A hydrodynamic mechanism of meteor ablation

Abstract

Context. Hydrodynamic conditions are similar in a molten meteoroid and a liquid drop in a high-speed airflow. Despite the fact that the latter is well-studied, both experimentally and theoretically, hydrodynamic instability theory has not been applied to study the fragmentation of molten meteoroids. Aims. We aim to treat quasi-continuous spraying of meteoroid melt due to hydrodynamic instability as a possible mechanism of ablation. Our objectives are to calculate the time development of particle release, the released particle sizes and their distribution by sizes, as well as the meteoroid mass loss law. Methods. We have applied gradient instability theory to model the behaviour of the meteoroid melt layer and its interaction with the atmosphere. We have assumed a spherical meteoroid and that the meteoroid has a shallow entry angle, such that the density of the air stream interacting with the meteoroid is nearly constant. Results. High-frequency spraying of the molten meteoroid is numerically simulated. The intermediate and final size distributions of released particles are calculated, as well as the meteoroid mass loss law. Fast and slow meteoroids of iron and stone compositions are modelled, resulting in significant differences in the size distribution of melt particles sprayed from each meteoroid. Less viscous iron melt produces finer particles and a denser aerosol wake than a stony one does. Conclusions. Analysis of the critical conditions for the gradient instability mechanism shows that the dynamic pressure of the airstream at heights up to 100 km is sufficient to overcome surface tension forces and pull out liquid particles from the meteoroid melt by means of unstable disturbances. Hence, the proposed melt-spraying model is able to explain quasi-continuous mode of meteoroid fragmentation at large heights and low dynamic pressures. A closed-form solution of the meteoroid ablation problem is obtained due to the melt-spraying model usage, at the meteoroid composition, initial radius and velocity being given.

Properties of small meteoroids studied by meteor video observations

“…Iron meteors have recently been studied by Campbell-Brown (2015) andČapek & Borovička (2017). Čapek & Borovička (2017) and Girin (2017) suggested that ablation is in the form of droplets released from a liquid layer at the surface of the body. So the grains in our model can be in fact iron droplets in this case.…”

A hydrodynamic mechanism of meteor ablation

“…Hydrodynamic mechanism of meteoroid ablation as a quasicontinuous spraying of the meteoroid melt was considered in part one of this work (Girin 2017), which is referred to here as Paper I. The mechanism consists in the meteoroid molten substance spraying in the form of fine liquid droplets due to the hydrodynamic "gradient" instability of conjugated (air-melt) boundary layers at the meteoroid body surface.…”

Atomic‐Scale Simulations of Meteor Ablation

“…Materials such as quartz and inhomogeneous materials may behave in a more complex manner that includes melting. Larger meteoroids deeper in the atmosphere which exceed the mean-free-path in size, however, should develop shocks and melting as predicted inČapek and Borovička (2017) and Girin (2017).…”

“…However, the single particle impacts influence the heating rate of the meteoroid, which determines the thermal mass loss rate as well. Thermal ablation is sometimes referred to as evaporation (Briani et al, 2013;Campbell-Brown & Koschny, 2004;Čapek & Borovička, 2017;Čapek et al, 2019;Ceplecha et al, 1998;Girin, 2017;Popova, 2004) or thermal mass loss (DeLuca & Sternovsky, 2019;Hill et al, 2004;Rogers et al, 2005;Thomas, 2017;Vondrak et al, 2008). We have chosen to use the term thermal ablation as it encapsulates all possible phase transitions due to the thermal energy imparted on the meteoroids surface from atmospheric particles.…”