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Title: The origin of CO in the stratosphere of Uranus
Authors: Cavalié, Thibault
Moreno, Raphael
Lellouch, Emmanuel
Hartogh, Paul
Venot, Olivia
Orton, G. S.
Jarchow, C.
Encrenaz, Thérèse
Selsis, Franck
Hersant, Franck
Fletcher, L. N.
Issue Date: Oct-2013
Host Document: vol:45
Conference: Divison for Planetary Science meeting edition:45 location:Denver, Colorado, USA date:6-11 October 2013
Article number: #312.14
Abstract: Oxygen-rich deep interiors of the Giant Planets cannot explain the discovery of H2O and CO2 in the stratospheres of the Giant Planets by Feuchtgruber et al. (1997) because these species are trapped by condensation around their tropopause levels (except CO2 in Jupiter and Saturn). Therefore, several sources in the direct or far environment of the Giant Planets have been proposed: icy rings and/or satellites, interplanetary dust particles and large comet impacts. CO does not condense at the tropopauses of Giant Planets, so that oxygen-rich interiors are a valid source. An internal component has indeed been observed in the vertical profile of CO in Jupiter (Bézard et al., 2002) and in Neptune (Lellouch et al., 2005), while an upper limit has been set on its magnitude by for Saturn (Cavalié et al., 2009). In addition to interiors, large comets seem to be the dominant external source, as shown by various studies: Bézard et al. (2002) for Jupiter, Cavalié et al. (2010) for Saturn and Lellouch et al. (2005) for Neptune. The first detection of CO in Uranus was obtained by Encrenaz et al. (2004) from fluorescent emission at 4.7 microns. Assuming a uniform distribution, a mixing ratio of 2x10-8 was derived. Despite this first detection almost a decade ago, the situation has remained unclear ever since. In this paper, we will present the first submillimeter detection of CO in Uranus, carried out with Herschel in 2011-2012. Using a simple diffusion model, we review the various possible sources of CO (internal and external). We show that CO is mostly external. We also derive an upper limit for the internal source. And with the thermochemical model of Venot et al. (2012), adapted to the interior of Uranus, we derive an upper limit on its deep O/H ratio from it.
Publication status: published
KU Leuven publication type: IMa
Appears in Collections:Institute of Astronomy

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