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arXiv · 1805.04416

Interferometric imaging of Titan's HC$_3$N, H$^{13}$CCCN and HCCC$^{15}$N

M. A. Cordiner·C. A. Nixon·S. B. Charnley·N. A. Teanby·E. M. Molter·Z. Kisiel·V. Vuitton
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Abstract

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 May 2017. 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 April 2015 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 $67\pm14$. 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.

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M. A. Cordiner, C. A. Nixon, S. B. Charnley, N. A. Teanby, E. M. Molter, Z. Kisiel, V. Vuitton. 2018-05-11. Interferometric imaging of Titan's HC$_3$N, H$^{13}$CCCN and HCCC$^{15}$N. https://doi.org/10.3847/2041-8213%2Faac38d

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