Evidence for methane and ammonia in the coma of comet P/Halley

Details Evidence for methane and ammonia in the coma of comet P/Halley Evidence for methane and ammonia in the coma of comet P/Halley

Nov 1987

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987a%26a...187..502a&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 187, no. 1-2, Nov. 1987, p. 502-512. BMFT-SNSF-supported research.

Astronomy and Astrophysics

Astrophysics

94

Ammonia, Chemical Composition, Cometary Atmospheres, Halley'S Comet, Methane, Abundance, Astronomical Spectroscopy, Giotto Mission, Ion Distribution

Scientific paper

Methane and ammonia abundances in the coma of Halley are derived from Giotto IMS data using an Eulerian model of chemical and physical processes inside the contact surface to simulate Giotto HIS ion mass spectral data for mass-to-charge ratios (m/q) from 15 to 19. The ratio (m/q) = 19/18 as a function of distance from the nucleus is not reproduced by a model for a pure water coma. It is necessary to include the presence of NH3, and uniquely NH3, in coma gases in order to explain the data. A ratio of production rates Q(NH3)/Q(H2O) = 0.01 - 0.02 results in model values approximating the Giotto data. Methane is identified as the most probable source of the distinct peak at m/q = 15. The observations are fit best with Q(CH4)/Q(H2O) = 0.02. The chemical composition of the comet nucleus implied by these production rates is unlike that of the outer planets. On the other hand, there are also significant differences from observations of gas phase interstellar material.

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