Titan Tholins as Amino Acid Precursors and Their Solubility in Possible Titan Liquidospheres

Experimental simulations have previously shown that tholins (complex solid organics) can be abundantly formed in Titan's atmosphere and that they contain precursors of amino acids. In this study, we investigated their relevance to possible chemical evolution toward the generation of life in various potential Titan environments (liquidospheres), using tholins synthesized by plasma discharge at low pressure (LP, 26 Pa) and high pressure (HP, 133 Pa). We focused our study on composition of amino acids recovered from LP and HP tholins, as well as on the solubility of these tholins in solvents such as hexane, acetonitrile, ethanol, methanol, water, and ammonia water. Both hydrolyzed extracts of LP and HP tholins were composed of a wide variety of amino acids. Tholins were dissolved more easily in polar solvents than in nonpolar ones: Ammonia water, simulating a potential Titan subsurface ocean, could dissolve tholins quite efficiently. These results show thus the possibility of starting chemical evolution toward life's origin in Titan's environment.