On the luminous efficiency of meteoritic fireballs

Abstract

Luminous efficiency values have been calculated empirically as a function of velocity and altitude for the Lost City, Innisfree, and Pribram meteorites. We have used a combined approach which utilizes the observed light data from the meteorite entries and the appropriate ablation rates via the entry model of ReVelle, which is generally consistent with the results of cosmic ray track analyses. Although our method reduces the absolute value of computed luminous efficiency via a total kinetic power balance equation, our results still exceed the modified Trailblazer results of Ceplecha and McCrosky for chondrites by about a factor of 5 for entry velocities of •<20 km/s. Our values of luminous efficiency (deduced with respect to a detector peaked in the visible) are -,,0.2-0.4% in the vicinity of peak ablation for Lost City and Innisfree, respectively. Results for Pribram are less certain but are -,,0.04% at peak ablation. In terms of numerical values and velocity dependencies our results agree we!! with appropriately modified laboratory simulation data of Givens and Page (1971). We conclude that the deduced photometric mass scale of fireballs should be revised downward by a factor of 5-10 so that a more accurate mass influx determination at the earth's orbit can be made.

The fall of the Grimsby meteorite—I: Fireball dynamics and orbit from radar, video, and infrasound records

“…A similar discrepancy in initial mass estimates between noble gas determinations and flight‐derived data was found for the Innisfree fireball (Goswami et al. 1978; ReVelle and Rajan 1979; Wetherill and ReVelle 1981), and Příbram (Ceplecha 1961; Bagnolia 1980). A possible explanation for these differences could be an unusual, nonspherical original meteoroid or multiple exposure history.…”

“…Interestingly, the initial mass estimates we find from the fireball data are more than an order of magnitude lower than suggested from preliminary noble gas neon ratio estimates (Cartwright et al 2010) which suggest an initial meteoroid radius >0.5 m, corresponding to an entry mass >600 kg for a spherical meteoroid. A similar discrepancy in initial mass estimates between noble gas determinations and flight-derived data was found for the Innisfree fireball (Goswami et al 1978;ReVelle and Rajan 1979;Wetherill and ReVelle 1981), and Prˇı´bram (Ceplecha 1961;Bagnolia 1980). A possible explanation for these differences could be an unusual, nonspherical original meteoroid or multiple exposure history.…”

The Innisfree Meteorite Fall: A Photographic Analysis of Fragmentation, Dynamics and Luminosity

“…The first term on the right side represents the loss of energy due to the ablation of mass and the second term the loss of energy due to decreased velocity of the meteoroid. For normal meteors and the upper portions of meteorite trajectories the first term is the dominant one, but, as shown by ReVelle and Rajan (1979) the second term may be expected to dominate in late stages of the flight of a meteorite and the luminosity may be due to gas cap effects in the shock wave area near the object.…”

“…To derive values of the luminous efficiency at points earlier than about t = 2.5 s or velocities above II km S·1 requires a detailed knowledge of rii, since the first term of equation (5) is the dominant term except late in the flight. The problem has been considered in some detail by Ceplecha (1980), ReVelle and Rajan (1979) and ReVelle (1980a, 1980b. Since we can estimate variations in monly by assuming proportionality to the luminosity, we estimate the mean luminous efficiency from the total light and estimates of the pre-atmospheric mass from ReVelle's work, mentioned above.…”

A predictive macroscopic integral radiation efficiency model

“…By using the free molecular flow value of these ratios the radiation efiSciency is predicted via this macroscopic approach without using further meteor data. If other nonintegral values of the radiation efficiency, such as those of ReVelle and Rajan (1979), are converted to the present definition, good agreement between the methods is obtained. Such agreement is also found for integral radiation efiSciency values computed reCently by Ceplecha for a number of the Prairie Network fireballs.…”