Nature 383, 418 - 420 (03 October 1996); doi:10.1038/383418a0

Spectroscopic evidence for interstellar ices in comet Hyakutake

William M. Irvine, Dominique Bockelee-Morvan^*, Dariusz C. Lis^†, Henry E. Matthews^‡§, Nicolas Biver^*, Jacques Crovisier^*, John K. Davies^‡, William R. F. Dent^‡, Daniel Gautier^*, Peter D. Godfrey, Jocelyn Keene^†, Amy J. Lovell, Tobias C. Owen^¶, Thomas G. Phillips^†, Heike Rauer^*, F. Peter  Schloerb, Matthew Senay^¶ & Kenneth Young^†

Five College Radio Astronomy Observatory, 619 LGRC, University of Massachusetts, Amherst, Massachusetts 01003, USA
^* Observatoire de Paris-Meudon, F-92195 Meudon Principal Cedex, France
Chemistry Department, Monash University, Clayton 3168, Australia
^¶ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, USA
^† California Institute of Technology, Downs Laboratory of Physics 320-47, Pasadena, California 91125, USA
^§ Herzberg Institute of Astrophysics, National Research Council of Canada, Ottawa, Ontario K1A OR6, Canada
^‡ Joint Astronomy Centre, 660 N. A'ohoku Place, University Park, Hilo, Hawaii 96720, USA

VOLATILE compounds in comets are the most pristine materials surviving from the time of formation of the Solar System, and thus potentially provide information about conditions that prevailed in the primitive solar nebula^1–3. Moreover, comets may have supplied a substantial fraction of the volatiles on the terrestrial planets, perhaps including organic compounds that played a role in the origin of life on Earth^4–6. Here we report the detection of hydrogen isocyanide (HNC) in comet Hyakutake. The abundance of HNC relative to hydrogen cyanide (HCN) is very similar to that observed in quiescent interstellar molecular clouds, and quite different from the equilibrium ratio expected in the outermost solar nebula, where comets are thought to form. Such a departure from equilibrium has long been considered a hallmark of gas-phase chemical processing in the interstellar medium⁷, suggesting that interstellar gases have been incorporated into the comet's nucleus, perhaps as ices frozen onto interstellar grains. If this interpretation is correct, our results should provide constraints on the temperature of the solar nebula, and the subsequent chemical processes that occurred in the region where comets formed.

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