Giotto IMS measurements of the production rate of hydrogen cyanide in the coma of Comet Halley

Details Giotto IMS measurements of the production rate of hydrogen cyanide in the coma of Comet Halley Giotto IMS measurements of the production rate of hydrogen cyanide in the coma of Comet Halley

May 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990angeo...8..319i&link_type=abstract

Annales Geophysicae (ISSN 0992-7689), vol. 8, May 1990, p. 319-325. Research supported by BMFT, DFG, and SNSF.

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Cometary Atmospheres, Giotto Mission, Halley'S Comet, Hydrocyanic Acid, Ion Production Rates, Mass Spectrometers, Abundance, Coma, Ion Density (Concentration), Comets, Halley, Spacecraft Observations, Giotto Mission, Ionosphere, Ims Instrument, Hydrogen Cyanide, Comae, Production Rate, Spectrometry, Abundance, Comet Nuclei, Photochemistry, Models, Theoretical Studies, Comparisons, Chemical Reactions, Equipment, Procedure, Compositon, Ions, Numerical Methods

Scientific paper

The ion composition measurements in the ionosphere of Comet Halley by the ion mass spectrometer (IMS) experiment on the Giotto spacecraft are used to estimate the relative abundance of HCN. From a comparison of the normalized number density of ions with mass-to-charge (M/q) ratio of 28 AMU/e with steady-state photochemical models, it can be determined that the production rate of HCN directly from the central nucleus is Q(HCN) is less than about 0.0002 Q(H2O) at the time of Giotto encounter. The related photochemical- model calculations also indicate that Q(NH3)/Q(H2O) at the time of Giotto encounter. The related photo-chemical model calculations also indicate that Q(HN3)/Q(H2O) equals about 0.005, in agreement with recent determination from ground-based observations. The estimated value of Q(HCN) is lower than the relative abundance of Q(HCN)/Q(H2O) of about 0.001, as derived from radio observations of the 88.6 GHz emission of the J = 1 - 0 transition of HCN. The difference may be the result of time variations of the coma composition and dynamics, as well as other model-dependent effects.

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