The Acetonitrile – Propane Co-Crystal: Characterization of a New Cryomineral Stable in Titan-Relevant Conditions

Some of the most common organic substances on Earth have also been observed on Titan, the largest moon of Saturn. In Titan’s atmosphere, photochemical processes induced primarily by UV radiation form a plethora of organic molecules that are carried to Titan’s surface where they can interact. In this study we replicate Titan surface conditions of a binary mixture of two abundant Titan organics – one polar and one nonpolar – and observe their interactions. We report the first experimental evidence of a new co-crystal between acetonitrile and propane. On Titan, this co-crystal or cryomineral would most readily form in areas where temperatures exceed the average surface temperature. Its presence could therefore record evidence of thermal alteration (e.g., impact, subsurface transport, or metamorphism). Co-crystals may influence Titan geomorphology at local and regional scales, and their different physical properties compared to pure components may inform sampling strategies and analysis for in situ missions to Titan such as Dragonfly.