Upper limits for undetected trace species in the stratosphere of Titan

Conor A. Nixon; Richard K. Achterberg; Nicholas A. Teanby; Patrick G. J. Irwin; Jean-Marie Flaud; Isabelle Kleiner; Alix Dehayem-Kamadjeu; Linda R. Brown; Robert L. Sams; Bruno Bézard; Athena Coustenis; Todd M. Ansty; Andrei Mamoutkine; Sandrine Vinatier; Gordon L. Bjoraker; Donald E. Jennings; Paul. N. Romani; F. Michael Flasar

doi:10.1039/C003771K

Upper limits for undetected trace species in the stratosphere of Titan†

Conor A. Nixon,*^ab Richard K. Achterberg,^ab Nicholas A. Teanby,^c Patrick G. J. Irwin,^c Jean-Marie Flaud,^d Isabelle Kleiner,^d Alix Dehayem-Kamadjeu,^de Linda R. Brown,^f Robert L. Sams,^g Bruno Bézard,^h Athena Coustenis,^h Todd M. Ansty,ⁱ Andrei Mamoutkine,^j Sandrine Vinatier,^b Gordon L. Bjoraker,^b Donald E. Jennings,^b Paul. N. Romani^b and F. Michael Flasar^b

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* Corresponding authors

^a Department of Astronomy, University of Maryland, College Park, MD, USA
E-mail: conor.a.nixon@nasa.gov
Fax: (+1) 301 286-0212
Tel: (+1) 301 286-6757

^b Planetary Systems Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA

^c Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, UK

^d LISA, CNRS, UMR 7583, Universités Paris 7 et Paris Est, 61 Avenue Général de Gaulle, Créteil, France

^e Department of Physics, College of Biological and Physical Sciences, University of Nairobi, P.O. Box 30197, Nairobi, Kenya

^f Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

^g Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA, USA

^h LESIA, Observatoire de Paris-Meudon, Meudon Principal Cedex, France

ⁱ Department of Space Science, Cornell University, Ithaca, NY, USA

^j Adnet Systems, Inc., Rockville, MD, USA

Abstract

In this paper we describe the first quantitative search for several molecules in Titan's stratosphere in Cassini CIRS infrared spectra. These are: ammonia (NH₃), methanol (CH₃OH), formaldehyde (H₂CO), and acetonitrile (CH₃CN), all of which are predicted by photochemical models but only the last of which has been observed, and not in the infrared. We find non-detections in all cases, but derive upper limits on the abundances from low-noise observations at 25°S and 75°N. Comparing these constraints to model predictions, we conclude that CIRS is highly unlikely to see NH₃ or CH₃OH emissions. However, CH₃CN and H₂CO are closer to CIRS detectability, and we suggest ways in which the sensitivity threshold may be lowered towards this goal.

This article is part of the themed collection: Chemistry of the Planets

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Upper limits for undetected trace species in the stratosphere of Titan†

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