Physical aspects of micrometeoroids dynamics in the Earth atmosphere

Many micrometeoroids arrive at the terrestrial atmosphere everyday at anytime. These tiny bodies come from the interplanetary medium and travel across the different atmospheric levels losing mass or modifying their charge and velocity due to several processes as ablation and thermoionic emission. In this study we analyze the dynamics of the bodies using some simplifying assumptions in order to study their deceleration, mass loss and heating along its trajectory across the atmosphere , we have also limited the analysis to the free molecular regimen that corresponds to meteoroids of very small radius for an altitude greater than 80 km and to the night side of Earth to avoid the role of photoemission emphasizing the role of thermoionic emission. We have also considered sputtering in order to know its relation with the meteoroid’s mass loss and taken into account just tiny bodies entering the atmosphere at normal angles and at different initial speeds. It has also been assumed by simplicity that the meteoroid mass loss is isotropic and we have taken the ion and electron densities as a function of altitude as well the ion and electron temperatures profiles from NASA Space Data Center using the IRI-95 atmospheric model. As the physical and thermodynamic properties of meteoroids are not well known, it is assumed a silicate composition with 2500 K and an average bulk density of spherical meteoroids ≈ 3 g/cm3 because it is the density of spherical meteoroids collected at the Earth’s surface. All results have been obtained solving the equations that describe the continuity of charge, mass, momentum and energy of 40 micron-sized meteoroids including the effect of sublimation, thermoionic emission and sputtering for different initial velocities. Mainly we have studied the role of sputtering, which is a process mentioned since 1958 by Öpik and physically it is seen as the ejection of individual atoms and molecules from the meteoroid due to impact with energetic atmospheric atoms/molecules. The results show that the meteoroids, achieve positive potentials during part of their path due to the thermoionic emission when the initial velocity is less than 50 km/s, in this case thermoionic emission and sublimation are the main loss mass processes meanwhile sputtering does not play a significant role here. A second interesting case has been analyzed solving the set of equations when initial velocities are above 50 km/s, in the case sputtering and sublimation are the most important mass loss processes for a micrometeoroid.