Experimental Observations of Meteor Ablation

Abstract

When micrometeoroids enter a planetary atmosphere, they heat up and lose mass through evaporation. The ablated mass is ionized through collisions with gas molecules, producing a plasma around the meteoroid which is visible to radar systems as a head echo. Radar observations of meteor head echoes play an important role in constraining the total mass of cosmic dust that is entering Earth's atmosphere. The nature of meteor head echoes is heavily influenced by the processes of ionization, heating, and drag that occur in meteor entry. To investigate these aspects of meteor ablation, experiments have been undertaken using the University of Colorado's 3 MV hypervelocity dust accelerator facility. U sing the accelerator, dust particles were shot at speeds of 1 - 70 km/s into an air chamber containing various gases held at pressures of 0.01 - 0.2 Torr to create simulated meteors. The air chamber contained multiple charge collectors to observe the charge production by the particles as they interacted with gas molecules and ablated. Experiments with iron and aluminum particles have determined the probability that an atom ablated from a meteor will produce an ion-electron pair, which is a steep function of velocity. Spatial observations of the charge production of iron and aluminum have been used to study the heating and ablation that meteors undergo when they enter an atmosphere. Further experiments with aluminum have investigated the drag that meteors experience, which is essential to understand in order to predict the amount of ionization that a meteor will produce. Observations of drag also act to constrain the total heating that meteors experience, and lend insight into the microphysical processes that occur during micrometeoroid entry into the atmosphere. Differential ablation has also been investigated, in which complex olivine and magnesite particles were observed to ablate more volatile elements before less volatile elements. These experiments enhance our understanding of meteor ablation with a variety of implications in atmospheric and space science, including improving our understanding of the chemistry of Earth's upper atmosphere and constraining the nature of Earth's dust environment.