Interferometric Imaging of Titan’s HC 3 N, H 13 CCCN, and HCCC 15 N

We present the first maps of cyanoacetylene isotopologues in Titan’s atmosphere, including H 13 CCCN and HCCC 15 N, detected in the 0.9 mm band using the Atacama Large Millimeter/submillimeter array (ALMA) around the time of Titan’s (southern winter) solstice in 2017 May. The first high-resolution map of HC 3 N in its v 7 = 1 vibrationally excited state is also presented, revealing a unique snapshot of the global HC 3 N distribution, free from the strong optical depth effects that adversely impact the ground-state ( v = 0) map. The HC 3 N emission is found to be strongly enhanced over Titan’s south pole (by a factor of 5.7 compared to the north pole), consistent with rapid photochemical loss of HC 3 N from the summer hemisphere combined with production and transport to the winter pole since the 2015 April ALMA observations. The H 13 CCCN/HCCC 15 N flux ratio is derived at the southern HC 3 N peak, and implies an HC 3 N/HCCC 15 N ratio of 67 ± 14. This represents a significant enrichment in 15 N compared with Titan’s main molecular nitrogen reservoir, which has a 14 N/ 15 N ratio of 167, and confirms the importance of photochemistry in determining the nitrogen isotopic ratio in Titan’s organic inventory.