a team led by CU-Boulder astrophysics professor Larry Esposito of the Laboratory for Atmospheric and Space Physics (LASP) has announced. The A ring is mostly empty space, and there is no indication yet that similar clumps exist in Saturn's other rings.
"The spacing between the clumps as determined by UVIS data is greater than the widths of the clumps themselves," Colwell said in press release. "If we could get close enough to the rings, these clumps would appear as short, flattened strands of spiral arms with very few particles between them."
Colwell gave a press briefing on new Cassini-Huygens observations at the 37th Annual Meeting of the Division of Planetary Sciences this week in Cambridge, England.
The UVIS team also detected a "tenuous" atmosphere of water vapor on Saturn's tiny moon Enceladus.
New observations using UVIS data, other spectrographs and images from Cassini- Huygens indicate water and grains of ice are being spewed from the moon's surface like gaseous jets that have been observed erupting from the surface of comets.
The rate of water released from Enceladus is enough to account for the "neutral oxygen" UVIS discovered around Saturn last year, Esposito said in a statement.
NASA also announced Monday that some of Saturn's rings are orbiting slower than once predicted by computer models.
The space agency also has found some unexpected clouds lurking under the upper reaches of Saturn's atmosphere.
"Unlike the hazy, broad, global bands of clouds regularly seen in Saturn's upper atmosphere, many of the deeper clouds appear to be isolated, localized features," said Dr. Kevin H. Baines, a member of the visual and infrared mapping spectrometer team from NASA's Jet Propulsion Laboratory, Pasadena, Calif, in a statement Monday. "They come in a large variety of sizes and shapes, including circular and oval shapes, donut shapes, and swirls."
The Cassini-Huygens entered orbit on Jun. 30, 2004 and shortly thereafter began sending images and data of Saturn back to Earth.
In January, the Huygens probe successfully descended into the atmosphere of Saturn's moon Titan. The probe also sent back images of Titan's rocky, orange surface.
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Saturn as observed by Cassini-Huygens on March 27, 2004
Astronomers have discovered that Saturn's D ring, the innermost of Saturn's 15 rings, has grown dimmer in the past 25 years and sections have moved up to 125 miles inward toward the planet. This discovery was made after astronomers compiled results predominantly from the Voyager 2 spacecraft, which passed Saturn in 1981, and the Cassini-Huygens probe which entered Saturn's orbit last year. 

Other rings were found to be rotating slower than had previously been estimated with computer models.  It was also discovered that the matter composing the rings is of far more widely varying temperatures than had been expected. Sections of Saturn's F ring were also recognised as breaking apart and reforming, depending on the location of one of Saturn's moons.

The rings, which are now iconic to Saturn, and known to be common to all Jovian planets in general, were first observed in 1610 by Galileo. The rings have recently become a subject of scientific interest to modern astronomers who believe they are similar in structure to the dust which orbited the Sun, in a similar pattern, and formed the planets some 4.5 billion years ago.

This, and other Cassini-related discoveries, were discussed at a meeting of the American Astronomical Society's division of planetary sciences on Monday.