ACETYLENE ON TITAN'S SURFACE

Titan's atmosphere is opaque in the near-infrared due to gaseous absorptions, mainly by methane, and scattering by aerosols, except in a few "transparency windows." Thus, the composition of Titan's surface remains difficult to access from space and is still poorly constrained. Photochemical models suggest that most of the organic compounds formed in the atmosphere are heavy enough to condense and build up at the surface in liquid and solid states over geological timescales. Acetylene (C2H2) net production in the atmosphere is predicted to be larger than any other compound and C2H2 has been speculated to exist on the surface of Titan. C2H2 was detected as a trace gas sublimated/evaporated from the surface using the Gas Chromatograph Mass Spectrometer after the landing of the Huygens probe. Here we show evidence of C2H2 on the surface of Titan by detecting absorption bands at 1.55 and 4.93 mu m using the Cassini Visual and Infrared Mapping Spectrometer at three different equatorial areas-Tui Regio, eastern Shangri La, and Fensal-Aztlan/Quivira. We found that C2H2 is preferentially detected in lowalbedo areas, such as sand dunes and near the Huygens landing site. The specific location of the v detections suggests that C2H2 is mobilized by surface processes, such as surface weathering by liquids through dissolution/ evaporation processes.