Hypervelocity collisions

The main observables that relate directly to small scale physical processes are the spectral properties of the meteor emissions and the physical properties of ionization trails. Both luminosity and ionization are derived directly from hypervelocity collisions between vaporized meteoroid species and atmospheric contituents. From Table 1, it is seen that, for example, a Mg atom evaporated from a Draconid meteoroid has a kinetic energy of 50 eV, while the same atom evaporated from a Leonid meteoroid has a kinetic energy of 630 eV when it collides with an atmospheric molecule. In both cases, the translational energy available to reactions is sufficient for inelastic processes such as electronic excitation and collisional ionization. As will be pointed out in Sec. 3, the respective cross sections increase dramatically with collision energy. Both the visual magnitude and the radar echo signatures of equally sized Draconid and Leonid meteoroids will thus differ substantially. 

Figure 1.1. Pressure-time diagram showing the conditions that can be achieved in various experimental and natural impacts. The Pt field for natural impact was calculated for projectile sizes from 10 m to 100 km, being representative for the documented cratering record on Earth. Hypervelocity collision of two planetary bodies will lead to even longer pulses with minutes duration. Projectiles smaller than 10 m may only cause strong shock waves if the impacted body does not have an atmosphere.

Studying the dynamics of hypervelocity gas/surface collisions under well-characterized conditions can provide insight into how a spacecraft s external surfaces will interact with the ionosphere/magnetosphere in orbit. 

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