Experimental insights into the azotosome hypothesis in Titan’s lake fluids

TL;DR

This study experimentally tests if acrylonitrile can form stable membranes in Titan's lakes, finding it likely forms crystals instead.

Contribution

First experimental validation of the azotosome hypothesis under simulated Titan conditions.

Findings

Acrylonitrile forms a stable cocrystal with ethane under Titan-like conditions.

Acrylonitrile shows minimal structural changes in liquid methane over experimental timescales.

Azotosome-like vesicles are unlikely to form in Titan's lake fluids.

Abstract

Since the discovery of hydrocarbon lakes and seas on Saturn’s moon Titan, there has been much speculation on whether these could serve as suitable environments to host exotic life. A decade ago, molecular dynamic simulations suggested that amphiphilic cyanide species such as acrylonitrile could self-assemble in these cold, nonpolar liquids to form stable closed membranes known as azotosomes, potentially compartmentalizing complex biochemical reactions. A subsequent thermodynamic study in 2020, however, concluded that azotosomes cannot exist under Titan’s conditions. Motivated by these incongruent computational results, this work undertakes the first experimental test of the azotosome hypothesis where we characterize acrylonitrile-methane and acrylonitrile-ethane mixtures under simulated Titan conditions using a combination of differential scanning calorimetry and Raman microscopy. The results indicate that acrylonitrile forms a stable molecular cocrystal with ethane while exhibiting little changes in the presence of liquid methane under experimental timescales. These findings suggest that the acrylonitrile-based azotosome structure would be unlikely to form in Titan’s lake fluids.

Acrylonitrile likely forms a cryomineral within Titan’s lake fluids rather than a vesicle structure akin to terrestrial liposome.

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