Fireball end heights: A diagnostic for the structure of meteoric material

Abstract

An earlier analysis of Prairie Network fireball trajectory data by the authors failed to discriminate between the varieties of meteoric materials that are thought to be present. The Lost City meteorite event offers a new calibration of the fireball data and prompts a new analysis intended to distinguish between ordinary chondritic meteorites and the more fragile early type carbonaceous chondrites. The carbonaceous material is expected to ablate more readily and thus to have shorter trajectories or higher end heights. Observational error and the natural dispersion in the structures produce severe smoothing effects, and the end height diagnostic is, in itself, not entirely convincing. However, after making a tentative division of the data, one can discern differences in orbits and beginning heights among the three end height groups. These are consistent with our expectation of the behavior of chondritic stones (group I), weak carbonaceouS chondrites (group II), and still more fragile cometary material (group III). We conclude that if the carbonaceous material occurs in reasonable abundance among the fireballs, it has been properly identified by this analysis. If either of the above conditions does not obtain in fact then there is little hope of discriminating between meteorite classes in the fireball data.Third, we assume that there is some direct 6257 6258 Ceplecha and McCrosky' Fireball End Heights relationship between a meteoroid's strength, asmeasured by its fragmentation or ablation rate, and its density. We will later show data that can be construed to support this view, but the best arguments in its favor will be one's everyday experience with a variety of, materials, which, for some, include the various chondritic meteorites discussed previously. Anearly qualitative result of the analysis of the PN data was the observation that there could be very great differences in end heights (end of visible trajectory) for fireballs of comparable brightness, velocity, and trajectory angle. The ratio of the amount of atmosphere penetrated can exceed 100:1. The meteor • end +0.6 -+0.4 -A ,,,, +0.2v oß -0.2 --0.4 --0.6 -ß ß ß ß ß ß I i ß ß ß ß / ß ß ! ß i i -4.4 -4.8 PE

5. Meteoroid Populations and Orbits

“…Except for the reasons given in favor of this identification in the paper by Ceplecha and McCrosky (1976) Ceplecha et al 1977). This fireball penetrated to 32 km and was a sure member of the group II; the extremely good spectral (15 A/mm) contain more than 500 features in the visible region and show relatively strong emissions of the CN molecule H^monstrating the abundance of carbon.…”

“…A recent study of populations among fireballs were based on data of 232 events photographed by the Prairie Network during 7 years. (Ceplecha and McCrosky 1976). The typical mass-range for fireballs is from 10 2 to 10 6 g. Different meteoroid populations were first recognized independently by Jacchia (1958) and Ceplecha (1958).…”

“…Four groups of different composition and structure were found among fireballs (Ceplecha and McCrosky 1976) and were denoted by Roman numerals eventually with a letter suffix. Group I is of the greatest density and contains Pribram (Ceplecha 1961) and Lost City meteorites, the only two meteorite falls photographed.…”

“…The fireball-group-I data can be considered as representative of ordinary chondrites. The orbital data for any detailed study should be taken from the original paper (Ceplecha and McCrosky 1976).…”

An Earth-grazing fireball from the Daytime ζ-Perseid shower observed over Spain on 2012 June 10

“…Again, this density was obtained from the NRLMSISE-00 atmosphere model (Picone et al 2002) and the luminous efficiency was calculated by means of the relationships defined by Ceplecha & McCrosky (1976). The shape-density parameter K, which depends on meteoroid density ρ m , shape factor A and drag coefficient Γ, is given by…”