Prebiotic Chemistry Insights for Dragonfly: Thermodynamics of Amino Acid Synthesis in Selk Crater on Titan

Saturn’s moon Titan presents a compelling test bed for probing prebiotic chemistry beyond early Earth. Impact-generated melt pools provide transient aqueous habitats in an otherwise cryogenic environment. We use Cantera equilibrium models to assess whether mixtures of hydrogen cyanide (HCN), acetylene (C 2 H 2 ), and ammonia (NH 3 ) can drive amino acid synthesis in Selk-sized craters. Across 21 amino acids (20 proteinogenic plus β -alanine), NH 3 -free systems yield only proline, alanine, and β -alanine, whereas adding as little as 1% NH 3 (relative to H 2 O) renders almost the full suite accessible, with yields peaking at 2% and tapering thereafter. The NH 3 -free alanine result implies alternative pathways beyond classical Strecker or aminonitrile hydrolysis, suggesting acetylene, abundant on Titan but scarce on early Earth, as a plausible feedstock. We identify acrylonitrile (detected on Titan) as a thermodynamically favorable intermediate that can convert to alanine under aqueous conditions in an NH 3 -free pathway. For glycine and alanine production from nitrile hydrolysis, comparison with laboratory kinetics shows that our equilibrium models predict near-complete conversion, while observed rates yield only partial products over weeks. Yet estimated chemical equilibration times (years to centuries) are far shorter than melt lifetimes (≥10 3 –10 4 yr), supporting plausibility of equilibrium in situ. These predictions are directly testable with the Dragonfly Mass Spectrometer, for which we recommend preflight standards to test proline, alanine, β -alanine, cysteine, and methionine. The first three offer the best chances for amino acid detection regardless of ammonia availability; the latter two offer diagnostic tools for determining the presence of reactive sulfur in postimpact Titan ponds.