Aug 20, 2015: Cassini's Final Close Views of Dione - A pockmarked, icy landscape looms beneath NASA's Cassini spacecraft in new images of Saturn's moon Dione taken during the mission's last close approach to the small, icy world. (Image Advisory can be found here.)
April 23, 2012
Today the Cassini Imaging Team presents to you a glimpse of what patience, care and painstaking analysis can bring. And it is glorious.
Recall the F ring of Saturn ... a solitary ring of icy debris, lying outside Saturn's main rings, that first came into view during the historic Voyager flybys of Saturn in the early 1980s. Voyager found a bright ring, shepherded into a tight orbital corridor by two of Saturn's moons, Prometheus and Pandora, the so-called 'shepherd moons.' The dynamical influence of these moons explained for the most part the F ring's narrowness.
But it was the complexity of this ring that baffled: isolated bright clumps, individual strands, braided regions, kinky segments all seemed at the time to be inexplicable. It was strongly suspected, however, that the ring's special location plays a major role: ie, it lies at a distance from Saturn where the planet's shearing tidal forces, still present here but weakening, are offered stiff competition by the coalescence-encouraging gravitational attraction among ring particles.
Fast forward 22 years, Cassini arrives at Saturn, and finds more of the same. But this time, it's different: now we imaging scientists have the luxury of observing the behavior of this ring closely for extended periods of time ... a gift resulting from the finely tuned orbital trajectory of the spacecraft that brings us at times sufficiently close to Saturn and the F ring to make detailed observations.
And that we've done. Tens of thousands of Cassini images later, we have come finally to understand the intricate workings of this most beguiling ring. We have learned that there is a heirarchy of gravitational influences at work in this strange beast, beginning with the channels and jets and small, loosely aggregated bodies that are created when Prometheus, whose orbit, like the F ring's, is eccentric, comes close to the ring. Some of these bodies soon get destroyed by collisions with other bodies or by the tidal forces from Saturn which eagerly rip them apart. But some are strong enough and survive long enough to plow their own way through the F ring, creating the fine, irregular structure and smaller jets that have now been found through careful inspection of images of the F ring taken over the past 8 years.
And so, we continue our Saturnian explorations knowing, with a certain satisfaction and pleasure, that one of our solar system's finest mysteries has yielded finally to our scrutiny.
Next, our voyage takes us out of the equatorial plane and up and over the rings, where we will enjoy repeated and prolonged looks at the intricate structures therein, and the polar regions of the planet. With nothing in our way, it's full speed ahead.
Carolyn Porco Cassini Imaging Team Leader Director, CICLOPS Boulder, CO