A year and a half into our explorations of Saturn and the images collected by our cameras are still breathtaking, our scientific findings startling.
In this past year alone, we have executed a dozen and a half close encounters with Saturn's icy satellites that surpass in detail the best undertaken by the Voyagers in the early 1980s. And of the 9 extremely close satellite flybys that Cassini will make during its entire nominal 4-year mission, six of them -- three of Enceladus, and one each of Hyperion, Dione, and Rhea -- occurred in the last year. It has been the Year of the Moon, and as a result, we have come to know these bodies intimately.
Hyperion is perhaps the strangest yet seen. While craters are to be expected on outer solar system bodies, the closely packed and deeply etched pits on Hyperion were not. The warming action of the sun on water ice lying beneath a darkened layer has apparently deepened and exaggerated the depressions already present through impacts. Still, it is hard to look at Hyperion and not think of the lifeforms that grow in terrestrial waters ... a strange juxtapositioning if there ever was one.
Other larger Saturnian moons are also very densely cratered. Rhea has shown itself to be heavily cratered even at very high resolution. And while Dione's limited tectonically modified regions are crossed by systems of complex, braided fractures and the ramparts of its craters are clean, fresh, and white, it too is largely a cratered body. Tethys, like Iapetus, boasts enormous conspicuous basins, the marks left by giant impacts. The surfaces of these moons are obviously very old. Even the great globe-encircling crack, Ithaca Chasm, for which Tethys is renowned is an ancient and battered feature.
And then there is Enceladus, a world apart and host to our most thrilling discoveries. Parts of this moon are marked by impacts, but mostly this small, 505-kilometer wide moon is criss-crossed by multiple generations of fractures, folds, and chasms ... clear signs of a complicated and geologically active past. The most detailed images taken so far of any Saturnian body were those of Enceladus' south polar region, and show a ridged, virtually crater-free and therefore young surface, littered with icy boulders. And most startling of all, the fractures straddling the south polar region are the warmest places on Enceladus, jetting tall fountains of vapor and fine, icy particles into space and supplying material to a gargantuan plume that towers over the moon's south pole. For planetary explorers like us, there is little that can compare to a sight like this on another celestial body. Enceladus, we have found, now joins Jupiter's moon Io, Neptune's moon Triton, and the Earth as the only bodies in the solar system known to be geologically active today.
Surprisingly, on none of these satellites do we see any evidence of the thick, volcanic ice flows that were believed to be responsible for whatever resurfacing has occurred in the Saturnian system. Not a trace of this process is found anywhere ... not within Dione's wispy terrain, not even on Enceladus. The modification of the surfaces of Saturnian moons appears to have taken place tectonically, with extensive fracturing and, in places, viscous degradation erasing any pre-existing impact scars. This is yet another ground-breaking result from our Saturnian investigations that we are only now beginning to absorb.
To map the uncharted terrains of other worlds is part of the lure of exploration. Like the terrestrial cartographers of old who assembled the best maps of the day from the findings gathered from distant lands by ships plying the oceans of Earth, we too have taken our collected images and composed them into maps, being released today, of seven of Saturn's moons. Future explorers to this sector of our solar system will one day rely on these charts and their derivatives to find their way among the moons of Saturn.
Meanwhile, Saturn and its rings have not gone unnoticed. Discrete eddies and clouds have over the last year become increasingly more visible in Saturn's northern hemisphere as the ring shadows, a visual element that lends a moody magnificence to the visage of Saturn, have begun to shorten and march southward with the advent of spring. We found the F ring enveloped by a spiral ring unlike any seen before, and home to a dizzying number of clumps and putative moonlets. Beyond the F ring, the G ring was seen in exquisite detail. Within the main rings, the ghostly features called 'spokes', imaged so well by Voyager and completely absent for Cassini's first year in residence, finally made an appearance, and glints of sunlight reflecting off the rings were captured for the first time. The examination of these and other discoveries is still in its infancy.
We celebrate this miraculous year by reveling in some of the planetary vistas we have been privileged to see as we wander the frozen reaches of this far-flung planetary system. Today, we are releasing some of them: the soft globe of Saturn inscribed by the delicate shadows of its stately rings, an occultation of Dione by Rhea, a color view of Titan wrapped in purple haze, Saturn in dazzling color, and the momentary turn of our gaze from Saturn and its companions to the Carina Nebula, 8,000 light years away.
We have made our mark. We have touched this place. Now, Saturn and all that surrounds it are as much a part of our cosmic view as the oceans and deserts of Earth. The exotic has become familiar, and that will be our legacy.
Happy Holidays to all. And remember ... life is good!
Carolyn Porco Cassini Imaging Team Leader CICLOPS/Space Science Institute Boulder, CO