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Tholins and their relevance for astrophysical issues

Published online by Cambridge University Press:  01 February 2008

E. Quirico ,
C. Szopa ,
G. Cernogora ,
V. Lees ,
S. Derenne ,
P. F. McMillan ,
G. Montagnac ,
B. Reynard ,
J-N Rouzaud  and
N. Fray
...Show all authors
E. Quirico
Affiliation:
Laboratoire de Planetologie de Grenoble, University Joseph Fourier CNRS, BP 53 38041 Grenoble Cedex 9, France email: [email protected]
C. Szopa
Affiliation:
Service d'Aeronomie, Universite Pierre et MarieCurie-Paris 6 et Universite de VersaillesReduit de Verrieres, Route des Gatines, 91371 Verrieres le Buisson, France
G. Cernogora
Affiliation:
Service d'Aeronomie, Universite Pierre et MarieCurie-Paris 6 et Universite de VersaillesReduit de Verrieres, Route des Gatines, 91371 Verrieres le Buisson, France
V. Lees
Affiliation:
Dept. of Chemistry and Materials Chemistry Centre, University College London, 20 Gordon Street, London WC1H 0AJGreat Britain
S. Derenne
Affiliation:
Laboratoire de Chimie Bioorganique et Organique Physique BioEMCo, Ecole Nationale Superieure de Chimie de Paris, 11, rue Pierre et Marie Curie 75231 Paris Cedex 05France
P. F. McMillan
Affiliation:
Dept. of Chemistry and Materials Chemistry Centre, University College London, 20 Gordon Street, London WC1H 0AJGreat Britain
G. Montagnac
Affiliation:
Laboratoire de Sciences de la Terre, Ecole Normale Superieure de Lyon, 46 allee d'Italie 69364 Lyon Cedex 7France
B. Reynard
Affiliation:
Laboratoire de Sciences de la Terre, Ecole Normale Superieure de Lyon, 46 allee d'Italie 69364 Lyon Cedex 7France
J-N Rouzaud
Affiliation:
Laboratoire de Geologie, Ecole Normale Superieure de Paris, 24 rue Lhomond 75231 Paris Cedex 5France
N. Fray
Affiliation:
Laboratoire Interuniversitaire des Systemes Atmospheriques, Universite Paris XII – Paris VII, 61 av. du Gal de Gaulle, 94010 Creteil cedex, France
P. Coll
Affiliation:
Laboratoire Interuniversitaire des Systemes Atmospheriques, Universite Paris XII – Paris VII, 61 av. du Gal de Gaulle, 94010 Creteil cedex, France
F. Raulin
Affiliation:
Laboratoire Interuniversitaire des Systemes Atmospheriques, Universite Paris XII – Paris VII, 61 av. du Gal de Gaulle, 94010 Creteil cedex, France
B. Schmitt
Affiliation:
Laboratoire de Planetologie de Grenoble, University Joseph Fourier CNRS, BP 53 38041 Grenoble Cedex 9, France email: [email protected]
B. Minard
Affiliation:
Chemistry Department, Pennsylvania State University, 104 Chemistry Building University Park, PA 16802United States of America
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Abstract

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Tholins are polymeric hydrogenated carbon nitrides formed from N2:CH4 mixtures exposed to electrical discharges. They are complex disordered solids, and their structural chemistry and formation processes are not yet fully understood. Tholins have been widely adopted as useful analogs of reddish organic solids associated with planetary bodies or in interstellar space (e.g., Titan's aerosols, reddish surfaces of outer objects, interstellar organics, etc.) for fitting astronomical observations. However, there has been little evidence to date that they in fact constitute pertinent model materials, i. e. with chemical structure/composition similar to those presumed to be present in planetary or interstellar organic solids. In this contribution, we first review recent advances made regarding the determination of composition and structure of tholins produced in the laboratory. They point to a high chemical selectivity in the range of functional groups present, the control of unsaturation by nitrogen, and the highly disordered character of the structures. In a second section, we discuss the relationship between chemistry and the optical properties of tholins, and we point out the lack of a unique relationship between the shape and strength of the visible absorption bands and the chemical composition or structure of the model tholins. The tholins exhibit similarities with HCN “polymers”, that are suspected to be present in cometary refractory dust. This points to the existence of possible similar polymerisation processes, and it suggests they could also be used as analogs of N-rich cometary organics. Laboratory-based studies of cometary dust might offer new insights on the “chemical relevancy” of tholins, as combined micro-analytical techniques will allow direct comparison of chemical information between the materials produced. In a third section we present recent results pertaining to the search for such compounds in cometary grains (Stardust grains, interplanetary dust particles - IDPs). We show that some N-rich spots in stratospheric IDPs are rich in cyanide species, but no tholin-like compounds or polymeric HCN have been detected to date.

Keywords

Comets: generaltholinsorganic matterchondrites
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 4 , Symposium S251: Organic Matter in Space , February 2008 , pp. 409 - 416
Copyright
Copyright © International Astronomical Union 2008

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