Dr. Carolyn Porco, will you please refrain from using the terms "believed" and "belief" in a scientific context. Only ancient peoples and bloody freaking creationists have 'beliefs'! Real scientists do not 'believe' or have 'beliefs'; instead, they hypothesize or have hypotheses; they conjecture, surmise, speculate, presume, or infer. Finally, when the facts are known, it then becomes an established theory. The English language has no shortage of suitable words to use in a scientific context, so there's no bloody excuse for using 'weak' words. Thank you.
P.S. The Bad Astronomer, Dr. Phil Plait, will confirm that I am a nitpicker!