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Cassini Uncovering More Secrets Of Saturn Rings
Pasadena CA (SPX) Jul 06, 2006 New images by the Cassini spacecraft of Saturn's diaphanous G and E rings are yielding clues about their structure and formation. A sequence of recent Cassini images, compiled into a brief movie by the spacecraft's imaging team, shows an arc of bright material looping around the inside edge of the G ring, a tenuous 7,000-kilometer (4,400-mile) wide band of dust-sized icy particles lying beyond the F ring by 27,000 kilometers (16,800 miles). Cassini passed between the F and G rings during its insertion into orbit in late June 2004. The G ring's arc is the same feature identified in images taken in May 2005. "We have seen the arc a handful of times over the past year," said Cassini team member Matt Hedman of Cornell University in Ithaca, N.Y. "It always appears to be a few times brighter than the rest of the G ring and very tightly confined to a narrow strip along the inside edge of the 'normal' G ring." Imaging team members now think this feature is long-lived and may be held together by resonant interactions with the moon Mimas of the type that corral the famed ring arcs around Neptune. "We've known since the days of Voyager that we had Jovian-type and Uranian-type rings within the rings of Saturn," said Cassini imaging team leader Carolyn Porco in Boulder, Colo. "Now it appears that Saturn may be home to Neptunian-type rings as well. Saturn's rings have it all." Porco was the first to work out the dynamics of the Neptunian arcs from Voyager observations. The scientists do not know exactly how the bright arc formed. One possibility is collisions between small, possibly meter-sized icy bodies orbiting within the G ring set loose a cloud of fine particles that eventually came under the influence of the moon Mimas. The new observation, however, suggests the remainder of the G ring itself might be derived from particles leaking away from this arc and drifting outwards. Future Cassini imaging observations are being planned to take a closer look at the G ring arc. Results from Cassini's previous encounters with Enceladus indicated its south polar geysers as the primary source of the E ring particles. Now, images of the E ring with finer resolution than has ever been obtained before show telling details that appear to confirm this relationship. The new images, taken when Cassini was in the ring plane and consequently showing an edge-on view, reveal a double-banded appearance to the ring, created because the ring is somewhat fainter close to the ring plane than it is 500-1,000 kilometers (300-600 miles) above and below. This appearance can result if the particles comprising the ring circle Saturn on inclined orbits with a very restricted range of inclinations. A similar effect is seen in the Jupiter's gossamer ring and in the bands of dust found within the main asteroid belt. Scientists think this special condition might arise for two reasons: The particles escaping from Enceladus and settling into Saturn orbit could begin their journey within a restricted range of velocities and therefore inclinations. Alternatively, the particles could begin with a large range of inclinations, but those orbiting very close to the ring plane get gravitationally scattered and removed from that region. Future studies of the E ring, including observations and dynamical models, should decide this issue. "We'll want images from a few other vantage points to be sure of the structure, and then we can test several models to see why these ring particles end up in such a distinct configuration," said Cassini imaging team member Joseph Burns, also of Cornell. Related Links Cassini Cassini images
Cassini Spots Another New Tiny Saturn Moon
Pasadena CA (SPX) Jun 29, 2006This magnified view shows tiny Polydeuces, a moon discovered by NASA's Cassini spacecraft last month, is a mere 3 kilometers (2 miles) across. Along with much larger Helene (32 kilometers, or 20 miles across), Polydeuces orbits Saturn at the same distance as large, icy Dione (1,126 kilometers, or 700 miles across). |
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