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[30.01] The HCN and CO₂ distribution on Jupiter

E. Lellouch, D.F Strobel, B. Bézard (Obs. Paris), G.L. Bjoraker, F.M. Flasar, P.N. Romani (NASA/GSFC)

Cassini/CIRS observations acquired in December 2000 have revealed very different latitudinal distributions for HCN and CO₂ on Jupiter (Kunde et al. 2004). HCN exhibits a maximum abundance at 45 S, a steady decrease towards the North up to 50 N and a sharp decrease poleward of 50 N and 45 S. In contrast, CO₂ has a fairly constant abundance from 30 S to 80 N, and a maximum southward of 60 S.

The source of HCN and CO₂ is thought to be the Shoemaker-Levy 9 collision in 1994, since observations immediately following the impacts have detected the abundant presence of HCN, CO, and H₂O; CO₂ can photolytically build from CO and H₂O. Different latitudinal profiles for these two species are therefore puzzling. Qualitatively, the maintenance of an HCN maximum at the impact latitude 6.5 years after the impacts may result from a dynamical isolation of the high southern latitudes, or from a destruction of HCN in auroral regions. The CO₂ maximum at high latitudes may be due to auroral precipitation of oxygen bearing material and its subsequent conversion to CO₂. An alternate explanation is that the different HCN and CO₂ distribution may reflect different horizontal transport of two species with possibly initially different vertical distributions.

We examine here some of these ideas. In particular, we use a simplified chemical-transport model to study whether the HCN distribution can result from purely diffusive transport, and to evaluate the auroral oxygen fluxes needed to produce the CO₂ maximum at Southern latitudes.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.