CO concentration in the upper stratosphere and mesosphere of Titan from VIMS dayside limb observations at 4.7 mu m

Year: 2017

Authors: Fabiano F., Lpez Puertas M., Adriani A., Moriconi M.L., D’Aversa E., Funke B., Lpez-Valverde M.A., Ridolfi M., Dinelli B.M.

Autors Affiliation: Dipartimento di Fisica e Astronomia, Universitá di Bologna, viale Berti Pichat, 6/2, Bologna, 40127, Italy; Istituto di Scienze dell’Atmosfera e del Clima (ISAC-CNR), via Piero Gobetti, 101, Bologna, 40129, Italy; Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía, s/n. E-18008, Granada, Spain; Istituto di Astrofisica e Planetologia Spaziali (IAPS-INAF), via del Fosso del Cavaliere, 100, Roma, 00133, Italy; Istituto di Scienze dell’Atmosfera e del Clima (ISAC-CNR), via del Fosso del Cavaliere, 100, Roma, 00133, Italy; Istituto di Fisica Applicata ”N.Carrara” (IFAC-CNR), Via Madonna del Piano, 10, Sesto Fiorentino (FI), 50019, Italy

Abstract: During the last 30 years, many works have focused on the determination of the CO abundance in Titan’s atmosphere, but no measurement above 300 km has been done yet due to the faint signal of CO. Nevertheless, such measurements are particularly awaited as a confirmation of photochemical models predictions that CO is uniformly mixed in the whole atmosphere. Moreover, since CO is the main atmospheric reservoir of oxygen, its actual abundance has implications on the origins of Titan’s atmosphere. In this work, we analyse a set of Cassini VIMS daytime limb observations of Titan at 4.7 mu m, which is dominated by solar-pumped non-LTE (non-local thermodynamic equilibrium) emission of CO ro-vibrational bands. In order to retrieve the CO abundance from these observations, we developed a non-LTE model for the CO vibrational levels. The retrieval of the CO concentration is performed following a bayesian approach and using the calculated non-LTE populations. The data set analysed consists of 47 limb scanning sequences-about 1500 spectra-acquired by VIMS in 2006 and 2007. CO relative abundance profiles from 200 to 500 km are obtained, for each set analysed. The mean result shows no significant variations with altitude and is consistent with the prediction of a well-mixed vertical profile. However, if compared with Earth-based mm measurements, a small vertical gradient is plausible. (C) 2017 Elsevier Inc. All rights reserved.

Journal/Review: ICARUS

Volume: 293      Pages from: 119  to: 131

KeyWords: Titan atmosphere; CO; Infrared observations; Spectroscopy
DOI: 10.1016/j.icarus.2017.04.014

Citations: 4
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