Formation of plasma around a small meteoroid: 1. Kinetic theory

摘要

Every second, millions of submilligram meteoroids enter the Earth's atmosphere producing dense plasmas. Radars easily detect these plasmas, and researchers use this data to characterize both the meteoroids and the atmosphere. This paper develops a first-principle kinetic theory describing the behavior of particles ablated from a small fast-moving meteoroid and then colliding with atmospheric molecules. These collisions result in partial ionization of the ablated particles and formation of a dense plasma around the meteoroid. This theory produces analytic expressions describing the spatial structure and velocity distributions of ions and neutrals near the ablating meteoroid. The analytical model will serve as a basis for a more accurate quantitative interpretation of radar measurements and should help calculate meteoroid and atmosphere parameters from radar head-echo observations. Plain Language Summary Every second, millions of submilligram meteoroids enter the Earth's atmosphere where they disintegrate, leaving behind atoms of iron, sulphur, carbon, oxygen, etc. Most of these small meteoroids cannot be seen by naked eye. However, when entering the atmosphere with the hypersonic speed of tens of kilometers per second, these meteoroids collide with atmosphere, heat up, and lose their material in a process called ablation. The ablated atoms and molecules further collide with atmospheric constituents, scatter, and ionize, producing dense plasmas around the meteoroid. Radars easily detect these plasmas and researchers use this data to characterize both the meteoroids and the atmosphere. This paper develops a first-principle theory describing the motion of ablated particles that happens after they collide once with atmospheric molecules. This theory produces analytic expressions describing the spatial structure and velocity distributions of ions and neutrals near the ablating meteoroid. The analytical model will serve as a basis for a more accurate quantitative interpretation of radar measurements and should help calculate meteoroid and atmosphere parameters from radar head-echo observations.