Physics
Scientific paper
Oct 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990georl..17.1813b&link_type=abstract
Geophysical Research Letters (ISSN 0094-8276), vol. 17, Oct. 1990, p. 1813-1816. Research supported by NASA and Southwest Resear
Physics
35
Atmospheric Composition, Cometary Atmospheres, Cosmic Plasma, Giotto Mission, Halley'S Comet, Interplanetary Dust, Abundance, Carbon Monoxide, Mass Spectroscopy, Methane
Scientific paper
Early analyses of the Ion Mass Spectrometer (IMS) data from the Giotto flyby of Comet P/Halley indicated significant abundances of CH(+)n (n = 1 to 4). The source of these ions was assumed to be frozen CH4 in the nucleus. An abundance of about 2 percent CH4 was consistent with this interpretation, resulting in a ratio of CH4/CO that is greater than the predicted limits for interstellar clouds or the solar nebula. However, subsequent analyses of data from the Giotto Neutral Mass Spectrometer indicate distributed sources of CO and H2CO in the coma that are most likely associated with organic (CHON) particles, rich in CH-bearing compounds that decay and produce CH(+)n species. A model is presented that qualitatively accounts for the measured spatial distribution of CO and H2CO, and indicates that most of the CH(+)n deduced from the Giotto IMS data may originate from organic compounds in the coma dust and not from volatiles released directly from the nucleus. As a consequence, the absence of CH4 in the icy phase of the nucleus is consistent with the observations with an upper limit of about 0.5 percent to the ratio CH4/CO. This is an important criterion for theories of comet formation.
Boice Daniel C.
Huebner Walter F.
Konno Ichishiro
Sablik M. J.
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