Surface-active substances in a laboratory simulated Titan's organic haze: Prebiotic microstructures

摘要

Titan, the largest satellite of Saturn, is a key planetary body for astrobiological studies due to its active organic chemistry, hydrocarbon lakes and possible subsurface water-ammonia liquids. We have investigated the physicochemical properties of organic compounds synthesized in a simulated Titan atmosphere. A laboratory analog of Titan's aerosols, called tholin, was produced by irradiation of a nitrogen/methane gas mixture. The primary aim was to determine whether tholin represent possible sources of surface-active substances that could have been involved in the formation of prebiotic structures. A tholin sample was extracted with chloroform-methanol and the chloroform soluble material was separated by two-dimensional thin layer chromatography. Fluorescence excited by UV light was used to identify the major components on the plates. After being scraped from the TLC plate, the components were eluted as specific fractions and investigated by surface chemical methods, FTIR, scanning electron microscopy and cyclic voltammetry. Fractions 1 and 2 were strongly fluorescent and surface active, producing films at air-water interfaces. When exposed to aqueous phases, components in fraction 1 form spherical microstructures resembling prebionts. The prebionts are precursor structures that might have evolved into the first living cells.