Experimental Study of Abiotic Synthesis Processes in a Hydrothermal Flow System: Implications for Organic Matter Formation in Extraterrestrial En-

Introduction: Hydrocarbons with an apparent abiotic origin are found in hydrothermal fluids from vents on unsedimented mid-ocean ridges. In particular, fluids from ultramafic-hosted hydrothermal systems contain significant quantities of many organic species other than methane [1-3]. Generation of significant amounts of long chain hydrocarbons was not reported in previous experimental studies [4-7]. This might be attributed to unknown critical factors that control abiotic formation of organic compounds in hydrother-mal systems, and limited experimental strategies in closed systems as well. Therefore, experimental studies in hydrothermal flow system are needed to systematically identify the chemical and physical factors that contribute to the formation of reduced carbon species at elevated temperatures and pressures. Furthermore, the similar reactions of methane and organic matter formation might occur in extraterrestrial environments. With the existence of organic compounds in meteorites [8-9] and detection of methane in Martian atmosphere [10], it is of importance to understand factors controlling abiotic organic synthesis. Experiments: Two experiments were conducted using a newly-designed hydrothermal flow-through system. A fixed volume (~100 ml) titanium reactor represents the central unit of the flow system. It is linked to a high-pressure fluid delivery system (Shi-madzu LC-10AT VP HPLC pump) that maintains constant flow rate during the experiments. The outlet side of the reactor is connected to a computer-controlled regulating valve that keeps the total pressure at a fixed value. A magnetic stirrer in the system permits the mineral reactant to be kept in suspension. Temperature control is provided by band heaters outside the reactor. The continuous inflow of fluid reactants combined with the same volumetric outflow rate of products provides a thermodynamically open system, in which the steady state can be sustained. Experiments were performed at 250 bars total pressure and at two different temperatures: 250