Composition and Properties of Dust from Comet Halley
Abstract
A study of the elemental and morphological properties of cometary dust is made using elemental composition data from the PUMA and PIA impact mass spectrometers that analyzed Comet Halley's dust on flyby missions in 1986. The study is unique in its special rigorous selection procedures and its resulting high quality data sets, the largest of which contains mass spectra from 279 dust particles. The results include findings that anhydrous mafic silicates, many rich in Mg composition, are a predominant and ubiquitous constituent of cometary dust. Iron sulfides are probably also a common constituent. Both silicates and sulfides occur as mineral grains smaller than the typical particle size, and they are mixed intimately with abundant organic "CHON" material. Sulfates and carbonates that would be produced by aqueous alteration seem to be very rare or nonexistent. Compositional dispersions of the major rock -forming elements in the cometary dust are quite unlike those seen in carbonaceous chondrites and serpentine-dominated hydrous interplanetary particles. The Halley data show evidence for olivines and low-Fe silicates that are absent from the hydrous smectite layer-silicate class of interplanetary particles, and this type of IDP also appears unlikely to be cometary material. The overall compositional dispersions in Halley's dust appear most similar to the anhydrous, porous chondritic class of interplanetary dust particles, lending additional support to the belief that this class of interplanetary particle has a cometary origin. Several lines of evidence indicate that extensive sublimation of volatile organic material in the dust occurs up to ~40 000 km from the comet nucleus, resulting in declining organic fractions in dust populations more distant from the nucleus. Sublimation may lead to fragmentation of the dust and elimination of the larger particles beyond this radius. Limited evidence has been found that published estimates of PUMA and PIA dust particle masses are too high by at least 2 orders of magnitude. The data appear consistent with a Greenberg-type model of organic CHON mantles on constituent silicate grains if sublimation of volatiles operates and produces the observed high variability in CHON-to-silicate composition.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1993
- Bibcode:
- 1993PhDT.........2L
- Keywords:
-
- INTERPLANETARY DUST;
- Physics: Astronomy and Astrophysics;
- Chemical Analysis;
- Chemical Composition;
- Cometary Atmospheres;
- Halley'S Comet;
- Interplanetary Dust;
- Mass Spectra;
- Iron Compounds;
- Olivine;
- Organic Materials;
- Silicates;
- Sulfides;
- Astrophysics