Presentation #414.05 in the session “Titan Atmosphere”.
Using observations made with the Atacama Large Millimeter-submillimeter Array (ALMA) in August 2016  and May 2017  (around the onset of Titan’s northern summer solstice), we mapped the spatial distributions of Titan’s atmospheric HNC, CH3CN and HC3N gases. These observations are contemporaneous with the last year of the Cassini mission, providing complementary HNC and CH3CN measurements, and a point of comparison for the HC3N measurements made by Cassini CIRS . The aim of this study is to improve our understanding of the impact of seasonal effects on the spatial distributions of these molecules. By observing the same molecular emission lines (in ALMA Band 7) over short timescales of less than one Titan month, we obtain new insights into the production, destruction, and transport of complex organic molecules. After correcting the ALMA datasets for differences in spatial resolution, absolute flux scale, and Titan’s distance, we observed a 16±3% decrease in the CH3CN flux (per beam) from Titan’s north pole during 2016-2017. By contrast, a much larger, 37±2% decrease was detected for HC3N. This is consistent with a longer photochemical lifetime of CH3CN, and indicates rapid photolysis of HC3N, combined with a loss of polar confinement of both gases due to the breakdown of Titan’s north polar vortex during the onset of northern summer .
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