Formation of dense plasma around a small meteoroid: Theory and simulations*

Every second, millions of small meteoroids hit the Earth from space, the vast majority too small to observe visually. Radars easily detect the plasma generated during meteoroid ablation and use this data to characterize the meteoroids and the atmosphere in which they disintegrate. Reflections of radar pulses from this plasma produce a signal called a head echo. This diagnostics requires a detailed quantitative understanding of formation of the meteor plasma.

We have developed a first-principle kinetic theory to describe the behavior of meteoric particles ablated from a fast-moving meteoroid and partially ionized through collisions with the atmosphere. This theory produces analytic expressions describing the ion and neutral density and their velocity distributions. Our recent fully kinetic particle-in-cell (PIC) simulations have confirmed the major results of the analytic theory and allowed obtaining better predictions. When used for calculating meteoroid masses, the new meteor plasma model can give meteoroid masses significantly different than those calculated from a spherically symmetric Gaussian distribution, which has been used to calculate the meteoroid masses in the past.