LABORATORY STUDIES OF DISSOLUTION GEOLOGY ON SATURN’S MOON TITAN

Dissolution geology can occur wherever there is a circulating fluid in contact with a soluble geological material for a long enough time. Here on Earth, we are used to materials such as halite, gypsum, calcite, dolomite, and even silica dissolving in water to create karstic landscapes. The amount of material that can be dissolved in a given volume coupled with the amount of circulating fluid determines how quickly a karstic system can develop. Highly soluble materials such as halite will be eroded quickly in high precipitation areas, while karstic systems in quartzite can take hundreds of millions of years to fully develop.

Saturn’s moon Titan extends geological processes to include cryogenic hydrocarbon fluids such as methane and ethane. The Cassini mission has provided evidence of a hydrocarbon-based cycle on Titan similar to the terrestrial water cycle. On Titan, recirculating hydrocarbon fluids are capable of dissolving some of the surface organic molecules derived from complex atmospheric photochemistry. Several terrain features resembling terrestrial karst have been observed on Titan, including polygonal karst-like terrain, closed valleys, and steep-sided lakes with morphologies similar to terrestrial karstic lakes. Recently, we have determined the solubility curves of benzene in cryogenic solutions of mixed hydrocarbon solvents. Based on our laboratory measurements and theoretical calculations we have determined a novel mechanism for the dissolution and deposition of organic materials involving dissolution during selective evaporation followed by precipitation during compositional mixing of methane-rich rainfall runoff liquids. This mechanism may explain the observed morphologies of the enigmatic steep-sided flat-floored basins in the polar regions of Titan.