A cometary origin for CO in the stratosphere of Saturn?

¹ Max Planck Institute für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany e-mail: cavalie@mps.mpg.de
² Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux (LAB), France
³ CNRS/INSU, UMR 5804, 33271 Floirac Cedex, France
⁴ LESIA, Observatoire de Paris, 92195 Meudon, France
⁵ National Research Council, Herzberg Institute of Astrophysics, Victoria, BC V9E 2E7, Canada

Received: 17 July 2009
Accepted: 24 November 2009

Abstract

Context. The CO(3–2) line has been observed in the atmosphere of Saturn. The CO(3–2) observation proves that an external source of CO exists in the stratosphere of the planet.

Aims. We attempt to constrain the type and magnitude of the external source of CO in the atmosphere of Saturn, by observing the emission core of the CO(6–5) line.

Methods. We observed the CO(6–5) line at the limbs of Saturn. We analysed the observations by means of a 1-D transport model of the atmosphere of Saturn, coupled with a radiative transfer model.

Results. We obtained a high signal-to-noise ratio spectrum that confirms the existence of an external source of CO in the stratosphere of Saturn. We demonstrated that a cometary origin of CO is the most probable, an impact occurring 220±30 years ago and depositing (2.1±0.4)  g of CO above 0.1 mbar. However, we cannot totally reject the possibility of CO originating (at least partially) in a steady source.

Conclusions. Complete photochemical modelling of the oxygen compounds is required to determine realistic error bars of the inferred quantities and to conclude on the origin of CO.