A cometary origin for CO in the stratosphere of Saturn?

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) × 1015 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. © 2010 ESO.