6.4 Meteors

Extract

After hearing so many technical descriptions of different high velocity particle experiments, one easily recognizes the paramount importance of sensors for gathering the experimental data on meteoric dust. In contrast the “classical” meteor astronomy and physics is using a less expensive “sensor”, the Earth’s atmosphere. The interaction of the meteor body with the air has to be recorded and thus our experimental data are just records of the natural phenomenon itself: integral light photographs, spectral photographs, recently also image intensifier photographs and videorecords. The only “active” method is the radar observation of the ionized trail. The close distance of the phenomenon to the observational sites enables one to determine the complete geometrical and dynamical data (heights, distances, velocities); the light recording gives the intensity of the emitted light at individual points of the trajectory, the radar recording gives the ionization intensity. A suitable physical theory is necessary to convert the basic observational data into meteor mass and other parameters. The drag equation yields the “dynamic” mass, the luminosity equation yields the “photometric” mass, and the ablation equation yields the “ablation” mass. Por a single meteor, these masses are dependent on parameters defined by the drag coefficient, shape, bulk density, ablation rate and luminous efficiency. Differences in the resulting masses of a meteoroid computed from the different methods at the same trajectory point are good relative measures of the structural and compositional differences. The absolute calibration may be a problem, but laboratory and rocket measurements of the luminous efficiency, calibrations by the Lost City and Pribram fireballs and several other direct and indirect methods can be used.