We report the first spectroscopic detection of ethyl cyanide (C 2 H 5 CN) in Titan's atmosphere, obtained using spectrally and spatially resolved observations of multiple emission lines with the Atacama Large Millimeter/submillimeter Array (ALMA). The presence of C 2 H 5 CN in Titan's ionosphere was previously inferred from Cassini ion mass spectrometry measurements of C 2 H 5 CNH + . Here we report the detection of 27 rotational lines from C 2 H 5 CN (in 19 separate emission features detected at > 3σ confidence), in the frequency range 222-241 GHz. Simultaneous detections of multiple emission lines from HC 3 N, CH 3 CN and CH 3 CCH were also obtained. In contrast to HC 3 N, CH 3 CN and CH 3 CCH, which peak in Titan's northern (spring) hemisphere, the emission from C 2 H 5 CN is found to be concentrated in the southern (autumn) hemisphere, suggesting a distinctly different chemistry for this species, consistent with a relatively short chemical lifetime for C 2 H 5 CN. Radiative transfer models show that C 2 H 5 CN is most concentrated at altitudes 200 km, suggesting production predominantly in the stratosphere and above. Vertical column densities are found to be in the range (1-5)×10 14 cm −2 .

We have discovered vinyl cyanide—a molecule that may be able to form cell-like membranes in lakes of hydrocarbon—on Titan.