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A two component model for thermal emission from organic grains in Comet HalleyObservations of Comet Halley in the near infrared reveal a triple-peaked emission feature near 3.4 micrometer, characteristic of C-H stretching in hydrocarbons. A variety of plausible cometary materials exhibit these features, including the organic residue of irradiated candidate cometary ices (such as the residue of irradiated methane ice clathrate, and polycyclic aromatic hydrocarbons. Indeed, any molecule containing -CH3 and -CH2 alkanes will emit at 3.4 micrometer under suitable conditions. Therefore tentative identifications must rest on additional evidence, including a plausible account of the origins of the organic material, a plausible model for the infrared emission of this material, and a demonstration that this conjunction of material and model not only matches the 3 to 4 micrometer spectrum, but also does not yield additional emission features where none is observed. In the case of the residue of irradiated low occupancy methane ice clathrate, it is argued that the lab synthesis of the organic residue well simulates the radiation processing experienced by Comet Halley.
Document ID
19890003969
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Chyba, Christopher (Cornell Univ. Ithaca, NY, United States)
Sagan, Carl (Cornell Univ. Ithaca, NY, United States)
Date Acquired
September 5, 2013
Publication Date
September 1, 1988
Publication Information
Publication: NASA, Washington, Infrared Observations of Comets Halley and Wilson and Properties of the Grains
Subject Category
Astronomy
Accession Number
89N13340
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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