Meteors
First, some nomenclature. A particle (smaller than an asteroid, but larger than dust) moving through space is known as a meteoroid. When it enters the Earth's atmosphere, it ablates and is heated, creates a plasma, and emits light - this is what we call a meteor. Finally, if any material survives and reaches the ground (typically only for very large meteoroids), the chunk of rock that reaches the ground is a meteorite.
Somewhere between 4 and 400 tons of material enters Earth's atmosphere daily in the form of meteors. The difficulty in narrowing down this uncertainly comes from the complex relationship between the meteoroid mass and measurable parameters: radar returns and optical brightness. A large part of current meteor research is attempting to relate radar and optical measurements to the parent meteoroid mass. |
Meteors have other impacts on our atmosphere as well. They are responsible for distinct metal layers in the upper atmosphere - discrete altitudes with large quantities of Sodium, Iron, and Potassium. These metal layers can be observed from space or from the ground using resonance lidar. Meteors also leave trails of ionization in the upper atmosphere, and these trails can be monitored and used as tracers for upper atmospheric winds. These winds drive upper atmospheric circulation and are a key factor in space weather.
Our Work
In the LAIR, we focus on improving our estimate of the mass flux entering the atmosphere. We use radar data, optical data, laboratory experiments, and numerical modeling of radar scattering from meteors to understand the relationship between the parent meteoroid and the measured parameters.
Left: Simulations of radar wave scattering from meteor plasma. The top and bottom shows show two different time snapshots of the electric fields; the three columns show meteors with different peak plasma density, relative to the wave frequency. The peak density defines a parameter called the plasma frequency, which determines how a wave of a given frequency will interact with the plasma. The left column is an "underdense" meteor, the middle column is critically dense, and the right column is "overdense"; we see that they respond to the radar wave quite differently! Using these simulations, we can improve our understanding and interpretation of radar observations. |
Right: The dust accelerator at CU’s Institute for Modeling Plasma, Atmosphere and Cosmic Dust (IMPACT). We’re currently working on an experiment that will accelerate particles of dust into a gas chamber, mimicking the behavior of meteors in Earth’s atmosphere. We’ll use these tests to characterize the amount of light given off by particles of different speeds and compositions, then apply that knowledge to optical observations of real meteors. |
Left: Dust particles are accelerated along a vacuum tube, then enter a pressurized chamber and begin to ablate. Charge-sensitive amplifiers detect the resulting ionization and photo-multiplier tubes measure the light generated during ablation. If the particle does not completely vaporize, any remaining mass is measured by the impact detector at the end of the chamber.
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References
- Limonta, L., S. Close, and R. A. Marshall (2019), A technique for inferring lower thermospheric neutral density from meteoroid ablation, Planetary and Space Science, doi: 10.1016/j.pss.2019.104735.
- Thomas, E., Simolka, J., DeLuca, M., Horányi, M., Janches, D., Marshall, R. A., Munsat, T., Plane, J.M. and Sternovsky, Z., 2017. Experimental setup for the laboratory investigation of micrometeoroid ablation using a dust accelerator. Review of Scientific Instruments, 88(3), p.034501, doi:http://dx.doi.org/10.1063/1.4977832.
- Janches, D., Swarnalingam, N., Carrillo-Sanchez, J.D., Gomez-Martin, J.C., Marshall, R., Nesvorný, D., Plane, J.M.C., Feng, W. and Pokorný, P. (2017), Radar Detectability Studies of Slow and Small Zodiacal Dust Cloud Particles. III. The Role of Sodium and the Head Echo Size on the Probability of Detection. The Astrophysical Journal, 843(1), 11pp, https://doi.org/10.3847/1538-4357/aa775c.
- Marshall, R. A., P. Brown, and S. Close (2017), Plasma distributions in meteor head echoes and implications for radar cross section interpretation, Planetary and Space Science, https://doi.org/10.1016/j.pss.2016.12.011.
- Marshall, R. A., and S. Close (2015), An FDTD model of scattering from meteor head plasma, J. Geophys. Res. Space Physics, 120, 5931–5942, doi:10.1002/2015JA021238.
- Close, S., R. Marshall, I. Linscott, S. Pifko, and D. Janches (2014), Interstellar particles detected by high-power large-aperture radar, Asteroids, Comets, Meteors 2014, vol. 1, p. 106.