Submillimeter Observations of Titan: Global Measures of Stratospheric Temperature, CO, HCN, HC 3 N, and the Isotopic Ratios 12 C/ 13 C and 14 N/ 15 N

Abstract

Interferometric observations of the atmosphere of Titan were performed with the Submillimeter Array on two nights in 2004 February to investigate the global average vertical distributions of several molecular species above the tropopause. Rotational transitions of CO, isomers of HCN, and HC3N were simultaneously recorded. The abundance of CO is determined to be 51 ± 4 parts per million (ppm), constant with altitude. The vertical profile of HCN is dependent on the assumed temperature but generally increases from 30 parts per billion at the condensation altitude (~83 km) to 5 ppm at ~300 km. Furthermore, the central core of the HCN emission is strong and can be reproduced only if the upper stratospheric temperature increases with altitude. The isotopic ratios are determined to be 12C/13C = 132 ± 25 and 14N/15N = 94 ± 13 assuming the Coustenis & Bezard temperature profile. If the Lellouch temperature profile is assumed, the ratios decrease to 12C/13C = 108 ± 20 and 14N/15N = 72 ± 9. The vertical profile of HC3N is consistent with that derived by Marten et al.