Computer Science
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28r.332b&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 332
Computer Science
4
Asteroid Belt, Comets, Cosmic Dust, Interplanetary Dust Particles, Phyllosilicates
Scientific paper
The measured He release profiles of step-heated IDPs provide a quantitative determination of the maximum temperature experienced by an individual IDP during entry into the atmosphere [1]. Using straightforward atmospheric entry models for dust [2,3], this temperature can be used to infer the entry velocity for particles with known mass and density. Together these techniques can distinguish the difference between typical asteroid dust that enters the atmosphere at velocities near 12 kms^-1 and typical comet dust that enters the atmosphere at velocities above 15 kms^-1. For 10 micrometer IDPs with similar densities the temperature difference for comet dust and asteroid dust is in the range of 200 degrees C to 300 degrees C or more. We have begun a project to identify origins for a substantial set of 5-micrometer stratospheric IDPs, a size picked as a large enough for He analysis but small enough that high velocity comet dust is not severely heated [4]. The bulk of each IDP is consumed by the He analysis but a dozen microtome slices of various thickness are extracted from each particle before He analysis and these samples form a resource for present and future analysis by a multitude of techniques. The masses, densities and bulk composition of each particle are also determined. From the analysis of 26 5- micrometer to 15- micrometer IDPs, we have found that more than half have minimum entry velocities consistent with origin by Poynting-Robertson spiral from the asteroid belt. Approximately 20% have velocities consistent with origin as comet dust with elliptical orbits. Some of the asteroid particles are hydrated IDPs while the two particles that had entry velocities >18 kms^-1 are anhydrous. The best studied of these is a classic "pyroxene" class IDP that is carbon rich and dominated by subunits that have been variously called "granular units" [5] and "tar balls." These fundamental subunits of what appear to be the most primitive IDPs are composed of glass enclosing large numbers of 1nm to 100nm rounded grains of kamacite and pyrrhotite. The elemental composition variations at the finest scale of the best studied cometary IDP are a very good match data from Halley [6]. References: [1] Nier A. O. and Schlutter D. J. (1992) Meteoritics 27, 166. [2] Flynn (1989) Icarus, 77, 287. [3] Love S. G. and Brownlee D. E. (1991) Icarus, 89, 26. [4] Brownlee et al. (1993) LPS XXIV, 205. [5] Rietmeijer F. J. M. (1992) Trends in Mineral., 1, 23. [6] Lawler et al. (1989) Icarus, 80, 225.
Bradley John P.
Brownlee Don E.
Joswiak David J.
Love Stanley G.
Nier Alfred O.
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