Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.5310r&link_type=abstract
American Astronomical Society, DPS meeting #39, #53.10; Bulletin of the American Astronomical Society, Vol. 39, p.521
Astronomy and Astrophysics
Astronomy
Scientific paper
The cometary plasma environment is largely influenced by a complex, closely linked series of chemical reactions. To better our understanding of this environment, we compare the results from our ion-chemical network calculation, consisting of a magnetohydrodynamics (MHD) as well as a chemistry model, applied to data from the Ion Mass Spectrometer collected during Giotto's fly-by at Comet 1P/Halley in 1986. The chemistry code, originally developed by Häberli et al. (1995, Astron. Ap. 297, 881), integrates the 24 most dominant species along streamlines which have been extracted from an MHD model of Comet 1P/Halley [Gombosi et al. (1996, JGR 101, 15233)]. The chemistry code includes a few hundred reactions for these species including photodissociation, photoionization, electron impact ionization, ion-molecule reactions, charge exchange, and dissociative ion-electron recombination.
In this work we compare the measured and modelled densities of the C+, CH+, CH2+, CH3+, N+, NH+, NH2+, NH3+, NH4+, O+, OH+, H2O+, H3O+, CO+, HCO+, H3CO+, and CH3OH2+ ions along the Giotto trajectory from 200 km to roughly 1000 km at closest approach. Our results are in good agreement, although, in order to reproduce the data in the vicinity of the nucleus, an additional source for C+, CH+, and CH2+ ions with a very distinct decrease within the first 3000 km is needed. The results are sensitive to the electron model we use since it cannot be calculated self-consistently in our ion-chemical network: The electron temperature is crucial for the recombination rates, and the high energy electrons (>15eV) contribute to the electron impact dissociation. Our improved model is based on the work done by Häberli et al. (1996, JGR 101, 15579).
Altwegg Kathrin
Balsiger Hans
Combi Michael R.
Gombosi Tamas I.
Hansen Kenneth Calvin
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