Measurements of the ionization coefficient of simulated iron micrometeoroids

Abstract

The interpretation of meteor radar observations has remained an open problem for decades. One of the most critical parameters to establish the size of an incoming meteoroid from radar echoes is the ionization coefficient, β, which still remains poorly known. Here we report on new experiments to simulate micrometeoroid ablation in laboratory conditions to measure β for iron particles impacting N2, air, CO2, and He gases. This new data set is compared to previous laboratory data where we find agreement except for He and air impacts > 30 km/s. We calibrate the Jones model of β(v) and provide fit parameters to these gases and find agreement with all gases except CO2 and high‐speed air impacts where we observe βair > 1 for velocities > 70 km/s. These data therefore demonstrate potential problems with using the Jones model for CO2 atmospheres as well as for high‐speed meteors on Earth.

Experimental setup for the laboratory investigation of micrometeoroid ablation using a dust accelerator

“…Given these inconsistencies, it was suggested that lowering β by one or two orders of magnitude would bring the radar measurements into better agreement with the ZDC model. However, the first results of this facility (reported in Thomas et al 1 ) showed that β is most likely not a significant factor in the discrepancy.…”

“…Recently, Thomas et al 1 reported the first scientific results from the ablation facility described in this article. That work measured the ionization coefficient of iron particles impacting N 2 , air, CO 2 , and He, and compared the new experimental values to a commonly used analytical theory 3 and past experimental work.…”

“…For completely ablated particles, the total collected charge directly yields the ionization coefficient of a given dust material-target gas combination. The first results of this facility measured the ionization coefficient of iron atoms with N 2 , air, CO 2 , and He target gases for impact velocities > 20 km/s, and is reported by Thomas et al 1 . The ablation chamber is also equipped with four optical ports that allow for the detection of the light emitted by the ablating particle.…”

“…Radar measurements play a critical role in the observation of the incoming extraterrestrial particles, as this technique is (1) sensitive to the size range where most of the mass input occurs 4 ; and (2) the existing radar facilities provide continuous observation. Particles entering the atmosphere with velocities >11 km/s produce luminous trails of ionized gas that allow for the detection and characterization of individual meteors [10][11][12][13] .…”

Impacts of Cosmic Dust on Planetary Atmospheres and Surfaces

“…An electrostatic dust accelerator has recently been used to generate metallic particles with velocities of 10-70 km s −1 , which are then introduced into a pressurized chamber where the particle partially or completely ablates over a short distance. The deceleration is used to determine the rate of mass loss, and an array of biased electrodes above and below the ablation path collect the ions and electrons produced along the ablation path, from which the ionization efficiency can be determined (Thomas et al 2016(Thomas et al , 2017. A model like CABMOD can then be used to calculate the height profile of the injection rates of the meteoritic constituents into a planetary atmosphere.…”