Proceedings IAU Symposium No. 229, pp. 249–271 (2006)
Physical and chemical properties of meteoroids as deduced from
observations
Jiri Borovicka
Astronomical Institute of the Academy of
Sciences, 251 65 Ondřejov, Czech Republic
Abstract.
A review of the current knowledge of physical properties and chemical
composition of meteoroids entering the Earth's atmosphere is presented.
Meteoroid penetration ability, ablation coefficients, beginning
heights,
light curves, fragmentation, and spectra are considered. The inferred
bulk densities, mechanical strengths, rotation, and atomic elemental
abundances are discussed. Cometary meteoroids are effectively grain
aggregates with low bulk density (100-1000 kg m-3), high
porosity and
low cohesivity. A volatile matrix holding the grains together may be
present. Presence of large amounts of organic material is not firmly
established. Small chunks (∼1 mm) of denser material are sometimes
contained in cometary meteoroids. Chemically, cometary grains are
similar to CI chondrites but there is a hint of enhancement of Na, Si,
and Mg and depletion of Fe, Cr, and Mg. Larger chemical diversity is
observed among small meteoroids on cometary orbits not belonging to
meteoroid streams. The relatively frequent Na-free meteoroids are
probably fragments of cometary irradiation crust. Asteroidal meteoroids
exhibit much lower mechanical strengths than stony meteorites, clearly
due to the presence of large scale cracks. Iron meteoroids dominate
among asteroidal meteoroids smaller than 1 cm.
Keywords: Meteors, meteoroids
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