LABORATORY SIMULATION OF KARST ON TITAN

Saturn’s giant moon Titan has a landscape made of organic molecules, which is exposed to hydrocarbon-based rains, rivers, and lakes. Many of Titan’s surface features could have resulted from dissolution, transport, and evaporite-formation of solid organic materials in a manner similar to dissolution/evaporation processes on Earth. We have constructed an experimental apparatus using a fiber optic UV probe able to determine the rate of dissolution and the amount of material dissolved in hydrocarbon fluids at Titan’s surface temperature of 94 K.

For our initial work, benzene was selected as our proxy Titan organic molecule – there is spectral evidence that it exists on Titan’s surface and has been detected in suprising amounts in Titan’s upper atmosphere. Our initial results demonstrate that a ca. 10 mg sample of solid powdered benzene dissolves in 100 mL of ethane to its saturation equilibrium in about an hour at 94 K. The saturation equilibrium is 18 mg per L. This compares to the value of quartz in water at neutral pH (9 mg per L). It should be noted that the waters of the Roraima massif in Venezuela, one of the areas with the best developed solutional landforms in quartzite, have dissolved silica concentrations of less than 1 mg per L.

While benzene was selected for initial laboratory investigation, there are other organic molecules on Titan that are predicted to have orders of magnitude higher solubility and higher abundance on the surface, notably acetylene and hydrogen cyanide. The solubility of acetylene in a methane/nitrogen Titan rainfall mixture at 95 K is predicted to be of the same magnitude as that of gypsum and water at 298 K (25 C).

Our results provide laboratory evidence that supports the case for alkane-based dissolution geology on Titan.