In late 1990, a collection of hundreds of scientists and as many engineers across the US and Europe were assembled together and given the charge to undertake a far-sighted interplanetary expedition of enormous scope and reach. The mission: Conduct a 4-year, in-depth, comprehensive scientific exploration of the Saturnian system.
The Voyager flybys of Saturn in the early 1980s had revealed a dynamically evolved planetary system with a startling degree of complexity within its rings and atmosphere and recorded on the surfaces of its moons. Those early brief explorations left us with an indelible impression of the bodies and phenomena to be found around Saturn, but also a gnawing sense of untapped potential, of secrets hidden from view, of scientific riches just beyond our grasp. We came to realize that Saturn and its companions offered what no other planetary system did: The promise of witnessing processes at work today that were similar to those responsible for configuring the solar system, for producing the habitable environment on the surface of our own planet, and even similar to those active on the early Earth. It was clear: We needed to return ... to stay.
The ambitious mission that would fulfill that promise became known as Cassini. It was slated to carry the most advanced instrumentation of its time and spend four years touring among Saturn's rings and moons in order to answer those pressing questions that remained after the Voyager visitations.
And it did just that.
Exactly four years ago to the minute as I post this Log, Cassini successfully entered into orbit and began an unprecedented comprehensive examination of the Saturn system. Four years ago tonight, we found ourselves flying in darkness over Saturn's rings at a swift 25 kilometers per second and closer to the planet and its rings than we had ever been or ever would be again in Cassini's four year tour. The images we collected during this maneuver remain the finest look we have had of the rings to date, and are still being mined by imaging scientists for the insights they hold into the workings of this great collection of icy debris for which Saturn is famed.
And that was just the beginning. Over the last four years, we have traveled over a half billion kilometers around Saturn, again and again, swooping down over its moons, intently watching the intricate motions of its clouds and eddies, and darting through the atmosphere of its largest moon, Titan. What we have seen over the course of our travels has informed, moved and amazed us. Our findings at Saturn are well documented, in word and image, on the pages of this website. Leisurely amble through them, stopping on any page, clicking on any link, and you will soon be reminded just how extraordinary an adventure it has been.
There is of course plenty more to come. Cassini is a robust and capable craft and will continue its work with ease. Officially, its mission has been extended for two years, during which Saturn, in its orbit around the Sun, will pass through equinox in August 2009. At that time, seen from Saturn, the Sun will pass northward through the ringplane and spring will arrive in the northern hemisphere. In concert, the ring shadows will slip from north to south, and our views of Saturn will begin to resemble those seen by Voyager 29 years earlier. For many of us, it will be a very sentimental time.
To explore a planetary system very much unlike our own is an occasion like no other. It has been hard going and exhausting for sure, but in return we have been rewarded beyond all imagining. Without equivocation, we on Cassini can proudly proclaim: Mission accomplished!
Carolyn Porco Cassini Imaging Team Leader CICLOPS Boulder, CO