Meteors
We endeavor to create the first comprehensive characterization of meteoroids and meteoroid plasmas (i.e. meteors) to understand their effects on the lower ionosphere and their threat to orbiting spacecraft. Meteoroids are naturally occurring objects in space that travel between 11 and 72.8 km/s and originate primarily from comets and asteroids. On average, over 100 billion meteoroids enter Earth’s atmosphere daily with masses larger than 1 microgram. These include shower meteoroids, which are associated with a parent body, as well as sporadic meteoroids, which form the background population. Although meteoroids have a profound effect on our space environment and produce plasma densities that are orders of magnitude greater than the background ionosphere, we understand very little about their fundamental properties. These include meteoroid mass and density that depends on orbit and velocity, the formation and distribution of irregularities in the lower ionosphere, the mass deposition rate into our atmosphere, the effects of meteoroid fragmentation on plasma formation, and the effect of the background electric and magnetic fields on plasma expansion and distribution. We seek to answer these questions by probing into the plasma that surrounds the meteoroid, known as the head echo, and behind the meteoroid, called the trail, in order to assess the threat to spacecraft. Our approach includes both experiment and modeling.
Radar studies
When a meteoroid enters the Earth's atmosphere, heats up, and ablates, a plasma forms. The plasma traveling with the meteoroid is called a meteor head, while the plasma that is left behind is called a meteor trail. By transmitting pulsed electromagnetic waves with a high-power large-aperture (HPLA) radar and measuring the waves that are scattered back, one hopes to characterize the plasma and its evolution and infer many properties of the parent meteoroid such as velocity, mass, density, and composition. The image below shows typical radar data for a meteor taken with the Jicamarca Incoherent Scatter Radar outside Lima, Peru. It plots signal to noise ratio (SNR) as a function of range and time the pulse was transmitted. The diagonal line on the left is the signal from a meteor head, while the high-SNR portion to the right is signal due to the accompanying trail.
Smaller "meteor radars" have an even longer history of observing trails. They receive what are called specular trail reflections, resulting when the radar beam is perpendicular to the meteor trail. Although the techniques are different, both radar methods provide unique insight into the meteoroid population.
Estimating Mass, Density, and Size
Since meteoroids themselves normally burn up before reaching the Earth's surface, it is impossible to directly measure their mass, density, and size. Instead we infer these values from radar measurements.
Modeling of Surrounding Plasmas
Particle-in-cell simulations provide insight into the dynamics of the plasmas that we see as meteors.
Orbit Determination
Once we know the position and velocity of a meteor with respect to the radar, we can determine its orbital elements and where it came from. While many meteors come from comet trails or asteroids, others may come from interstellar sources. High Power Large Aperture (HPLA) radars can measure a meteor's position and velocity with enough accuracy to determine whether an meteoroid's origin is interstellar or not. To further increase certainty, we model effects such as solar radiation pressure, Poynting-Robertson drag, and Lorentz forces, which disproportionately affect small particles.
People
Publications
- Pifko, S., Janches, D., Close, S., Sparks, J., Nakamura, T., & Nesvorny, D. (2013). Modeling the meteoroid input function at mid-latitude using meteor observations by the MU radar. NASA Technical Papers. https://ntrs.nasa.gov/citations/20120014292
- Volz, R., & Close, S. (2012). Inverse filtering of radar signals using compressed sensing with application to meteors. Radio Science, 47(6). https://doi.org/10.1029/2011RS004889
- Close, S., Volz, R., Loveland, R., Macdonell, A., Colestock, P., Linscott, I., & Oppenheim, M. (2012). Determining meteoroid bulk densities using a plasma scattering model with high-power large-aperture radar data. Icarus, 221(1), 300-309. https://doi.org/10.1016/j.icarus.2012.07.033
- Vertatschitsch, L., Sahr, J., Colestock, P., & Close, S. (2011). Meteoroid head echo polarization features studied by numerical electromagnetics modeling. Radio Science, 46(6), 1-9. https://doi.org/10.1029/2011RS004774
- Zinn, J., Close, S., Colestock, P., MacDonell, A., & Loveland, R. (2011). Analysis of ALTAIR 1998 meteor radar data. Journal of Geophysical Research: Space Physics, 116(4). https://doi.org/10.1029/2010JA015838
- Loveland, R., Macdonell, A., Close, S., Oppenheim, M., & Colestock, P. (2011). Comparison of methods of determining meteoroid range rates from linear frequency modulated chirp pulses. Radio Science, 46(2), 1-8. https://doi.org/10.1029/2010RS004479
- Close, S., Kelley, M., Vertatschitsch, L., Colestock, P., Oppenheim, M., & Yee, J. (2011). Polarization and scattering of a long‐duration meteor trail. Journal of Geophysical Research: Space Physics, 116(1). https://doi.org/10.1029/2010JA015968
- Volz, R., & Close, S. (2011). A compressed sensing approach to observing distributed radar targets. URSI GASS. https://ieeexplore.ieee.org/abstract/document/6050984?casa_token=XqjgwKiD-iYAAAAA:REgI3swMl7KFe9hJogMZ5omFtuc-IBDFGg6O4NgO-s48xVaGeheoKf1BkOxTCOzOl3leo6Zs
- Yee, J., & Close, S. (2011). Diffusion of plasmas from ablating meteoroids in the ionosphere. AIAA Atmospheric Space Environments Conference. https://arc.aiaa.org/doi/abs/10.2514/6.2011-3148
- Close, S., Colestock, P., Cox, L., Kelley, M., & Lee, N. (2010). Electromagnetic pulses generated by meteoroid impacts on spacecraft. Journal of Geophysical Research: Space Physics, 115(12). https://doi.org/10.1029/2010JA015921