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Formation of Prebiotic Molecules in Liquid Water Environments on the Surface of Titan

Wednesday, November 5, 2008
Neish (Univ of AZ)

Saturn's moon Titan represents a unique locale for studying prebiotic chemistry. Reactions occurring in its thick nitrogen-methane atmosphere produce a wide variety of carbon, hydrogen, and nitrogen containing organic molecules. If these molecules are exposed to liquid water, they may react further to produce oxygen-containing species, a key step in the formation of biomolecules.

On average, Titan's surface is too cold for liquid water. However, models indicate that melting caused by impacts and/or cryovolcanism may lead to its episodic availability. In this work, I calculate the freezing timescale of one potential cryovolcanic feature on Titan, the putative dome Ganesa Macula. I then determine the extent to which aqueous organic chemistry can proceed on Titan by measuring the rate coefficients of Titan analogue organic molecules ("tholins") with low temperature aqueous solutions. These reactions produce oxygenated species with half-lives between 0.4 and 7 days at 273 K (in water) and between 0.3 and 14 days at 253 K (in 13 wt. % ammonia-water). Tholin hydrolysis in aqueous solutions is thus very fast compared to the freezing timescales of impact melts and volcanic sites on Titan, which take hundreds to thousands of years to freeze. The fast incorporation of oxygen, along with new chemistry made available by the introduction of ammonia, may lead to the formation of molecules of prebiotic interest in these transient liquid water environments.

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