Methanol and hydrogen sulfide in comet P/Halley

Details Methanol and hydrogen sulfide in comet P/Halley Methanol and hydrogen sulfide in comet P/Halley

Aug 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...288..315e&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 288, no. 1, p. 315-329

Astronomy and Astrophysics

Astrophysics

45

Abundance, Gas Composition, Halley'S Comet, Hydrogen Sulfide, Ion Density (Concentration), Methyl Alcohol, Astronomical Models, Chemical Reactions, Giotto Mission, Mass Spectroscopy, Photodissociation

Scientific paper

The Neutral Mass Spectrometer on the Giotto spacecraft measured the gas and ion composition in the coma of comet P/Halley. A detailed model of the ion chemistry inside the contact surface located at 4660 km is used to interpret the measured ion desnity profiles in the 32 to 35 amu/e mass range. The masses 33 and 35 amu/e are dominated by the protonated methanol and hydrogen sulfide ions CH3OH2(+) and H3S(+). Both profiles are essentially compatible with CH3OH and H2S originating from the nucleus only. The production rates relative to water are Y(CH3OH) = Q(CH3OH)/Q(H2O) = 1.7% and Y(H2S) = 0.41%. Our Y(CH3OH) agrees well with a determination from IR spectra obtained about 6 weeks after the Giotto encounter with P/Halley. In 7 other comets IR and microwave observations give Y(CH3OH) values between about 0.7 and 6%, indicating that the methanol abundance shows a strong variability from comet to comet. In three other comets Y(H2S) values between 0.2 and 0.5% have been reported. In addition to H2S(+), only ions containing minor isotopes of H, C, O and S contribute to mass 34 amu/e (e.g. (34)S(+), (13)CH3OH2(+), CH4DO(+)). These contributions can be calculated from the measured densities of the ions containing the major isotopes and the H2S(+) contribution from the measured H3S(+) density. From mass 34 amu/e we can also derive an upper limit of 1% for the abundance of deuterated methanol. This limit is at most marginally compatible with a direct interstellar origin of the CH3OH in P/Halley as the measured interstellar abundance of deuterated methanol is 1 to 6%.

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