Geologic settings for aqueous organic synthesis on Titan revisited.

The photochemistry in Titan's cold reducing atmosphere is an evolutionary dead end. However, the hydrocarbons and nitriles deposited from the atmosphere can undergo aqueous synthesis into prebiotic molecules in ephemeral settings such as impact melt sheets. We re-examine the longevity of aqueous solutions on Titan, noting that recent measurements of the thermal conductivity of ammonia-rich ices suggest that the melt pockets may be longer-lived than previously thought. We propose an important role in surface organic reactions for ultraviolet sunlight transported to the surface as chemical energy stored in acetylene and released by polymerization at Titan's surface.