Determination of Meteor Parameters Using Laboratory Simulation Techniques

Abstract

Atmospheric entry of meteoritic bodies is conveniently and accurately simulated in the laboratory by techniques to be described which employ the charging and electrostatic acceleration of macroscopic solid particles in the 0.02 to 1 μ diameter range. Velocities from below 10 to above 50 km/s are achieved for particle materials which are elemental meteoroid constituents (e.g.: Fe, Si, Mg) or mineral compounds with characteristics similar to those of meteoritic stone (e.g.: FeTiO3). The velocity, mass, and kinetic energy of each particle are measured nondestructively, after which the particle enters a target gas region. Because of the small particle size, free molecule flow is obtained at target pressures ≦ 10 torr. At typical operating pressures (0.1 to 0.5 torr), complete particle ablation occurs over distances of 25 to 50 cm; the spatial extent of the atmospheric interaction phenomena (luminous trails, ionized wakes, etc.) is correspondingly small, simplifying many experiments. Procedures have been developed for measuring the spectrum of light from luminous trails and the values of fundamental quantities defined in meteor theory: heat transfer coefficient λ, drag coefficient Γ, ionization probability β, and photographic luminous efficiency τpg. Results of these measurements are presented, with emphasis on recent, improved evaluations of τpg and β over wide velocity ranges; it is shown that the laboratory values of τpg for iron are in excellent agreement with those for 9 to 11 km/s artificial meteors produced by rocket injection of iron bodies into the atmosphere. Also discussed in some detail is the relevance of these measurements to the interpretation of meteor observations and the methods of inferring from them numerical values of τpg and β for natural meteors.