Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...291..324h&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 291, no. 1, p. 324-336
Astronomy and Astrophysics
Astrophysics
24
Astronomical Models, Dust, Halley'S Comet, Hydrodynamics, Hypervelocity Impact, Ionization, Shock Waves, Astronomical Spectroscopy, Cometary Atmospheres, Gas Dynamics, Giotto Mission, Space Density, Vega Project
Scientific paper
The process of ion formation upon hypervelocity impact of small dust particles on a solid surface is treated within a hydrodynamic approach. The model mainly uses the Thomas Fermi equation of state for the high pressure temperature shock states in the dust and in the target 107 - 108 bars, 105 - 106 K, as well as for the expansion isentrope. Spectoscopic data are used to calculate the ionization in the expanded state. The conditions investigated are related to the 1986 flyby of VEGA1, VEGA2 and GIOTTO spacecraft at Comet Halley (upsilon: 79.2, 76.8, 68.4 km/s respectively, dust mass range: 10-15 less than Md less than 10-12 g, density range 1 less than rhod less than 3 g/cu,cm) and to some extent ionization data from these missions are used. For an impacting dust particle of given mass, density and chemical composition, the model gives the limiting relative ion numbers in the expanding impact plasma cloudlet, i.e. the ion numbers of the individual chemical elements, normalized to one element, at large expansion times. Such information has not been obtained up to now within a closed theoretical model. It is shown that the procedure can be used in the opposite direction to determine a chemical composition from measured ion spectra. Example calculations for the Halley case resulted in chemical compositions which approximately agree with the results of previous data reductions, which were based on empirical methods. They also reveal an interesting dependence on mass and density. It has been found that the effects of increasing density are partly balanced by those of decreasing mass, such that the influence of both parameters may be considerably reduced under certain conditions.
Hornung Klaus
Kissel Jeff
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