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Astron. Astrophys. 341, 312-317 (1999)

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Titan's atmospheric haze: the case for HCN incorporation

L.-M. Lara 1, E. Lellouch 2 and V. Shematovich 3

1 Solar System Division, ESA Space Science Department, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands
2 DESPA, Observatoire de Paris-Meudon, F-92195 Meudon Principal Cedex, France
3 Institute of Astronomy of the Russian Academy of Sciences, 48 Pjatnitskaja str., 109017 Moscow, Russia

Received 8 June 1998 / Accepted 28 September 1998


It is suggested that the incorporation of HCN in Titan's atmospheric haze may be an important process affecting the HCN profile and the C/N ratio in Titan's haze. By introducing a loss to the haze term for HCN (i.e. a production term of "poly-HCN") in the photochemical model of Lara et al. (1996), we have improved the model's ability to simultaneously reproduce the observed HCN and C2 hydrocarbon profiles in Titan's lower stratosphere. The loss rate of HCN by this process may be a few times 108 cm-2 s-1. The calculated C/N ratio in the haze, assuming that the haze is primarily produced from C6H2, C8H2 and "poly-HCN", is approximately equal to 2, in agreement with the composition of laboratory tholin analogues.

Key words: molecular processes – planets and satellites: individual: Titan

Correspondence to: L.M. Lara (llara@estec.esa.nl) or E. Lellouch (lellouch@megasx.obspm.fr)

© European Southern Observatory (ESO) 1999

Online publication: November 26, 1998