Physical and chemical properties of meteoroids as deduced from observations

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.

Constraining the luminous efficiency of meteors

“…The higher bulk density values have stony-iron meteorites (4-6 g/cm 3 ) and iron meteorites (4-8 g/cm 3 ) which are highly differentiated meteorites possibly representing cores of large asteroid parent bodies broken apart by catastrophic collisions. However such a high bulk density iron objects expected to be rare exception among observed meteors (Borovička, 2006). Consolmagno and Britt (1998) make a note that most meteorites are substantially denser than their suggested asteroid analogous which must have larger porosity because of presence of empty space on scales larger than the size of the meteorites.…”

Bulk density of small meteoroids

“…The cometary meteoroid bulk density is consistent with the bulk density inferred for the several cometary nuclei (cf. Asphaug & Benz 1996;Davidson & Gutierrez 2004, 2005 suggesting microporosity could dominate cometary nucleus structure for HTC/NICs. However, we caution that most of these measurements are for Jupiter-family comets.…”

“…Fragmentation also explains the production of the physical wake in meteor observations. Grains of different A&A 530, A113 (2011) masses, predicted by the dustball model, decelerate at different rates, leading to an elongated luminous region (Borovicka 2005). Many video meteors observed with short exposures show this wake (Fisher et al 2000).…”

“…Working on the same data, Bellot Rubio et al (2002), using the single body theory which neglects fragmentation entirely, found bulk densities ranging from 400 kg m −3 to 4800 kg m −3 . The complete model of meteoroid ablation must take into account fragmentation and dynamical properties of the meteoroids simultaneously (Borovicka 2005), as described and applied by Borovicka et al (2007), and Kikwaya et al (2009).…”

Pre-accretionary and parent body histories of a cometary aggregate particle

“…The IDP L2011K7 parent body was then probably a comet nucleus with small 'pebbles' (Rietmeijer, 2004a) without necessarily being a rubble-pile (Gombosi and Houpis, 1986;Weissman, 1986). Evidence for small-scale textural heterogeneity in comet nuclei exits in the form of cm-size meteoroids in comet debris trails (Ishiguro et al, 2002), meteors (Spurný and Borovicka, 1999) including the Perseids associated with Halley-type Comet 109P/ Swift-Tuttle (Koten and Borovička, 2001), and dense structurally coherent $1 mm cometary meteoroids (Borovička, 2006). The open space in CP IDPs was presumable filled with ice when resident in comet nuclei (Bradley and Brownlee, 1986).…”