The Physics of Meteors

Abstract

AbstractInteraction of a meteoroid penetrating the atmosphere can be described through its motion, ablation, luminosity, ionization and the geometry of its trajectory. A theoretical description may be based on the so called “single body theory”, generalized to allow for discrete fragmentation. Such a concept is fully able to simulate the motion and ablation (mass loss) of meteoroids from millimeter to meter sizes recorded through photographic techniques (the best precision of such observations is better than ±10 m in observed heights). Observed distances and heights as a function of time can be fit to this model with the intrinsic precision of the geometrical data. The majority of meteoroids follow the “single-body theory” closely: large values of the ablation coefficients derived from observations favor continuous fragmentation under very low dynamical pressures as the main process of ablation. The rest, some 20 to 30%, can be described by one or more discrete fragmentation points in addition to continuous fragmentation. Dynamic pressures at these grossfragmentation points are also very low, if compared with the strength of stony meteorites.On the other hand, luminosity and ionization are not as well understood. Existing detailed spectral records show mostly radiation in form of emission lines of ablated meteoroid material with excitation temperatures in the range of 3000 to 5000 K. Additional theoretical modeling is called for.Photographically documented meteorite falls can be used for computation of luminous efficiencies, because the terminal mass and bulk density are known in these cases. Recently, photographs of the Lost City meteorite fall were remeasured with special attention to visible trails of fragments. The new analysis revealed two main discrete fragmentation points that are in perfect agreement with the geometrically resolved trails based on the dynamics. Moreover, Adolfsson (1996) found an artificial periodic signal originating from the switching shutter and after removing this signal, he was able to find an initial rotation period of 3.3±0.3 s and also the rotation phase of the Lost City meteoroid. A solution for the motion, ablation and rotation of the Lost City meteoroid is now completely self-consistent throughout the whole photographed trajectory and yields an initial mass of m = 163 ± 5 kg. The luminous efficiency was found to be 6.1% at v = 13 km/s (for 4500 K), this is ∼ 10x larger than the values determined from artificial meteors, i.e., from masses of 1 g fired downward from high-altitude rockets by shaped-charge.