I realized that  I forgot to mention the evidence for life on Titan in last night's "Eyes of Earth" presentation (slide 100).So here it is: Titan is the only world we know, other than Earth, that has a liquid on its surface. Its thick atmosphere is mainly composed of methane. It rains methane on Titan, replenishing its lakes, rivers and seas. Methane is an (alkane) gas on earth. Alkanes are the simplest hydrocarbons, all of which are present on Titan, including ethane, propane, and my favorite– acetylene–(which my dad used in his shop to cut and weld steel).As noted, these are gases on earth, but they are liquids on Titan due to its extremely cold -290F surface temperature. Our life is water-based, but scientists have speculated that liquid methane-based life is possible. Well, one of the "signs" of methane based life is depletion of hydrogen. When the Huygens lander touched down on Titan, having analyzed its thick atmosphere all the way to the surface, guess what? It reported a depletion in hydrogen in the zone immediately above the surface, in line with estimates by the scientists. Given lack of certain complex molecules, it is doubtful intelligent life could evolve on Titan, but there well may be something swimming around in its lakes.  One more supporting  fact: methane is quickly destroyed in our atmosphere by solar radiation, enough of which reaches Titan to have the same effect. But,  curiously, methane is sustaining in Titan's air. It could be due to geologic processes, but it it more easily explained as a by-product of life. So food for thought. Phil