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About Saturn & Its Moons

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Rings - Recent Discoveries

Saturn's Infrared Ring
Saturn's Infrared Ring
Oct. 6, 2009

NASA Space Telescope Discovers Largest Ring Around Saturn

PASADENA, Calif. -- NASA's Spitzer Space Telescope has discovered an enormous ring around Saturn -- by far the largest of the giant planet's many rings.

Artist's depiction of 'Saturn's Recycling Rings.'
Artist's depiction of clumps in Saturn’s rings.
As Cassini enters an extended mission at Saturn, many mysteries about the rings have been uncovered, while new data continue to refine scientists' understanding.

For instance, regarding ring structure, Cassini observations have penetrated most parts of the densest ring, the B ring, allowing scientists to figure out how much material is there. Measurements called "occultations," in which the light from a star going behind the rings, or the radio beam from Cassini itself, is monitored, have found several times the amount of matter in the densest rings than we were able to measure before Cassini, and discovered entirely new kinds of clumps and channel-like structures that we are just now beginning to study in detail.

The occultations -- more than several dozen in number in a variety of geometries -- also tell us more about how particle sizes vary across the rings than ever before. Knowing more about where the large and small particles reside tells us about the underlying dynamics -- the vigor with which local collisions occur. Some of the "particles" seen in the occultations appear to be extended clumps or strands of material which come and go quickly -- local gravitational clumps that form and dissipate.

Moreover, the composition of the rings is now much better characterized by data from several other instruments (while we still don't completely understand just what is in there besides water ice). Spectral "fingerprinting" by the Cassini Visible and Infrared Mapping Spectrometer (VIMS) instrument clearly vary across the rings, in systematic ways. Interpretations of these data are slower in coming. VIMS has found key evidence for iron (probably rocky material) embedded in the dominant water ice -- more abundant in some places than others. Hints of organic (nitrogen-carbon bearing) material have also been seen, but again only in some regions. Cassini's cameras have taken color images which show much more clearly than before how composition changes from place to place.

Daphnis At Work
Cassini discovered the wave-making moon Daphnis orbiting in the Keeler Gap.
The interplay of moons large and small with the ring material is one of the most important features of ring structure. In two regions where tribes of small moonlets coexist with strands of ring material, complicated, shifting patterns emerge. The multi-stranded F ring, lying just outside the edge of the main rings, has changed in several dramatic ways since Voyager caught a fleeting glimpse of it two decades ago, and it seems to be changing before our eyes, with clumps of material coming and going like fireworks. Cassini has discovered a new moonlet clearing its own empty gap in the A ring, and expects to find others. Strange, streaky structure has been discovered in and around the edges of another, wider gap where a larger moon resides, giving us deeper insights into the "shepherding" process whereby moons clear gaps. Cassini has even detected objects no larger than a football field, deeply buried in the A ring and too small to clear a real gap, by their effects on nearby ring material. These propeller-shaped objects seem to be part of a range of objects smaller than real moons but larger than the common, meter-sized ring particles, and represent either fragments of the original ring parent, or merely temporary agglomerations of material.

Scientists long wondered if the moon Enceladus was the source Saturn’s diffuse E ring, which is densest around the orbit of the bright, icy moon. With the discovery of geologic activity on Enceladus , which causes comet-like jets of vapor and ice particles to spray out of the moon’s south polar region, Cassini confirmed that this is indeed the case.

Cassini instruments have also found that the rings have their own tenuous atmosphere which consists mainly of oxygen. No, you couldn't breathe it (it's very sparse) but just how this came to be is keeping modelers busy and might even have implications for some of the strange colors we see in the rings. Also during this all-too-brief visit to the inner depths of the system, Cassini's Radio and Plasma Wave Science (RPWS) instrument detected tones which might be plasma waves caused by marble-sized meteoroids hitting the rings at 129,000 kilometers per hour (80,000 miles per hour)!

Impacts like these might be responsible for causing the ghostly, radial features called "spokes" which covered the rings when Voyager went past. Cassini has also observed and imaged many of these spokes. For more information on these phenomenon, see Spokes in Saturn's Rings.