Mathematics – Logic
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27r.286s&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 286
Mathematics
Logic
2
Scientific paper
It is commonly assumed that comets are pristine bodies which still contain relatively unaltered material from the beginning of our solar system. Therefore, in March 1986 the chemical composition of Halley's dust particles was investigated by time- of-flight mass spectrometers on board the Vega 1 & 2 and Giotto spacecraft using the high relative velocity of 70-80 km/s between spacecraft and Halley for the generation of ions by dust impact ionization (see e.g. Kissel, 1986; Jessberger et al., 1988). This paper investigates the overall chemical variation among the dust particles with special emphasis on rock-forming elements to derive a mineralogical model of the dust and to give constraints to the evolution of cometary and preplanetary matter. The interpretation is based on 123 selected spectra obtained by the mass spectrometer PUMA 1 on Vega 1. Selection criteria, interpretation of raw data and examined instrumental effects are described in more detail elsewhere (Schulze and Kissel, 1992). The bulk composition of Halley's dust is characterized for the rock-forming elements by cosmic abundances within the experimental uncertainty of factor two (see also Jessberger et al., 1988). A small systematic deviation of the abundances can be used for a revision of the ion yields. The volatile elements carbon and nitrogen, however, are significantly enriched to CI-chondrites. A histogram of the Mg/(Mg+Fe)-ratios shows typical peaks at about 0 and 1 which indicate separated phases for Mg and Fe and an anhydrous nature of the dust (e.g. Brownlee et al., 1987; Bradley, 1988). However, also a broad peak occurs at 0.5. Mg-rich spectra are characterized by an excellent Mg-Si correlation with a narrow range of Mg/Si ratios at about 1. Also oxygen is correlated with Mg and Si. Fe-rich spectra partly show a good Fe-S correlation. However, several spectra are rich only in Fe or S. A cluster analysis of the spectra regarding Na, Mg, Al, Si, S, Ca, and Fe revealed seven groups. These groups partly correspond to classifications of interplanetary dust particles (Brownlee et al., 1982). Half of the spectra have chondritic abundances within the experimental uncertainty. About 25% are dominated by Mg and Si indicating a significant portion of Fe-poor Mg silicates in the dust. Nearly 7% of the spectra are typically enriched in Fe and S due to pure Fe sulfide grains which seem to be partly enriched in Ni. Rarely, particles extremely rich in iron occur. Many silicatic spectra show a sulfur excess of unknown origin. Interpreting this heterogeneity in terms of mineralogy indicates that about half of Halley's dust grains are almost monomineralic and composed of Mg-rich silicates (enstatite and/or forsterite), Fe sulfides and Fe metal. Hydrated silicates and magnetite seem to play only a small role. The prevalence of minerals which were formed at rather high temperatures according to the condensation sequence (above ~600 K), is evidence that equilibration to Fe-rich and hydrated silicates by diffusion reactions at lower temperatures is a process too slow to affect these dust particles in their formation environment (Fegley and Prinn, 1988), and that these particles were not intensively altered at low temperatures in the comet. References: Bradley J.P. (1988) Geochim. Cosmochim. Acta. 52. 889-900. Brownlee D.E., Olszewski E., and Wheelock M.M. (1982) Lunar Planet. Sci. XIII, 71-72. Brownlee D.E., Wheelock M.M., Temple S., Bradley J.P., and Kissel J. (1987) Lunar Planet. Sci. XVIII, 134-135. Fegley B. and Prinn G. (1989) The formation and evolution of planetary systems (eds. H.A. Weaver and L. Danly), pp. 171-211. Cambridge. Jessberger E.K., Christoforidis A., and Kissel J. (1988) Nature 332, 691-695. Kissel J. (1986) Europ. Space Agency Spec. Publ. 1077, 67-83. Schulze H. and Kissel J. (1992) Earth Planet. Sci. Lett., submitted. Kissel J. and Krueger F.R. (1987) Appl. Phys. A42, 69-85.
Kissel Jeff
Schulze Henrik
No associations
LandOfFree
Chemical Heterogeneity and Mineralogy of Halley's Dust does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Chemical Heterogeneity and Mineralogy of Halley's Dust, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Chemical Heterogeneity and Mineralogy of Halley's Dust will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1209905