Titan is theorized to be a huge "leftover" from the dense "cometary stage" of solar system formation, and probably composed of cometary materials like those in today's Oort Belt. That would mean that it has a core of nickel-iron and rocky matter [the two commonest comet types], surrounded by some water ice. The atmosphere is heavily Nitrogen, with a couple of percent hydrocarbon [almost all Methane but dashed with Ethane].
The temperatures are cold enough to get Methane/Ethane rain. These rains should accumulate in seas. The seas may have some water ice, but mainly hydrocarbon. When the sunlight hits the Methane in the atmosphere it should split some molecules and Titan's orangey color should result.
Carl Sagan was always trying to push for NASA funds by speculating on possible life reservoirs here in the Solar System [while violently opposing UFO research --- while secretly being fascinated by it, as I personally know]. His view of Titan was that the ultraviolet light impacts on the hydrocarbon atmosphere and maybe the sea of Titan might be biogenic. He and a colleague did closed glass atmosphere studies irradiating "Titan-atmosphere-like" gases and were able to produce globs of goo. This goo was a complex hydrocarbon mixture called tholins, but without the nitrogen added in [in key areas] it was not "on the road" to life.
Sagan had two motivations for his research: 1). fascinate the public so they'd write congressmen to support the space program [there was a republican cost-cutting bill not long ago for instance to actually zero NASA out, thankfully that didn't "float", but NASA has been under regular assault as an unproductive element of the US economy, so advocates like Sagan were necessary]; and 2). get himself elected into the National Academy of Sciences (Carl had quite an ego, but the NAS considered more of a media personage than a fundamental researcher).
He failed at his second goal, maybe because his Cornell colleague did most of the lab work and everybody knew it --- I don't know if he later squeaked in somehow, but Tholins didn't do it. But he pretty much succeeded at his first goal as the Titan-may-have-life concept has stuck. The proposed NASA submarine would not be aimed at Titan if the idea that Life-just-barely-could-be-there wasn't about. It's a really long shot. To get from somethings like the tholins to replicator molecules would require an undersea energy source [big heat] which is possible, a concentrated way of utilizing hard-to-bust Nitrogen gas in the presence of hard-to-come-by Carbon --- surprising little evidence of ammonia there [maybe in undersea ice], and [this is probably a showstopper] some undersea environment which would allow radiation-excited fragments of simple carbon and nitrogen containing molecules to maintain densities suitable for molecule-building reactions.
Still, if certain politicians will let us, let's go for it.
p.s. for dshans, the "methane evolution issues" popular today refer to cows BELCHING not farting. You, possibly as has happened before, have gotten the wrong end of the .... er .... schtick.
