Pii: S0273-1177(01)00057-6

Although lightning has not been observed in Titan's atmosphere, the presence of methane rain in the troposphere suggests the possibility of electrical activity in the form of corona and/or lightning discharges. Here we examine the chemical effects of these electrical processes on a Titan simulated atmosphere composed of CH4 in N2 at various mixing ratios. Corona discharges were simulated in two different experimental arrays. For the detection of reactive intermediates we used a mass spectrometer to study the main positive ions arising by bombarding low-energy electrons from a hot filament into low-pressure methane. The final stable products, generated by applying a high voltage in a coaxial reactor with either positive or negative polarity, were separated and detected by gas chromatography-Fourier transform infrared spectroscopy and electron impact mass spectrometry (GC-FTIR-MS). Lightning discharges were simulated by a hot and dense plasma generated by a Nd-YAG laser and the final products were separated and detected by GC-FTIR-MS. Corona discharges produce linear and branched hydrocarbons as well as nitriles whereas lightning discharges generate mainly unsaturated hydrocarbons and nitriles. Lightning discharges are about 2 orders of magnitude more efficient in product formation than corona discharges. © 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved. INTRODUCTION Titan possesses an atmosphere often compared to that of the primitive earth (Raulin et al., 1982, Clark and Ferris, 1997). It is mainly composed of nitrogen with a surface pressure of 1.5 bar and has a wealth of organic material. Moreover, Titan may support a methane cycle, resembling Earth's hydrologic cycle, with clouds, rain, and possibly seas or lakes. On September 4 and 5, 1995, spectra recorded within four windows of near-infrared revealed flux enhancements of 14 to 200%, indicative of the presence of a hurricane-sized cloud system (Griffith el al., 1998). These clouds occur at a relatively low altitude (15+10 km), at low latitudes, and appear to cover ~9% of Titan's disk. More recent observations are indicative of the daily presence of sparse clouds covering less than 1% of the area of the satellite (Griffith et al., 2000). Thermodynamics of Titan's atmosphere and clouds' altitudes suggest that convection governs their evolution. Titan's daily clouds reach a common height that suggest that latent heat plays a larger role in fueling Titan's weather whereas on the earth solar radiation dominates. Their short lives point to the presence of methane rain. The detection of clouds and convective activity in the lowest region of the atmosphere suggest the possibility of electrical activity in Titan's troposphere. In fact corona and lightning discharges are not