HR: 0800h
AN: P41A-0199    [Abstracts]
TI: Modeled Ion Densities of Comet 1P/Halley: a Comparison With Giotto's Ion Mass Spectrometer
AU: * Rubin, M
EM: rubinmar@umich.edu
AF: Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109-2143, United States
AU: Hansen, K C
EM: kenhan@umich.edu
AF: Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109-2143, United States
AU: Gombosi, T I
EM: tamas@engin.umich.edu
AF: Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109-2143, United States
AU: Combi, M R
EM: mcombi@umich.edu
AF: Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109-2143, United States
AU: Altwegg, K
EM: kathrin.altwegg@space.unibe.ch
AF: Physikalisches Institut, Universität Bern, Sidlerstrasse 5, Bern, 3012, Switzerland
AU: Balsiger, H
EM: hans.balsiger@space.unibe.ch
AF: Physikalisches Institut, Universität Bern, Sidlerstrasse 5, Bern, 3012, Switzerland
AB: 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, with 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 modeled 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 200~000~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 comet, an additional source for C⁺, CH⁺, as well as the CH₂⁺ ions is needed. First investigations indicate that all three species are emerging from the same source which needs to have a short scale length of less than 500~km in order to accommodate with the measurements. Finally, we also show our results of the contact surface which is well resolved and in good agreement with the Giotto data.
DE: 6008 Composition (1060)
DE: 6025 Interactions with solar wind plasma and fields
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting