Cruising around Saturn for the last decade has given us the chance to survey, in great detail and at our leisure, the worlds that inhabit this part of our solar system. It was, after all, the reason for our being here: To set eyes on the uncharted terrains forming the surfaces of Saturn's many moons and document in images, for posterity, the landforms and geological histories recorded there. That one might find present day activity anywhere in the solar system other than the Earth is a planetary explorer's great hope, and we had, as a matter of good planning, come prepared.
Nevertheless, happening upon the wondrous sight of soaring fountains of icy spray at the southern tip of the small moon, Enceladus, was intoxicating and profoundly moving ... not only for the sheer spectacle of it but for the weight of its meaning. Here was a place that was not ancient and long dead, but alive and bursting forth with activity. It said what some of us had long thought: this little moon just might be home to a subterranean body of liquid water that could be the best find of the entire mission.
Because of the scientific importance of our discovery, Cassini's trajectory was altered to send us repeatedly, during the course of the mission, close to the moon's south pole, and the teams assigned to each of Cassini's onboard instruments sprung into action. Results came pouring in: excess heat was found radiating from the basin, and along with the icy particles seen in our images came water vapor with traces of organic compounds. It was thrilling.
I took responsibility for the imaging team's observations of Enceladus' geysers and planned, along with members of my research group, a comprehensive survey of the region that took place over nearly 7 years.
Today, after more than five years of analysis and thought, our findings are finally published online. We have found in total 101 distinct geysers, one hundred of which erupt from the four, prominent, now famous `tiger stripe' fractures crossing the region. Comparison of our findings with those of other instruments, and with calculations of the magnitude and orientation of tidal forces that flex the surface on a daily basis has brought us to a conclusion that strengthens what we had all, little by little, over time, come to believe. In casting your sights on the geysering glory of Enceladus, you are looking at frozen mist that originates deep within the solar system's most accessible habitable zone.
As we contemplate the approaching end of Cassini's travels around Saturn, we dream of the day, hopefully not far in the future, when we can return to Enceladus to answer the question now uppermost in the mind: Could a second genesis of life have taken hold on this small icy moon of a hundred and one geysers? For we now know this: if life is indeed there, it is there for the taking.
Carolyn Porco Cassini Imaging Team Leader Director, CICLOPS Boulder, CO