image: Scientists have long suspected that small moons hiding among the ring's strands might be producing some of the unusual structure observed in the F ring. While the shepherd moon Prometheus is the main culprit behind the strange behavior of Saturn’s F ring, it cannot explain all observed features. The current dilemma facing scientists is that Cassini is detecting extended objects – like those pictured here – that may be either solid moons or just loose clumps of particles within the ring.
This montage of four enhanced Cassini narrow angle camera images shows bright clump-like features at different locations within the F ring.
Two objects in particular, provisionally named S/2004 S3 and S/2004 S6, have been repeatedly observed by Cassini over the past 13.5 months and 8.5 months, respectively. The orbits for these two objects have not yet been precisely determined, in part because perturbations from other nearby moons make the orbits of objects in this region complicated. Thus scientists cannot be completely confident at the present time if they in fact have observed new sightings of S3 and S6, or additional transient clumps.
The upper two images show features that may be S6. From previous observations, S6 appears to have an orbit that crosses that of the main F ring. This unexpected behavior currently is a subject of great interest to ring scientists.
The upper left image was taken on June 21, 2005 and shows an object in the outer ringlets of the F ring. The longitudinal (or lengthwise) extent of the feature is approximately 2,000 kilometers (1,200 miles). The radial resolution on the ring is about 13 kilometers (8 miles) per pixel.
The image at upper right was taken on June 29, 2005 and shows a bright feature within the F ring’s inner ringlets. The radial extent of the feature seen here is about 2,000 kilometers (1,200 miles); the radial resolution is 36 kilometers (22 miles).
The image at lower left was taken on August 2, 2005 and shows a feature that may be S3. S3 has been found to have an orbital path that is tightly aligned with that of the main F ring. The radial resolution in the image is 3.5 kilometers (2.2 miles) per pixel.
The lower right image was taken on April 13, 2005 and has a radial resolution of 7 kilometers (4 miles) per pixel. This object does not appear to be either S3 or S6.
Structures like knots and clumps within the F ring often are transient, appearing and then disappearing within months. Repeated observation of the objects seen in this region hopefully will give scientists firm evidence about whether these features are actual moons that disturb the material around them or perhaps the short-lived products of interactions between the F ring and larger moons such as Prometheus.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.
Credit: Cassini Imaging Team & NASA/JPL/Space Science Institute