As another year in Saturn orbit and sixteen additional revolutions around the planet come to a close, we look back on the spoils of 2006, a Year of Surveillance, when we dove in close and enjoyed repeated looks at the bodies and phenomena we discovered during our first 1.5 years around the ringed planet.
We continued to eye the never-ending jetting of fine icy particles from the south pole of Enceladus. Discovered in 2005, this magnificent phenomenon is now impossible to overlook and readily apparent any time we observe Enceladus at high phase.
Orbiting close to the ringplane as we did for the first half of the year, it was easy to capture 30-km diameter Pan protruding above and below the very much thinner rings, as it cruised along in its orbit. Early analyses of the sizes, shapes and densities of ring-region moons like Pan, Daphnis, Atlas, Prometheus and Pandora, indicate that these bodies have attained their present dimensions by accreting the ring material around them until they can now grow no more. Thus it would appear that Pan and its ring-region companions are not themselves the result of the original catastrophic disruption of a larger body that likely created the rings, though they may contain in their interiors the remnants of such destruction around which smaller ring particles later accreted.
In July, we climbed once again into a highly inclined orbit, allowing direct inspection of the rings and the moons in and around them. And once again, we sighted in Saturn's B ring the faint transient features called spokes, now a common sight in Cassini's images of the B ring. Around the same time, we collected an awesome set of high resolution images of the F ring, revealing for the first time astonishing structures -- like delicately entwined silver threads -- very likely the dynamical consequences of interactions with small moons in the rings. We were also treated to a far better view than before of the radially narrow arc of ring material that was discovered in 2005 to form the sharp inner edge of the G ring, and are closer to believing that it does indeed owe its existence to a gravitational perturbation by the Saturnian moon, Mimas. Finally, additional high resolution images and analyses of the structures within Saturn's innermost D ring pointed to a startling conclusion: a vertically warped, continuous spiral structure in the outer D ring could only reasonably be explained by an impact into that region in 1984 ... the 'Comet Shoemaker-Levy 9' of Saturn's rings. Who would have imagined when we started on this journey that we would be capable of pinpointing a ring-altering impact event to recent times?
But perhaps the most memorable event of the whole year was the 9 hour interval when Cassini was favorably positioned -- above the rings, far from the planet, and deep within its shadow -- to image for the first time the inner Saturnian system as no human had ever seen it: in full, end to end, during a total eclipse of the Sun. This was an event that saw the discovery of two new rings, yielded a breathtaking view of Enceladus exhaling its bright spray and wreathing Saturn in a sparkling blue ring of crystalline ice, and, finally, occasioned a fleeting glimpse of our own lovely planet, Earth, cradled in the arms of Saturn's rings. We will be lucky to see anything so moving again.
In keeping with our tradition of marking the close of another year living among the denizens that travel the realm of Saturn, we are releasing today a collection of images, maps, movies, and anaglyphs of some of the ringed planet's most unusual companions. That we have lived to witness such remarkable sights, that we have had in our lifetime the privilege to explore and know intimately another planetary system as remote and wondrous as Saturn's, is itself extraordinary and cause for celebration.
And so, as 2006 passes into history and 2007 knocks on our door, let this special moment in time and your presence in it lift your spirits, make you shout and be ever so grateful to be alive. We are not here for long. Let's enjoy it while it lasts.
Happy New Year to all!
Carolyn Porco Cassini Imaging Team Leader CICLOPS/Space Science Institute Boulder, CO