[X] My Assistant

[Guest_AlexBlackwell_*]

Hunter Waite et al. have a paper ("The Process of Tholin Formation in Titan's Upper Atmosphere") to be published in the May 11, 2007, issue of Science; there is also an accompanying Perspectives piece ("Titan's Organic Factory") by Sushil Atreya.

The embargo will be lifted in a hour or two, so if do not have embargo access, the direct links to the articles probably will not be accessible until then. However, you can click here for a brief description.

Also, Opher et al. have a paper ("The Orientation of the Local Interstellar Magnetic Field") with an accompanying Perspectives piece ("A Local Wiggle in the Turbulent Interstellar Magnetic Field") by Jokipii. Again, unless you have embargo access, click here for a brief description.

[TheChemist]

I don't know if this has been already mentioned, but there is a new Titan atmospheric photochemistry model published
in two papers in Planetary and Space Science, articles in press page. Apologies, this is a long and badly-formatted post.

The model article is :
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Coupling photochemistry with haze formation in Titan's atmosphere. Part I: Model description
In Press, Accepted Manuscript, Available online 12 September 2007,
P.P. Lavvas, A. Coustenis and I.M. Vardavas
PDF (812 K)
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The validation with Cassini Huygens data :

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"Coupling photochemistry with haze formation in Titan's atmosphere. Part II: Results and validation with Cassini/Huygens data"
In Press, Accepted Manuscript, Available online 12 September 2007,
P.P. Lavvas, A. Coustenis and I.M. Vardavas
PDF (2433 K)
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I think I can bend the rules and provide the abstracts (after all, they will be available to non-subscribers shortly)

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Abstract Part I
We introduce a new 1D coupled Radiative / Convective - Photochemical - Microphysical model for a planetary atmosphere and apply it to Titan. The model incorporates detailed radiation transfer calculations for the description of the shortwave and longwave fluxes which provide the vertical structure of the radiation field and temperature profile. These are used for the generation of the photochemistry inside the atmosphere from the photolysis of Titan's main constituents, nitrogen (N2) and methane (CH4).
The resulting hydrocarbons and nitriles are used for the production of the haze precursors, whose evolution is described by the microphysical part of the model. The calculated aerosol and gas opacities are iteratively included in the radiation transfer calculations in order to investigate their effect on the resulting temperature profile and geometric albedo. The main purpose of this model is to help in the understanding of the missing link between the gas production and particle transformation in Titan's atmosphere. In this part, the basic physical mechanisms included in the model are described. The final results regarding the eddy mixing profile, the chemical composition and the role of the different haze precursors suggested in the literature are presented in Part II along with the sensitivity of the results to the molecular nitrogen photoinization scheme and the impact of galactic cosmic rays in the atmospheric chemistry.
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Abstract Part II
"The new one-dimensional radiative-convective/photochemical/microphysical model described in Part I is applied to the study of Titan's atmospheric processes that lead to haze formation. Our model generates the haze structure from the gaseous species photochemistry. Model results are presented for the species vertical concentration profiles, haze formation and its radiative properties, vertical temperature/density profiles and geometric albedo. These are validated against Cassini/Huygens observations and other ground-based and space-borne measurements. The model reproduces well most of the latest measurements from the Cassini/Huygens instruments for the chemical composition of Titan's atmosphere and the vertical profiles of the observed species.
For the haze production we have included pathways that are based on pure hydrocarbons, pure nitriles and hydrocarbon/nitrile copolymers. From these, the nitrile and copolymer pathways provide the stronger contribution, in agreement with the results from the ACP instrument, which support the incorporation of nitrogen in the pyrolised haze structures. Our haze model reveals a new second major peak in the vertical profile of haze production rate between 500 and 900 km. This peak is produced by the copolymer family used and has important ramifications for the vertical atmospheric temperature profile and geometric albedo. In particular, the existence of this second peak determines the vertical profile of haze extinction.
Our model results have been compared with the DISR retrieved haze extinction profiles and are found to be in very good agreement. We have also incorporated in our model heterogeneous chemistry on the haze particles that converts atomic hydrogen to molecular hydrogen. The resultant H2 profile is closer to the INMS measurements, while the vertical profile of the diacetylene formed is found to be closer to that of the CIRS profile when this heterogenous chemistry is included."
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This post has been edited by alan: Oct 14 2007, 03:18 PM

Reason for edit: improved formating

[Webscientist]

A living mist?

[ngunn]

A living mist?

Let's take that one head on. The formation of each haze particle is presumably a quasi-random cumulative process leading in one direction only - its eventual deposition on the surface of Titan. For anything remotely resembling life to get going you need a cyclic process where the outcome of one cycle alters the conditions in which the next cycle occurs, thereby affecting its outcome, and so on. It's not impossible to imagine such things happening on Titan, though even if there are I'm sure there would still be semantic disputes about the term 'life'. However IMHO haze particle formation is not such a process.

If you were speaking 'poetically' please forgive me for being a terrible pedant.