The composition of Titan’s lower atmosphere and simple surface volatiles as measured by the Cassini-Huygens probe

The Cassini-Huygens Probe Gas Chromatograph Mass Spectrometer (GCMS) determined the composition of the Titan atmosphere from ~140km altitude to the surface. After landing, it returned composition data of gases evaporated from the surface. Height profiles of molecular nitrogen (N2), methane (CH4) and molecular hydrogen (H2) were determined. Traces were detected on the surface of evaporating methane, ethane (C2H6), acetylene (C2H2), cyanogen (C2N2) and carbon dioxide (CO2). The methane data showed evidence that methane precipitation occurred recently. The methane mole fraction was (1.48 0.09) x10 in the lower stratosphere (139.8 km to 75.5 km) and (5.65 0.18) x10 near the surface (6.7 km to the surface). The molecular hydrogen mole fraction was ± ± (1.01± 0.16) x10 in the atmosphere and (9.90± 0.17) x10 on the surface. Isotope ratios were 167.7 0.6 for N/N in molecular nitrogen, 91.1 32 ± ± 1.4 for C/C in methane and (1.35± 0.30) x10 for D/H in molecular hydrogen. The mole fractions of Ar and radiogenic Ar are (2.1 0.8) x10 and (3.39 33