First observation of CO at 345 GHz in the atmosphere of Saturn with the JCMT. New constaints on its origin

International audienceWe have performed the first observation of the CO(3-2) spectral line in the atmosphere of Saturn with the James Clerk Maxwell Telescope. We have used a transport model of the atmosphere of Saturn to constrain the origin of the observed CO. The CO line is best-fit when the CO is located at pressures less than (15± 2) mbar with a mixing ratio of (2.5±0.6)×10-8 implying an external origin. By modelling the transport in Saturn's atmosphere, we find that a cometary impact origin with an impact 200-350 years ago is more likely than continuous deposition by interplanetary dust particles (IDP) or local sources (rings/satellites). This result would confirm that comet impacts are relatively frequent and efficient providers of CO to the atmospheres of the outer planets. However, a diffuse and/or local source cannot be rejected, because we did not account for photochemistry of oxygen compounds. Finally, we have derived an upper limit of 1×10-9 on the tropospheric CO mixing ratio

CO in the atmospheres of Saturn and Uranus. Observations at millimeter and submillimeter wavelengths.

An external supply of oxygenated compounds exists in outer planets. Carbon monoxide has been detected in each giant planet. The source of CO has been proved to be dual (internal and external) in Jupiter and Neptune, but this is still unclear in the case of Saturn and Uranus. Therefore, constraining the amount of CO in the troposphere and stratosphere of these planets would help solve this problem. We performed observations of Saturn and Uranus at millimeter and submillimeter wavelengths in the CO (1-0), (2-1) and (3-2) lines. Observations were carried out with the IRAM 30-m telescope (Pico Veletta, Spain) in September 2006 and with the JCMT 15-m telescope (Hawaii, USA) in January 2008. We have recorded broad multi-band spectra of each planet. The results of these observations are presented and discussed

CO in the atmospheres of Saturn. Observations at millimeter and submillimeter wavelengths.

Water and carbon dioxide have been detected in the stratospheres of the outer planets. Because both species condense at the tropopause (except CO2 in Jupiter and Saturn), their presence in the stratospheres implies an external origin (interplanetary dust, sputtering from the satellites and/or rings, large meteoritic impacts). Carbon monoxide has been detected in each giant planet. Because this compound does not condense at the tropopause, it can also have an internal origin. The source of CO has been proved to be internal and external in Jupiter and Neptune, but this is still not clear in the case of Saturn and Uranus. Therefore, constraining the amount of CO in the stratosphere and/or high troposphere of these planets would help solve this question. We performed observations of Saturn at millimeter and submillimeter wavelengths in the CO (1-0), (2-1) and (3-2) lines. Observations were carried out with the IRAM 30-m telescope (Pico Veleta, Spain) in September 2006 and with the JCMT 15-m telescope (Hawaii, USA) in January 2008. We have recorded broad multi-band spectra. We have used our photochemical model to constrain the CO supply in the atmosphere of Saturn. The results of these observations will be presented and discussed. IRAM is supported by INSU/CNRS (France), MPG (Germany), IGN (Spain). This work has benefited from research funding from the European Community's Sixth Framework Program under RadioNet contract R113CT 2003 5058187