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Astron. Astrophys. 334, L41-L44 (1998)


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Letter to the Editor

Detection of methyl radicals (CH3) on Saturn *

B. Bézard 1, H. Feuchtgruber 2, J.I. Moses 3 and T. Encrenaz 1

1 DESPA, Observatoire de Paris, F-92195 Meudon, France
2 Max-Planck-Institut für Extraterrestrische Physik, D-85748 Garching, Germany
3 Lunar and Planetary Institute, Houston, TX 77058-1113, USA

Received 23 March 1998 / Accepted 20 April 1998

Abstract

We report the first detection of methyl radicals (CH3) in the upper atmosphere of Saturn . Emission from the [FORMULA] Q-branch of CH3 at 16.50 µm was detected from observations with the Short-Wavelength Spectrometer of the ISO satellite. A CH3 column density in the range 1.5-7.5 [FORMULA] 1013 molec cm-2 is derived, taking into account uncertainties in the data calibration, CH3 band strength, and atmospheric model. Results are compared with predictions of photochemical models. The CH3 abundance is mostly sensitive to the poorly known methyl recombination rates and to the eddy mixing profile. The ISO observations imply either CH3 recombination rates larger than used in current photochemical models, or an eddy mixing coefficient near the methane homopause smaller than inferred from Voyager ultraviolet measurements.

Key words: Planets and satellites: Saturn – infrared: solar system

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of NASA and ISAS. The SWS instrument is a joint project of the SRON and the MPE

Send offprint requests to: B. Bézard (Bruno.Bezard@obspm.fr)

© European Southern Observatory (ESO) 1998

Online publication: May 15, 1998

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